identified hadrons from snn = 130 gev au-au collisions measured in phenix

Nov27,2001 ICPAQGP2001, Jaipur Julia Velkovska

Identified Hadrons from sNN = 130 GeV Au-Au

collisions measured in PHENIX Julia Velkovska (BNL) for PHENIX

• Identified hadron measurements in PHENIX

– Identified charged hadrons via TOF

– Neutral pions using EMC

• Results– Transverse momentum spectra (identified charged hadrons)

– <pT> and dN/dy as a function of Npart

– Combine with 0 measurement - > ratios at high pT for 10% central

– Decomposition of the charged hadron spectra to mesons and baryons

• Conclusions and outlook


Identified charged hadronsTracking system:

Drift Chamber , PC1

p/p = 0.6% + 3.5% p (GeV/c)

Timing system: BBC - start

TOF - stop

= 115 ps

Acceptance: deg

PID :

momentum dependent bands in mass2


Two analyses with very different systematics• pair measurement (yields from invariant mass distributions) • yields extracted statistically – large combinatorial background• requires many events• difficult at low pT

• signal to background improves at higher pT

Neutral pion measurement

PbSc PbGl


Identified charged hadron spectra

•Intergrate the spectra to obtain <pT> and dN/dy•Use the data where measured •Extrapolate to 0 and to œwith several different functions •Extrapolation fractions:30+/-6% for

40+/-8% for K+/-

25+/-7.5% for p and pbar


Mean transverse momentum

• Mean pt growing with Npart and mass - consistent with flow• (Anti)proton < pT> significant increase from pp collisions • The same relative increase from peripheral to central for all particles

20+/- 5 % increase

20+/- 5 % increase


Centrality dependence of hadron yields per participant

• Excellent agreement between published charged multiplicities and identified hadron multiplicities!

• Is the increase in dNch/dp) due to hard processes ?• How do the different particle species contribute to the total yield ?


Centrality dependence of identified charged hadron yields

• (Anti)proton yields per participant pair rise faster than pion yields with Npart !

• Similar behavior in K+ , K-, p and p• Different from AGS and SPS Pb-Pb

21% +/- 6% (stat) +/- 8%(syst)

72% +/- 9 % (stat) +/- 20%(syst)

94%+/-11%(stat)+/-26%(syst) for K+

66%+/-12%(stat)+/-20%(syst) for K-


Centrality dependence of identified hadron ratios

•Kaon, proton and anti-protonyields rise faster than the pions.•Significant fraction of the charged multiplicity increase with centrality is due to kaons and baryons !

•Proton/kaon and anti-proton/kaon ratios flat within errors•Anti-proton production follows strangeness production


Hydro + cascade or baryon junctions + pQCD ?

5% central

D. Teaney et.al.Hydro+cascade

I.Vitev et.al.Baryon junctions+pQCD


Identified hadron spectra in central Au-Au collisions

Excellent agreement between charged and neutral pions !(anti)proton – pion crossing confirmed!


Nucleon to Pion Ratios

p/and p/rising with pT p/and p/rising or saturating at high pTDifferent from pp collisions - (anti)protons don’t come from jets


Anti-proton /proton ratio in Central Au-Au Collisions

flat or falling?Not enough

statistics in year 2000 run

PHENIX has x 200 morestatistics on tape

from year 2001 runX.N.Wang

Hydro predicts a flat line

pQCD – pbar/p is falling

as a function of pT


Hadron suppression at high pT

high pT hadron suppressiondifferent suppression for h and


Decomposing the hadron spectra to mesons and nucleons

• Subtract anti-protons and protons from charged

hadrons

•Compare the meson spectrum to 0

Difference in high pT charged hadron

And 0 suppression primarily due to

nucleons


• PHENIX has measured identified hadrons over a broad momentum range

• Internal consistency:– Identified charged and neutral pions– Charged and identified charged spectra– Charged multiplicity and identified hadron multiplicity

• Protons dominate over pions at high pt in central collisions • p/ratio rising with pt , approaching 1 and suggestive for saturating

behavior – more statistics needed• Mean pT increases with Npart similarly for all particle species• dN/dy per participant pair rises faster for kaons, protons and anti-

protons than for pions• Hadron suppression at high pt

– Different high pt behavior for mesons and baryons

Conclusions


Present run started July 2001 > 60M Au + Au min bias eventscollected p + p run just startingNew detectors for hadron measurement:• 8 complete sectors of EMCAL (6 PbSc, 2 PbGl)• PC2 and PC3 on West arm• Rebuilt drift chamber• Upgraded trigger

Charged hadrons and pT > 10 GeV/c

High pT behavior of p-/p and p-/ratios both in Au-Au and pp with high statistics and as a function of centrality

Study centrality dependence of hadron production with finer binning

Outlook - Year 2 Run

GeV 200NN s


Extra slides


0 - 5 %

ZD

C5–15 %

15-30%

30-60%60-92 %

Measuring Collision Centrality

Zero Degree Calorimeters (ZDC) - sensitive to spectator neutrons

BBC – charged particlies form the collision zone

Good min bias trigger –measured 92+/-4 % of the total geom cross-section

Using a combination of the ZDC’s and BBC’s we can define centrality classes.

Glauber model to determine Npart BB

C



mid - central peripheral

In central collisions:

at pT ~ 2GeV/c anti -proton yields comparable to pion yields

Protons cross the pions ~ 1.6 GeV/c


Charged hadrons

• single particles, no combinatorial background

• better per-event statistics, need fewer events for same pT range

• momentum reconstruction increasingly difficult with higher pT

Drift Chamber PC1: tracking

PC3 - used to cut background


What about mT scaling ?

identified hadrons from snn = 130 gev au-au collisions measured in phenix

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