Heavy Ion Experiments atvci.hephy.at/2001/talks/Thursday/Pernegger.pdf · Heavy Ion Experiments at...
Transcript of Heavy Ion Experiments atvci.hephy.at/2001/talks/Thursday/Pernegger.pdf · Heavy Ion Experiments at...
Heavy Ion ExperimentsHeavy Ion Experimentsat at
Heinz Pernegger/CERN,MIT
Vienna Conference on Instrumentation 2001 22/2/2001
STAR
Relativistic Heavy Ion Relativistic Heavy Ion Collider Collider @BNL@BNL
• A dedicated facility for Heavy Ion Physics at BNL
STAR
RHIC SpecificationsRHIC Specifications• Two independent superconducting rings
– 3.83 km rings– Beam crossing=106ns
• Can collide Au-Au– top energy 100+100 AGeV/c– in 60 bunches with 109/bunch– store time = 10 hours– average Luminosity = 2 x 1026 /cm2s
• But also for p+p– top energy 250+250 GeV/c– average Luminosity = 2 x 1032 /cm2s– polarized (for spin measurements)
• And nearly any nucleus on any nucleus– including asymmetric collisions
Rf storage cavities
Blue and yellow rings
Aim of Aim of RHIC’sRHIC’s heavy ion experimentsheavy ion experiments
• Study nuclear matter at extreme energy density– phase transition into a deconfined QGP
• 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
AGSAGS
SPSSPSRHICRHIC
What to look for ?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– pT spectra– strangeness
enhancement– mini-jets– J/Ψ suppression– HBT– …
Difference to HEP?Difference to HEP?
Multiplicity!Multiplicity!
– Fine granularity– good track separation– detector with low
ambiguties– particles are low
momentum (multiple scattering)
– maybe not ultimate spatial resolution
• (low momentum -> large sagita)
• But also “low multiplicity” high rate pp collisions
• Need to handle this (at <1kHz)
STAR TPC L3 displaySTAR TPC L3 display
Difference to HEP?Difference to HEP?
Low and highLow and high ppTT matters matters • Most particles have low
momenta (few x 100 MeV/c)
• Flavour dynamics: want to study events for particle composition
• Jet quenching: Look at high momentum part of pTdistribution (2-20GeV/c)
• Need tracking with low pTacceptance
� π (>70MeV/c) ,K (>200MeV/c) , p (>300MeV/c)
• Low pT particle identification is crucial
Bild momentum distribution
• Good azimutal coverage at mid-rapidity– anisotropic particle production
(“elliptic flow”)– particle correlations (space-time
evolution of source)
Difference to HEP?Difference to HEP?
HermeticityHermeticity & & Rare signalsRare signals
• Acceptance up to extreme pseudo rapidities (|η| up to 5) – “exclusive” multiplicity
measurements– particle ratios in extreme
forward direction
• Acceptance to electrons– to be sensitive to heavy flavor
production (D0,B0), γ*->e+e-
• BUT they are rare!
• good electron identification by combing detectors (tracking+RICH+EMCal)
Al l tracks
E lec t ron enr i ched s amp l e
(us ing RICH)
E/p matching for
p>0.5 GeV/c t racks
Phenix
General requirements:General requirements:
DAQs and triggers for high rate + lowmultiplicity pp-collisions
Tracking with high granularity and lowamibuties to handle n x 1000 particles/collision
Layout with acceptance in low pT and wide rapidity range
Sensitivity to rare probes (e,µ,γ)combinedEMCals/Cherenkov
Experiments with dynamic rangeExperiments with dynamic range
TOF, dE/dx, RICH:Low & high pTparticleidenification
Be prepared for the unexpected:maintain flexibility
Detector technologies usedDetector technologies used
Brahms Phenix Phobos Star
Tracking TPC TEC, pad/drift chamber
Silicon pad detector
TPC
Particle ID TOF, RICH TOF (p,K,p) Threshold-RICH (e -)
dE/dx with sil icon, 1 TOF wall
dE/dx with TPC, RICH,
ET, P0 - Shachlik EMCal - Emcal
Multiplicity Scintilator Mult-detector
Pad chamber, Silicon multiplicity TPC (barrel+forward)
Trigger Forward Scintilator+ZDC
Cherenkov beam-beam counter+ZDC
Forward Scinilator+ZDC
Scinilator Barrel+ZDC
RHIC Performance during RUN2000RHIC Performance during RUN2000
• Performance during the first physics run at RHIC (June-September 2000) :– 60 bunches per ring ü– 5×108 Au/bunch ü– Initial storage energy: 2 runs at different energy
• short run at γ = 30 [28 GeV/nucl.] • long run at γ = 70 [66 GeV/nucl.] ü• This energy is below the lowest quench of any DX magnet. • Full operating current for 100 GeV/nucl. reached at end of run)
– Luminosity: 2 × 1025 cm-2 s-1 ü
– Integrated luminosity: a few (µb) -1 ü
Accelerating a gold bunch in RHICAccelerating a gold bunch in RHIC
Injection Transition energy Storage energy
Bun
ch le
ngth
[ns
]
Transition energy crossingTransition energy crossing
Transition energy ∆Ε = 200 MeV
RHIC is first superconducting, slow ramping accelerator to crosstransition energy:
Cross unstable transition energy with radial energy jump (2000):
Beam energy
Slow and fast particles remain in step.ð increased particle interaction (space charge)ð short, unstable bunches
Cross unstable transition energy by rapidly changing transition energy (2001):
Transition energy
Beam energy
Avoids beam loss and longitudinal emittance blow-up
Year 2000 condition Year 2001 condition
Collision rate at experimentsCollision rate at experimentsC
olli
sion
rat
e [H
z]
BRAHMS: Lpeak = 3.3 × 1025 cm-2 s-1
Lave = 1.7 × 1025 cm-2 s-1
[ σ(Au+Au → ≥1n + ≥1n) = 10.7 b (theor.)]
