Nov2,2001High P T Workshop, BNL Julia Velkovska High pt Hadrons from sNN = 130 GeV Au-Au collisions measured in PHENIX Julia Velkovska (BNL) for PHENIX.

Nov2,2001 High PT Workshop, BNL Julia Velkovska

High pt Hadrons from sNN = 130 GeV Au-Au

collisions measured in PHENIX Julia Velkovska (BNL) for PHENIX

• High pT measurements in PHENIX

– Identified protons and anti-protons – 3.5 GeV/c

– Neutral pion analysis – up to 4 GeV/c

– Charged hadron analysis - up to 5 GeV/c

• 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


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


Measuring Collision Centrality

Zero Degree Calorimeters (ZDC) Sensitive to spectator

neutrons

Using a combination of the ZDC’s and BBC’s we can define Centrality Classes

0 - 5 %

ZD

C

BBC

5 - 10 %


Identified charged hadron spectra

Central

mid - centralperipheral


Hydro + cascade or baryon junctions + pQCD ?

5% central

Hydro+cascadeD. Teaney et.al.

Baryon junctions + pQCDI.Vitev et.al.

Both theories can describe the data up to 3 GeV/c


Mean transverse momentum

• Mean pt growing with Npart and mass - consistent fith 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


Yields as a function of Npart

• Is the increase in dNch/dp) due to hard processes ?

• How does the yield per participant behave for different particles ?


Identified charged hadron yields

• Anti-proton and proton yields per participant pair rise faster than pion yields with Npart !

• Different from SPS Pb-Pb

20 +/- 6% increase

65 +/- 7 % increase


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 10 more

statistics on tape from year 2001

run


• p/p ratio falling with pT

– Jet quenching moves the p/p ratio below the pp value

– PHENIX will measure pp collisions this year

• p/ ratio has a peak which changes with centrality

hydrodynamics

• p/p ratio flat with pT

• p/ ratio steadily rising with pT

Theory expectations:pQCD++


High density QCD expects mT scaling :

The data are consistent with mT scaling up to 3.5 GeV.


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


We can measure it - can you predict it for sNN = 200 GeV Au-Au collisions ?

• (Anti)proton / pion ratio as a function of pT for different centralities

• anti-proton / proton ratio as a function of pT for different centralities

• <pT> as a function of Npart and mass

• dN/dy as a function of Npart and mass

• High pT suppression for mesons and baryons

• All these taken together can help differentiate between different production mechanisms at high pT


• PHENIX measured p,p,0,h up to 3.5,4,5 GeV/c• All measurements are internally consistent• Protons dominate over pions at high pt in central collisions• Mean pT increases with Npart similarly for all particle species• dN/dy per participant pair rises faster for (anti)protons than for

pions• p/ratio rising with pt , approaching 1 and suggestive for

saturating behavior – more statistics needed• p/p ratio flat or falling at high pt - inconclusive due to low

statistics• Hadron suppression at high pt

– Different high pt behavior for mesons and baryons

Conclusions


Present run started July 2001Hope to collect: ~ 300 mb-1 Au + Au ~ 3.5 pb-1 p + p

Will be able to pin down the high pT behavior of p-/p and p-/ratios both in Au-Au and pp

New detectors:• 8 complete sectors of EMCAL (6 PbSc, 2 PbGl)• Rebuilt drift chamber• Multiplicity vertex detector (MVD)• South Muon Spectrometer• Upgraded trigger• Upgraded data aquisition

Outlook - Year 2 Run

GeV 200NN s

Nov2,2001High P T Workshop, BNL Julia Velkovska High pt Hadrons from sNN = 130 GeV Au-Au collisions measured in PHENIX Julia Velkovska (BNL) for PHENIX.

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