Post on 16-Oct-2020
The H1 Experiment at HERAThe H1 Experiment at HERA
1.1. The HERA AcceleratorThe HERA Accelerator2.2. Some Examples of H1 Some Examples of H1 epep PhysicsPhysics3.3. The H1 DetectorThe H1 Detector
HERA-I 1992 – 2000HERA-2 2003 – 2007
Ep = 820 / 920 GeVEe = 27.5 GeV
center of mass energy = 300 / 318 GeV
HERA at DESY2 collider exp’s:
H1 / ZEUS : ep physics
2 fixed target exp’s:HERMES : spin physicsHERA-B: CP-violation, B-physics
6.3 km
a1
Slide 2
a1 apis, 7/2/2003
15m – 30m under surface
HERA Tunnel
HERA Components
1) Cavities to accelerate: 130 / 2 MV for electrons / protons 2) Magnets to bend and focus the beams
3) Ulta-high vacuum:~ 10-9 mbar
… much more …
Classification of accelerators Classification of accelerators ……
1 1 -- fixed target fixed target low center of mass energy, high low center of mass energy, high luminocityluminocity
2 2 –– collidercollider high center of mass energy, lower high center of mass energy, lower luminocityluminocity
HERA & Collider family
Complementary physics programsHERA is the only ep collider
Why different colliders ?
Electrons: “point-like”, lower energyProtons : sizable objects, higher energy access different fields …
Luminocity
Luminocity L determines the event rate N for each cross section σ:
LN ⋅= σ
Luminocity given by accelerator parameters:
yx
peNNfnL
σπσ4⋅=
n … number of bunchesf … frequencyN1/2 … particles per bunchσx/y … beam profiles
Typical values : number of bunches n = 180bunch crossing time 1/f = 96 nsecNe/p = 3 / 7 1010 ppbσx/y = 190 / 50 μm
γepep →1) Cross section: Bethe - Heitler process (pure QED !)
( ) ( ) tNNtL BHBgBH ⋅−= σ/
Luminocity Measurement at H1Principle: take a known cross section and measure event rate
L = N/σ
2) Event rate: use e-tagger and photon detector close to the beam line
ttttttttttttttttttt
3) Subtract (beam gas) backgrounds
HERA Luminocity Upgrade
Aim: Increase L by factor 4 – 5 to reach at end of HERA integrated 1000 bp-1 ???
How: 1) increase the beam currents Ie/p = 40/90 mA 60/140 mA2) squeeze the beams at the interaction point magnets in H1/ZEUS
Additional: longidutinal e polarization
Spin rotators(transverse self-polarization by synchrotron radiation, Sokolov- Ternov effect)
HERA Luminocity HERA luminosity 1992 – 2000
Days of running
Inte
grat
ed L
umin
osity
(pb
-1)
1993
19941995
1996
1997
1998
99 e-
1999 e+
2000
15.03.
10
20
30
40
50
60
70
50 100 150 200
10
20
30
40
50
60
70
1
1-
100 :pe15 :pe
−+
−
≈
≈
pbLpbL
Days of running
H1
Inte
grat
ed L
um
inos
ity
/ p
b-1
Status: 16-Aug-2006
0 500 1000 15000
100
200
electronspositrons
HERA-1
HERA-2
HERA-2: 500pb-1
An example - Beauty productionσb
vis(ep eBBX eD*μX) ~ 200 pbFor typical sample of 100pb-1 N = σ L 20.000 eD*m events Branching ratio (D* Kππ) ~ 2.5% few 100 signal events
A HERA shift …1) “massage” magnets: zero rest fields by hysteresis2) Ramp the protons to 40 GeV3) Fill the protons in HERA 4) Ramp the protons to 920 GeV5) Ramp the electrons/posirons to 12 GeV6) Fill the electrons/positrons in HERA
… nothing happens – no collisions !!!7) Steer proton and e+/e- bunches to collisions8) Take data until currents are too low
24h history of a typical HERA fill
Some Milestones to HERA
1911 Rutherford: 1911 Rutherford: αα –– particles on Goldparticles on Goldatomic structureatomic structure
1956 1956 HofstaedterHofstaedter: : epep scatterinscatterin at 200 at 200 MeVMeVproton form factorsproton form factors
1964 1964 GellGell--Mann/Zweig: Mann/Zweig: hadronhadron multipletsmultipletsquarks with Q = +/quarks with Q = +/-- 1/3, +/1/3, +/-- 2/32/3
1968 SLAC: 1968 SLAC: epep fixed target scattering at 20 fixed target scattering at 20 GeVGeVprotons made of protons made of partonspartonspartonspartons = quarks & gluons= quarks & gluons
1992 HERA: 1992 HERA: epep collidercollider experiments H1 and ZEUexperiments H1 and ZEUprecise structure of the proton precise structure of the proton ……..
