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 p0 measurement - > ratios at high pT for 10% central
– Decomposition of the charged hadron spectra to mesons and baryons
• Conclusions and outlook
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Identified charged hadrons
Tracking system:
Drift Chamber , PC1
dp/p = 0.6% + 3.5% p (GeV/c)
Timing system:
BBC - start
TOF - stop
s = 115 ps
Acceptance:
D f = 45 deg
D h = 0.7
PID :
Nov2,2001
momentum dependent bands in mass2
High PT Workshop, BNL
Julia Velkovska
Neutral pion measurement
PbSc
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PbGl
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
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Charged hadrons
Drift Chamber PC1: tracking
PC3 - used to cut background
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single particles, no combinatorial background
better per-event statistics, need fewer events for same pT range
momentum reconstruction increasingly difficult with higher pT
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
ZDC
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
Nov2,2001
5 - 10 %
0-5%
High PT Workshop, BNL
Julia Velkovska
BBC
Identified charged hadron spectra
Central
peripheral
Nov2,2001
High PT Workshop, BNL
mid - central
Julia Velkovska
Hydro + cascade or baryon junctions + pQCD ?
Hydro+cascade
D. Teaney et.al.
5% central
Baryon junctions + pQCD
I.Vitev et.al.
Both theories can describe the data
up to 3 GeV/c
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Mean transverse momentum
20+/- 5 % increase
20+/- 5 % increase
• 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
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Yields as a function of Npart
• Is the increase in dNch/dh / (0.5 Np) due to hard processes ?
• How does the yield per participant behave for different particles ?
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Identified charged hadron yields
20 +/- 6% increase
65 +/- 7 % increase
• Anti-proton and proton yields per participant pair rise faster
than pion yields with Npart !
• Different from SPS Pb-Pb
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Identified hadron spectra in central Au-Au collisions
Excellent agreement between charged and neutral pions !
(anti)proton – pion crossing confirmed!
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Nucleon to Pion Ratios
p/p+ and p/p0 rising with pT
p/p- and p/p0 rising or saturating at high pT
Different from pp collisions - (anti)protons don’t come from jets
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
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
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Theory expectations:
pQCD++
• 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/p ratio has a peak which
changes with centrality
hydrodynamics
• p/p ratio flat with pT
• p/p ratio steadily rising with pT
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
High density QCD expects mT scaling :
The data are consistent with mT scaling up to 3.5 GeV.
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Hadron suppression at high pT
high pT hadron suppression
different suppression for h and p0
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Decomposing the hadron spectra to mesons and nucleons
• Subtract anti-protons
and protons from charged
hadrons
•Compare the meson
spectrum to p0
Difference in high pT
charged hadron
And p0 suppression
primarily due to
nucleons
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
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
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Conclusions
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PHENIX measured p,p,p0,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/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
Nov2,2001
High PT Workshop, BNL
Julia Velkovska
Outlook - Year 2 Run
Present run started July 2001
Hope to collect:
~ 300 mb-1 Au + Au
s NN = 200 GeV
-1
~ 3.5 pb p + p
Will be able to pin down the high
pT behavior of p-/p and p-/p
ratios both in Au-Au and pp
New detectors:
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8 complete sectors of EMCAL
(6 PbSc, 2 PbGl)
Rebuilt drift chamber
Multiplicity vertex detector (MVD)
South Muon Spectrometer
Upgraded trigger
Upgraded data aquisition
Nov2,2001
High PT Workshop, BNL
Julia Velkovska