RHIC II Workshop, 11/11/05 1 EM Probes at RHIC II Zhangbu Xu (BNL) For the RHIC-2 EM-Probes Working Group (co-convenors: G. David, R. Rapp, XZB) http://www.phenix.bnl.gov/WWW/publish/david/rhicii Talks by members at April Workshop R. Rapp (Nov. PAC meeting) Simulations from individuals First Draft of Working Group Document
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RHIC II Workshop, 11/11/051 EM Probes at RHIC II Zhangbu Xu (BNL) For the RHIC-2 EM-Probes Working Group (co-convenors: G. David, R. Rapp, XZB) .
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RHIC II Workshop, 11/11/05 1
EM Probes at RHIC II
Zhangbu Xu (BNL)
For the RHIC-2 EM-Probes Working Group(co-convenors: G. David, R. Rapp, XZB)
http://www.phenix.bnl.gov/WWW/publish/david/rhicii_emTalks by members at April Workshop
R. Rapp (Nov. PAC meeting)Simulations from individuals
QCD Phase DiagramA thermodynamic stateA thermodynamic state is specified by a set of values of all the thermodynamic parameters necessary for the description of the system. --- statistical mechanics by K. HuangTemperature (T), chemical potential (, pressure(P) …
1. Chemical/thermal Equilibrium at certain stage of the evolution
2. At the predicted QCD phase boundary
3. persistent from SPS to RHIC
4. Below the phase boundary atAGS and SIS
5. Can we put a point above?
RHIC II Workshop, 11/11/05 5
Experimental Signatures
• Vector Meson Properties• Thermal Dileptons• Direct Photons
The Lost Sword 刻舟求剑 (Fable, 《呂氏春秋》 ~250B.C.)
RHIC
RHIC II Workshop, 11/11/05 6
EM Emission and Chiral Symmetry
at Tc: Chiral
Restoration
)Im(Ims
dsf AV
2
)Im(Imsds)qq( AVs 2 [Brown-rho, Rapp…]
nucl-th/0409054
RHIC II Workshop, 11/11/05 7
Low-Mass Vector Mesons at RHIC
• hadron liquid close to Tc: , “melt”, more robust?
• baryon+antibaryons important Energy Scan!!
RHIC II Workshop, 11/11/05 8
Dilepton from HI
smooth transition HG → QGP liquid?Integrated yields from several stages
R. Rapp, hep-ph/0010101
RHIC II Workshop, 11/11/05 9
QGP Temperature and Composition
• thermal window: q0 , Mee≈ 2GeV
• photons: jet-QGP interactions compromise T-sensitivity• less so for dileptons; charm?
Direct Photons Intermed.-Mass Dileptons
Energy Scan
RHIC II Workshop, 11/11/05 10
Detector Upgrades
• PHENIX – Hadron Blind Detector (HBD)
reject conversion and Dalitz decay– Silicon Vertex Tracking Detector
Measure charm background
• STAR– Time-of-Flight
TPC+TOF+EMC Electron/muon Identification– Heavy Flavor Tracker (HFT)
TPC+HFT reject conversion, Dalitz decay and HFe
– Data Acquisition System (1KHz minbias rate)
RHIC II Workshop, 11/11/05 11
Measuring Low Mass Electron Pairs in PHENIX
Hardware• Compensate magnetic field with an inner coil to preserve e+e- pair opening angle (foreseen in original design B0 for r 50-60cm)• Compact HBD in inner region
Strategy • Identify signal electrons with p > 200 MeV/c from vector mesons in the outer PHENIX detectors
• Identify low momentum electrons with p < 200 MeV/c (mainly from Dalitz pairs and conversions) in the HBD
Requirements * Electron efficiency 90% * Double hit recognition 90% * Modest rejection ~ 200C. Woody, RHICII EM probes group meeting, 04/30/05
RHIC II Workshop, 11/11/05 12
Resulting Low Mass Pair Spectrum with the HBD
• Combinatorial background is reduced by more than two orders of magnitude• limited by combinatorial background from open charm• A precision measurement of charm using the Silicon Vertex Tracking Detector.
C. Woody, RHICII EM probes group meeting, 04/30/05
RHIC II Workshop, 11/11/05 13
Rates for Vector Meson Production
• ’s produced in || < 0.5• e+,e- into PHENIX central arm acceptance• pT,e > 200 MeV/c
Consider Run 8 (200 GeV Au x Au, 4x Design Luminosity) :
• Lpeak = 30 x 1026 cm-2 s-1
• L ave store = 8 x 1026 cm-2 s-1
• 20 KHz peak min. bias rate• 5.4 KHz avg min. bias rate• 10 week dedicated HBD run (central field in configuration)• RHIC x PHENIX = 0.5 x 0.5 = 0.25
N e+e- = 1.2 x 105 produced in PHENIX acceptance
8.2 x 109 min. bias events produced
N e+e- = 1.5 x 10-5 / min.bias evente+e- PHENIX1 : 0.9 : 0.7
C. Woody, RHICII EM probes group meeting, 04/30/05
Lower energy 30GeV2 = 44
RHIC II Workshop, 11/11/05 14
STAR MRPC-TOFr Electron PID
Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!2 in azimuth, |eta|<1
electrons
Clean electron PID can be obtained up to PT< 3 GeV/c. This is used to measure the semileptonic decay of open charm.Hadron rejection power at 10-5. M. Shao et al., nucl-ex/0505026Higher pT: TPC+TOF+EMC
3σ signal a1 π± 54M events ! Interesting but difficult (Type B)
Cocktail
P. Fachini
RHIC II Workshop, 11/11/05 27
Vector MesonCSR
• Experimental observation of modification of Vector Spectral Function significant by itself
• Model calculation of V-A Spectral Function:Calculate vector and axialvector spectral functions as a function of temperature and density (including as many of the constraints, Weinberg sum rule) in a chirally invariant model.
