The Ξ0(1530) Resonance from sNN=200 GeV p+p Collisions in STAR at RHIC

Richard Witt

University of Bern, Switzerland

for the STAR Collaboration

Presentation Overview

Motivation

Analysis Technique (very brief)

Ξ Spectra

Ξ0(1530) Signal Extraction

Ratios

Summary & Outlook

Motivation

Ξ0(1530)

Ξ-

π+

Λ

π-

p

π-

What is the Xi*?

Spin 3/2 multi-strange

baryon resonance

Well established (4-star)

Two charge states

Only Ξ0 in this analysis

Long-lived (cτ~21 fm)

Why Xi*?

Ξ feed-down correction

Model constraint

Rescattering in Au+Au

Why not?

Rare, σ ~ few b

4-particle final state

<pT>/<mT>~βT

Motivation

STAR Preliminary

Why Xi*?

Clarify <pT> trend in p+p

PDG (note on Ξ resonances):

“...there has not been a single

new piece of data on Ξ

resonances since our 1988

edition.”

Because we can

It's cool

It's not trivial

Decay Length

Daughter DCA

DCA to PV

Pos. Daughter

DCA

Neg. Daughter

DCA

Mult.

Analysis Technique

p

p+p @s = 200 GeV

Example Ξ- in a p+p Event

Topological Decay Identification

Several Geometrical Cuts

DCA, Decay Length, etc.

Corrections from Embedding

Embedding in Red

Data in Black

Ξ-

Λ

π-

π-

 p+p Results

Total Data Set:

~10 million events after quality cuts

Sufficient Statistics for 12 Bins in pT

0.5  pT  5.0 GeV/c

〈pT〉 from mT-Exponential Fits:

Ξ- : 0.97 ± 0.02 (stat.) GeV/c

Ξ+ : 0.95 ± 0.02 (stat.) GeV/c

dN/dy from mT-Exponential Fits:

Ξ- : 0.00181 ± 0.00008 (stat.)

Ξ+ : 0.00178 ± 0.00008 (stat.)

0(1530) Background Subtraction

STAR Preliminary

p+p @s = 200 GeV

STAR Preliminary

p+p @s = 200 GeV

STAR Preliminary

p+p @s = 200 GeV

Ξ*

Ξ*

Ξ's and primary π's

Mixed events (red)

Cuts on:

Event must contain Ξ

Number of Ξ's +/- 2

Event vertex Z +/- 5cm

Multiplicity +/- 2

0(1530) Signal Extraction

STAR Preliminary

p+p @s = 200 GeV

STAR Preliminary

p+p @s = 200 GeV

STAR Preliminary

p+p @s = 200 GeV

Ξ*

Ξ*

Fit Breit-Wigner + linear BG

Mass, good agreement

Slightly wider (~1 σ)

Ξ*

Ξ*

0.5 < pT ≤ 1.0

1.0 < pT ≤ 1.5

1.5 < pT ≤ 2.0

2.0 < pT ≤ 2.5

2.5 < pT ≤ 3.0

3.0 < pT ≤ 3.5

STAR Preliminary p+p @s = 200 GeV

STAR Preliminary p+p @s = 200 GeV

STAR Preliminary p+p @s = 200 GeV

STAR Preliminary p+p @s = 200 GeV

STAR Preliminary p+p @s = 200 GeV

STAR Preliminary p+p @s = 200 GeV

0(1530) & Anti-0(1530) pT Bins, p+p

500 MeV/c bins

Low pT BG?

More stats.

* &  Ratios in p+p

STAR Preliminary

p+p @s = 200 GeV

pT-averaged Ξ/Ξ: 0.90 ± 0.048

pT-averaged Ξ*/Ξ*: 0.74 ± 0.38

Ξ & Ξ* Ratio Flat in pT (within errors)

0(1530) in d+Au

STAR Preliminary

d+Au@s = 200 GeV

STAR Preliminary

d+Au @s = 200 GeV

STAR Preliminary

d+Au @s = 200 GeV

Ξ*

Ξ*

Much stronger signal

Only half the d+Au statistics

* &  Ratios in d+Au

STAR Preliminary

d+Au @s = 200 GeV

pT-averaged Ξ/Ξ: 0.85 ± 0.031

pT-averaged Ξ*/Ξ*: 0.89 ± 0.27

Ξ & Ξ* Ratio Flat in pT (within errors)

Summary & Outlook

Richard Witt -- University of Bern

RHIC/AGS User's Meeting, BNL 5/14/2004

Ξ0(1530) measured in p+p & d+Au

Anti-Ξ*/Ξ* measured vs. pT (statistics limited)

2 M p+p events not yet analyzed

Some run scenarios will double p+p minbias

Only half d+Au analyzed so far

No signal (yet) in Au+Au events at any energy

Physics?

BG too high?

Just me?

Embedding on the way

Tune cuts more carefully

Corrected spectra & yields for p+p & d+Au

The STAR Collaboration

Argonne National Laboratory• Institute of High Energy Physics, Beijing• Institute of Physics, Bhubaneswar• University of Bern, Switzerland• University of Birmingham• Brookhaven National Laboratory• University of California, Berkeley• University of California, Davis• University of California, Los Angeles• Carnegie Mellon University• Creighton University• Laboratory for High Energy (JINR), Dubna• Particle Physics Laboratory (JINR), Dubna• University of Frankfurt• Indiana University, Bloomington• Institut de Recherches Subatomiques, Strasbourg• Jammu University• Kent State University• Institute of Modern Physics, Lanzhou• Lawrence Berkeley Laboratory• Max-Planck-Instit fuer Physik, Munich• Michigan State University• Moscow Engineering Physics Institute• Indian Institute of Technology, Mumbai• City College of New York• Ohio State University• Panjab University• Pennsylvania State University• Institute of High Energy Physics, Protvino• Purdue University• University of Rajasthan• Rice University• Universidade de Sao Paulo• University of Science and Technology of China (USTC)• Shanghai Institue of Nuclear Research (SINR)• SUBATECH, Nantes• Texas A & M• University of Texas, Austin• Tsinghua University• Variable Energy Cyclotron Centre, Kolkata• Warsaw University• Warsaw University of Technology• University of Washington• Wayne State University• Institute of Particle Physics, Wuhan• Yale University

RHIC/AGS User's Meeting 2004 p+p & d+Au Strange Spectra

K0, Lambda, & Xi spectra & yields from the 2002 pp run

RHIC AGS p+p d+Au K0 Lambda Xi

Richard Witt

2002-09-29T11:47:31