Narrow bunches @ Brahms, Phenix
Wide bunches @ Phobos, Star *
* will be reduced during next run
RUN2000 integrated AuRUN2000 integrated Au--Au luminosityAu luminosity
Lave = 0.8 × 1025 cm-2 s-1
Availability: 47 %(last 6 days @ BRAHMS)
6.5 6.5 µµbb--11
STARSTAR
• Emphasis:– Track ~ 1000 charged particles in |η| < 1
ZCal
Silicon Vertex Tracker
Central Trigger Barrel or TOF
FTPCs
Time Projection Chamber
Barrel EM Calorimeter
Vertex Position Detectors
EndcapCalorimeter
Magnet
Coils
TPCEndcap & MWPC
ZCal
RICH
Events at StarEvents at Star
Data Taken June 25, 2000.
Pictures from Level 3 online display.
Central AuCentral Au--Au collision @ STARAu collision @ STAR
STAR detectorSTAR detector
• 0.5 Tesla magnet– 0.25 for year 1
• Trigger – CTB– ZDC– Level 3
• Year 1 detectors– TPC– RICH– 1 SVT ladder
Star TPCStar TPC
• Gas : P10 (Ar-CH4 90%-10%) @ 1 atm• Drift voltage : -31 kV
60 cm
127 cm
190 cm
Inner sector2.85 × 11.5 mm2 pad1750 pads
Outer sector6.2 × 19.5 mm2 pad3940 pads
TPC first preliminary resultsTPC first preliminary results
Track length (cm)
σ dE
/dx
/(
dE
/dx
) (%)
• Drift velocity– laser (coarse)– track matching between halfs
(fine)
• Tracking– Position resolution
• 500 µm
– 2-Track resolution• 2.5 cm
– Momentum resolution• 2%
• dE/dx resolution– gain monitored by pulser + offline– Good particle separation using dE/dx
• 7.5%
STAR RICH detectorSTAR RICH detector
• Extends STAR’s PID capabilities into high pTrange
• can study flavourdependence of hard processes– low rate, inclusive
measurement– can do with “1-arm”
• Developed by CERN RD-26 in ALICE framework headed
• ALICE RICH Prototype Module (1 m2)
• Radiator = C6F14 Liquid• Photo Converter
– CsI (λ < 210 nm)
• Ionization Detector– MWPC pad chamber & CH4 Gas
STAR RICH acceptanceSTAR RICH acceptance
• Extend PID beyond TPC TOF: 1 < p < 3 GeV/c π K2 < p < 5 GeV/c p
• 160 x 85 cm2 ⇒ 1 m2
• Radial Distance of 2.4 m• |y| < 0.2
Star PID withStar PID with dEdE//dxdx and RICHand RICH
Star PID through track topologyStar PID through track topology
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STAR SVT (silicon drift vertex detector)STAR SVT (silicon drift vertex detector)
Silicon Drift DetectorsSilicon Drift Detectors
• design resolution <20µm• 1st year commissioning run
PHOBOSPHOBOS– Emphasis
è very large |η|<5.4 for multiplicity & flow measurements
è 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 (~109)
• through fast DAQ (n x 100Hz)• small detector
Octagon/Vertex
Spectrometer Arm Ring
Silicon everywhereSilicon everywhere• Multiplicity array
– 1 layer barrel + 2x 3 rings
• Spectrometer– 16 layer silicon pad
detectors
1 of 10 layouts:
14 cm• Thin detectors
– low multiple scattering– less background
• Compact detector close to IP
• Pad detectors: same technology for– multiplicity measurement by signal
integration in larger pads– PR+tracking+dE/dx PID with
smaller pads
PHOBOS: Why silicon pads everywhere?PHOBOS: Why silicon pads everywhere?
