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Identified Charged Hadrons at Midrapidity in p-p Collisions at RHIC

Identified Charged Hadrons at Midrapidity in p-p Collisions at RHIC. Mark Harvey Brookhaven National Laboratory Quark Matter 2004 Oakland January 11-17. Differential Invariant Cross Section. Experimental Definition:

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Identified Charged Hadrons at Midrapidity in p-p Collisions at RHIC

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  1. Identified Charged Hadrons at Midrapidity in p-p Collisions at RHIC Mark Harvey Brookhaven National Laboratory Quark Matter 2004 Oakland January 11-17

  2. 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/ppin 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!

  3. 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

  4. PHENIX Detector Beam-Beam Counter (BBC) Trigger, timing and collision information Drift Chamber (DC) Charged particle tracking and momentum information Pad 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:

  5. BBC TOF 's K's P's Particle Detection and Measurement 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 Full m2 Distribution p-p @ root s = 200 GeV In p-p, clean pion and kaon separation out to |p| ~ 1.6 GeV/c; TOF timing resolution ~135 ps

  6. Differential Invariant Cross Section in p-p collisions of Pions spectra, Characterized by power law; exhibit concave shape +,K+,P -,K-, P Kaon spectra, Fall-off exponentially in pT Proton spectra, ‘Characterized by Boltzman shape’

  7. Differential Invariant Cross Section Magnitude of the charged pionaverage cross section is in excellent agreement with published pi zero work The p-p XSECT for pions measured out to 10 orders of magnitude in pT! Phys. Rev. Lett. 91, 241803 (2003)

  8. Ratios… Pion, KaonandProton ratios are flat in pT -/+; 0.967+/-0.001+/-0.14 K-/K+; 0.90+/-0.01+/-0.14 P/P; 0.70 +/- 0.01 +/- 0.15 Shaded boxes represent systematic errors estimates

  9. Particle Ratios for three Collision Systems See Talk of Felix Matathias

  10. K/ Ratios… K/ Ratios increase steadily with increasing pT No apparent indication of saturation in this limited pT range Shaded boxes represent systematic errors estimates

  11. K+/+ Ratios for threeCollision Systems All three systems show similar rising trend; comparable magnitudes

  12. P/ Ratios… P/ Ratios increase rapidly for pT < 1.4 GeV/c – flattens around 0.4 (0.3) for the positive (negative) particles at higher pT Shaded boxes represent systematic errors estimates

  13. 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%) See Talk of Felix Matathias

  14. 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

  15. Integrated RdAu In lower pT range, Integrated  and P RdAu are essentially constant w.r.t. ; probe of low momenta region soft physics (Npart) 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 See Talk of Felix Matathias

  16. 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

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