Heavy Ion Experiments at

Transcription

1 Heavy Ion Experiments at STAR Heinz Pernegger/CERN,MIT Vienna Conference on Instrumentation /2/2001

2 Relativistic Heavy Ion A dedicated facility for Heavy Ion Physics at BNL STAR

3 RHIC Specifications Two independent superconducting rings 3.83 km rings Beam crossing=106ns Blue and yellow rings Can collide Au-Au top energy AGeV/c in 60 bunches with 10 9 /bunch store time = 10 hours average Luminosity = 2 x /cm 2 s But also for p+p top energy GeV/c average Luminosity = 2 x /cm 2 s polarized (for spin measurements) Rf storage cavities And nearly any nucleus on any nucleus including asymmetric collisions

4 Aim of RHIC s heavy ion experiments Study nuclear matter at extreme energy density phase transition into a deconfined QGP RHIC SPS AGS RHIC is dedicated to heavy ion physics it is a collider to get to top CM energy with more than 30 weeks of running per year allows to vary initial conditions (energy, collision system pp,pa,aa) Experiments at RHIC a comprehensive set of detectors to look at many different signatures

5 What to look for? Study bulk properties Look at many different parameters and signatures energy density flavour dynamics in-media effects soft & hard process particle correlation Vary basic conditions centrality energy system size The is no real SM of heavy ion physics & no gold plated events predictions vary therefore maintain flexibility avoid single-signatures experiments multiplicity p T spectra strangeness enhancement mini-jets J/Ψ suppression HBT

6 Difference to HEP? Multiplicity! Need to handle this (at <1kHz) Fine granularity good track separation detector with low ambiguties particles are low momentum (multiple scattering) maybe not ultimate spatial resolution (low momentum -> large sagita) STAR TPC L3 display But also low multiplicity high rate pp collisions

7 Most particles have low momenta (few x 100 MeV/c) Flavour dynamics: want to study events for particle composition Difference to HEP? Low and high p T matters Jet quenching: Look at high momentum part of p T distribution (2-20GeV/c) Need tracking with low p T acceptance π (>70MeV/c),K (>200MeV/c), p (>300MeV/c) Low p T particle identification is crucial Bild momentum distribution

8 Good azimutal coverage at mid-rapidity anisotropic particle production ( elliptic flow ) particle correlations (space-time evolution of source) Difference to HEP? Hermeticity & Rare signals Acceptance to electrons to be sensitive to heavy flavor production (D0,B0), γ*->e+e- BUT they are rare! E/p matching for p>0.5 GeV/c tracks All tracks Acceptance up to extreme pseudo rapidities ( η up to 5) exclusive multiplicity measurements particle ratios in extreme forward direction Phenix Electron enriched sample (using RICH) good electron identification by combing detectors (tracking+rich+emcal)

9 General requirements: Tracking with high granularity and low amibuties to handle n x 1000 particles/collision DAQs and triggers for high rate + low multiplicity ppcollisions Layout with acceptance in low p T and wide rapidity range Experiments with dynamic range Be prepared for the unexpected: maintain flexibility Sensitivity to rare probes (e,µ,γ) combined EMCals/Cherenkov TOF, de/dx, RICH: Low & high pt particle idenification

10 Detector technologies used Brahms Phenix Phobos Star Tracking TPC TEC, pad/drift chamber Particle ID TOF, RICH TOF (p,k,p) Threshold-RICH (e-) Silicon pad detector de/dx with silicon, 1 TOF wall TPC de/dx with TPC, RICH, ET, P0 - Shachlik EMCal - Emcal Multiplicity Scintilator Multdetector Pad chamber, Silicon multiplicity TPC (barrel+forward) Trigger Forward Scintilator+ZDC Cherenkov beambeam counter+zdc Forward Scinilator+ZDC Scinilator Barrel+ZDC

11 RHIC Performance during RUN2000 Performance during the first physics run at RHIC (June-September 2000) : 60 bunches per ring Au/bunch Initial storage energy: 2 runs at different energy short run at γ = 30 [28 GeV/nucl.] long run at γ = 70 [66 GeV/nucl.] This energy is below the lowest quench of any DX magnet. Full operating current for 100 GeV/nucl. reached at end of run) Luminosity: cm -2 s -1 Integrated luminosity: a few (µb) -1

12 Accelerating a gold bunch in RHIC Bunch length [ns] Injection Transition energy Storage energy

13 Transition energy crossing RHIC is first superconducting, slow ramping accelerator to cross transition energy: Slow and fast particles remain in step. increased particle interaction (space charge) short, unstable bunches Cross unstable transition energy with radial energy jump (2000): Cross unstable transition energy by rapidly changing transition energy (2001): Transition energy Ε = 200 MeV Transition energy Beam energy Beam energy Year 2000 condition Avoids beam loss and longitudinal emittance blow-up Year 2001 condition

