The H1 Experiment at HERA

Transcription

1 The H1 Experiment at HERA 1. The HERA Accelerator. Some Examples of H1 ep Physics 3. The H1 Detector

2 a1 HERA at DESY collider exp s: H1 / ZEUS : ep physics fixed target exp s: HERMES : spin physics HERA-B: CP-violation, B-physics HERA-I HERA km E p = 80 / 90 GeV E e = 7.5 GeV center of mass energy = 300 / 318 GeV

3 Slide a1 apis, 7//003

4 HERA Tunnel 15m 30m under surface

5 HERA Components 1) Cavities to accelerate: 130 / MV for electrons / protons ) Magnets to bend and focus the beams 3) Ulta-high vacuum: ~ 10-9 mbar much more

6 HERA & Collider family Classification of accelerators 1 - fixed target low center of mass energy, high luminocity collider high center of mass energy, lower luminocity Complementary physics programs HERA is the only ep collider

7 Why different colliders? Electrons: point-like, lower energy Protons : sizable objects, higher energy access different fields

8 Luminocity Luminocity L determines the event rate N for each cross section σ: N = σ L Luminocity given by accelerator parameters: Typical values : number of bunches n = 180 bunch crossing time 1/f = 96 nsec N e/p = 3 / ppb σ x/y = 190 / 50 μm L = n f N e N p 4πσ x σ y n number of bunches f frequency N 1/ particles per bunch σ x/y beam profiles

9 Luminocity Measurement at H1 Principle: take a known cross section and measure event rate L = N/σ 1) Cross section: Bethe - Heitler process (pure QED!) ep epγ ) Event rate: use e-tagger and photon detector close to the beam line ttttttttttttttttttt 3) Subtract (beam gas) backgrounds L () t = ( N N ) BH Bg / σbh t

10 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 I e/p = 40/90 ma 60/140 ma ) 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)

11 HERA Luminocity Integrated Luminosity (pb -1 ) HERA luminosity e e - + p : p : L 15pb 1 L 100 pb e H1 Integrated Luminosity / pb HERA-: 500pb -1 Status: 16-Aug-006 HERA- electrons positrons HERA e Days of running Days of running An example - Beauty production σ b vis (ep ebbx ed*μx) ~ 00 pb For typical sample of 100pb -1 N = σ L ed*m events Branching ratio (D* Kππ) ~.5% few 100 signal events

12 A HERA shift 1) massage magnets: zero rest fields by hysteresis ) Ramp the protons to 40 GeV 3) Fill the protons in HERA 4) Ramp the protons to 90 GeV 5) Ramp the electrons/posirons to 1 GeV 6) Fill the electrons/positrons in HERA nothing happens no collisions!!! 7) Steer proton and e+/e- bunches to collisions 8) Take data until currents are too low 4h history of a typical HERA fill

13 Some Milestones to HERA 1911 Rutherford: α particles on Gold atomic structure 1956 Hofstaedter: ep scatterin at 00 MeV proton form factors 1964 Gell-Mann/Zweig: hadron multiplets quarks with Q = +/- 1/3, +/- / SLAC: ep fixed target scattering at 0 GeV protons made of partons partons = quarks & gluons 199 HERA: ep collider experiments H1 and ZEU precise structure of the proton.

14 The Rutherford Experiment Rutherford 1911 E k 98 % go through % strongly deflected 0.1 % back scattered dσ dω ( Z Z ) 1 1 E k sin 4 1 ( Θ / ) point-like nucleus R~ m compared to atom size ~ m positive core with all mass, negative cloud (no Plum Pudding structure Thomson) Beginning of nuclear / particle physics

