Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 1...
Transcript of Italo-Hellenic School of Physics 2005 – Martignano June 2005 C.Roda University and INFN Pisa 1...
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
1
Calorimetry at LHCCalorimetry at LHC
Why should I want a calorimeter ?
Interactions relevant for Electromagnetic Calorimeters
Calorimeter characteristics: linearity and resolution
The ATLAS and CMS em calorimeters: different choices
Hadronic interactions and issues relevant to hadron calorimeters
ATLAS and CMS hadronic calorimeters
C.Roda
INFN & Universita` di Pisa
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ReferencesReferences
R. Wigmans, “Calorimetry, Energy Measurements in Particle Physics” all figures without other cited source are from this book
Priscilla B.Cushman, “Electromagnetic and Hadronic Calorimeters”
D.Prieur, “Etalonnage du calorimetre electromagnetique du detector ATLAS”, PhD Thesis
M.Diemoz, “Calorimetri elettromagnetici a cristalli per la fisica delle alte energie” Lezioni Villa Gualino 3.2.2005
U.Amaldi, “Fluctuations in Calorimetry measurements” 1981 Phys.Scr.23 409
C.W.Fabjan and F.Gianotti, “Calorimetry for particle physics”, Reviews of Modern Physics, Vol.75, October 2003
R.Wigmans et al., “On the energy measurement of hadron jets”
ATLAS & CMS TDRs
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What is a Calorimeter ?What is a Calorimeter ?
The Calorimeter concepts originates from thermodynamics: thermally isolated box containing a substance under study of which we want to measure the temperature. “Our” calorimeters also measure temperature as an energy measurement. The very basic concept is thus taken from thermodynamics but the sensitivity we need is much higher, the effect of 1 TeV (1 eV = 10-19 J) in 1 liter of water (cwater = 4.19 J g-1K-1) at 20o is:
T = E / cwater M = 1.6 10-7 / 103 4.19 = 3.9 10-7 K
the sensitivity that we need is much higher.…also calorimeter in particle and nuclear physics are invasive devices:
Calorimeters are detectors able to measure the particle energy through total absorption. The first idea to use calorimeter was originated by the need to measure not only charged particles (bending magnetic field) but also neutral particles: 0 …there were born around the 1970 …
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Wigm
ans - C
alorim
etry
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Key role in the pastKey role in the past
UA2 measurement of W → jj invariant mass before and after background subtraction, the wider is the peak the more difficult it is to see the signal on the QCD background. The sigma of the signal peak is 8 GeV of which 5 GeV are attributed to calorimeter resolution. Here the resolution is not enough to separate the W and Z peaks.
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General charcteristicsGeneral charcteristics
• Sensitivity both to neutral and charged particles;• Energy measurement precision (more or less) with E
spectrometer measurement precision with p;• Do not need magnetic field (infact it is easier without);• Shower length ln(E) thus dimension are compact;• Particle identification;• Not only E but also spatial measurement through
segmentation;• They can have a fast response, useable at high rate and
for trigger signals.
CALOE
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Key role in LHCKey role in LHC
Higgs discovery: H → H → ZZ → 4 e (particle identification against jets)
SUSY discovery: easiest event signature is given by excess of events high ET miss e high pT jets;
top mass measurement tt → WWbb → ljjbb, W → jj; precise ET miss measurement requires precise and hermitic
calorimetries. forward jet tagging …
I hope I have convinced you that there are numerous reasons why we need a calorimeter…Also we will see how some of the mentioned physics channels will be used to define the design requirements of the LHC calorimeters.
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A few concepts on Electromagnetic interactions
A few concepts on Electromagnetic interactions
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How does a EM shower forms ?How does a EM shower forms ?
e interaction with matter First issure is to understand the mean energy
deposit/interactionPhoton Electrons and Positrons
PDG 2004 PDG 2004
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What do we need to understand …What do we need to understand …
Since the cross section of these processes depends on the particle energy the relevance of each process changes as the shower develops. The cross section depends on Z of the material thus the characteristics of the signal depends strongly on the type of material we use to build the calorimeter. Now we try to better understand the relevant points of this processes for what concerns shower formation.
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Electron and positron BremsstralungElectron and positron Bremsstralung
Radiation of real photons in Coloumb field nuclei.
QED
0/0
0
Xx
Brem
eEEX
E
dx
dE 0/
00
Xx
Brem
eEEX
E
dx
dE
• mean energy loss per unit length (per gr-1cm2) proportional to energy of the particle;
• Scaling factor for high energy ele in one X0 the particle reduces its energy by 63%.
• X0 can be multiplied by the density to measure in cm
E > 100 MeV it is the most important process for energy loss for e+e-
][180 2
20 cmgr
Z
AX
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Ionization lossIonization loss
Interactions of electrons with the atoms characterized by many interactions with a small release of energy.
92.0
71024.1
610
Z
MeVE
Z
MeVE
c
c
cioniz
cBrem
c EEdx
dEE
dx
dE )()(
Material Z X0/cm Ec/MeV
Liquid Ar 18 14 37
Fe 26 1.8 22
Lead 82 0.56 7.4
Sol
Liq
Two regimes of energy loss → the border is set by the critical energy EC:
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Electrons vs photonsElectrons vs photons
There is a main difference between the interactions of electrons (and positrons) and photons with matter at high energy. Electrons loose energy but they do not disappear, photons as they interact they are destroyed.
dx
dE )(E
electrons photons
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Pair productionPair production
Interaction of photons with the field of the nucleus (or of the electrons):
nucleus → nucleus + e+ e-
Threshold: E ≥ 2 me
pairx
pairAApair
eIxI
N
A
XN
A
/0
09
7
High energy approssimation, E independent
Reduction of photon beam intensity.
