identified charged hadrons at midrapidity in p-p collisions at rhic

Mark Harvey, BNL Quark Matter 2004 Conference January 11-17

Identified Charged Hadrons at Midrapidity in p-p

Collisions at RHICMark Harvey

Brookhaven National LaboratoryQuark Matter 2004

Oakland January 11-17


Differential Invariant Cross Section

• Experimental Definition:– Measurement of Luminosity (L) in p-p collisions Beam-Beam

Counter (BBC) triggered events• Ed/d3p = 1/2 1/pT 1/L dN/dydpT

where L = Nevent/ppBBC

• Application to A-A collisions:– The differential invariant yield in A-A collisions may be decomposed

into a soft phenomenological piece and a hard pQCD component • EdNAB/d3p = Npart EdNsoft/dyd2pT + Ncoll 1/pp

in EdNhard/dyd2pT

• Soft piece is model based;e.g.,– LUND string model u ud– Dual Parton Model ud d

• Hard component – pQCD calculation which model high pT (> 2.0 GeV/c) physics g g g g

• Cross section sensitive to two important pieces of physics!


Physics Motivation• Differential Invariant p-p Cross Section provides

– baseline measurement for disentangling of nuclear effects arising in d-Au and Au-Au collisions

– Hard-scattered partons give rise to hadronic sprays; i.e., jets

• Physics implications: – Careful examination of Nuclear Modification

Factors; e.g., RdAu and RAuAu

– Observation of jets give rise to high pT enhancement; i.e., Cronin effect

– Lack of high momentum enhancement jet suppression


PHENIX Detector

Beam-Beam Counter (BBC)

Trigger, timing and collision information

Drift Chamber (DC)Charged particle tracking

and momentum informationPad Chambers (PC1-PC3;

in analysis, use only PC1)3D space-point information

on charged particles

Time-Of-Flight (TOF) Detector

Timing information and charged hadron identification

Identified Charged Hadron Analysis Detection Elements:


Particle Detection and Measurement

TOF BBC

High Resolution Time-of-Flight (TOF) detector

TOF time resolution: 120 ps, relative to 2 cut in m2; K/ separation up to 2 GeV/c; P/K separation extends up to pT = 4

GeV/c - (Au-Au)

Beam-Beam Counter (BBC) provides start clock trigger

In p-p, clean pion and kaon separation out to |p| ~ 1.6 GeV/c; In p-p, clean pion and kaon separation out to |p| ~ 1.6 GeV/c; TOF timing resolution ~135 psTOF timing resolution ~135 ps

P'sK's

Full m2 Distribution 's p-p @ root s = 200 GeV


Differential Invariant Cross Section in p-p collisions of

+, K+, P -, K-, P

Pions spectra, Characterized by power law; exhibit concave shape

Proton spectra, ‘Characterized by Boltzman shape’

Kaon spectra, Fall-off exponentially in pT


Differential Invariant Cross Section

Magnitude of the charged pion averagecross section is inexcellent agreementwith published pi zero work

Phys. Rev. Lett. 91, 241803 (2003)

The p-p XSECT for pions measuredout to 10 orders of magnitude in pT!


-/+; 0.967+/-0.001+/-0.14

K-/K+; 0.90+/-0.01+/-0.14

P/P; 0.70 +/- 0.01 +/- 0.15

Ratios…

Shaded boxes represent systematic errors estimates

Pion, Kaon and Proton ratios are flat in pT


Particle Ratios for three Collision Systems

See Talk of Felix Matathias


K/ Ratios…

K/ Ratios increase steadily with increasing pT


No apparent indicationof saturation in this limited pT range


K+/+ Ratios for threeCollision Systems

All three systems show similar rising trend; comparable magnitudes


P/ Ratios…

P/ Ratios increase rapidlyfor pT < 1.4 GeV/c –flattens around 0.4 (0.3) for the positive (negative) particles at higher pT



P/ Ratios for three Collision Systems

p-p, min bias d-Au and peripheral Au-Au are directly comparable Results are in agreement (within ~10%)



RdAu ~ 1; implication: partonic momenta not significantly decreased in traversing hot medium

RAuAu considerably less than 1; implication:jet quenching due to hard scattered parton absorption in hot medium

See poster of Henner Buesching


In lower pT range, Integrated and PRdAu are essentiallyconstant w.r.t. ; probe of low momenta region soft physics (Npart)

Integrated RdAu

Higher pT (1.5-2.3):Integrated RdAu

approaches unity for the pions while proton enhancement is seen; i.e., similar to effects at lower energies



Summary• Differential invariant cross section of identified charged

hadrons in p-p collisions – baseline for d-Au and Au-Au – Excellent agreement between charged pion average and

published pi zero result– High precision measurement of pions out to 10 orders of

magnitude!• Particle Ratios:

– Like particles; agree very well, independent of collision system– K/ ratios rise steadily in limited pT range– P/ ratios saturate, no clear evidence of turn over in measured

pT window• Integrated RdAu of identified charged hadrons in specific

momenta regions provides sensitive probe of underlying effects in nuclear matter

identified charged hadrons at midrapidity in p-p collisions at rhic

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