measurement of low mass vector mesons by e + e - pairs in s nn =200gev d+au collision at phenix
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- Yuji Tsuchimoto - QM2004 -1
槌本 裕二 Yuji Tsuchimotofor PHENIX collaborationtsuchimoto@bnl.gov
Experimental Quark Physics groupHiroshima University, Japan
Measurementof low mass vector mesonsby e+e- pairsin sNN=200GeV d+Au collision at PHENIX
(refer talk by R.Seto in parallel2 on Jan.13)
- Yuji Tsuchimoto - QM2004 -2
Motivation
The chiral symmetry is partially restored at normal nuclear density.
Mass modification of vector mesons is expected.
Quark mass in vacuummu ~ md ~ 5 MeV/c2
ms ~ 100 MeV/c2
Effective quark massin hadron
mu ~ md ~ 300 MeV/c2
ms ~ 500 MeV/c2
(partial) chiral symmetry breaking
T.Hatsuda and S.Lee
QCD sum rules for vector mesons in the nuclear medium
(Phys.Rev.C46-1 1992)
- Yuji Tsuchimoto - QM2004 -3
previous experiments
KEK E325
K.Ozawa et al. Observation of / Meson Modification in
Nuclear Matter (Phys.Rev.Lett 86-22)
G. Agakichiev et al. Low-mass e+e− pair production in 158A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse Momentum (Phys.Lett.B422:405-412,1998 )
Vector meson mass may be modified in dense matter. What happened in hot matter at RHIC?
(refer talks by A.Cherlin(CERES) and R.Muto(E325) in parallel2 on Jan.13)
- Yuji Tsuchimoto - QM2004 -4
low-mass mesons : mass 782 MeV/c2, 8.4 MeV/c2
: mass 769 MeV/c2, 150 MeV/c2
Mass modification will be larger than : mass 1019 MeV/c2, 4.2 MeV/c2
Branching ratio of →KK to →e+e- may be changed by mass modification.
We expect no large modification at d+Au collision for each.
- Yuji Tsuchimoto - QM2004 -5
PHENIX detector RHIC : p+p, d+Au, Au+Au sNN = 200GeV (500GeV for p+p)
BBC → trigger/centrality/vertex PHENIX Central Arms can det
ect electrons, photons, hadrons within the same region, || < 0.35 (||<0.38 for )
Drift Chamber → pT
EMC → energy RICH → electron ID
- Yuji Tsuchimoto - QM2004 -6
Electron identificationhtemp
Entries 79462Mean 2.162RMS 1.243
]EMC matching [0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
50
100
150
200
250
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400
htempEntries 79462Mean 2.162RMS 1.243
e mc s dr {m ass <3 .5&&(dif_c z >15 ||dif_ cph i>0.0 4)&&(-1 00 <e _ z ed+2*z vtx&&-1 00 <p_z e d+2 *z v tx &&e_ z e d+2 *z vtx< 90 &&p_ z e d+ 2*z v tx <9 0 &&z v tx<35 )&&(e _m inInvm as s>0 .1&&p _m inInv mas s>0.1)&&(e _m in PhiV> 0.1 &&p _minPhiV>0.1)}
Cut EMC matching < 4
0.5 < E/p < 1.5 n0>=2 Ghost track cut
reject worse matching track If z<1 and <0.1 in the DC position.
RICH ring sharing cut reject one track if z<10 and <0.1
in the RICH position randomly.
EMC matching
22 z Matching
We used the following cuts.
htempEntries 43446Mean 0.7459RMS 0.3339
energy / momentum0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80
50
100
150
200
250
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400
htempEntries 43446Mean 0.7459RMS 0.3339
e _e op {ma ss<3.5 &&(dif_cz >1 5||dif_c phi>0 .04 )&&(-10 0<e _z ed+2*z v tx &&-1 00<p_ z ed+2 *z v tx&&e_ z e d+2 *z v tx<90&&p_ z e d+2 *z v tx<90&&z vtx<3 5)&&e mc sdr<2&&(e _m inInvmas s >0 .1&&p_ minInvm as s>0 .1)&&(e_m inPhiV>0 .1&&p_ minPhiV>0.1 )}Energy/momentum
select
- Yuji Tsuchimoto - QM2004 -7
Ghost track rejection
Ghost tracks share a close hit position in the drift chamber. We rejected one of the tracks randomly if z<1cm and <0.1 rad.