Photons scaling factor is of the same order of electrons: pair = 9/7 X0 1.3 X0
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Photoelectric and Compton interactionPhotoelectric and Compton interaction
3
5
E
ZicPhotelectr
A → A+ e- e → ’ e’
E
EZCompton
ln
In both interactions secondaries do not follow the direction of the incident electron, almost no reminder of initial particle direction.
shows strong dependence on Eshell
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Direction of particles that release energy ?Direction of particles that release energy ?
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Photon cross sectionsPhoton cross sections
3
5
E
Zricphotoelect
E
EZCompton
ln
CarbonZ = 6
LeadZ = 82
ZlungBremsstrah P
article
Da
ta B
oo
k 20
04
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In summary how the shower is formedIn summary how the shower is formed
The shower is formed through a process of particle multiplication that degrades the particle energy;
Interplay between different interaction processes depends on Z of material;
As the energy of the particles reaches very low energies eV,KeV, electrons and positrons are absorbed by the material which is “heated” by the released energy.
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Scaling of shower profile with E and X0Scaling of shower profile with E and X0
The position of the shower maximum XMaximum is approximatly described as a function of X0 – since both gamma pair and brem scale with it - and the particle initial energy by the simple formula:
00 ln t
Ec
EXX Maximum
to= - 0.5 for electrons
0.5 for photons
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Electron longitudinal shower profileElectron longitudinal shower profile
Electron longitudinal shower profile in copper
Shower maximum moves with energy as log(E)
[Wigm
ans – Text B
ook]
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Photon/electron differencePhoton/electron difference
Few photons do not interact at all
Almost no electrons do not release
[Wigm
ans – Text B
ook]
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X0 scaling is approximateX0 scaling is approximate
Shower Mx is deeper in Lead than in Aluminium: multiplication continues for longer since critical energy is lower in Lead than in Aluminum (7.4 MeV vs 43 MeV).
[Wigm
ans – Text B
ook] 10 GeV e-
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X0 scaling is approximateX0 scaling is approximate
Shower “decade” slowlier in lead than in aluminum since the total number of particle created is 3 times higher than in Aluminium.
[Wigm
ans – Text B
ook] 10 GeV e-EGS4
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Consequence on longitidunal Shower containment
Consequence on longitidunal Shower containment
Pe
rce
ntu
al s
how
er
con
tain
me
nt
More radiation lengths of U than of Al needed to absorb 95% of em showers.
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Calorimeter dimensionCalorimeter dimension
6.908.0%95 ZXX Max
Calorimeters of 25X0 allows to contain electron showers at 1% up to 300 GeV.
25X0 25-50 cm
Material needed for 95% shower containment:
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Transverse profileTransverse profile
The lateral shower development is dominated by two effects:
• multiple scattering at the early phase of the shower;
• long free path for low energy photons in Compton energy range.
The measurement of the transverse size, integrated over the full longitudinal range, is given by the Molière radius (same units as X0):
)(21 0
MeVEc
XMeVRM
On average 90% of the shower is contained in 1 RM.
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Transverse profileTransverse profile
10 GeV e- in copper
Transverse profile at various depths.
Two regimes: multiples scattering and Compton photons travelling away from the axis.
Material Z X0/cm Ec/MeV RM/cm
LAr 18 14 37 8
Fe 26 1.8 22 1.7
Lead 82 0.56 7.4 1.6
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What are the particle that deposit energyWhat are the particle that deposit energy
Fraction of energy deposited to the material by a 10 GeV electron:
The low energy particles are responsible for most of the energy deposition.
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What is the range of the particle that release energy
What is the range of the particle that release energy
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From energy deposit to signal From energy deposit to signal
From the energy deposit we have to generate the signal. Two calorimeter design possibilities:
Homogeneous: the calorimeter consists of a single material which acts both as absorber and active device that transform all e+ e- energy deposit in signal.
Sampling: absorber and active device are made of different materials and signal is generated from a sample of the total e+ e- energy deposit.
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Signal generationSignal generation
The most used techniques to generate the signal in calorimeters are:
• Cerenkov radiation from e+ e-• Scintillation signals • Ionization of the detection medium
All these tecniques are characterized by a threshold energy which is the minimum detectable energy Es.
Light collection
Charge collection
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What I need from the calorimeter What I need from the calorimeter
Linearity in a given energy range: Signal = a E
The larger the range the more difficult it is for example range @ LHC [MIP → TeV]
Signal/Energy: pC/GeV, ADC count/MeV …
The request might seem easy but many different source might spoil the calorimeter response (a).
a =
Sig
nal/E
nerg
y
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Factors that affect the linearityFactors that affect the linearitySpoiling the linearity:• Saturation effects: of electronics, of energy deposition … • Leakage (transverse or lateral)• noise, this at low side Example: PMT saturation.
Injected charge (a.u.) Injected charge (a.u.)
PM
T s
ign
al (
a.u
.)
PM
T s
ign
al/i
nje
cted
ch
arg
e
Linearity within 2%1
1.02
0.98
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What else I need from a calorimeterWhat else I need from a calorimeterResponse to monochromatic
source of energy E
Calorimeter signal
background
H good resolution
Signal = constant
integrated B →
S/B 1/
… but = f(calo)
(calo) defines the energy resolution for energy E.
m
H bad resolution
Perfect good bad
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What affects the resolutionWhat affects the resolution
Up to this moment we have described the <mean> behaviour of the calorimeter, fluctuations around this value are the sources of the calorimeter resolution.
The sources of fluctuations are various:
• Signal quantum fluctuations (i.e.: photoelectric statistics …)
• Sampling fluctuations
• Shower leakage
• Instrumental effects (i.e.: structural non-uniformity, electronic noise, light attenuation, …)
Usually in each calorimeter, and in each energy range, one of these sources dominates.