( )( )2/sin11
422
21Θ
∝Ω kE
ZZddσ
point-like nucleus R~ 10 -14m compared to atom size ~ 10 -10m positive core with “all” mass, negative cloud (no Plum Pudding structure – Thomson)
Ek 98 % go through2 % strongly deflected0.1 % back scattered
The Rutherford Experiment
Rutherford 1911
Beginning of nuclear / particle physics
( ) ( )
( )( )
( )( ) rerQGrerQG
MMQ
QGQG
GGQ
GQBGGQA
QBQA
cMQ
EE
QE
iqrM
iqrE
VV
ME
M
E
MME
Mottep
MottDirac
RuthMott
32/3
232/3
2
222
2222
2
22222
222
2222
222
22
d 2
1)( ,d 2
1)(
GeV 8.0 with /1
179.2/)()(
)! (anomalous 79.2)0( momentum mag. 1 (0) chargeproton :0
2)( ,1 )( :with
2
tan)()(
4/ with 2
tan21
2cos'
2cos'4
∫∫ ==
≈⎟⎟⎠
⎞⎜⎜⎝
⎛
+≈=
===
=++=
⎟⎠⎞
⎜⎝⎛ Θ
+=
=⎟⎠⎞
⎜⎝⎛ Θ
+=
Θ⋅≡⋅
Θ=
μπ
ρπ
τττ
σσ
ττσσ
σασElectron spin
Proton spin & mass
Proton form factors charge distribution ρ(r)magnetic moments µ(r)
Measurements :
dipole formula
proton radius via Fourier transformation
Elastic ep Scattering - TheoryFrom the Rutherford to the Rosenbluth formula …
Rosenbluth
McAllister, Hofstadter : SLAC 1956 188 / 236 MeV electron beam
Elastic ep Scattering - Experiment
Deviation from point-like object due to proton form-factorsnot sensitive enough for Q2 – dependence, proton radius ~ 10-15 m
e- H2 gas
higher energies are more sensitive to smaller objects: Heisenberg Δx Δp ≥ ħ resolution λ ≥ ħ / Qmax
due to inelasticity complete description needs additional variable: W, ν, ...
approach 1-photon exchange, higher orders processes suppressed αem ~ 1/137
( )ke( )'ke
( )qγ
PW
( )
( ) 222
222
2
'
2/sin'4
'
QMMqPW
EE
EEqQ
kkq
−+=+=
−=
Θ=−=
−=
ν
ν
( ) ( ) ( )( )2/tan,2, 221
22 Θ+= QWQWMottep ννσσ
Inelastic ep Scattering - Theorie
Form factors (Q2 ) Structure functions (Q2,ν)
SLAC-MIT 1969: electrons 7 – 18 GeV
Mottep σσ /
Two big surprises: 1) no extrapolation of elastic form factors ~ Q-8
like scattering off point-like particles !2) σep / σMott depends weakly on Q2
Scaling of structure functions(Bjorken 1967)
( ) ( )
( ) ( )xFQW
xFQMWMQxQ
22
2
12
1
22
,
, : 2
define ,
→
→=∞→
νν
νν
ν
Inelastic ep Scattering - Experiment
Gell-Mann/Zweig 1964: “Eightfold way” - hadrons ordered in SU(3) multiplets3 quark flavours q form baryons (qqq) and mesons (q,q)
Feynmann 1969-1972 : Parton model - proton made by point-like partons
e
P
parton
e’Natural ansatz: Partons are Quarks ?
inelastic ep scattering = sum of elastic eq scatteringparton momentum fraction x with pobability u(x), d(x)
partons 1/2spin for 2
...)(91)(
94)(
91)(
94
21
2
FxF
xdxuxdxuxF
=
⎟⎠⎞
⎜⎝⎛ ++++=
Measured : Charged Quarks carry ~ 50% of proton momentum, other half by neutral partons = gluons
Proton Structure : Quark – Parton Model
-
Quark-Parton Model : Proton = valence + sea quarks + gluons sea quarks quark-antiquark pairs from vacuum …
1)1) Kinematics Kinematics 2)2) Proton structureProton structure3)3) PomeronPomeron structurestructure4)4) Photon structurePhoton structure
…… much more, but not discussed here. much more, but not discussed here.
