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Strangeness Production in p+p collisions at 200 GeV

Strangeness Production in p+p collisions at 200 GeV. Mark Heinz University of Bern, Switzerland For the STAR collaboration HotQuarks Taos NM, July 2004. Contents. Motivation STAR Results Experimental comparisons PYTHIA comparisons Summary. Motivation.

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Strangeness Production in p+p collisions at 200 GeV

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  1. Strangeness Production in p+p collisions at 200 GeV Mark Heinz University of Bern, Switzerland For the STAR collaboration HotQuarks Taos NM, July 2004

  2. Contents • Motivation • STAR Results • Experimental comparisons • PYTHIA comparisons • Summary Mark Heinz

  3. Motivation • P-P collisions are a baseline to compare heavy-ion results to • Study pQCD (PYTHIA) mini-Jet production in a “clean” environment • Study systematic behavior of <pt> vs event multiplicity for strange particles Mark Heinz

  4. Results – Data Sample • RHIC Run 2001/2002 • Total data sample ~14 M events (usable ~ 11M) • Trigger: Beam-Beam Counters (BBC) • Strange particle PID: • Decay topology (V0s, Xis) • dE/dx from TPC Required Correction to raw data: • Primary Vertex-efficiency • MC-Study • Pile-up • Vertex matching & CTB (central trigger barrel) • Reconstruction efficiency • Embedding • Feed-down • Xi vs Lambda embedding MC-Study 14% lost vertices 10% fake vertices PrimVtx position (true-found) Mark Heinz

  5. Composite fit : mt-exponential (low pt) & powerlaw (high pt) Particle Spectra 1: K0short (sd ) |y|<0.5 STAR Preliminary • Decay: π-+ π+ (br. 64%) • dN/dy = 0.128 ± 0.008 • <pt> = 0.603 ± 0.006 • Systematic Errors: • <pt> : 2% (Cuts) + 4% (Fit) • Yield: 11% (Cuts) + 4% (Fit) Low Pt acceptance : 150Mev UA5-Comparison (|y|<2.0): <pt> = 0.53 +0.08,-0.06 dN/dy = 0.11 +- 0.05 Mark Heinz

  6. Particle Spectra 2: Lambda (uds) STAR Preliminary • Decay: p+ π- (br. 68%) • dN/dy = 0.086 ± 0.007 • FD corrected = 0.066 ± 0.004 • <pt> = 0.76 ± 0.05 • Ratio = 0.90 ± 0.02 Composite fit: mt-exp & pt-exp |y|<0.5 UA5-comparison (|y|<2.0) <pt> = 0.8 +0.2,-0.14 dN/dy = 0.08 ± 0.02 Systematic Errors: <pt> : ~10 %, Yield: ~15 % Low Pt acceptance : 300 Mev Mark Heinz

  7. Particle Spectra 3: Xi- (dss) Decay: Λ+ π- (br. 99.9%) dN/dy = 0.0018 ± 0.0002 <pt> = 0.96 ± 0.05 Ratio = 0.90 ± 0.05 UA5-comparison (|y|< 3.0) <pt> = 0.8 +0.4,-0.2 dN/dy = 0.0025 ± 0.0015 Low Pt acceptance : 500 MeV Systematic Errors: <pt> : ~20 %, Yield: ~40 % Mark Heinz

  8. Omega and Anti-Omega • Not enough statistics for pt-spectra • Anti-particle/particle Ratio is 0.9+-0.1 Mark Heinz

  9. <pt> vs particle mass • Measured particles over large mass range • Mass dependence, but not from flow • Nice agreement with phenomenological curve established by ISR (25GeV) • Strange baryons and resonances are above the curve Mark Heinz

  10. Multiplicity dependence of <pt> • How to define Multiplicity ? • Definition of Ncharge is experiment dependant (pseudo-rapidity acceptance coverage) Mark Heinz

  11. Mini-Jet Theory/HIJING (Wang&Gyulassy) Ncharge distribution for 200 GeV (UA5) • Mini-jet X-section becomes significant at √200 GeV • Geometrical scaling breaks (ratio of σinel / σelastic non-constant) • Inelastic X-section: • σinel = ΣσnJet NJet=1 Contribution of Mini-jets is considerable at n>30. NJet=2 PRD 45,844 (1992) Mark Heinz

  12. <pt> vs Ncharge : FermiLab – UA1 1992: E735 Fermilab p+p – 1.8 TeV 1996: CERN SPS UA1 p+p – 630 GeV Δ (<pt>Pbar ) ~ 25% Δ (<pt> Kch ) ~ 20% Δ (<pt>Lambda ) ~ 55% Δ (<pt> K0s ) ~ 50% -0.36< η < 1.0 Lambda 55% K0s RHIC prediction 50% h- K0s: | η |<2.5, Lambda: |η|<2.0 Pt-Coverage: 0.4-7.0 GeV/c Fitfunction: Powerlaw(K0s), pt-Exp (Lambda) Phys Lett B 336 (1996) Pt-Coverage: 0.2-1.5 GeV/c Nch measured over 6.5 units η Fit: pt-exp Phys Lett B 282 (1992) Mark Heinz

  13. <pt> vs multiplicity: STAR Composite fit Powerlaw fit Mt-exponential fit • Measurement is dependant on the parameterization used (fit function to spectra) • Increase in <pt> for Lambda (35%) is stronger than for K0s (20%) STAR Preliminary STAR Preliminary Lambda K0Short Δ <pt> ~ 35% Δ <pt> ~ 20% Mark Heinz

  14. Parton <pt> vs Multiplicity Pt correlation Parton/Final Mini-Jets in PYTHIA • String fragmentation (Lund Model) • Pythia-Settings (6.2/MSEL1) • Correlations between pt of hard parton process and event multiplicity • Correlation between pt of parton process and final state pt Mark Heinz

  15. Spectra at mid rapidity |y|<0.5 (K0s,Lambda) |y|<0.75 (Xi) PYTHIA and data disagree in: Shape of pt-spectra & <pt> Yield PYTHIA: Pt-Spectra Xi K0short Lambda Data Pythia Data Pythia Data Pythia Mark Heinz

  16. PYTHIA: <pt> vs multiplicity K0short Lambda • Systematic & statistical errors shown • PYTHIA underpredicts the magnitude and correlation strength between <pt> and multiplicity for measured strange particles Recently CDF (Fermilab) has also shown the discrepancy between PYTHIA And data for <pt>h+- vs Nch (PRD 65,2002) Mark Heinz

  17. Summary • Highest statistics measurement in p+p (200GeV) of neutral strange and multi-strange particles • Yield and <pt> are consistent with previous measurements from UAx/Fermilab experiments • PYTHIA fails to describe the shape of the spectra and the multiplicity dependence of <pt> Future Work • More work to be done to get <pt> of Xi and Φ as function of multiplicity • Long Paper is in the works for publication this fall Mark Heinz

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