• Compare results with Lattice QCD
• Detailed Experimental-Thoery comparison vs energy/density scanPerform detailed comparisons of the in-medium effects on the vector correlator with dilepton data (centrality, excitation function, mass and q_t-spectra), which requires a realistic expansion model (e.g. hydro/transport).
RHIC II Workshop, 11/11/05 28Mass (GeV)
subtracted spectrumthickness of linerepresents statistical error
Vacuum Vector mesons
QGPQGP
15% at m=2GeVNeeds ~+-2%
R. Seto, RHICII EM probes group meeting, 04/30/05
crude charm RHIC 2
Charm Background in PHENIX Dilepton
RHIC II Workshop, 11/11/05 29
Charm/Dalitz Background in STAR
DDbar e+e- correlations can be measured (<+-10%)Dalitz rejection: Inner Detector tracking: SSD+HFT+Vertexin progress
RHIC II Workshop, 11/11/05 30
Direct Photons Temperature
• pQCD+QGP+HG+Jet• Extract temperature
difficult • Energy Scan important• Detailed model
comparison
RHIC II Workshop, 11/11/05 31
Residual Correlation from HBT
Background = 4x signalSubtract from known ±± HBTSandweiss/Chikanian (Yale) in progress
0
0
0
e+
e-
0
e+
e-
Similar effect for virtual photons?Negligible with HBD
RHIC II Workshop, 11/11/05 32
drop. mass (norm.)
[RR+Wambach ’99]
• -meson “melting” , dropping mass?• address: absolute norm., pt-dep., M > 0.9GeV (4→!)• “cocktail-“ (+smooth signal)? vector dominance? • precision data essential to rule out models
Recent Advances at SPS: Power of Precision
drop. mass (norm.)drop. mass (norm.)
NA60
RHIC II Workshop, 11/11/05 33
Electromagnetic Probes at SPSDileptons
MediumEffects!10% QGP
[RR+ Shuryak ’99]
HG: 4→
30% QGP
[Turbide,RR+Gale’04]
Direct Photons
[Liu+ RR’05]
Central Pb(158AGeV)+Pb
RHIC II Workshop, 11/11/05 34
What needed at the SPS?
Experimentally:• Low-mass e+e: drop. mass vs. broad., energy scan [run time]
• Cronin enhancement vs. temperature [systematic p-A]
• Isolation of charm dileptons [vertex detector]
• Redundancy
Physics: • QGP subdominant ?!
• early thermalization (v2) ?!
RHIC II (dedicated QCDLab) has it all
RHIC II Workshop, 11/11/05 35
Conclusion• EM probes are directly sensitive to the
chiral symmetry properties and to the temperatures of the partonic system
• There are three major measurements related to the questions above
• Each with complemental/redundant techniques• Challenges:
not only confirm a theory, but rule out incorrect ones requires precision data in M, qt , centrality and √s
• RHIC (detectors) positioned to meet the challenges: - Dalitz suppression / charm ID; redundancy - energy-scan (006-200GeV!?)
• Theory Homework: chiral theory with baryons, sQGP, dilepton components, …
RHIC II Workshop, 11/11/05 36
Remarks
• Am I too negative? 哀兵必胜“ pessimistic” troops win
• Continue pushing our detectors to their limits
• Understand the strength and weakness
• Am I too positive?I don’t think of all the misery, but of all the beauty that still remains. – Anne Frank
• Continue exploration of techniques and simulations
• Understand and reduce the background
CHARM DILEPTON
I believe we can fly, RHIC II will provide us with wings
RHIC II Workshop, 11/11/05 37
2.2 EM Emission and Chiral Symmetry
~ “- a1(1260)” (chiral partners)
Axial-/Vector in Vacuum
pQCD cont.
)Im(Ims
dsf AV
2
at Tc: Chiral
Restoration
)T(fMqxdd
dN Bee23
2
44
Imem ~ [ImD+ImD/10+ImD/5]
• Low-Mass Dilepton Rate:
-mesondominated!
• Axialvector Channel: ± invariant mass-spectra ~ Im Da1(M) ?!
RHIC II Workshop, 11/11/05 38
T=1.4Tc
[Tokyo]
Spectral Functions
Thermalization at RHIC study the phase diagram: • (highest) temperature of the matter• chiral symmetry restoration (mass generation!)• medium effects on spectral properties above + below Tc
Introduction I: EM-Probes -- The Basic Questions
Inevitable consequences of QGP, link to lattice QCD
1.0 T/Tc
m‹qq›-
[Bielefeld]
Chiral CondensateQCD Phase Diagram
RHIC II Workshop, 11/11/05 39
(ii) Heavy Partons + Multiple Bound States
→ based on finite-T lattice potentials approach to “zero-binding line” ~ stable-mass-resonance
[Shuryak,Zahed, Brown, …]
• thermal parton scattering through bound states?• composite interactions? quark scaling?
Dilepton Radiationratio to pert. qq rate
Mee/mq
_
RHIC II Workshop, 11/11/05 40
Cocktail comparison
• Data and cocktail absolutely normalized
•Cocktail from hadronic sources•Charm from PYTHIAPredictions are filtered in PHENIX acceptance
•Good agreement in 0 Dalitz•Continuum:hint for enhancement not significant within systematics
•What happens to charm?•Single e pt suppression•angular correlation???