Physics with H1
HERA Kinematics
x
Q2 /
GeV
2
y =
1
y = 0.
004
HERA 1994-2000
Fixed Target Experiments:
NMC
BCDMS
E665
SLAC
10-1
1
10
10 2
10 3
10 4
10-6
10-5
10-4
10-3
10-2
10-1
1
For the inclusive ep scattering 2 variables are sufficient: x and Q2
measure: 1) only electron2) or hadrons3) or combined (better resolution)
From SLAC to HERA:
x : 0.1 0.0001Q2: 10 10000 GeV2
High Q2 Deep Inelastic Event
HERA experiments extend kinematicrange in x 10-4 and Q2 104 GeV2
F2 dominates the cross section at small xand not too large y = (E-E’) / E
F2 increase towards smaller x increasing number of sea quarks
naïve Quark-Parton model seems to be not the full story:
( )[ ]12
24
2
2
2 1 2 FxyFy
xQdxdQd
+−=πασ
HERA F2
0
1
2 Q2=2.7 GeV2 3.5 GeV2 4.5 GeV2 6.5 GeV2
0
1
2 8.5 GeV2 10 GeV2 12 GeV2 15 GeV2
0
1
2 18 GeV2
F 2 em
22 GeV2 27 GeV2 35 GeV2
0
1
2 45 GeV2 60 GeV2
10-3
1
70 GeV2
10-3
1
90 GeV2
0
1
2
10-3
1
120 GeV2
10-3
1
150 GeV2
x
ZEUS NLO QCD fit
H1 PDF 2000 fit
H1 96/97ZEUS 96/97
BCDMSE665NMC
( ) ( )222 , QxFxF →
Proton Structure : F2 from H1 / ZEUS
Scaling violations
HERA F2
0
1
2
3
4
5
1 10 102
103
104
105
F 2 em-lo
g 10(x
)
Q2(GeV2)
ZEUS NLO QCD fit
H1 PDF 2000 fit
H1 94-00
H1 (prel.) 99/00
ZEUS 96/97
BCDMS
E665
NMC
x=6.32E-5 x=0.000102x=0.000161
x=0.000253
x=0.0004x=0.0005
x=0.000632x=0.0008
x=0.0013
x=0.0021
x=0.0032
x=0.005
x=0.008
x=0.013
x=0.021
x=0.032
x=0.05
x=0.08
x=0.13
x=0.18
x=0.25
x=0.4
x=0.65
QCD predicts scaling violations due to the following partonic subprocesses:
splitting functions Pqq(x/z) ….
at higher Q2 probes smaller distances , the quark might have radiated a gluon not visible at lower Q2
evolution of parton densities in Q2 described byDGLAP equations:
zdz
x zx
ggPQzgzx
gqPQzqsQd
Qxdg
zdz
x zx
qgPQzgzx
qqPQzqsQd
Qxdq
∫ ⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠⎞
⎜⎝⎛
⎟⎠⎞⎜
⎝⎛+⎟
⎠⎞
⎜⎝⎛
⎟⎠⎞⎜
⎝⎛=
⎟⎠⎞⎜
⎝⎛
⎟⎠⎞⎜
⎝⎛
∫ ⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠⎞
⎜⎝⎛
⎟⎠⎞⎜
⎝⎛+⎟
⎠⎞
⎜⎝⎛
⎟⎠⎞⎜
⎝⎛=
⎟⎠⎞⎜
⎝⎛
⎟⎠⎞⎜
⎝⎛
1 2,2,2log
2,
1 2,2,2log
2,
α
α
Proton Structure : QCD
SLAC
Procedure:
assume q(x,Q2), g(x,Q2) atQ2
0~ 1 GeV2
fit ansatz to F2 by evolvingDPFs using DGLAP to higher Q2 using
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
10-4
10-3
10-2
10-1
x
xf(x
,Q2 )
H1 PDF 2000H1ZEUS-S PDFZEUS-S PDFCTEQ6.1CTEQ6.1
Q2=10 GeV2
xuV
xdV
xg(×0.05)
xS(×0.05)Results:
valence quarks dominateabove x ~ 0.05
at lower x mainly gluons and sea quarks
Proton Structure : Parton Density Functions
… optical theorem ( )( )0Im 4 =Θ= Atot πλσ
Hadronic reactions:Regge model:
exchange of Regge trajectories
( )( ) ( ) 100,Im1 −=≈== ttot stsA
sασ
Donnachie,Landshoff:
45.008.0 −+= BsAstotσ
Leading trajectory, responsible for the cross section increase, is related to theexchange of the Pomeron with …
tP 25.008.1 +=α
Pom
eron
Reggeon
Pomeron : History
Light scattering:
X
Y{{
t
γ( pX)
( pY)
Two systems X and Y well separated in phasespace with low masses MX ,MY << W
System Y : proton or p-dissociation carries most of the hadronic energy