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Simple model: a particle of energy E will produce N signal quanta:
N E/Ec
N is the number of e+ e- that realese energy by ionization and excitation. The signal S is proportional to the total track length (T) :
T X0 E/Ec
The measured energy EM is proportional to the particle energy E:
EM= k T
Resolution and signal quanta fluctuationResolution and signal quanta fluctuation
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E
t
TTTkkT
kT
E
E TTk
M
M cos1)()(22
Resolution and signal quanta fluctuationResolution and signal quanta fluctuation
Stochastic term
Assuming (for the moment) that k = 0
EM= k T
Fluctuation of number of track segments is poissonian →
gaussian for large number of track segment
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Resolution and signal quanta fluctuationsResolution and signal quanta fluctuationsThe intrisic limit to the energy resolution is given by the maximum detectable track length which depends on the signal threshold energy:
Tdetectable = fs T fs X0 E/Ec
fs fraction of N particles over energy threshold Es. Thus:
EM = k Tdetectable k fs X0 E/Ec
sectable
ectable
M
M
fETkT
kT
E
E
ectable
111)()(
detdet
det
Low energy threshold for detecting → high fs
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Crystal calorimeters have best intrinsic limit on energy resolution
Crystal calorimeters have best intrinsic limit on energy resolution
Compare processes with different energy threshold
Scintillating crystals
/)%31(~/ GeVEE
eV~EE gaps
MeV/1010 42
Cherenkov radiators
MeV7.0~En
1s
/)%510(~/ GeVEE
GeV/2000600
/)%52(~/ GeVEE /)%3.003.0(~/ GeVEE
Real Resolution with all contributions:
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Resolution in sampling calorimeters Resolution in sampling calorimeters In sampling calorimeters there is a further contribution to
fluctuations which is due to the sampling procedure and usually dominates other stochastic fluctuations:
Absorber plates
Active mean
Electron shower in a cloud chamber with lead absorber
Rossi gave a semi-emipirical expression for the sampling fluctuations considering the fluctuation of the number of particles crossing “a set of active layers equally spaced at distance x”:
Emip
EN
Emip = energy lost by a mip on a
sampling layer (Active + absorber)
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Resolution in sampling calorimeters Resolution in sampling calorimeters
EEmip
E
E
M
M 1)(
The higher the number of planes the smaller the Emip → the better the energy resolution
However this is clearly only part of the story …
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Sampling fluctuationsSampling fluctuationsThe previous formula however fails to describe the correct dependence of the resolution with the active layer thickness … it goes in the opposite direction.
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Sampling fluctuationsSampling fluctuations
We have seen that the calorimeter signal is given by many low energetic ( MeV) e+ and e-:
• e+ e- created in active layers
• e+e- created in absorber that reach the active layers
• the pathlength of particles with E 1MeV is fraction of the distance between active layers thus increasing the number of boundary surfaces between layers increases the contribution to the signal
The fluctuations depend on:
Sampling fraction
Sampling frequency
)()(
)(
absorberEactiveE
activeEf
mipmip
mipsamp
dd/2
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Sampling fluctuationsSampling fluctuations
Ef
da
E
E
sampM
M 1)(
fsamp ↓ resolution
↓d ↓ resolution
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Other contribution to energy resolutionOther contribution to energy resolution
Many other sources affect the energy resolution which can be parametrized as the sum of three terms added in quadrature assuming independent sources:
c
E
b
E
a
E
E
a = stochastic term, fluctuations in signal quanta
b = noise term (Stot = Sparticle + Snoise): electronic noise but also contribution from pile-up
c = smearing of the calorimeter response due any structure non uniformity that cause variation in the signal generation, non hermetic coverage (cracks)
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Resolution constant termResolution constant term
It is the leading term at high energies. It is affected by non uniform response of the detector as a function of the impact point position (equalization), temperature… It is mainly related to the precision and stability of setting working conditions … EM = kTdetectable where now we are considering the variation of k:
...)(
kE
E k
M
M
Very hard work to have a low constant term in order not to spoil resolution at high energy expecially if the stochastic term is low….
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Resolution and shower leakageResolution and shower leakage These fluctuations are non poissonian since are due to
fluctuations in numbers of interactions in first calo layer …and increase with ln(E) lateral shower leakage much less fluctuating the
longitudinal one Usefull parametrization for longitudinal fraction energy
lost f < 10%:
)f50f41(EE
2
L
i.e. for f = 5% → 13% degradation in energy resolution
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Resolution and shower leakageResolution and shower leakageC
HA
RM
Co
llabo
ratio
nN
IM 1
980
17
8,2
7
Percentual energy loss
Longitudinal dominated by first interaction, lateral by fluctuations of many low energy particles
pair = 9/7X0
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Which is the source I should take care of …Which is the source I should take care of …
Es.: ATLAS EM barrel Calorimeter
0.7%
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A Calorimeter for the Large Hadron ColliderA Calorimeter for the Large Hadron Collider
1034
1033
<1032
Lumi
cm-2s-1
100
10
0.3
Int. Lumi/y
fb-1
14 LHC(high lumi)
14 LHC(low lumi)
1.8TeVatron Run I
ECM
TeV
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Good and Bad at LHCGood and Bad at LHC
1110
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Minimum bias e pileup per bunchMinimum bias e pileup per bunch
tot(pp)100 mb
10 102 103 104
Centre-of-mass energy (GeV)
tot (pp) and inel = tot- el - diff
@ LHC inel 70 mb
Pileup:<n> = inel x L x t = 70 mb x 1034 cm-2s-1 x 25 ns 20 interactions/BC
Big change with respect to previous machines:LEP: t = 22 s <n> << 1SppS: t = 3.3 s <n> 3HERA: t = 96 ns <n> << 1Tevatron : t = 3.5 s <n> << 1Tev RunII: t = 0.4 s <n> 2
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Minimum bias characteristics Minimum bias characteristics
<pT> ~ 500 MeV
pp inelastic events at s = 14 TeV Roughly speaking at high Roughly speaking at high luminosity:luminosity:
dncharged/d dnneutral/d 7.5 in = 1
+- <pT> 0.6 GeV
da 0 <pT> 0.3 GeV
pseudo rapidity
Calorimeter acceptance –5 < < 5 ( = 0.8o):
most energy is lost down the beam pipe
~ 1100 GeV transverse energy (~ 3000 particles) in the calorimeters every 25 ns
Nch
/
= 1
E(T
eV)\
= 1
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A calorimeter for this environmentA calorimeter for this environment
ATLAS and CMS have been designed to:Minimize the pile-up in:Minimize the pile-up in: time: fast detector with a time response compatible with the bunch crossing distance 25/50 ns space: high granularity thus high number of channels Radiation resistance: Radiation resistance: appropriate tecnique for each rapidity range. Measurement of neutrinos: Measurement of neutrinos: high ermeticity Use of performance on important channels Use of performance on important channels to define the reuirement on calorimeter performance. For EM calorimeters H→ …
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Performance for Em calorimeters: H→Performance for Em calorimeters: H→
2/2
1
2
2
1
1
tgEEmm
c
E
b
E
a
E
E
Natural width: for MH 100 GeV → H /MH ≤ 10-3
Experimental width of m = 2 E1 E2 (1 - cos ) :
E
mrad 50)(
Same for ATLAS and CMS …
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ATLAS and CMS calorimeter systems are completely different
ATLAS and CMS calorimeter systems are completely different
Solenoidal inner section +
Toroidal outer section
Solenoidal field up to muon spectrometerPictures approximately to scale …CMS requires
a compact detector
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Very similar requirements but …Very similar requirements but …
ATLAS and CMS makes different choices: ATLAS require segmented calorimeter to have redudant mesurement of angle
CMS relies on vertex reconstruction from tracking and point to homogenous calorimeter with very low stochastic term aiming for excellent energy resolution.