15 Elastic ep Scattering - Theory From the Rutherford to the Rosenbluth formula Electron spin σ Mott = 4α E' Q cos Θ E' σ E Ruth cos Θ Proton spin & mass σ Dirac = σ Mott 1+ τ tan Θ with τ = Q / 4M c Proton form factors charge distribution ρ(r) magnetic moments µ(r) Measurements : dipole formula σ G ep E = σ ( Q Q Mott with : ) = G A( Q = 0 : M A( Q ( Q ) + B( Q proton mag. ) = ( G + τ G ) ( 1+ τ ), E ) tan charge M G G E M 1 ) / Q / M momentum Θ (0) = 1 V B( Q (0) =.79 Rosenbluth with ) = τ G M V M (anomalous!) 0.8 GeV proton radius via Fourier transformation G E ( Q ) = 1 ( π ) 3/ iqr 3 ρ() r e d r, GM ( Q ) = ( π ) 1 3/ μ iqr 3 () r e d r

16 Elastic ep Scattering - Experiment McAllister, Hofstadter : SLAC / 36 MeV electron beam e - H gas Deviation from point-like object due to proton form-factors not sensitive enough for Q dependence, proton radius ~ m

17 Inelastic ep Scattering - Theorie higher energies are more sensitive to smaller objects: Heisenberg Δx Δp ħ resolution λ ħ / Q max due to inelasticity complete description needs additional variable: W, ν,... approach 1-photon exchange, higher orders processes suppressed α em ~ 1/137 e( k) P γ ( q) e( k' ) W q = k k' Q W = q = ν = E E' = 4EE'sin ( Θ / ) ( P + q) = M + Mν Q σ ep ( ( ) ( ) W ν, Q + W ν, tan ( / ) ) = σ Q Mott 1 Θ Form factors (Q ) Structure functions (Q,ν)

18 Inelastic ep Scattering - Experiment SLAC-MIT 1969: electrons 7 18 GeV σ ep / σ Mott Two big surprises: 1) no extrapolation of elastic form factors ~ Q -8 like scattering off point-like particles! ) σ ep / σ Mott depends weakly on Q Scaling of structure functions (Bjorken 1967) Q, ν Q define x = : Mν MW 1 ν W ( ν, Q ) F1 ( x) ( ν, Q ) F ( x)

19 Proton Structure : Quark Parton Model Gell-Mann/Zweig 1964: Eightfold way - hadrons ordered in SU(3) multiplets 3 quark flavours q form baryons (qqq) and mesons (q,q) - Feynmann : Parton model - proton made by point-like partons Natural ansatz: Partons are Quarks? inelastic ep scattering = sum of elastic eq scattering parton momentum fraction x with pobability u(x), d(x) e e F = xf x = F u( x) d( x) u( x) + for spin 1/ partons 1 9 d( x) +... P parton Measured : Charged Quarks carry ~ 50% of proton momentum, other half by neutral partons = gluons Quark-Parton Model : Proton = valence + sea quarks + gluons sea quarks quark-antiquark pairs from vacuum

20 Physics with H1 1) Kinematics ) Proton structure 3) Pomeron structure 4) Photon structure much more, but not discussed here.

21 HERA Kinematics From SLAC to HERA: x : Q : GeV Q / GeV 10 4 HERA Fixed Target Experiments: NMC 10 3 BCDMS E665 y = 1 10 SLAC For the inclusive ep scattering variables are sufficient: x and Q 10 measure: 1) only electron ) or hadrons 3) or combined (better resolution) y = x

22 High Q Deep Inelastic Event

23 Proton Structure : F from H1 / ZEUS HERA F Q =.7 GeV 3.5 GeV 4.5 GeV 6.5 GeV GeV 10 GeV 1 GeV 15 GeV GeV GeV 7 GeV 35 GeV HERA experiments extend kinematic range in x 10-4 and Q 10 4 GeV F dominates the cross section at small x and not too large y = (E-E ) / E d σ = πα 4 dq dx Q x [( 1 y) F + y x F ] 1 em F GeV 60 GeV GeV 150 GeV 70 GeV GeV F increase towards smaller x increasing number of sea quarks naïve Quark-Parton model seems to be not the full story: F ( x ) F ( x ), Q 1 0 ZEUS NLO QCD fit H1 PDF 000 fit H1 96/97 ZEUS 96/97 BCDMS E665 NMC Scaling violations x

