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Basic definitions and introductory remarks • Ionization ...iaselli/Fisica dei...
Transcript of Basic definitions and introductory remarks • Ionization ...iaselli/Fisica dei...
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• Basic definitions and introductory remarks
• Ionization energy loss
• Time of Flight
• Cherenkov radiation
• Transition radiation
Advised textbooks:R. Fernow, Introduction to Experimental Particle Physics, Cambridge University PressR.S. Gilmore, Single particle detection and measurement, Taylor&Francis, 1992G. F. Knoll, Radiation Detection and Measurement, John Wiley and Sons, New York W. R. Leo, Techniques for Nuclear and Particle Physics Experiments, Springer, 1994
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Complete event analysis (based on the reconstruction of conservation laws): 4-momenta of secondary particles
Deflection in a magnetic field
(+ sign of particle’s charge)
Calorimetry(destructive measurement, effective for neutral particles only)
PID measurement2
242 cpcmE +=
“m” uniquely identifies the internal quantum numbers of the particle
Example:
(p,E)
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Very useful for neutral particles and leptons because of their peculiar interactions with media: electron quickly produces an em shower, µ travels through the entire detectorHadronic showers from π, K, p all look alike and calorimeter energy resolution is not enough to allow measuring mass from m2=E2-p2
example: p=2 GeV/c, Eπ= 2.005 GeV, EK= 2.060 GeV
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The lateral spread of the shower is mainly governed by the multiple scattering of the electrons (Moliereradius RM ).95 % of the shower is contained inside a cone of size 2RM
Various complex processes involved:hadronic and electromagnetic
components
Hadronic shower
charged pions, protons, kaons ….Breaking up of nuclei (binding energy), neutrons, neutrinos, soft γ’smuons …. → invisible energy
neutral pions → 2γ →electromagnetic cascade( ) 6.4)(lnn 0 −≈ GeVEπ
Large energy fluctuations → limited energy resolution
Hadronic showers are much longer and broader than electromagnetic ones !
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Identification method: calculate the invariant mass with all possible daughter candidates
( )2
jj
2
i i2 cpEc1massinvariant M
−== ∑∑
No PID one K identified
two Ks identified φ Κ+Κ−
mφ=1020 MeV/c2
Decay vertex may be reconstructed if it is far from interaction point and daughters are charged
Combinatorial background is
often criticalPID mandatory
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Branching ratios: Bd→π+π− = 0.7×10−5, →K± πm = 1.5×10−5
Bs→K+K− = 1.5×10−5, →K± πm = 0.7×10−5
PID PID
LHCbLHCb
Purity=13%Purity=84%Efficiency=79%
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Bs → Ds KMajor background: Bs → Ds π (No CP violation)
PID PID
LHCbLHCb
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70’s: Hydrogen bubblechamber
1978: BEBC
A Look at the Past A Look at the Past
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A “Modern” Approach to PID
A “Modern” Approach to PID
ALICE at LHC
Silicon trackers +TPC (PID with energy loss)Ring Imaging Cherenkov detector
TOFTRD
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Basic LayoutBasic Layout
magnetic field|p|,charge
Layers of silicon detectors with excellent position (0(10 µm)) and double track (0(100 µm)) resolution near the primary collision region •detection of secondary vertices (short-lived strange and heavy flavorparticles)• impact parameter resolution σ(rφ) ~ 50 µm for pt ~ 1 GeV/c• primary vertex resolution: ~ 10 µm• momentum resolution improvement• PID with energy loss
TPC, away from the interaction region, at more moderate particle densities • tracking (δp/p at the level of 1% for low momenta)• PID with energy loss