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ATLAS and CMS electromagnetic calorimetersATLAS and CMS electromagnetic calorimeters
• Compact • Excellent energy resolution• Fast • High granularity• Radiation resistance• E range MIP → TeV
Homogeneous calorimeter made of 75000 PbW04
scintillating crystals
• good energy resolution• Fast • High granularity• Longitudinally segmented• Radiation resistance• E range MIP → TeV
Sampling LAr-Pb, 3 Longitudinal layers + PS
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CMS choice: crystal calorimeterCMS choice: crystal calorimeter
Compact Transverse segmentation
Material X0/cm Ec/MeV RM/cm
Fe 1.8 22 1.7
Lead 0.56 7.4 1.6
PbWO4 0.89 2.2
Crystal dimensions:
longitudinal 25 X0 = 22.2 cm
Transverse 1 RM = 2.2 cm
95% of the shower contained in 2 RM
Module type 2 - Rome
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CMS electromagnetic calorimeter: fastCMS electromagnetic calorimeter: fast
Conduction band
valence band
bandgap
E, T
Slow component is induced by defects and impurities.
In high quality crystals 80% is emitted in 25 ns.
200 300 400 500 600 700
inte
nsity
(a.u
.)
wavelength (nm)
Stokes shift
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Photon detectors for CMSPhoton detectors for CMS
Example of problematics due to the readout device and to the experimental environment.
NIM
A37
8 (1
996)
410
-426
Very sensitive to magnetic field (4T) … not impossible but very much care should be taken to correct for all the effects and loss of amplification.
One of the drawback with PbWO4 is the low light yield 100 /MeV thus photon detector should amplify the light: first choice PMTs.
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Photon detectors for CMSPhoton detectors for CMS
Si-PhotoDiode
OK for B field, however … no moltiplication → very large tails from electrons going through the silicon.
Si-Avalanche PhotoDiode
OK for B field, however … x25 moltiplication and good resolution.
NIM
A37
8 (1
996)
410
-426
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The constant term in the resolutionThe constant term in the resolution
Many sources to be kept under control:• Longitudinal uniformity of light collection• Strong light yield variation with temperature (-
2.3%/0C)• APD gain variation with applied tension
(-3%/Volt) and termperature (-2.3%/0C)• Light collection uniformity• light transmission due to radiation damageOther terms:Leakage front and rear
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CMS EM ResolutionCMS EM Resolution
E
MeV
E
129%40.0
%93.2
Resolution as a function of energy from test on beam:• final prototype matrix
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A slice of ATLAS electromagnetic calorimeterA slice of ATLAS electromagnetic calorimeter
Sampling: accordion lead structure filled with LAr
47 cm
• Longitudinal dimension:
25 X0 = 47 cm (CMS 22 cm)
• 3 longitudinal layers
4 X0 0 rejections separation of 2 photons very fine grain in
16 X0 for shower core
2 X0 evaluation of late started showers
• Total channels 170000
Particles from collisions
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Signal formation in LArSignal formation in LAr
GerbeEM
e-
e-
e+
Plo
mb
E ~ 1kV/mm
Argonliquide
Ele
ctro
de
ions
e-
HTIphys
E
Signal is given from collection of released electrons
Drift velocity depends on electron mobility and applied field. In ATLAS :
Lar gap 2 mm
V = 2kV
HV
400 ns 16 LHC BC
LAr
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Good and bad with LArGood and bad with LAr
High number of electron-ion pair producedNo amplification neeeded of signal, low fluctuationsLiquid → Very uniform response (purification)Stability with timeMain fluctuations are due to sampling fluctuationsIntrinsically radiation hardcheap slow time response 400 ns boling temperature 87K → criogeny neededTemperature sensitivity 2% signal drop for T=1
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LAr Calorimeter in the LHC environment …LAr Calorimeter in the LHC environment …In order to cope with the pileup background the time response is shaped with a short resolving time pulse with 0 time integral, in this way the pileup integral is 0 but only a part of the signal is kept:
Each “” is a bunch crossing
Signal used is only a fraction thus I need good S/N
but shaping time has 0 time integral → mean value of pileup is cancelled.
Signal
Shaping time
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LAr Calorimeter at LHC rates …LAr Calorimeter at LHC rates …
The “perpendicular” geometry allows to have low detector capacitance (series of electrodes) and signal close to preamplifier (low inductance) this give high S/N.