24 Proton Structure : QCD HERA F QCD predicts scaling violations due to the following partonic subprocesses: em F -log 10 (x) 5 x=6.3e-5 x= x= x= x= x= x= x= x= ZEUS NLO QCD fit H1 PDF 000 fit H H1 (prel.) 99/00 ZEUS 96/97 4 x=0.001 x=0.003 BCDMS E665 NMC 3 x=0.005 x=0.008 x=0.013 x=0.01 x=0.03 x=0.05 splitting functions P qq (x/z). at higher Q probes smaller distances, the quark might have radiated a gluon not visible at lower Q evolution of parton densities in Q described by DGLAP equations: x=0.08 x= x=0.18 x=0.5 SLAC x=0.4 x= Q (GeV ) dq x, Q 1 x x = α q z Q P g z Q P s, qq +, qg d log Q x z z dg x, Q 1 x x = α q z Q P g z Q P s, gq +, gg d log Q x z z dz z dz z

25 Proton Structure : Parton Density Functions Procedure: assume q(x,q ), g(x,q ) at Q 0 ~ 1 GeV fit ansatz to F by evolving DPFs using DGLAP to higher Q using xf(x,q ) H1 PDF 000 ZEUS-S PDF CTEQ6.1 Q =10 GeV xu V 0.5 xg( 0.05) 0.4 xd V Results: valence quarks dominate above x ~ xs( 0.05) at lower x mainly gluons and sea quarks x

26 Pomeron : History Light scattering: ( ( 0) ) σ tot = 4 πλim A Θ= optical theorem Hadronic reactions: Regge model: exchange of Regge trajectories σ tot = 1 s Im α ( t= 0) 1 ( A( s, t = 0) ) s Reggeon Pomeron Donnachie,Landshoff: σ tot = As + Bs Leading trajectory, responsible for the cross section increase, is related to the exchange of the Pomeron with α P = t

27 { { a7 a8 Pomeron : Signatures non-diffractive event diffractive event no visible forward activity Two systems X and Y well separated in phase space with low masses M X,M Y << W System Y : proton or p-dissociation carries most of the hadronic energy System X : vector meson, photon or photon-dissociation γ Pomeron t X ( p X ) Y ( p Y ) Exchange of colourless object - Pomeron with low momentum fraction x P

28 Slide 6 a7 apis, 8/1/003 a8 apis, 8/1/003

29 Diffraction : Models Notation: hard = perturbative process, parton level Starting from alternative frames two classes of models : Proton rest frame Breit frame formation time τ~ 1 / M p x long at small x Standard DIS scheme LO: gluons, gluon ladders Exchange object with partonic structure fluctuates in colour dipoles Virtual photon qq, qq+g, point-like couplings to partons, standard partonic cross sections combine soft & hard processes by Dynamics evolve diffractive PDFs in x / Q different parton transverse momentum by DGLAP / BFKL schemes Colour Dipole Models Resolved Pomeron Models

30 Pomeron : Parton Structure QCD Fit Model: 1) Use QCD hard scattering factorization: σ γ*p p X = σ γ*i f D i σ γ*i = universal partonic cross section same as in inclusive DIS = diffractive PDFs, x P & t = const. f id ) Parton ansatz for exchange: Pomeron = q(z)+q(z) + g(z) z Σ(z,Q ) a Singlet H1 00 σ r D NLO QCD Fit z z g(z,q ) H1 00 σ r D NLO QCD Fit (exp. error) (exp.+theor. error) H1 preliminary Gluon z Q [GeV ] ) Use NLO DGLAP to evolve diffractive PDFs to Q > Q 0 = 3 GeV H1 00 σ r D LO QCD Fit Gluon momentum fraction 75 ±15 % at Q = 10 GeV and remains large up to high Q

31 Photon Structure : Basics Classic Photon - pure electromagnetic - no (partonic) structure Heisenberg -quantum fluctuations - partons / hadrons Rise described by s α with α 0.08 like pp, pp, πp, hadron reaction Photon behaves like a hadron what s the partonic structure?