e.m. calorimeterTOF and TRD
RICH
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Measuring the Particle VelocityMeasuring the Particle Velocity
( )( )
2
222
21
221
22122
221
222
2
2
2)(
0
mdm
factor) (Lorentz ;
pcmm
cpmm
pdp
pdpd
mcEmcp
−≅
∆
∗+∆
=−
≅
+
=
==
ββ
βββββ
ββγ
γγβ
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0,1 1 10 100 1000
Particle Identification Techniquesp (GeV/c)
π-K identification rangesTR+dE/dx
Cherenkov
dE/dx
TOF150 psFWHM
electron identification
The applicable methods depend strongly on the particle momentum (velocity) domain of interest
PID techniques are based on the detection of particles via their interaction with matter: ionization and excitation (Cherenkov light & Transition Radiation)
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identifiedAABB
BidentifiedAAB
totalAidentifiedAAA
NN
NNefficiency
−≠
−→
−−→
∑==
==
/ioncontaminat,
ε
ε
higher efficiency -> larger contamination
(example: ALICE-ITS simulation)
purity= 1-contamination
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Momentum (GeV/c)10-1 1 101 102 103
10-2
10-1
1
10
Det
ecto
r le
ngth
(m)
ToF (100ps@FWHM)RICH
TR+dE/dx
dE/dx
3σ separation for π/K
Liquid-SolidAero
gel
Gases
Separation Power
AB
BA SSnσσ
−== power separation
N.B. in case of samples with different population:at a given separation power, the resulting contaminationof the largest populated sample of particles in the other species will be larger by a factor equal to the ratio between the relative populations
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Basic processes occurring when a charged particle traverses a mediumbeing surrounded by a cloud of virtual photonsthat interacts with atoms in the medium
• ionization and excitation of the atoms of the medium (secondarily produced electrons could further ionize the medium)
• radiative phenomenaCherenkov radiationTransition radiation
Overall effect: the particle loses energyDetection of the energy lost is the physical
basis of many of the techniques used in charged particle detectors
Energy Loss MechanismsEnergy Loss Mechanisms
Ionization trail: particle’s trajectory and velocity information
δ-ray
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e-
θ
khh , photonvirtual
ω
0, mpparticle ∫∫∞
ω
∞ σ−=
v dEdpddpEdEn
dxdE
/
2
0
(photon)
time
space
A Batom
fastchargedparticle
Modern approach (unitary description in terms of matter properties): Allison and Cobb (1980)• Charged particle moves in a dielectric medium through which virtual photons propagate • The particle loses energy by doing work against the field created by the medium polarization
atom
ionization by close collisions δ-electrons
exci
tatio
n
ioni
zatio
n by
di
stan
t col
lisio
n
belo
w e
xcita
tion
thre
shol
d
energy transfer/photon exchange
rel.
prob
abili
ty Schematically !(after Gilmore)
photons are virtual, their energy and momentum are independent E≠pc• the integral must be performed over both energy and momentum separately• virtual photon behaviour approximated with a combination of cross sections for the interactions of real photons allowing to perform the momentum integration for virtual photons
ω= hEkp h=
∫∞
−=0
dEdEdEn
dxdE σ
density of atoms: n=ρNA/A
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Classical approach : Bethe-Bloch equation modified to include the Fermi effectAverage specific energy loss:
Valid only for particles with m>me
• dE/dx does not depend on m but on the charge z• Non relativistic region: dE/dx ∝1/β2
(more precisely as β-5/3)• Minimum: at βγ = 3÷4 (Minimum Ionizing Particle)
• At high βγ: dE/dx ∝lnγ2 (relativistic rise)• Density effect: δ(βγ)
(medium polarization reduces long range effects)saturates at βγsat: 230 Ar
68.4 CH455.3 C2H642.4 C4H105.6 Si
22
2ln2130710
2
2max
222
2
2
−−−⋅−=
ZCδβ
IEγβcm
βztρ
AZ.
