Misaki Ouchida (Hiroshima University) For the PHENIX collaboration
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Transcript of Misaki Ouchida (Hiroshima University) For the PHENIX collaboration
Measurement of ω mesons via radiative decay mode in A+A collisions
at √SNN=200GeV RHIC-PHENIX
Misaki Ouchida(Hiroshima University)For the PHENIX collaboration
2007 Autumn JPS Meeting
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OUTLINE
• Low Mass Vector Mesons• Hadron Suppression• RHIC-PHENIX• Apply Cuts• Estimate Background• Efficiency • Results• Discussion & Conclusion
Introduction
Experimental Setup
Analysis
Results
Conclusion
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Low Mass Vector Mesons
Introduction
QGP ~10fm/c
23fm/clife time: 46fm/c 0
Measure this!
• Short lifetime (23 fm/c)-> Include the information of QGP• Large branching ratio (9%)• No ρ-contribution (major problem for e+e-measurement)
Lots of advantages…Why ?
Why ?
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Physics…
Low pT High pT
Siganl for Chiral Symmtery Restoration
Siganl for Hadron Suppression
Heavy Ion Collisions
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Suppression as a Probe of QGP
PRL 91. 072301 (2003)
)/(
)/)(/1(
Tpp
AB
TAA
evtAA dydpdT
dydpdNNR
Nuclear Modification Function
QGP
In the absence of nuclear effects: RAA=1
The inclusive pi0 production in Au+Au
Hadron Production will be suppressed due to the jet quenching occurred in the heavy-ion collisions as an effect of the matter
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Data Set : Au+Au collisions√SNN=200 GeV(taken in 2003~2004),The number of event : 1.06 G
99.7% of the speed of light
circumference:3.8 km
Trigger detectors2 muon arms2central arms (include Electro Magnetic Calorimeter)
RHIC-PHENIX
PHENIX Detector
Experimental Setup
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Apply Cuts
Cuts for photon IDShower Shape, TOF Cut
Kinematical Cuts for Reconstruction
Cuts for pi0 legsChose the symmetric energy - both photons in the same sector
222 )(3
0 PEEM Analysis
Quest for omega in huge huge Backgroundat Au+Au Collisions!
~ Resolution 1 ~
pT(ω) [GeV/c]
S/√
B (
sig
nif
ican
ce)
No Cuts
Best Cuts・ Transverse Momentum of ・ Photon Energy・Width of Invariant Mass
0 Rising Minimum Cuts
Use Best Cuts that improve S/√B (significance) the most
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Black: FG
[GeV/c^2]
Peripheral (cent 60~92 %)3.5<pT<4.5[GeV/c]
Magenta:BG1+BG2+BG3
BG3
BG2
BG1
Gaussian (Mean and With are Fixed by Embedding simulation)
after subtraction of
BG1+BG2+BG3
coun
t
Reconstructed invariant mass
~ Resolution 2 ~
Estimate Background
There it is!!!!
Mixed event0sK
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Analysis
Efficiency=
CentralPeripheral
Embedding to the background
Background
The number of measured ω
The number of input ω
Efficiency
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ResultsLines reporesent estimated yield from p+p collisions scaled by Ncoll Without
nuclear matter effect, measurements follow lines
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Results
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Discussion & Conclusion
We could extract omega via radiative decay mode in Au+Au by overcoming huge combinatorial backgrounds by Applying Best Cut, and Subtracting Background.From the results, we could suggest the sign of Hadron Suppression as the probe of the matter created in the heavy ion collisions.
It is suggested that omega meson yield suppressed in central Au+Au collisions
Out LookAu+Au Results should be finalized…(detail systematic study is needed)How about Cu+Cu collisions?
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Back Up
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Chiral Symmetry RestorationIntroduction
Hadron masses link to the quark condensate, <qq>.
Chiral Symmetry Restored<qq> → 0
Chiral Symmetry is spontaneously broken, <qq>~250 MeV3
There is a transition of the system that constitute mass
Hardron masses change !?
ー
ー
ー
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Correct Mass Distributionusing correlation between pi0 and omega
Omega mass [GeV/c^2]
Pi0
mas
s [G
eV/c
^2]
. ・・・・
Apply this correction function to all pT
PROFILEExpected Improvement of S/N
Resolution 3
782 [GeV/c]
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Other R_AA
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K0short Estimation Check~Question~
“Isn’t it too much?”
previous plot Peripheral (cent 60~92 %)3.5<pT<4.5[GeV/c]
K0->2pi0 Production
AN535(Run5 p+p) ResultsFitted by Hagedorn function
Estimated Au+Au peripheral spectrum
Ncoll scaling
Calculate estimated number(much more than omega num.)
Ks/pi0 ratio --- 0.438 (AN535)Ks BR --- 31.05%
Omega/pi0 ratio --- 0.85(PPG64)Omega BR --- 8.92 %
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K0short Estimation Check
Efficiency of reconstructing 3 gamma from K0s must be much higher than reconstructing 4 gammas
catch 4 gammas and reconstruct
catch 3 gammas and reconstruct
Using K0s single simulation
about 10 times
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Cut Optimization
・ Pi0 Momentum Cuts・ Photon Energy Cuts・ Pi0 Mass Width
Great influence on the peak significancePi0 Momentum
CutsPhoton Energy Cut
Pi0 Mass Width
Default
Cut#1
Cut#2
Cut#3
Cut#4
S/√B
ex. 4.5<ωpT<5.5 (GeV/c)
If there’s no cut, S/B< 1/1000….→Have to improve it by the selection
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Best Cuts