Reconstruction of Reconstruction of Mesons Mesons in Kin K++KK-- Channel at Channel at s=200 s=200 GeV by the PHENIX GeV by the PHENIX Experiment at RHICExperiment at RHIC

Mohammed Muniruzzaman University of California

Riverside

MotivationMotivation

An enhanced -meson production has been suggested as a signature for the formation of a deconfined phaseMedium modifications of -meson properties might be related to the expected chiral phase transitionThe change in the branching ratio in leptonic and hadronic channels may point to the chiral symmetry restoration.

Sensitive to strangeness enhancementLifetime of ( ~44fm/c) makes it a wonderful probe of the deconfined phase

R. Rapp nucl-th/0204003

PHENIX in Run-IIPHENIX in Run-IIPHENIX Central Arm

Capable of Measuring hadrons, electrons and photons

Time-of-Flight Detector

ElectromagneticCalorimeter

Tracking:

Kaon Identification

Excellent Particle Identification Capability

Pad Chamber3

Drift Chamber Pad Chamber1

Run ConditionRun Condition

Au-Au at Ecm=200 GeVAt 42 b-1

Vertex between 45 cmOver 50% of Data accumulated in the last two weeks of Au-Au Run

p-p at Ecm=200GeV at 700 nb-1

FY2000Ecm=130 GeV

FY2001 – 02Ecm=200 GeV

PHENIX during last 10 daysRHIC Beam Delivered at PHENIX

92 million min-bias data recorded for Au-Au Run

After Imposing Strict Data Quality Control, 27 Million min-bias data were selected for analysis

PHENIX Event DisplayPHENIX Event DisplaySo many Tracks !!

Need good Particle ID

K+K- analysis is possible if we can point out which tracks are kaons

Particle IdentificationParticle IdentificationParticle Identified through High Resolution Time-of-Flight Detector Particle Identified through

Electromagnetic Calorimeter

Data Sample SelectionData Sample Selection27 Million Minimum Bias Au+Au eventsTrack Selection

3 track projection matching at PC33 matching on PC3Best quality DC tracks

Energy Loss in TOF > 2 MeVMomentum between 200MeV/c and 1.2 GeV/c in Time of FlightMomentum upto 900 MeV/c in EMCal3cut on the calibrated mass2 of kaon5 above the Pion mass2 band

Mass squared of Particles are Calculated. Sample is selected on its mass2 Distribution3around the peak of mass2

Invariant MassInvariant Mass

Actual pairs Mixed background

Mixed N+- Normalized by Actual Pair N++ and N--as 2(N++.N--)

Fit with a Breit-Wigner Convoluted with a Gaussian

Signal : 1141±87.4

Invariant 2kInvariant 2k

Actual pairs Mixed background

Mixed N+- Normalized by Actual Pair N++ and N--as 2(N++.N--)

Another approach to extract signal by looking at the difference of 4-momenta of kaons: k = (p1-p2)2

Advantages:Pushes the peak away from the

kinematic edgePuts any correlated pairs into a

different region of phase space

Signal : 1135±116.86

Background Background above above

Investigate background above , m~1.07 GeV

Make looser PID cut (4)Subtraction done by normalizing to region above peak Larger contamination from secondary peak

Ks from misidentified momentum in the TOF array?

Reconstruct mass assuming particles are pionsPeak shows up at ~494 MeV ~MK

Make a tighter PID cut 1Extra mass peak largely disappears

“Ks?”

“”

Ks

4 PID Cut

1 PID Cut

mkk

m

Acceptance vs mAcceptance vs mtt 3 Centrality Classes– 0%-10%, 10%-40%, 40%-92%

8 Mt Bins 1.6-1.8,1.8-2.0,2.0-2.2,2.2-2.4,2.4-2.6,2.6-2.8,2.8-3.0,3.0-4.0Fitting for each centrality and Mt bins are done by fixing the values of mass and from the fit of min bias, and letting the constant free.

S= 35 S/B=1/3.1

mid-central high pt10%-40% centrality,

3.0<mt<4.0

S= 145 S/B=1/12.1

4

Central low pt0%-10% centrality,

1.8<mt<2.2

Work in progress toward mt distribution

Peripheral40%-92% centrality,

2.0<mt<2.2

S= 38 S/B=1/1.45

Invariant Mass in EMCalInvariant Mass in EMCal

Actual pairsMixed background

Advantages: Large Acceptance Kaons accepted upto p<900 Mev Complements the TOF measurements in the low mt

region

SummarySummaryUsing the excellent PID capability of PHENIX Time of Flight Detector is reconstructed via K+K- channel for the Au-Au Collisions at SNN=200GeV. The mass is fitted with a Breit-Wigner Convoluted with a Gaussian with a resolution of 1.2 MeV determined from simulation. The preliminary fit values for the mass and agrees well the PDB values. The systematic errors on these numbers are still under investigation.With the available statistics 3 bins of centrality and 8 bins in mt could be made which enabled us to study the yield of . This analysis is still in progress.It has been demonstrated that can be reconstructed through Electromagnetic Calorimeter. This will enable us to accumulate more statistics and probe into the low mt region.