The accordion geometry allows to have this feature without very large variation of sampling fraction for perpendicular crossing particles.
Series
Parallel
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Signal in ATLAS electromagnetic calorimeterSignal in ATLAS electromagnetic calorimeter
The accordion geometry makes also the calorimeter particularly hermetic, much easier to get the signal out but also “solve” the time response problem
Signals on copper electrodes due to current induced by electrons:
2 mm gap in 500 ns
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LAr barrel EM calorimeter after insertion into the cryostat
The cryostate for the ATLAS electromagnetic calorimeter
The cryostate for the ATLAS electromagnetic calorimeter
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ATLAS EM calorimeterATLAS EM calorimeter
The constant term in the resolution is dominated by: the equalization of the electronic readout. The equalization procedure requires to know the shaping function of each cell at few percent level → equalization with an electronic control signal the non uniformity in the electric field and in the sampling fraction introduced by the accordion structure.
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Contribution to constan term in resolution ATLAS em
Contribution to constan term in resolution ATLAS em
90 GeV e-
Some contribution also come from variation of sampling fraction due to the accordion structure
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Which uniformity do I get ?Which uniformity do I get ?
Scan on a complete module with monoenergetic electrons
Scan in
Const. term 0.57% over ~ 500 spots
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Comparing the design resolution Comparing the design resolution
E (GeV)
(E
)/E
Many of us are working to make this resolutions become reality for the whole calorimeter
CMS vs ATLAS
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Comparing the resolution on prototypes modules
Comparing the resolution on prototypes modules
E (GeV)
(E
)/E
E (GeV)(
E)/
E
%7.0)(
25.0
)(
%10)(
GeVEGeVEE
E%5.0
)(
2.0
)(
%7.2)(
GeVEGeVEE
E
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Comparison of performances on H→Comparison of performances on H→
Resolution on invariant mass:
CMS 0.7 GeV
ATLAS 1.2 GeV
CMS better resolution requires a very precise control of constant term
ATLAS has better power to measure the direction → potentially a higher efficiency
… is a question of point of views …
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Two calorimeters two points of viewTwo calorimeters two points of view
CMS goes for excellent energy resolution thus points on a technique which has a very small stochastic term, also requires a very compact calorimeter for B field choice
ATLAS points to a moderate energy resolution but to a tecnique where the intrinsic uniformity is almost for free and requires also angle reconstruction and more powerful capabilities for particle id.
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Hadronic interactionsHadronic interactions
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An extra complication…An extra complication…
231
int 35 gcmAeraction
The extra complication of strong and nuclear interation makes hadron calorimeters more difficult to optimize. The performance that one can expect from an hadron calorimeter at the moment are resolution of the order of 50% - 100%/E and linearity with a few percent 5% (recall 3%-10 %/E and <1% for EM calorimeters.
The first hadron interaction is governed by:
X0,
I [
cm]
Material Z I/cm X0/cm
Fe 26 16.8 1.8
Cu 29 15.1 1.4
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Hadron interactionsHadron interactions
When a hadron interact the are two components:Electromagnetic fraction: , 0 → s and develop and electromagnetic shower same as the one we already discussed.Hadron fraction: neutrons, protons, pions. As an example in lead this energy deposit is divided in:
56% ionizing particles (2/3 spallation protons)10% neutrons (very low energy neutrons)34% invisible (mainly nuclear binding energy, few pion decays …)Average deposit from simple model (Wigman).
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The electromagnetic fractionThe electromagnetic fraction
The average electromagnetic energy fem depends on the energy of the incident particle E0:
1
0
1
k
em E
Ef
k 0.8 and E0 = average energy needed for 0 production 1 – 2 GeV. This is obtained assuming that 30% of energy goes to 0 at each interaction, the value of k is related to the track multiplicity.
Gabriel et al.
E (GeV)
Fe E0 = 0.7 GeV k = 0.8
Pb E0 = 1.3 GeV k = 0.8
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Global view of mean energy depositGlobal view of mean energy deposit
Lead
f0
MIP
Rev.Mod.Physics Vol.75 Oct.2003
Invisible
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What are the implication of this type of showerWhat are the implication of this type of shower
We have seen that there are two types of shower components: electromagnetic Ee() and hadronic Eh().
The calorimeter reponse to the two components is
different: e, h in general e > h.
Calorimeter response to hadrons: Rh = eEe+ h Eh
Ee >> EhEe <<Eh
Rh = eEe+ h Ehe > h
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What are the implication of this type of showerWhat are the implication of this type of shower
We have seen that there are two types of shower components: electromagnetic Ee() and hadronic Eh().
The calorimeter reponse to the two components is
different: e, h in general e > h.
Calorimeter response: R = eEe+ h Eh
Ee >> EhEe <<Eh
Rh = eEe+ h Ehe = h
R
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What are the implication of this type of showerWhat are the implication of this type of shower
Calorimeter response to hadrons and electrons:
h
e
h
e
e
h
Ef
R
R
e
11 0
Often indicated as e/h
eee
eehhh
ER
EER
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Non linearity due to e/hNon linearity due to e/h
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Longitudinal Hadronic shower shapeLongitudinal Hadronic shower shape
95% containment 300 GeV 8 i.e.: 85 cm U.
For electron containment of same energy 10 cm U.
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Longitudinal leakageLongitudinal leakage
Position of shower maximum: tmax ln(E)
For 98% containment of 10 GeV = 2, for 100 GeV 7
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Mean is a rough concept for hadrons …four different longitudianl profiles
Mean is a rough concept for hadrons …four different longitudianl profiles
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Transverse shower shapeTransverse shower shape
Two components: em core + non-em halo mainly non relativistic particles
95% containment 80 GeV 1.5 / 32 cm
For electrons 95% containment of same energy 3.5 cm
A factor 9 for in both directions.
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Lateral leakageLateral leakage
The em components increases and the shower gets sharper.