dxdE e
Ionization Energy LossIonization Energy Loss
2121 cm MeV gmipdxdE −÷≈
Z=atomic number of the medium;I~Z•12 eV=effective ionization potential;Emax=max energy transfer (I ≤ dE ≤ Emax)
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( )222 ln1 γβ
β∝
dxdE
βγmp =m from simultaneous measurement of p and dE/dx
Fermi plateau is a few percents above the minimum in solid and liquid media, 50-70% in high Z noble gases at STP -> PID in the relativistic rise region only possible in gases!π/K separation (2σ) requires a dE/dx resolution of few percents
Particle ID using the specific energy loss dE/dx
Average energy loss in 80/20 Ar/CH4 (NTP)(J.N. Marx, Physics today, Oct.78)
( )dxdEdxdEdxdEn
B
BA
///
σσ−
=
(dE/
dx)/
(dE/
dx) m
in
:”cross-over” regions (as wide as + 100 MeV/c)ambiguites-> complementary PID mandatory
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<dE/dx> is practically measured by evaluating ∆E in a short interval δxthis is not necessarily the average energy lost in the given slice of material-> the distribution shows large fluctuations and Landau tail
Fluctuations in the energy loss dE/dx
Most interactions involve little energy exchange -> the total energy loss from these interactions is a Gaussian (central limit theorem). Few interactions involve large energy exchange-> Landau tail
Because of the high energy tail, increasing the thickness of the detector or choosing high Z material does not improve σ(dE/dx). Indeed the relative width of Gaussian peak reduces but probability of high energy interaction rises -> tail gets bigger
(B. Adeva et al., NIM A 290 (1990) 115)
1 wire 4 wires
L: most likely energy lossA: average energy loss
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(M. Aderholz, NIM A 118 (1974), 419)
Samples must not be too many:for each total detector length L, there existsan optimal N
Rule of thumb: at least N=100 for a total tracklength of 3-5 m/atm
• Choose material with high specific ionization• Divide detector length L in N gaps of thickness T.• Sample dE/dx N times• Calculate truncated mean, i.e. ignore samples with (e.g. 40%) highest values• Also pressure increase can improve resolution. Drawback: reduced relativistic
rise due to density effect !
Improve dE/dx resolution and fight Landau tails
Thick absorber: large chance of high energy δ ray production cancels the reductionof fluctuations -> (dE/dx)A – (dE/dx)B < Landau fluctuationsUsual method of measuring dE/dx is:
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Particle Separation
– dE/dx resolution (A.H. Walenta et al. Nucl. Instr. and Meth. 161 (1979) 45)
n: number of sampling layers,t: thickness of the sampling layer (cm)p: pressure of the gas (atm)
Remarks:• σ does not follow the n-0.5 dependence owing to the Landau
fluctuations;• if the total lever arm (nt) is fixed, it is better to increase n;
so long as the number of produced ion-pairs is enough in each layer.
( )dxdEBdxdEAdxdEBAN DS /
)(/)(/);(.. σ−
=
( ) 36.032.047.043.0 )(/ −÷−−÷− ⋅∝ ptndxdEσ
dE/dx & Separation Power
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Time Projection Chamber → full 3-D track reconstruction• x-y from wires and segmented cathode of MWPC• z from drift time -> precise knowledge of vD (LASER calibration + p,T corrections)
• dE/dx
Gate open Gate closed∆Vg = 150 V
Drift over long distances → very good gas quality required
Space charge problem from positive ions, drifting back to medial membrane → gating
TPC: basic principle
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80’s: 6.4 TeV Sulphur - Gold event (NA35)
TPC
Tracker evolutionTracker evolution
STREAMER CHAMBER
2000: STAR
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• Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm, 50,000 Liters
• Voltage : - 31 kV at the central membrane 148 V/cm over 210 cm drift path
420 cm
Self supporting Inner Field Cage:Al on Kapton using Nomexhoneycomb; 0.5% rad length
STAR TPC
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Two-track separation 2.5 cmMomentum Resolution < 2%
Space point resolution ~ 500 µmRapidity coverage –1.5 < η < 1.5
A Central Event Typically 1000 to 2000 tracks
