# Presentation: 501051

## Strangeness Production in p+p collisions at 200 GeV

- Mark Heinz
- University of Bern, Switzerland
- For the STAR collaboration
- HotQuarks
- Taos NM, July 2004

- Mark Heinz

## Contents

- Motivation
- STAR Results
- Experimental comparisons
- PYTHIA comparisons
- Summary

- Mark Heinz

## 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

## 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

## Particle Spectra 1: K0short (sd ) 

- Composite fit :
- mt-exponential (low pt)
- & powerlaw (high pt)

- 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

- |y|<0.5

- UA5-Comparison (|y|<2.0):
- <pt>   = 0.53 +0.08,-0.06
- dN/dy = 0.11 +- 0.05

**STAR Preliminary**

- Mark Heinz

## Particle Spectra 2: Lambda (uds)

- 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

- Systematic Errors:
- <pt> : ~10 %, Yield: ~15 %

- Low Pt acceptance : 300 Mev

- _UA5-comparison (|y|<2.0)_
- <pt>   = 0.8 +0.2,-0.14
- dN/dy = 0.08 ± 0.02

**STAR Preliminary**

- Mark Heinz

## 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

- Low Pt acceptance : 500 MeV
- Systematic Errors:
- <pt> : ~20 %, Yield: ~40 %

- _UA5-comparison (|y|< 3.0)_
- <pt>   = 0.8 +0.4,-0.2
- dN/dy = 0.0025 ± 0.0015

- Mark Heinz

## Omega and Anti-Omega

- Not enough statistics for pt-spectra
- Anti-particle/particle Ratio is 0.9+-0.1

- Mark Heinz

## <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

## Multiplicity dependence of <pt>

- How to define Multiplicity ?
- Definition of Ncharge is experiment dependant (pseudo-rapidity acceptance coverage)

- Mark Heinz

## Mini-Jet Theory/HIJING (Wang&Gyulassy)

- PRD 45,844 (1992)

-  Mini-jet X-section becomes significant at √200 GeV
-  Geometrical scaling breaks (ratio of σinel / σelastic non-constant)
- Inelastic X-section:
- σinel = Σ σnJet

**NJet=2**

**NJet=1**

**N****charge**** distribution for 200 GeV (UA5)**

- Contribution of Mini-jets is considerable at n>30.

- Mark Heinz

## <pt> vs Ncharge : FermiLab – UA1

- <pt> vs Ncharge : FermiLab – UA1

- Pt-Coverage: 0.2-1.5 GeV/c
- Nch measured over 6.5 units η
- Fit: pt-exp
- Phys Lett B 282 (1992)

**1992: E735 Fermilab **
** ****p+********p – 1.8 TeV**

**RHIC prediction**

**1996: CERN SPS UA1**
**p+********p – 630 GeV**

**K0s**

**Δ**** (****<pt>****Lambda**** ) ~ 55%**
**Δ**** (<pt> ****K0s**** ) ~ 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)

- 55%

- 50%

**Δ**** (****<pt>****Pbar**** )  ~ 25%**
**Δ**** (<pt> ****Kch**** ) ~ 20%**

- -0.36< η < 1.0

**Lambda**

- Mark Heinz

## <pt> vs multiplicity: STAR

- Measurement is dependant on the parameterization used (fit function to spectra)
- Increase in <pt> for Lambda (35%) is stronger than for K0s (20%)

- Composite fit

**Powerlaw fit**

**Mt-exponential fit**

**Δ**** <pt> ~ 20%**

**Δ**** <pt> ~ 35%**

- K0Short

- Lambda

**STAR Preliminary**

**STAR Preliminary**

- Mark Heinz

## 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

## PYTHIA: Pt-Spectra

- Spectra at mid rapidity
- |y|<0.5 (K0s,Lambda)
- |y|<0.75 (Xi)
- PYTHIA and data disagree in:
- Shape of pt-spectra & <pt>
- Yield

- Data
- Pythia

- Data
- Pythia

- Data
- Pythia

**K0****short**

**Lambda**

**Xi**

- Mark Heinz

## PYTHIA: <pt> vs multiplicity

- Recently CDF (Fermilab) has also shown the discrepancy between PYTHIA
- And data for <pt>h+- vs Nch (PRD 65,2002)

-  Systematic & statistical errors shown
-  PYTHIA underpredicts the magnitude and correlation strength between <pt> and multiplicity for measured strange particles

**K0****short**

**Lambda**

- Mark Heinz

## 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