150 GeV
10 GeV
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Energy resolutionEnergy resolution
The energy resolution is dominated by fluctuations in: • visible energy - ultimate limit for hadronic fluctuations• em component – this is the dominant factor in calorimeter with e/h 1 as is the case for non compensated calorimeter
em component
150 GeV -
As we have seen this fluctuation induces a worse resolution as e/h is different from 1.
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Effect of e/h on hadron lineshape Effect of e/h on hadron lineshape
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Dealing with e/hDealing with e/h
The calorimeters with e/h 1 are said to be non-compensated. In order to recover linearity and to improve the hadronic resolution two possible strategies:Hardware compensation: tuning the sampling fraction, sampling frequency and the type of materials used in sampling calorimeters it is possible to enhance the response to the hadronic part of the shower thus reaching e/h = 1Software compensation exploting the longitudinal and transverse segmentation of the calorimeter it is possible to correct event by event the reconstructed energy by weighting differently em-like deposits and hadron-like deposits.ATLAS and CMS have chosen the software compensation.
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An hadronic calorimeter for LHCAn hadronic calorimeter for LHC
The same consideration made for EM requirements in LHC environment (radiation hardness, rates …) are true for Hadronic calorimeters. Calorimeters will have the main impact on performances for:
Jets : collimated particles with different energies produced by parton hadronization
ET miss: Jets are the worst reconstructed objects thus have impact on Et miss resolution
Single hadrons i.e. from tau or W decaysRequest on resolution and linearity set with benchmark channels: W → jj, top mass, sensitivity to compositness
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Response to jetsResponse to jets
Jets are composed by many low energetic particles. Very semplified model for jet composition.
100 GeV jet
R.W
igm
an
s et a
l. “On
the
en
erg
y m
ea
sure
me
nt o
f ha
dro
n je
ts”
It is very important to understand the behaviour of the calorimeter up to 1 GeV hadron to understand the performances to jets.
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The Hadronic calorimeter The Hadronic calorimeter
The hadronic calorimeter is composed by:
- EM calorimeter section (about 1 , 25X0)
- Hadronic calorimeter section
We will see that the performances on hadrons are due to both these sections.
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LAr/Cu 1.7 <|| < 3.2
4 longitudinal sections
ATLAS Hadronic sectionATLAS Hadronic section
Both hadronic and em
LAr/Cu or W 3.2 <|| < 4.9
3 longitudinal sections
Tile Calorimeter || < 1.7
Fe / Scintillator
3 longitudinal sections
Longitudinal depth about 8 -10
Different technologies to cope with higher radiation at higher eta.
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Atlas central hadronic sectionAtlas central hadronic section
Barrel
Ext. Barrel
Principle of operation of TILE
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TileCal - Sezione centraleTileCal - Sezione centrale
Tile Preassembly
TileCal modules
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CMS Hadronic sectionCMS Hadronic section
Central Hadronic || < 1.7 :
Brass/Scintillator + WLS
2 + 1 (HO) Longitudinal section
5.9 + 3.9 (|| =0)
Endcap Hadronic 1.3< || < 3 :
Brass/Scintillator + WLS
2/3 Longitudinal sections
Forward calorimeter 2.85 < < 5.19:
Ferro/fibre di quarzo
Brass has been chosen since it is a non magnetic material
COIL
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CMS Hadron CalorimeterCMS Hadron Calorimeter
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CMS and ATLASCMS and ATLAS
• The choices made for the hadronic central section by ATLAS and CMS are similar: sampling calorimeters with scintillator as active material. • In both case the dominant factor on resolution and linearity is the e/h 1
ATLAS: e/hhad 1.4 e/hem 1.5
CMS: e/hhad 1.4 e/hem 1.6
• ATLAS higher segmentation and better stochastic term gives better total resolution
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e/h at work…e/h at work…
15%
E/
p
e/e/
Ebeam (GeV)Ebeam (GeV)
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CMS Energy resolution on pionCMS Energy resolution on pion
interacting in HCAL
In HCAL or ECAL
no weigthing
o passive weighting
dynamic weighting
Effect of different e/h + no longitudinal sampling in EM
%4%101
E
E
%5%122
E
E
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ATLAS energy resolution on pionsATLAS energy resolution on pions
EE
8.1%8.1
%9.41
E
Linearita < 2%
Shown for ATLAS but
similar for CMS
NIM
A44
9(20
00)
461-
477
EM scale
Corrected with longitudinal samples
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CMS and ATLAS CalorimeterCMS and ATLAS Calorimeter
ATLAS has much higher longitudinal segmentation thus correct the hadron signal with sw compensation.
CMS has chosen a non segmented em calorimeter and a less segmented hadron calorimeter thus is more difficult to obtain sw compensation
Also the presence of the coil and calorimeter design of CMS starts with a much higher stochastic term
It should be noticed that when considering jets there are many effects related to jet reconstruction (out of cone correction, parton to jet calibration…) that affect the resolution.
Again we see a different point of view … a different bet
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ConclusionsConclusions
I hope I have given you an idea of what are the reasons behind the design and the choices of the calorimeters. I have skipped many items that are important for calorimeters:• Calorimeter calibration, how do I set the E scale …• Calorimeter monitoring, how do I keep the E scale • Effect of detector integration on calo performances• Particle ID with calorimeters• position measurement with calorimeters• Jet reconstruction and calibration• …..you can find much more than I said in the references that I listed at the beginning of the presentation.
Good luck and I wish to all of us a great discovery times …
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Back up SlidesBack up Slides
Dist. from PMT (cm)
Np
e/M
eV 16.5
16
15.5
15
14.5
14
13.5
13
12.5
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25
all polishedRa = 0.34 Ra = 0.24
• all polished Ra=0.34 Ra=0.24
• A non uniformity of the light collection in the shower max region may significantly contribute to the constant term in the energy resolution.
