Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC
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Transcript of Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC
Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC
Joakim NystrandUniversitetet i Bergen
for the PHENIX Collaboration
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
What is PHENIX?
PHENIX = Pioneering High Energy Nuclear Interaction eXperimentA large, multi-purpose nuclear physics experiment at the Relativistic Heavy-IonCollider (RHIC)
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
A world-wide collaboration of 500 physicists from 51 Institutions in 12 countries
The PHENIX collaboration
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
The PHENIX detector2 CentralTracking arms
2 Muon arms
Beam-beam counters
Zero-degree calorimeters(not seen)
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Charged particle tracking: • Drift chamber • Pad chambers (MWPC)
Particle ID: • Time-of-flight (hadrons)• Ring Imaging Cherenkov(electrons)• EMCal (, 0)• Time Expansion Chamber
Acceptance:|| < 0.35 – mid-rapidity = 2 90
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Example of a central Au+Au event at snn =200 GeV
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Centrality DefinitionCentrality impact parameter
Two measures:
Np : Number of participating nucleons
Ncoll : Number of binary (nucleon-nucleon) collisions
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Centrality Determinartion
For each centrality bin, <Np> and <Ncoll> are calculated from a Glauber model. Centrality <Ncoll> <Np> 0 – 10% 95594 325310 – 20% 60359 235520 – 30% 37440 1675 • • • • • •
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
• Combine the hits in PC1 and PC3. • The result is a sum of true combinations (from real tracks) and combinatorial background. • Determine the combinatorial background by event mixing
MultiplicityHow many particles are produced (at mid-rapidity)? How does the multiplicity scale with centrality, Np or Ncoll?
B=0Experimental Method
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Multiplicity per 2 participants
HIJINGX.N.Wang and M.Gyulassy, PRL 86, 3498 (2001)
EKRTK.J.Eskola et al, Nucl Phys. B570, 379 andPhys.Lett. B 497, 39 (2001)
K. Adcox et al. (PHENIX Collaboration), Phys. Rev. Lett. 86(2001)3500
Au+Au at s=130 GeV
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
200 GeV130 GeV HIJINGX.N.Wang and M.Gyulassy, PRL 86, 3498 (2001)
Mini-jetS.Li and X.W.Wang Phys.Lett.B527:85-91 (2002)
EKRTK.J.Eskola et al, Nucl Phys. B570, 379 andPhys.Lett. B 497, 39 (2001)
KLND.Kharzeev and M. Nardi, Phys.Lett. B503, 121 (2001)D.Kharzeev and E.Levin, Phys.Lett. B523, 79 (2001)
PHENIX preliminary
Multiplicity at s=200 GeV
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
PHENIX preliminary
200GeV/130GeV
Stronger increase in Hijing than in datafor central collisions
Multiplicity ratio (200/130) GeV
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Variation with snn
To guide the eye
)ln(5.0
1sBA
dy
dN
Nch
p
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
0 Identification with EmCal
Background subtracted
Original spectrum
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
K. Adcox et al. (PHENIX Collaboration) Phys. Rev. Lett. 88(2002)022301
Suppressed 0 yield at high pT
A remarkable observation:
Yield above pT 2 GeV/c scales with Ncoll in peri-pheral collisions but is suppressed in central collisions!A possible indication of ”jet-quenching” Bjorken (1982), Gyulassy & Wang (PRL(1992)1480), HIJING
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
dydpdN
dydpNdNpR
Tppinelppcoll
TAAEVTTAA //
/)/1()(
02
02
The ratio RAA
Quantify the deviation from binaryscaling through RAA:
Au+Au 200 GeVS.S. Adler et al. (PHENIX Collaboration)PRL 91(2003)072301.
p+p 200 GeVS.S. Adler et al. (PHENIX Collaboration)hep-ex/0304038, to be published in PRL.
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Suppression of charged hadrons
A similar suppression seen also for charged hadrons at high pT.
Au+Au 200 GeVS.S. Adler et al. (PHENIX Collaboration)nucl-ex/0308006, submitted to PRC.
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Suppression at high pT in AA vs. pp How about pA (or dA)?
Absence of suppression in dA suggest that the effect seen in central AA is due to the dense matter created in the collisions.
Intial or Final State Effect?
d+Au 200 GeVS.S. Adler et al. (PHENIX Collaboration)PRL 91(2003)072303.
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Charged-particle Identification
Central arm detectors: Drift Chamber, Pad Chambers (2 layers), Time-of-Flight.
Combining the momentum information(from the deflection in the magneticfield) with the flight-time (from ToF):
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
The yield is extracted by fitting the m2 spectrum to a function for the signal (gaussian) + background (1/x or e-x)
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Correction for acceptance and efficiency normalized d and d pT spectrum:
The spectrum has been fit to an exp. function in mT, exp( -mT/T)
More about the slopes (Teff) later…
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
How are nuclei and anti-nuclei formed in ultra-relativistic heavy-ion interactions?
1. Fragmentation of the incoming nuclei. Dominating mechanism at low energy and/or at large rapidities (fragmentation region). No anti-nuclei.
2. Coalescence of nucleons/anti-nucleons. Dominating mechanism at mid-rapidity in ultra-relativistic collisions. Only mechanism for production of anti-nuclei.
2
3
3
23
3
p
pp
d
dd dp
NdEB
dp
NdE
Coalescence
A deuteron will be formed when a proton and a neutron are within a certain distance in momentum and configuration space.
where pd=2pp and B2 is the coalescence parameter, B2 1/V. Assuming that n and p have similar d3N/dp3
This leads to:
Imagine a number of neutrons and protons enclosed in a volume V:
The reality is more complicated…B2 depends on pT not a direct measure of the volume
Possible explanation: Radial flow.
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
A. Polleri, J.P. Bondorf, I.N. Mishustin: ”Effects of collective expansion on light cluster spectra in relativistic heavy ion collisions” Phys. Lett. B 419(1998)19.
Introducing collective transverse flow generally leads to an increase in B2 with pT.
The detailed variation depends on the choice of nucleon density and flow profile.
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
For the special case
TT
fd eR
rvv
0
)2
exp()(2
2
T
TT
rrn
Linear flow profile + Gaussian density distribution
Teff independent of fragment mass, Teff(d) = Teff(p)
The gaussian parameterization + linear flow profile give too little weight to the outer parts of the fireball, where the flow is strongest.
Experimentally, d Teff = 51526 MeV p Teff = 3266 MeV*
* mid-central collisions, 40-50% centrality.
d Teff = 48826 MeV p Teff = 3316 MeV*
Joakim Nystrand, Universitetet i Bergen
PT03, Copenhagen 9-10 October
Conclusions
• Nearly logarithmic increase in multiplicity per
participant with s AGS SPS RHIC
• yield suppressed at high pT in central Au+Au
collisions.
• yield not suppressed in d+Au collisions
Suppression in central Au+Au collisions is a final state
effect, caused by the dense medium.
• deuteron/anti-deuteron spectra at mid-rapidity probes
the late stages of relativistic heavy ion collisions.
A lot of new exciting data (only a fraction was shown in this talk)