32 γ Photon Structure: F & LEP Traditional place is : e + e - at LEP Principle: use highly-virtual photon to probe a quasi-real photon Deep Inelastic photon - photon scattering similar ansatz as for proton structure: d σ dxdq πα = 4 xq γ γ [( 1+ ( 1 y) ) F ( x, Q ) y F ( x, Q )] L Scaling violations well-described by partonic photon models GRV

33 Photon Structure : Parton Density Functions Use partons of proton to probe the photon Signature: jets with large transverse energy Resolved Photon Jets σ jet fluxγ fq / γ fq / p M quarks dominate at high x, no valence quark peak as F p gluons dominate low x as expected by QCD α -1 x γ (q(x γ ) + q (x γ ) + 9/4 g(x γ )) H1 Data GRV 9 1 quark/antiquark contribution f q /γ Gluons Quarks (LEP) <p T > = 74 GeV x γ

34 Other Physics Topics Total cross section QCD dynamics, running coupling constant α s Electroweak physics Heavy flavours : charm, bottom Beyond the standard model: SUSY, lepto-quarks, exited Fermions. Hope for large luminocity at HERA-

35 H1 Detector p ~ 400 physicists 40 institutes 11 countries e +/- ~ 800 t not visible: front-end electronics in the trailer

36 Detector Principles Charged Particles

37 Detector Principles Neutral Particles

38 Principle Collider Detector General structure : order to reach best resolution. Add front and rear caps 4π

39 H1 Detector Side View

40 Tracking Detectors : Basics Ionization most relevant process for tracking detectors Bethe-Bloch formula: de dx = 4πN A Z 1 1 mec γ β max δ re mec z ln T β A β I Gaseous detectors: Only β dependency, others are constants.. few collisions charge amplification in strong electric field of anode wires Silicon detectors: more collisions charge collection only relativistic rise Z/A~0.5 Side effect: β = β(m) used for particle ID MIP

41 H1 Tracking Detectors

42 H1 Tracking Drift Chambers The basic H1 tracking detector, Resolution~ 0. mm

43 H1 Tracking Silicon 0.3 mm Silicon results in ~3.000 electron-hole pairs, Resolution ~ 10 μm

44 H1 Tracking Muon Chambers Muon detectors are instrumented iron layers In the outermost position

45 Calorimeter - Basics 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) types of showers: 1) electromagnetic via bremstrahlung & pair production small lateral size ) hadonic via strong interaction plus electromagnetic less contained Material Properties R L (cm) E c (MeV) λ a (cm) Lead Iron Tungsten λ a = nuclear absorption length Energy resolution: σ E σ E E E (7.5 5)% = EM E (35 80)% = hadronic E

46 H1 Calorimeters - Overview

47 Main Calorimeters Liquid Argon & Spacal Both are sampling calorimeters (no cristals!) LAr: 70m 3 Argon interspaced with lead ( EM) and steel plates (hadronic) Spacal: scilillating fibers embedded in lead matrix 0.5 / 1 mm fibers for EM / hadronic part Energy resolution: test beam, kinematic peak, cosmic muons, EM : σ E E ~ % E[ GeV ] + 1% EM : σ E E ~ 7% E[ GeV ] + 1 Had : σ E E ~ 50% E[ GeV ] + % Had : σ E ~ 50%

48 H1 Trigger System Despite the vacuum of 10-9 bar the p rest gas interactions dominate by a factor of ~ 1000 over e-p interactions only a Trigger Processor makes e-p physics possible H1 trigger has 3 levels: L1:.3 μsec,, logical combination of trigger elements of subdetectors stops the pipeline, rate 1 khz L: topological/neuronal decision starts the readout, rate ~ Hz L4: PC farm, event building, data logging, rate ~ 5 Hz Without Trigger System NO Useful Data!!!

49 some spare slides

50 The HERA Parameters

51 HERA Bunch Structure

52 HERA Beam Currents

53 H1- A typical DIS Event

54 HERA Resolution Power Resolution ~ 1/Q HERA DIS reaches m

55 H1 Cosmic Muons No beams needed Test subdetectors Alignement of components Clear input: minimum ionizing particle