14 Collision rate at experiments BRAHMS: L peak = cm -2 s -1 L ave = cm -2 s -1 [ σ(au+au 1n + 1n) = 10.7 b (theor.)] Collision rate [Hz] Narrow Brahms, Phenix Wide Phobos, Star * * will be reduced during next run

15 RUN2000 integrated Au-Au luminosity 6.5 µb -1 L ave = cm -2 s -1 Availability: 47 % (last 6 BRAHMS)

16 Emphasis: STAR Track ~ 1000 charged particles in η < 1 Magnet Coils TPC Endcap & MWPC Time Projection Chamber Silicon Vertex Tracker FTPCs ZCal ZCal Endcap Calorimeter Barrel EM Calorimeter Vertex Position Detectors Central Trigger Barrel or TOF RICH

17 Events at Star Data Taken June 25, Pictures from Level 3 online display. Central Au-Au STAR

18 STAR detector 0.5 Tesla magnet 0.25 for year 1 Trigger CTB ZDC Level 3 Year 1 detectors TPC RICH 1 SVT ladder

19 Star TPC Gas : P10 (Ar-CH4 1 atm Drift voltage : -31 kv 190 cm Outer sector mm 2 pad 3940 pads 127 cm 60 cm Inner sector mm 2 pad 1750 pads

20 TPC first preliminary results Drift velocity laser (coarse) track matching between halfs (fine) de/dx resolution gain monitored by pulser + offline Good particle separation using de/dx 7.5% Tracking Position resolution 500 µm 2-Track resolution 2.5 cm Momentum resolution 2% ( x d ) E σ d /d / E /d x Track length (cm)

21 STAR RICH detector Extends STAR s PID capabilities into high pt range can study flavour dependence of hard processes low rate, inclusive measurement can do with 1-arm Radiator = C 6 F 14 Liquid Photo Converter CsI (λ < 210 nm) Ionization Detector MWPC pad chamber & CH 4 Gas Developed by CERN RD-26 in ALICE framework headed ALICE RICH Prototype Module (1 m 2 )

22 STAR RICH acceptance Extend PID beyond TPC TOF: 1 < p < 3 GeV/c π K 2 < p < 5 GeV/c p 160 x 85 cm 2 1 m 2 Radial Distance of 2.4 m y < 0.2

23 Star PID with de/dx dx and RICH

24 Star PID through track topology

25 STAR SVT (silicon drift vertex detector) 25

26 Silicon Drift Detectors design resolution <20µm 1st year commissioning run

27 PHOBOS Emphasis very large η <5.4 for multiplicity & flow measurements very low pt acceptance (π:>50mev/c) Multiplicity array + 2-arm spectrometer with full PID, momentum measurement Minimize the number of technologies: All Si-strip tracking Si multiplicity detection PMT-based TOF Unbiased global look at very large number of collisions (~10 9 ) through fast DAQ (n x 100Hz) small detector

28 Silicon everywhere Octagon/Vertex Multiplicity array 1 layer barrel + 2x 3 rings Spectrometer 16 layer silicon pad detectors Spectrometer Arm Ring

29 PHOBOS: Why silicon pads everywhere? 1 of 10 layouts: Thin detectors low multiple scattering less background Compact detector close to IP 14 cm Pad detectors: same technology for multiplicity measurement by signal integration in larger pads PR+tracking+dE/dx PID with smaller pads

30 f PHOBOS: Full coverage multiplicity measurement h Rings Octagon Rings Run 5374 Event Charged multiplicity for forward+mid rapidity (on event-by-event basis) full phi coverage anisotropy of particle production can deal with occupancies >80% dn/dη 3 Rings Octagon h 3 Rings

31 protons Kaons PHOBOS Spectrometer Tracking and vertex determination momentum resolution 2% vertex resolution µm PID with de/dx in silicon de/dx resolution = 7.5% identical to STAR TPC de/dx resolution high dynamic range for stopping particle p pions K p

32 Multiplicity s trivial dependence: Centrality measurement at RHIC The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision Spectators Zero-degree Calorimeter Many things scale with N part : Transverse Energy Particle Multiplicity Particle Spectra Participants Spectators Only ZDCs measure N part N = A part N spec Detectors at 90 o