per event into the TPC
STAR TPC
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Anti - 3He
dE/dx PID range:
~ 0.7 GeV/c for K/π~ 1.0 GeV/c for K/p
PID via dE/dx with the STAR TPC
12
πK
p d
eµdE
/dx
(keV
/cm
)
0
8
4
Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm
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Pb+Pb @ 158 GeV/nucleon
NA49 TPCs
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Field Cage Inner Vessel
drift gas90% Ne - 10%CO2
gas volume88 m3
Central membrane frame
ALICE TPC
6x105 channels, corresponding
to 6x108 pixels in space
560 cm
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Field Strips
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TPC Assembly
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E. NappiNch(-0.5<η<0.5) = 8000slice: 2o in θ
Projection of a slice (2o in θ)
Nr. of Pixels:570,132 pads x 500 time bins
Projection of the entire drift volume into the pad plane; dNch/dy = 8000(~ 2 x 104 charged particle tracks)
Nr. of hits = 19,431,047
Challenge: Track Density in Pb-Pb
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TPC dE/dx performanceTPC dE/dx performanceAt dN/dy = 8000 At dN/dy = 4000
σ dE/dx = 10 % σ dE/dx = 7 %
σ dE/dx =10%
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Drift Velocity Control:Pressure (mbar)
5.44
5.45
Drif
t vel
ocity
(cm
/µs)
1010 1020
• Lasers for coarse value• Fine adjustment from tracking
TPC: experimental issues
• mechanical tolerances (gain and electrical field)• stability of high voltage power (gain)• space charge effects (track distortion)• gating efficiency (background)• temperature, pressure (drift velocity)
examplesfrom STAR
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6.9
3.0
2.8
4.6
6.4
7.5
6.6Calc.(%)
7.0Ar/CO2 /CH4 =89/10/110.8372Drift ch.MKII/SLC*
2.8Ar/CH4 /iC4H10 =88.2/9.8/2 41.0159Jet ch.OPAL*
3.0Ar/CH4=80/ 208.50.4183TPCPEP*
4.5Ar/CH4=90/ 1010.4338TPCALEPH*
5.7Ar/C2H6=50/5011.451Drift ch.CLEO II
7.2He/C4H10=80/2011.440Drift ch.Babar
5.1He/C2H6=50/5011.552Drift ch.BelleMeas.(%)Gasp (bar)t (cm)nType
• Higher pressure gives better resolution, however, the relativistic rise saturate atlower βγ. 4 – 5 bar seems to be the optimal pressure• Higher content of hydro-carbons gives better resolution (Belle and CLEO II).
Landau distribution (FWMH); 60 % for noble gas, 45% for CH4,33% for C3H6
( ) 32.043.0 )(41.0/ −− ⋅= ptndxdE calcσdE/dx Detector Performance
* Data from M. Hauschild (NIM A 379(1996) 436)
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L=particle’s path between
two counters
t=time to traverse L
For two particles:
For known momentum p:
In the non-relativistic limit (β~0.1):
Time of flight: basicsTime of flight: basics
tLv == speed particle
( ) ( )[ ]
( ) ( )mmtmm
cmLtm
pLmm
pLt
cpcmcpcmpcL
pcE
pcE
cLt
cL
vvLttt
cvvvmmm
∆=−=∆⇒∆=−=∆
+−+=
−=∆
−=
−=−=∆
==≅=≅
1212
2/122421
2/1224222
12
121212
1212
1111
β
ββ
β
Consequently, for a time resolution of ∆t=200 ps and a flight path L=1 m, it is possible to discriminate between low-energy particles to better than 1% level of accuracy
12
22
−==Ltcp
cpm
γβ
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12
22−=
Ltcpm
Combine TOF with momentum measurement2
42
LdL
tdt
pdp
mdm
+γ+
=Mass resolution
TOF difference of two particles at a given momentum
−≈
+−+=
−=∆ −
22
212
2222
2221
2121
2/1/111 mm
pLcpcmpcm
cL
cLt
ββ
Time of flight for relativistic particlesTime of flight for relativistic particles
For momenta above some GeV/c the resolution in mass discrimination is almost lost
+−
+=
∆=
222211
pcm
pcm
cLtN BA
ttAB
t σσσ
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In ALICE, the time resolution
of TOF is 100 ps
3σ separation equivalent to
300 psdifference
π/K up to 2.2 GeV/c K/π up to 3.7 GeV/c
L=4 m
Momentum limit at 3 σMomentum limit at 3 σ
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From Theory to Practice
From Theory to Practice
TOF PID asenvisaged in
ALICEfor Pb-Pb collisions
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TOF: experimental issuesTOF: experimental issues
Start and stop countersfast detectors:
plastic scintillators (well assessed technology)gaseous detectors (old technology, new advances)