• Uniformity can be controlled by depolishing one lateral face with a given roughness
Light Collection Uniformity
Uniformity treatment
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Particle IDParticle ID
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20000 photons pT : 6060 GeV : -2.5 2.5
Vertex de génération: point d’interaction d’ATLAS
Dispersion réaliste sur la position du vertexZ
r
5.6 cm5.6 cm
15
15
mm
Point d’interaction Point d’interaction typique du LHC (typique du LHC ( ) )
6060
E
mrad60 E
mrad60
résolution angulaire
Simulation complète du détecteur (GEANT3)
Reconstruction sans bruit électronique, sans effet d’empilement
Regroupement des cellules dans des amas 3x3 (compartiment milieu)
Résolution angulaire – photons pointantsRésolution angulaire – photons pointants
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Jet adronico Jet adronico
Ric
ostr
uzio
ne
Jet di partoni (hard scattered parton e
FSR)
Jet calorimetrico
Jet di particelle dopo
l’adronizzazione
Generazionecascata partonica
(FSR)
Adronizzazione
Hard scattering partone-
partone
Cascata elettromagnetica ed
adronica nei calorimetri
Un algoritmo di ricostruzione dei jet deve essere applicabile a jet calorimetrici, di particelle e di partoni
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Il calorimetro di CMSIl calorimetro di CMS
EM calorimeter || < 3 :
PbW04 crystals
1 sezione longitudinale 1.1 ,
= 0.0174 0.0174
Central Hadronic || < 1.7 :
Cu(70%)+Zn(30%)/scintillatore+WLS
2 + 1 (HO) sezioni longitudinali
5.9 + 3.9 (|| =0)
= 0.087 0.087
Endcap Hadronic 1.3< || < 3 :
Cu(70%)+Zn(30%)/scintillatore+WLS
2/3 sezioni longitudinali 10
= ~0.15 0.17Forward calorimeter 2.85 < < 5.19:
Ferro/fibre di quarzo = ~0.175 0.17
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CM
SC
MS
Compensazione Compensazione
CMS e/h = 1.4
ATLAS e/h = 1.36/1.5
S = 15%-12% per E 20-300 GeV
e/e/ in in scala
elettromagnetica (ATLAS)
Erec = EEM + ( H1 + H2 + H3)
un alto segnale in H1 indica presenza di un adrone e quindi il segnale in EM e` sottostimato > 1 corregge per e/h < 1. Il coefficiente utlizzato e` costante.
AT
L AS
AT
LAS
correzione simile a CMS indicata con “benchmark” correzioni per EM e Had. Cal. per la non compensazione con coefficienti costanti.
metodo H1 [NIM-A1809(1981)429] :
Erec = WEM(Ecell,Epart)Ecell +
WHAD(Ecell,Epart)Ecell
W ottenuti minimizzando la risoluzione
e/e/
Ebeam (GeV)Ebeam (GeV)
Had. Cal.
HB
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ATLAS e CMS Test BeamsATLAS e CMS Test BeamsN
IM A
449(
2000
) 46
1-47
7
ATLAS: EM LAr + TileCal
Linearita < 2%
/E
benchmarkH1
EE
8.1%8.1
%9.41
E
BenchmarkH1
120% 5%E
E E
NIM
A45
7 (2
001)
75-
100
CMS: EM LAr + TileCal
15%
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Fase 2 : ricostruzione del segnale associato al jet di particelle.
• definizione dell’algoritmo di costruzione del jet : cono, KT, ... per associare i rilasci di energia generati da particelle appartenenti allo stesso jet;
• come si riporta la scala di energia alle particelle che hanno generato il jet.
Fase 2 : jet di particelle Fase 2 : jet di particelle
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Resolution on ETmiss QCD and tails Resolution on ETmiss QCD and tails
calocells
TE
ETmiss resolution on QCD di-jet events
2 events containing 1 neutrino at high pT
if leading jet undetected
ricostruiti
Tail on ETmiss are a dangerous background for SUSY
Z ( ) + jetfull simulation
Events with ETmiss > 50 GeV
EB/B
(p
xmis
s,p
ymis
s)ATLASATLAS
•Rejection factor for Z+jet >10-3
• The distribution of (jet) di Z+jet allows to monitor the efficiency losses in crack region.
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Come definire un jet calorimetrico ?Come definire un jet calorimetrico ?
E’ un problema aperto che si sta ampiamente discutendo (anche in CDF e D0 hep-ex/0005012-10/5/2000). Ci
sono vari dettagli che devono essere definiti :
• Metodo : come associare celle calorimetriche appartenenti allo stesso jet (cono, KT ....);
• come decidere se due jet ricostruiti come oggetti separati sono da unire in uno stesso jet (splitting/merging);
• come ottimizzare la velocita` di esecuzione;
• come definire le quantita` cinematiche dei jet ricostruiti.
Inoltre deve essere possibile applicare l’algoritmo a calcoli QCD in modo da poter ottenere predizioni senza introdurre ulteriori parametri.
Jet algo
rithm
Recom
bination schem
e
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Jet algorithm 1 : conoquello che viene specificato da Snowmass (1990) algorithm
Jet algorithm 1 : conoquello che viene specificato da Snowmass (1990) algorithm
1. si considerano tutte le torri nello spazio (,);
2. per ogni torre si associano le torri a distanza dal centro minore di R (R = 2 2);
3. se il centro geometrico del cono (C,C) coincide con il centroide pesato con ET il jet e` considerato stabile.
Dettagli importanti non sono definiti in questa procedura : preclustering, ET seed (diminuzione tempo di esecuzione),
splitting/merging.
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Jet algorithm 1 : cono snowmass rivisto
Jet algorithm 1 : cono snowmass rivisto
1.si considerano tutte le torri nello spazio (,) con ET > ETseed;
2.per ogni torre si associano le torri a distanza minore di R = 22
3. se il centro geometrico del cono (C,C) coincide con il centroide pesato con ET il jet e` considerato stabile.