33 RHIC s ZDC Based on Tungsten/fiber sampling cal each experiment uses 3 segments forward/backward The ZDC provides measurement of spectator neutrons (protons are bend away), i.e. Event selection timing information, i.e. Trigger Luminosity monitor for RHIC (σ tot = 10.7b) Provides normalization between experiments, i.e. makes their results comparable

34 Event Selection & N participant (e.g. PHOBOS) Combine ZDC with forward scintilator array ( paddle counters ) Define centrality classes (fraction of cross section) Data ZDC signal Paddle signal (a.u.) Use model calculation to extract N part (Hijing + Geant) MC Paddle signal Centrality selection + estimate for N part N part

35 PHENIX Layout 2 central spectrometers West 2 forward spectrometers 3 global detectors South East North 35

36 PHENIX during installation Event Characterization Si strips and pads (MVD) Cerenkov (Beam-Beam) Tracking Central Arms Drift Chambers Pad Chambers Time Expansion Chamber (TEC) Muon Arms Cathode Strip Chambers (mutr) Iarocci Tubes (muid) Particle Identification Time-of-Flight scintillators de/dx (TEC) threshold RICH TOF in EmCal Calorimetry Lead-scintillator (PbSc) Pb-glass (PbGl) January, 1999 W.A. Zajc 36

37 PHENIX year 1 configuration Tracking PID pad chamber drift chamber TOF EMCal + RICH (e-) Global observables + event selection Cherenkov BBC ZDC silicon MVD (engineering run)

38 PHENIX EMCal

39 PHENIX EMCal performance Reliable measurement of total transverse energy E T = (1.17±0.05) E EMCal good energy resolution π 0 identification + TOF information (resolution 200ps)

40 PHENIX electron ID: all sub-systems systems in concert High p T electrons in PHENIX:

41 Combined Tracking Beam-Beam Counter Time-of-Flight array provides excellent hadron identification over broad momentum band: PHENIX Hadron Identification TOF

42 BRAHMS Goal: identified spectra over a broad range of rapidity and p T Two magnetic dipole spectrometers forward & mid rapidity rotating segments with magnet+tpc+rich Cover large(st) p T -y by scanning Event & Vertex selection multiplicity tile, silicon pad

43 Tracking based TPC (vertical drift) in small azimuthal slice PID based TOF hodoscopes Cherenkov BRAHMS Acceptance

44 BRAHMS TOF PID separation in year 1 Example: Particle Identification achieved in Mid-Rapidity Spectrometer K p π p/k to 2.2 GeV/c K/p to 1.5 GeV/c time of flight resolution 120 ps

45 Vertex Determination in BRAHMS (as an example...) Large RMS of interaction diamond next year σ=15-20 cms Select useable vertex range with beam-beam counters fast cherenkov array on +z & - z vertex by time difference σ(bb)~2.6cm... And use tracking to get precision (BRAHMS TPC) 2 m Disadvantage many recorded event are rejected in analysis with small acceptance -> large corrections But also opportunity for small experiments acceptance can be artificially increased by using different vertex samples

46 1.25 atm of C4 F10 and C5 F12 mixture pe detection Preview for next year: BRAHMS RICH Measured refraction index: n = cm cm Average # of p.e : 20 RICH radius vs FS momentum

47 Summary I With RHIC the heavy-ion physics community has entered a new era of better understanding nuclear matter and its phenomena RHIC accelerator is the first dedicated heavy-ion collider and provides unparalleled capabilities. The RHIC community has put together a very comprehensive set of experiments and met the challenges of segmentation dynamic range diversity & flexibility data analysis

48 How to summarize the detector performance? by physics results in just 5 months after data taking! Phobos, Phenix & Star already published papers on charged particle multiplicity, anti-p/p ratio, elliptic flow and presented a real firework display of first preliminary results at Quark Matter 2001: PHOBOS PHENIX BRAHMS - elliptic flow - particle ratios - dn ch /dη vs centrality - dn ch - full 4-π dn ch /dη - Particle ratios at η ~0 and 3 - particle ratios vs p T and centrality - dn ch STAR - h- multiplicity - identified p T distribution - particle ratios - elliptic flow (vs p T ) - particle correlation - p T fluctuations - dn ch & Et - elliptic flow (vs p T ) - particle correlations - identified p T spectra for charged particles - π 0 p T spectra - first electron spectra

49 Thanks to W. Busza, J. Harris, F. Videbaek, W. Zajc, T. Roser, S. Ozaki, P. Steinberg, R.Pak, S. White, A.Drees, G. Roland, G. van Nieuwenhuizen, F. Retiere, E. Schyns, B. Lasiuk, B. Nielsen