Specific signal processing (timing+charge measurements)pulse height analysis->digital conversion to stop a fast digital clock
discriminators (specifically designed for slewing correction)TDCs
Calibrations – corrections for cable lengths, counters delay time….Continuous stability monitoring
start counter stop counter
particle
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production of scintillation light (luminescence)
Scintillation CountersScintillation Counters
Dynodes Anode
e l e c t r i c a lp u l s e
Photocathode
photon
photoelectron
∼ 106 secondary electrons
particle
scintillator light guide photon detectorMatches the scintillatorshape to the PMT’s round face and transports photons (total internal reflection & external reflector)
convert photons to electronsthus providing an electrical signal
Nphoton~ 2 •104/cm
1 photon/100 eV
fish-tail
QE = Np.e./Nphotons
dynode gain = 3-2010 dynodes with gain=4
M = 410 ≈ 106
cm/MeV2~dx/dE
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ScintillatorsScintillators
Two types:
Inorganic crystals (high density and Z materials: NaI, CsI,…)good light yield, too slow for TOF application (OK for e.m. calorimeter)
Organic scintillators (low Z material: polystyrene doped with fluorescent molecules to shift light from UV to visible & monocrystals: naphtalene, anthracene, p-terphenyl….)Excitation at molecular level
The light yield is lower than for inorganic scintillators because of recombination and quenching effects of the excited molecules. Fast, suited for TOF application
photons / MeV Decay time
CsI(Tl) 50000 800 ns
Pilot U 11000 1.4 nsDensity (g/cm3)
1.03
4.5
representativescintillators
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• Excitation: A0->A1 (∆E=EA1-EA0=absorption spectrum)• Vibrational energy transfer to other molecules nearby: A1->B1• Scintillation: B1->B0 (∆E=EB1-EB0=emission spectrum)• Decay from the vibrationally excited ground state to energetic minima: B0->A0
Because of the energy lost by vibrational quanta:emission and absorption spectra are shifted in wavelength
scintillator is transparent to the light it produces
Organic ScintillatorsOrganic Scintillators
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Number of photo-electrons
25.0~ >< QE
Photon detector transit time spread limits the TOF performance:
• Line-focus type PMT : 250 ps (Philips XP2020)
• Fine-mesh type PMT : 150 ps ( Hamamatsu R2490-05)
• Micro-channel Plate : 55 ps (Hamamatsu R2809U)
Design Issues
( ) λλλλ dQEDeNN Lphpe ⋅⋅⋅⋅= ∫ − )()(phl
Nph∼104/cmL=scintillator length, lph(λ)=photon attenuation lengthD=photon collection efficiency (including geometry factors)
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Expected timing resolution for long counters
From W. B. Atwood (SLAC) 1980:
pet N
cmLcmps )()(87~ 2/1 ⋅⋅ −σ
14390250R6680BC4084 x 6 x 255Belle420180180XP2020SCSN382 x 3 x 300R. Stroynowski240210300R1828BC4124.2 x 13 x 400TOPAZ125110270XP2020BC4085 x 10 x 280E. Nappi
5350200R1828SCSN234 x 3.5 x 100T. Sugitate110140180R1332SCSN383 x 20 x 150T. Tanimori
60120200XP2020NE1143x 15 x 100G.D.Agostini
σt(exp)σt(meas)λatt (cm)PMTScintillatorCounter size (cm)
(T x W x L)Exp. application
Overall Time Resolution
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EXAMPLES:Scintillator based TOF EXAMPLES:Scintillator based TOF
grid:
Small, but thick scintillators8 x 3.3 x 2.3 cm
long scintillators (48 and 130 cm), read out on both sides
From γ conversion in scintillators
Flight path=15 m
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PID with TOF only
Combined PID: TOF + dE/dx (TPC)
T rel.
= T
/ Tπ
NA49:TOF + dE/dxNA49:TOF + dE/dx
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Central Arm Detectors
Finely segmented high resolution TOF at mid-rapidtyKeep the occupancy level < 10 %
1500≅dy
dNch segments1000≅
~ 100 cm2/segment
∆φ = 45 deg. , ∆η = 0.7
•Scintillator: Bicron BC404• decay constant : 1.8 ns• attenuation length : 160cm
•PMT : Hamamatsu R3478S• Rise time : 1.3 ns• Transit time : 14 + - 0.36 ns
• Consists of 960 plastic scintillators• Flight path= 5 m• PMT readout at both ends of scint. (1920 ch.)