PHOBOS: Full coverage multiplicity measurementPHOBOS: Full coverage multiplicity measurement
ηη
Octagon 3 Rings3 Rings
Run 5374Event 79495
dN/d
η
• Charged multiplicity for forward+mid rapidity (on
event-by-event basis)• full phi coverage
– anisotropy of particle production
• can deal with occupancies >80%
0 +3-3 +5.45.4
φφ
ηη
Rings RingsOctagon
ππ
p
K
protons
Kaons
pions
PHOBOS SpectrometerPHOBOS Spectrometer• Tracking and vertex determination
– momentum resolution 2%– vertex resolution 300-400µm
• PID with dE/dx in silicon– dE/dx resolution = 7.5% – identical to STAR TPC dE/dx resolution– high dynamic range for stopping particle
Multiplicity’s trivial dependence:Multiplicity’s trivial dependence:
Centrality measurement at RHICCentrality measurement at RHIC
“Spectators”
Zero-degreeCalorimeter
“Spectators”
Many things scale with Npart:• Transverse Energy• Particle Multiplicity• Particle Spectra
“Participants”
Only ZDCs measure Npart
specpart NAN −=
Detectors at 90o
The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision
RHIC’s RHIC’s ZDCZDC
• 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 (σtot =
10.7b)
Provides normalization between experiments, i.e. makes their results comparable
Event Selection & Event Selection & NNparticipantparticipant (e.g. PHOBOS)(e.g. PHOBOS)
• Combine– ZDC with– forward scintilator array
(“paddle counters”)
Paddle signal
ZDC
sign
al
Paddle signal (a.u.)
Npart
• Define centrality classes (fraction of cross section)
MC
Data
• Use model calculation to extract Npart (Hijing + Geant)
Centrality selection + estimate for Npart
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PHENIX LayoutPHENIX Layout
– 2 central spectrometers
– 2 forward spectrometers
– 3 global detectors
West
EastSouth
North
W.A. Zajc 36
PHENIX during installationPHENIX during installation
January, 1999
• 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)
PHENIX year 1 configurationPHENIX year 1 configuration
• Tracking– pad chamber– drift chamber
• PID– TOF– EMCal + RICH (e-)
• Global observables + event selection– Cherenkov BBC– ZDC– silicon MVD (engineering run)
PHENIX PHENIX EMCalEMCal
PHENIX PHENIX EMCal EMCal performanceperformance
• Rel iable measurement of total transverse energy E T = (1.17±0.05) E E M C a l
• good energy resolut ion
� π0 identification
• + TOF information (resolution 200ps)
PHENIX electron ID: all subPHENIX electron ID: all sub--systems in concertsystems in concert
High pT electrons in PHENIX:
PHENIXPHENIX HadronHadron Identification TOFIdentification TOFCombined
– Tracking– Beam-Beam Counter– Time-of-Flight array
provides excellent hadron identification over broad momentum band:
BRAHMSBRAHMS
• Two magnetic dipole spectrometers– forward & mid rapidity– rotating segments with
magnet+TPC+RICH
• Cover large(st) pT-y by scanning • Event & Vertex selection
– multiplicity tile, silicon pad
• Goal:– identified spectra over a broad range of rapidity and pT
BRAHMS AcceptanceBRAHMS Acceptance
• Tracking based– TPC (vertical drift) in small
azimuthal slice• PID based
– TOF hodoscopes– Cherenkov
BRAHMS TOF PID separation in year 1BRAHMS TOF PID separation in year 1
Example: Particle Identification achieved in Mid-Rapidity Spectrometer
p/K to 2.2 GeV/cK/ππ to 1.5 GeV/c
π
K p
time of flight resolution 120 ps
Vertex Determination in BRAHMS Vertex Determination in BRAHMS (as an example ...)(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
2 m
• ... And use tracking to get precision (BRAHMS TPC)
• 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
1.25 atm of C4 F10 and C5 F12 mixture
pe detection
Measured refraction index: n = 1.00203
cm
cm
Average # of p.e : 20
Preview for next year: BRAHMS RICHPreview for next year: BRAHMS RICH
RICH radius vs FS momentum
Summary ISummary 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
How to summarize the detector performance ?How to summarize the detector performance ?
• 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 resultsat Quark Matter 2001:
… by physics results in just 5 … by physics results in just 5 months after data taking !months after data taking !
• STAR
- h- multiplicity- identified pTdistribution - particle ratios- elliptic flow (vs pT)- particle correlation- pT fluctuations
• PHOBOS
- elliptic flow- particle ratios- dNch/dη vs centrality- dNch/dη @η=0- full 4-π dNch/dη
• PHENIX
- dNch/dη @η=0 & Et- elliptic flow (vs pT)- particle correlations - identified pT spectra for charged particles- π0 pT spectra- first electron spectra
• BRAHMS
- Particle ratios at η ~0 and 3- particle ratios vs pT and centrality- dNch/dη @η=0
Thanks toThanks 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