mid-rapidity hadron production studied with the phenix detector at rhic joakim nystrand...

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)



A world-wide collaboration of 500 physicists from 51 Institutions in 12 countries

The PHENIX collaboration



The PHENIX detector2 CentralTracking arms

2 Muon arms

Beam-beam counters

Zero-degree calorimeters(not seen)



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



Example of a central Au+Au event at snn =200 GeV



Centrality DefinitionCentrality impact parameter

Two measures:

Np : Number of participating nucleons

Ncoll : Number of binary (nucleon-nucleon) collisions



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 • • • • • •



• 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



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



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



PHENIX preliminary

200GeV/130GeV

Stronger increase in Hijing than in datafor central collisions

Multiplicity ratio (200/130) GeV



Variation with snn

To guide the eye

)ln(5.0

1sBA

dy

dN

Nch

p



0 Identification with EmCal

Background subtracted

Original spectrum



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



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.



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.



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.



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):



The yield is extracted by fitting the m2 spectrum to a function for the signal (gaussian) + background (1/x or e-x)



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…



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.



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.



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*



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)

mid-rapidity hadron production studied with the phenix detector at rhic joakim nystrand...

Documents

bergen pt03

gev slide

phenix collaboration

eye slide

phenix detector

wang phys

centrality determinartion

centrality bin