385cm
200cm
200cm
PHENIX TOFPHENIX TOF
TOF
start timing
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Prism light guideto reduce dead space
PMT
Scintillator slat
PHENIX Preliminary
pK+
K-
π+
π-
p
e+
e-
pK+
π+(a.u
.)
PID cut
PHENIX Preliminary
m2 [GeV/c2]
w/o PID cut
TOF intrinsic timing resolution ~120 ps has been achieved without slewing correction
PHENIX TOF PERFORMANCEPHENIX TOF PERFORMANCE
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1949: J. Keuffel (Caltech) planar spark counters1970: Y. Pestov (Novosibirsk): 1st example of resistive plate chamber: glass electrode (Pestov glass)+ metal electrode
Excellent time resolution ~ 50 ps or better!
Many drawbacks:• long tail of late events• mechanical constraints (high pressure)• non-commercial glass• nasty gas composition (contains butadiene)
ALICE R&Dtest beam: σt ≈ 40 ps !
pressure vessel
TOF with fast gaseous detectorsTOF with fast gaseous detectors
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Gas Amplification in Parallel Plate ChambersGas Amplification in Parallel Plate Chambers
cathode
anode
Uniform and high electric fieldElectron avalanche according to Townsend: N = No eαx
If set minimum gas gain at 106 (10 fC signal) and maximum gain as 108 (streamers/sparks produced above this limit), then sensitive region first 25% of gap
Only avalanches initiated close to anode produce detectable signal on pickup electrodes
A parallel plate chamber cannot perform as a fast gas detector:
• time jitter ≈ time to cross gap ≈ gap size/drift velocity• electron drift velocity ∼cm/µs -> few µm gap• low detection efficiency (for 1 e-ion pair about 30 eV is needed) !!
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E
Volts !
E
5 mV/div
20 mV/div
20 mV/div
50 mV/div
E
From Avalanche to SparkFrom Avalanche to Spark
As soon as the number of electrons in the avalanche reaches ~10 8(Raether’s criterium):the space charge becomes so relevant to balance the external field, the subsequent recombination of electrons and ions generate UV photons that initiate other avalanches (streamer) up to the spark regimeFAST (signal formation driven by UV light rather by slower electrons) but high dead time
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τdischarge << τrecovery= ρε ~ 10 ms
Recovery time long electrodes behave as insulators while electrons reach the anode the electrical field is quenched locally (a small region of almost 0.1 cm2
will appear “dead” for ~ 10 ms)
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
Ci
R
HV
Resistive Plate ChambersResistive Plate Chambers
Pestov idea:use as anodic electrodea high resistivity glass !!Concept extended to RPCswith both electrodes withhigh resistivity
particle
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Requirements:(a) Small gaps to achieve a high time
resolution(b) Very high gas gain (immediate
production of signal)(c) Possibility to stop growth of avalanches
(otherwise streamers/sparks will occur)
C. Williams – INFN Bologna (1999):add boundaries that stop avalanche development. These boundaries must be invisible to the fast induced signal -external pickup electrodes sensitive to any of the avalanches
Designing a Fast Gaseous Detector Designing a Fast Gaseous Detector
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MULTIGAP RESISTIVE PLATE CHAMBER
Stack of equally-spaced resistive plates with voltage applied to external surfaces
Pickup electrodes on external surfaces (resistive plates transparent to fast signal)
Anode 0 V
(-2 kV)
(-4 kV)
(-6 kV)
(-8 kV)
Cathode -10 kVFlow of electrons and negative ions
Flow of positive ions
Internal plates electrically floating!