System X : vector meson, photon or photon-dissociation
Pomeron : Signaturesnon-diffractive event diffractive event
no visibleforwardactivity
Exchange of colourless object - Pomeronwith low momentum fraction xP
Pomeron
a7a8
Slide 26
a7 apis, 8/21/2003
a8 apis, 8/21/2003
Proton rest frame Breit frame
Diffraction : Models
Starting from alternative frames two classes of models :
Standard DIS scheme
formation timeτ~ 1 / Mp xlong at small x
Colour Dipole Models Resolved Pomeron Models
Notation: hard = perturbative process, parton level
LO: 2 gluons , … gluon ladders ← Exchange → object with partonic structure
fluctuates in colour dipoles ← Virtual photon → point-like couplings to partons, qq, qq+g, … standard partonic cross sections
combine soft & hard processes by ← Dynamics → evolve diffractive PDFs in x / Q2
different parton transverse momentum by DGLAP / BFKL schemes
_ _
0
0.1
0.2
0
1
0
0.1
0.2
0
1
0
0.1
0.2
0.2 0.4 0.6 0.8 10
1
0.2 0.4 0.6 0.8 1
H1 2002 σrD NLO QCD Fit
z Σ(
z,Q
2 )
z g(
z,Q
2 )
Q2
[GeV2]
6.5
15
z z
90
Singlet Gluon
H1 preliminary
H1 2002 σrD NLO QCD Fit
(exp. error)(exp.+theor. error)
H1 2002 σrD LO QCD Fit
Gluon momentum fraction 75 ±15 % at Q2 = 10 GeV2
and remains large up to high Q2
Pomeron : Parton Structure
1) Use QCD hard scattering factorization:
σγ*p → p’X = σγ*i fiD⊗σγ*i = universal partonic cross section
same as in inclusive DISfiD = diffractive PDFs, xP& t = const.
2) Parton ansatz for exchange:
Pomeron = ∑q(z)+q(z) + g(z)
a
3) Use NLO DGLAP to evolve diffractivePDFs to Q2 > Q0
2 = 3 GeV2
QCD Fit Model:
Photon Structure : BasicsPhoton Structure : Basics
Rise described by s α with α ∼ 0.08like pp, pp, πp,… hadron reaction
Classic Photon- pure “electromagnetic”- no (partonic) structure
Heisenberg-quantum fluctuations- partons / hadrons
Photon behaves like a hadronwhat’s the partonic structure ?
Photon Structure: F2 & LEPγ
Traditional place is : e+e- at LEPPrinciple: use highly-virtual photon to probe
a quasi-real photon
( )( ) ( ) ( )[ ]2222
24
2
2
2
,,112 QxFyQxFyxQdxdQ
dLγγπασ
−−+=
Deep Inelastic photon - photon scatteringsimilar ansatz as for proton structure:
Scaling violations well-describedby partonic photon models …GRV
Photon Structure : Parton Density FunctionsUse partons of proton to probe the photon
Signature: 2 jets with large transverse energy
Resolved Photon2
//2 Mffflux pqqjet ⋅⋅⋅∝ γγσ
xγ
α-1 x
γ (q
(xγ)
+ q
¯ (xγ)
+ 9
/4 g
(xγ)
)
H1 Data
GRV 92
quark/antiquark contribution
0
2
4
6
8
10
12
14
16
10-1
1
<pT2> = 74 GeV2
Quarks (LEP)
Gluons
γ/qf
quarks dominate at high x, no “valence quark” peak as F2
p
gluons dominate low x as expected by QCD
2 Jets
Total cross sectionTotal cross sectionQCD dynamics, running coupling constant QCD dynamics, running coupling constant ααss
Electroweak physicsElectroweak physicsHeavy Heavy flavoursflavours : charm, bottom: charm, bottomBeyond the standard model: SUSY, Beyond the standard model: SUSY, leptolepto--quarks, quarks, exited Fermions exited Fermions ……..
