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.