In this example: 2 kV across each gap (same E field in each gap) since the gaps are the same size - on average - each plate has same flow of positive ions and electrons (from opposite sides of plate) - thus zero net charge into plate. STABLE STATE
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Anode 0 V
(-2 kV)
(-4 kV)
(-6 kV)
(-8 kV)
Cathode -10 kV
-6.5 kV Low E field - low gain
High E field - high gain
Decreased flow of electrons and increased flow of positive ions - net flow of positive charge. This will move the voltage on this plate more positive than -6.5 kV (i.e. towards 6 kV)
Internal plates take correct voltage - initially due to electrostatics but kept at correct voltage by flow of electrons and positive ions - feedback principle that dictates equal gain in all gas gaps
MGRPC: OPERATIONAL STABILITY
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Schott A2(0.5 mm thick)
Schott 8540(2 mm thick)
Anode electrode 3 x 3 cm2
Cathode electrode 3 x 3 cm2
Schott A14(0.5 mm thick)
5 cm
Single cell Multigap RPC
0 1000 2000 3000time difference between start counter and MRPC [ps]
1000
100
10
1
Gaussian fit σ = 77 ps
Tail of late signals 29 events / 17893 events
= 0.16 %
-1000-2000
12 kV
Subtract jitter of start counters of33 ps give time resolution of 70 ps
5 gas gaps of 220 micron
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
8 9 10 11 12 13 14Applied HV (kV)
60
80
100
120
140
Efficiency [%]Resolution [ps]
SPRING 1999
Effic
iency
[%]
Coun
ts / 5
0 ps
Reso
lution
[ps]
MRPC PERFORMANCE
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The red hits/track corresponds to a single particle(π in this case)
Hits in inner tracker
TPC hits
Hits in TOF array
TOF with very high granularity needed!
ALICE TOF
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Along the beam direction
each sector divided into 5 modules
i.e 5 x 18 = 90 modules in total
1674 MRPC strips in total
160 m2 and 160,000 channels
ALICE TOF GEOMETRY
A standard TOF system built of fast scintillators + photomultipliers would cost >100 MCHF
TOF ARRAY arranged as a barrel
with radius of 3.7 mDivided into 18 sectors
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130 mmactive area 70 mm
M5 nylon screw to hold fishing-line spacer
honeycomb panel (10 mm thick)
external glass plates 0.55 mm thick
internal glass plates (0.4 mm thick)
connection to bring cathode signal to central read-out PCB
Honeycomb panel (10 mm thick)
PCB with cathode pickup pads
5 gas gaps of 250 micron
PCB with anode pickup pads
Cross section of double-stack MRPC (5x250 µm gaps per stack)made of resistive plates ‘off-the-shelf’ soda lima glass
Silicon sealing compound
PCB with cathode pickup pads
Flat cable connectorDifferential signal sent
from strip to interface card
Mylar film (250 micron thick)
120 cm
Standard unit detector
there will be ~ 1600 strips
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Dottorato in Fisica Maggio 2005“Fisica dei rivelatori” Identificazione delle particelle
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404550556065707580
5.0 5.5 6.0 6.5
020406080
100
5.0 5.5 6.0 6.5
Efficiency [%]
Applied voltage [kV]Resolution [ps]
strip 12strip 10
Applied voltage [kV]
strip 12strip 10
Typical time spectrum
Typical performance
1000
800
600
400
200
01500 25002000 3000 35001000
STRIP 10 H.V. +- 6 kV
Time with respect to timing scintillators [ps]
0 500 1000-500-1000
1200
1000
800
600
400
200
0
STRIP 10 H.V. +- 6 kV
Time with respect to timing scintillators [ps]
Entri
es/5
0 ps
Entri
es/5
0 ps
Uncorrected time spectrum
time spectrum after correction for slewing
σ = 66 ps minus 30 ps jitterof timing scintillator = 59 ps
σ = 53 ps minus 30 ps jitterof timing scintillator = 44 ps
10 gaps of 220 micron
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Strip 10 effective voltage 11.4 kV
Strip 12 effective voltage 11.4 kV
Strip 10 applied voltage 11.4 kV
Strip 12 applied voltage 11.4 kV
Strip 10 effective voltage 11.4 kV
Strip 12 effective voltage 11.4 kV
Strip 10 applied voltage 11.4 kV
Strip 12 applied voltage 11.4 kV
Equivalent flux of through-going charged particles [Hz/cm2]
Efficiency [%] Time resolution [ps]
50556065707580859095
100
0 200 400 600 800 1000 1200 1400 16000
102030405060708090
0 200 400 600 800 1000 1200 1400 1600
GAMMA IRRADIATION FACILITY AT CERN
Investigated performance with muon beam while test device irradiated with high flux of 662 keV gammas
TOF: rate capability
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Particle Identification Ranges
Efficiency and contamination at high density (dN/dy = 8000)
B = 0.2 T
B = 0.4 T