First measurement of the meson production with PHENIX experiment at RHIC

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First measurement of the ? - meson
production with PHENIX experiment at RHIC
Victor Ryabov for the PHENIX Collaboration
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• Measurement of ?-meson production in different
  decay channels (??p0pp-, ??p0?, ??ee-) carries
  information about possible modification of the
  media produced in HI collisions.
• Measurement of hadronic decays of the ?-mesons
  in pp collisions creates a baseline for the
  comparison to other decay modes and collision
  systems
• Comparison ??hadrons vs. ??di-electrons in pp
• Comparison of the same ratio in AA
• ? is an important ingredient for calculation of
  electron cocktails used in various PHENIX
  analyses.
• Vector-to-Pseudoscalar meson ratio (?/?0) at
  high pT tells us about the production of q-qbar
  bound states.
• High pT results on ? and K0S add to the picture
  of the meson RdA in dAu interactions measured at
  RHIC

• Motivation

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• Decays under study
• Experimental setup
• Analysis details
• Acceptances
• Phase space
• Systematic errors
• Results
• Spectra, cross-checks and comparisons
• RdA
• ?/p0 ratio
• Measurement of the mass peak
• Summary and Outlook

• Outline

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Run 3
Charge particles (p p-) DC-PC1 Momentum
resolution No pID for pp- Neutrals
particles (po g) EMC Energy and space
resolution
p
p0???
p-

• Experimental Setup

PHENIX acceptance -0.35 lt h lt 0.35 2 x 90o for
two arms
(see poster 203 in sec.6)
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?0? decay channel ? - meson m 783 MeV, BR
8.5
Run 3 data
? ?- ?0 decay channel ? - meson m 548 MeV,
BR 23.1 ? - meson m 783 MeV, BR 88.8
Minv, GeV

• Decays under study

Minv, GeV
?0 ?0 decay channel K0S - meson m 498 MeV, BR
31.1
Minv, GeV
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PHENIX has different acceptance and trigger
efficiencies for the decays under
study Consistency of the results is a powerful
cross check
K0S?p0p0?????
??p0pp-???pp-
??p0?????
Geometrical acceptance

• Acceptance

Trigger efficiency
Combined
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p0 Ekin
GEANT assumes uniform density of the
phase-space We used measured (e.g.PRL(1962)
325) density distribution profile resulting in
5-15 correction depending on pT Correction
applies to ??p0pp- while ??p0 ? is unaffected
and remains a cross check.
p- Ekin
p Ekin

• Phase space density

1.0 0.5
3.0 5.0 7.0
9.0 pT GeV/c
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• Calorimeter related errors
• Geometrical acceptance 4-8
  
• Energy resolution
  1-5
• Energy scale
  3-23
• Tracking related errors
• DC-PC1 tracking efficiency
  negligible
• Matching cuts 2
• Momentum cuts for charged tracks negligible
• Run by run variation 2-3
  
• Trigger related errors
• ERT trigger efficiency
  3-7
• Trigger efficiency and correction
  10
• Analysis uncertainties
• ?0 selection cuts
  3-10
• Conversion correction uncertainty
  3-6
• Peak extraction uncertainty 9-13
• Branching ratio uncertainties
  0.8-5
• Phase space correction
  2-8

• Systematic errors

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• spectra in pp

First result on the ?-meson production at RHIC
energy. Broad pT coverage from
2.5-9.5GeV/c Good agreement between two
independent decay modes

• w

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• spectra in dAu

First result on the ?-meson production in
dAu. Broad pT coverage from 3 GeV/c to 9
GeV/c Good agreement between to independent
decay modes

• w

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hep-ex/0501059

• spectra

K0S spectra up to pT of 6.5 GeV/c in pp and
8.5GeV/c in dAu Gap between K0S and K K-
measurement prevents direct comparison to
Time-of-Flight measurements (talk by Maya
Shimomura). PHENIX results are consistent with
measurements of STAR in the region of overlap and
go to higher pT. Provides a good cross check for
analysis approach

• S

• 0

• K

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CERES-TAPS measured ?-meson production in
hadronic collisions at lower pT At v31 GeV (pBe
E706) spectrum have steeper slope

• Comparison to existing data

Instead of comparing spectra we can compare ?/p0
ratio
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First result on the Vector/Pseudo-scalar meson
ratio at RHIC at high pT Ratios are similar in
pp and dAu and close to 1 Ratios do not change
in a range of pT from 2 GeV/c to 9 GeV/c within
systematic errors PYTHIA (default) tuned to LEP
data at lower vs suggests slightly higher ratio

• ratio

pp

• w/p

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p0
?
K0S
f
RdA measured for ? - mesons is consistent with 1
within the systematic errors Heavier mesons tend
to show higher value of RdA

• dA

• w

• R

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?0??-
PHENIX can measure position of the centers of
?-meson mass peaks at different pT. Current
(run3) measurements are limited by
statistics. Possibility to measure the width of
? is under investigation In run3 the widths of
the peaks is about 22 MeV at natural width of
8.5 MeV
Minv, GeV

• mass

• w

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Counts
PHENIX can measure ? - mesons in AuAu at vsNN
200 GeV See clear signal in ???0? channel at
pT gt 7 GeV/c Statistics of Run4 let to measure
centrality dependence at high pT (poster 193,
session 6)
AuAu
???0?
clear ? peak
miss-ID ?? combinatorics

• First look at
• AuAu data

Half of Run4 statistics, loose cuts
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• The first measurement of the ?-meson production
  at RHIC in pp and dAu systems is shown
• The spectra are measured in pT range from 2.5 to
  9.5 GeV/c,
• Two decay modes for ?-meson give consistent
  results,
• RdA 1.3 0.2 in the range of measurement,
• ?/p0 (inclusive) 0.9 0.1 in pp,
• Ratio is independent of pT within systematic
  errors,
• ?-meson mass is consistent with the PDG value,
• Clear peaks are seen in AuAu data at high pT
• K-meson measurement is consistent with existing
  results and extended to substantially higher pT.
• Future plans
• Run5 pp with x15 more statistics,
• Run4 AuAu with 1.5B events on tape,
• Run5 CuCu with statistics comparable to AuAu,
• Other decay modes.

• Summary and
• Outlook

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• Backups

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Statistics of Run3 dAu is sufficient only to see
the indication of ?-meson in ??ee- channel. No
comparison can be done with hadronic
channel Statistics of Run4 AuAu allows to
produce estimation of the dN/dy (poster 195,
session 6)

• Comparison to
• dielectron channel

counts
dAu