4. man mano che si raggiungono dei jet stabili le torri assegnate al jet non vengono riutilizzate (HLT).
4. i jets che condividono piu` di una percentuale S di energia vengono uniti altrimenti le torri in comune si assegnano al jet piu` vicino.
R ETseed S
ATLAS 0.7 * 2 GeV 50%
CMS 0.5 * 2 GeV -
CDF 0.4/0.7 ** 1 GeV 75%
(*) High luminosity. (**) 0.4 top analysis / 0.7 QCD.
Recombination scheme
CM
SC
MS
AT
LAS
AT
LAS
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Jet algorithm 2 : kTJet algorithm 2 : kT
Tiene conto della vicinanza in R in impulso trasverso (kT) e non associa ad ogni cluster una forma predefinita :
2
2ij2
jT,2
iT,ij
2iT,ii
D
ΔR)k,min(kd
kd
Collineari (if R<<1 )
Risoluzione in R = 1
d =
se (dmin = dii) jet
se (dmin = dij) uniscono ij (4-vector
sum) in un nuovo dii
Si ottengono jet separati da R > D;
Per ogni coppia di torri i,j
j j j
j j
j j
j
j
jj j
j
j
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E(jet-celle) E(jet-particelle)E(jet-celle) E(jet-particelle)
10 bin in costanti di calibrazione (p2 p1 p0) in modo da
riportare il valor medio dell’energia trasversa ETrec
all’energia delle particelle nel cono ETgen:
<ETric>=p2*(ET
gen)2+p1*ETgen+p0
pseudorapidity
CMSCMS algoritmo
a cono
QCD jets
DA
Q&
HLT
TD
R (
2002
)
DA
Q&
HLT
TD
R (
2002
) 070181
.E
.
E
σ
070481
.E
.
E
σ
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
127
E(Jet-cell) E(jet-particelle)E(Jet-cell) E(jet-particelle)
metodo alla H19 bin in ET costanti di calibrazione Wi per i vari sample
longitudinali del calorimetro EM e HAD in modo da minimizzare la risoluzione percentuale in energia :
ATLASATLAS
evtevent evtparticleT
icalsezievtTi
E
EwD
2
,,
,,
1
Energia del jet costruito dalle particelle MC piu` vicino al jet ric. in R
I pesi sono ottenuti su jet calcolati con KT ma funzionano bene anche per l’algoritmo a cono.
Al momento la dipendenza da dei pesi non e’ inclusa si includera` non appena si avra sufficiente statistica
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
128
CMS + jet CMS + jet
Dopo 3 mesi a bassa luminosità errori statistici < 1%
Calibrazione k(Etjet) dalla posizione di Et
jet_cal/Et_reco.
Trigger apposito per di “bassa” energia
forward
barrelEnd cap
109
Full simulation
CM
S IN
220
2/07
1 CM
S IN
220
2/07
1
Correlazione pT - pTjet per la generazione
A basse energie fondo elevato da -brem e dal decadimento di mesoni.
Selezione : -jet , isolamento, Et di altri jet nello evento,… con S~10% riducono il fondo per Et
>100 GeV, sotto studio possibili selezioni più stringenti per Et piu` basse.
Alta statistica ma...
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
129
ATLAS Z+jetATLAS Z+jet
Z + jet + jet jet
TZT pp
La calibrazione si ottiene imponendo :
verificata solo approssimativamente per la presenza di ISR
Efficienza per la selezione degli eventi 10%
30% running efficiency
in 1 mese si hanno circa 30000 Z+jet nel barrel (1033 cm-2sec-1)
Prima della calibrazione
6%
Dopo la calibrazione
rawT
ZT
rawT
p
pp
5 fb-1
light jets1%
Studio con fast simulation
AT
L-P
HY
S-2
002-
026
partoneT
partoneT
calT
p
pp
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
130
Controllo della calibrazione all’inizio di LHC : mtop
Controllo della calibrazione all’inizio di LHC : mtop
Single lepton channel Period evts dMtop(stat)
1 year 3x105 0.1 GeV
1 week 1.9x103 0.4 GeV
CDF http://cdf.lbl.gov/~currat/talks
Final CDF Mt = 176.0 4.0 5.1 GeV
RUNI = 2 fb-1
Incertezza sulla scala jet e b-jet unconstrained fit
RUNII 0.7
jet unc. Mtop(jet) Mtop(bjet)
1% 0.9 GeV 0.7 GeV
5% 11 GeV 3.5 GeV
1033cm-2sec-1
Eventi in top m
ass window
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
131
1033cm-2sec-1
Risoluzione su massa A0 Risoluzione su massa A0
ATLASATLAS CMSCMS
ATLAS CMS
M(A ) 450 500
M 440 521
/M 12% 15%
M/M -2% +4.2%
Tagli analisi :
jet jet
ET jet > 60 GeV
ETmiss > 0
(j1-j2) < 1750
Tagli analisi :
jet jet, ll,ljet
ET jet > 40 GeV ET l > 20 GeV
ETmiss > 0
(j1-j2) < 1660
Confronto per simili condizioni :full simulation - pythia6.1 - pile-up
CM
S N
OT
E
2003
/006
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
132
Risoluzione su ETmiss QCDRisoluzione su ETmiss QCD
calocells
TE
ETmiss resolution on QCD di-jet events
(p
xmis
s,p
ymis
s)ATLASATLAS
missing ET atteso 0;
risoluzione consistente con quanto trovato per eventi con alto missing ET.
Phys TDR A0 to tau tau
0.46*ET
Italo-Hellenic School of Physics 2005 – Martignano June 2005
C.Roda University and INFN Pisa
133
ATLAS e CMS Test BeamsATLAS e CMS Test Beams
60% a 100 GeV20% a 400 GeV
Regione in “avanti”
Regione in “avanti” : Hadronic LAr EC
Risoluzione in energia dopo la correzione per il leakage :
NIM
A48
2 (2
002)
94-
124
E a bE E
%2.5
%2.62
E E