Hope for large Hope for large luminocityluminocity at HERAat HERA--22
Other Physics Topics …
~ 400 physicists40 institutes11 countries
H1 Detector
e+/-
p
~ 2800 tnot visible: front-end electronics in the trailer
Detector Principles – Charged Particles
Detector Principles – Neutral Particles
Principle Collider Detector
General structure : order to reach best resolution ….
Add front and rear caps … 4π
H1 Detector – Side View
Tracking Detectors : Basics
Ionization most relevant process for tracking detectors Bethe-Bloch formula:
⎥⎦
⎤⎢⎣
⎡−−−=
22ln14 2max
2
222
21
2222 δββγ
βπ T
Icm
AZzcmrN
dxdE e
eeA
MIP
relativistic rise
Z/A~0.5
Gaseous detectors: few collisions charge amplification in strong electric field of anode wires
Silicon detectors:more collisions charge collection only
Side effect:β = β(M) used for particle ID
Only β dependency,others are constants ..
H1 Tracking Detectors
The basic H1 tracking detector,Resolution~ 0.2 mm
H1 Tracking – Drift Chambers
0.3 mm Silicon results in ~32.000 electron-hole pairs,
Resolution ~ 10 μm
H1 Tracking – Silicon
H1 Tracking – Muon Chambers
Muon detectors areinstrumented iron layersIn the outermost position
Calorimeter - Basics
hadronic
EM
EE
EEE
E
)%8035(
)%255.7(
−=
−=
σ
σ
Material PropertiesRL(cm) Ec (MeV) λa(cm)
Lead 0.56 7.4 17.2Iron 1.76 20.7 16.8Tungsten 0.35 8.0 9.6
λa= nuclear absorption length
Principle: force the particles to shower and “count” number of shower particles(collect all charged particles by fields at electrodes, or convert to light
by scintillation on measure light intensity)
2 types of showers: 1) electromagnetic via bremstrahlung & pair production small lateral size2) hadonic via strong interaction plus electromagnetic less contained
Energy resolution:
H1 Calorimeters - Overview
Main Calorimeters – Liquid Argon & SpacalBoth are sampling calorimeters (no cristals !) …
%2][
%50~ :Had
%1][
%13...10~ :EM
+
+
GeVEE
GeVEE
E
E
σ
σ
Energy resolution: test beam, kinematic peak, cosmic muons, …
LAr: 70m3 Argon interspaced with lead ( EM) and steel plates (hadronic)
Spacal: scilillating fibers embedded in lead matrix0.5 / 1 mm fibers for EM / hadronic part
%50~ :Had
1][
%7~ :EM
Eσ
σ+
GeVEEE
Despite the vacuum of 10Despite the vacuum of 10--99 bar the p bar the p –– rest gas rest gas interactions dominate by a factor of ~ 1000 over interactions dominate by a factor of ~ 1000 over ee--ppinteractionsinteractions
only a Trigger Processor makes only a Trigger Processor makes ee--pp physics possiblephysics possibleH1 trigger has 3 levels:H1 trigger has 3 levels:L1: 2.3 L1: 2.3 μμsecsec, logical combination of trigger elements of , logical combination of trigger elements of subdetectorssubdetectors stops the pipeline, rate 1 kHz stops the pipeline, rate 1 kHz L2: topological/neuronal decision starts the readout, rate L2: topological/neuronal decision starts the readout, rate ~ 100~ 100……200 Hz 200 Hz L4: PC farm, event building, data logging, rate ~ 5 HzL4: PC farm, event building, data logging, rate ~ 5 Hz
Without Trigger System NO Useful Data !!!
H1 Trigger System
…some spare slides
The HERA ParametersThe HERA Parameters
HERA Bunch StructureHERA Bunch Structure
HERA Beam CurrentsHERA Beam Currents
H1H1-- A typical DIS EventA typical DIS Event
HERA Resolution PowerHERA Resolution Power
Resolution ~ 1/QResolution ~ 1/Q
HERA DIS reaches HERA DIS reaches
m1810−
No beams neededNo beams neededTest Test subdetectorssubdetectorsAlignementAlignement of of componentscomponentsClear input: minimum Clear input: minimum ionizing particleionizing particle……
H1 Cosmic Muons