We also cut ring shared tracks if z<10cm and <0.1 rad in RICH. We choose better E/p track.
Z difference on DC [cm]
difference on DC [rad]
- Yuji Tsuchimoto - QM2004 -8
Conversion Rejection by invariant mass and PhiV
htempEntries 8238Mean 0.2124RMS 0.2488
phiv [rad]0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
10
102
103
htempEntries 8238Mean 0.2124RMS 0.2488
phiv {0 .1 <m a ss&&m as s <0 .35&&(0.5<e_e op&&e_ e op<1 .5 &&0.5 <p_e op&&p_ eop<1.5)&&(-1 0 0<e_ z ed +2 *z vtx&&-10 0<p_ze d+2*z v tx &&e_z ed+2 *z vtx<9 0&&p_ z ed+2*z v tx <90 &&z v tx <3 5 )&&e m c sdr<2&&(dif_c phi>0 .04 ||di f_c z >15)&&ghost==0}
20.1 < inv mass < 0.35 GeV/c
e+e- pair from photon conversion has small phiv and small mass.we cut those pairs at low-background region Kill all tracks if PhiV<0.1 for mass<400MeV
• PhiV is angular orientation between pair tracks’ surface and magnet field. Conversion pair has 0 PhiV in principle. Kill all tracks if mass<100MeV
PhiV ( 100<mass<400MeV )
Mixing
CutCut
PhiV
- Yuji Tsuchimoto - QM2004 -9
ERT electron trigger &Event selection
Front-end electronics and data storage limit trigger and recording rate.
Give priority for electron events to record. ERT electron trigger by
RICH & EMC online
Analyzed 31M of ERT-electron Triggered Events.Corresponds to 1.9G minimum bias (raw trigger)50% of total data taken during run3
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
1
10
102
103
104
105
electgron momentum [GeV/c]
Minimum bias triggered
ERT triggered
see poster by F.Kajihara(Instr4) about ERT trigger
- Yuji Tsuchimoto - QM2004 -10
Invariant Mass Spectra
Background estimated by event mixing with offline ERT-electron trigger emulation Use 500-600,1100-1200 MeV region for normalization of Opposite arm. Use 850-950,1100-1200 MeV region for normalization of Same arm.
]2invariant mas s [GeV/c-e+e0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.50
20
40
60
80
100
- Yuji Tsuchimoto - QM2004 -11
Invariant mass spectra Fit is to relativistic B-W convoluted with gaussian
M=1.0177 0.0023 GeV/c2
=4.46 MeV/c2 (fixed) exp=8.1 2.1MeV/c2
2/DOF=13.6/13
- Yuji Tsuchimoto - QM2004 -12
Acceptance Correctionwith ERT trigger efficiency
Throw 2M of single decay into e+e- with slope 440MeV
Use GEANT for response
Use the efficiency to get corrected mT spectra [GeV]-mTm
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
acce
ptan
ce
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
) acceptance (3-e+ to e
MB acceptance
AcceptanceWith ERT
- Yuji Tsuchimoto - QM2004 -13
mT spectrum
dN/dy=.056 .015(stat) 50%(syst)
T=326 94(stat) 53%(syst) MeV
PHENIX Preliminary
- Yuji Tsuchimoto - QM2004 -14
mT spectra comparison with KK results
Those points are agreed within error bars
ee channel dN/dy=.056.015(stat) 50%
(syst) T=32694(stat)53%(syst) M
eV KK channel
dN/dy = 0.04230.0063(stat) (+0.0076,-0.0073) (syst.)
T (MeV) = 429 27 (stat) 35 (syst)
PHENIX Preliminary
see poster by D.Pal(Spectra9) for KK data
- Yuji Tsuchimoto - QM2004 -15
dN/dy / Nparticipant
dN/dydAuee =.056.015(stat) 50%(syst) increases from dAu to AuAu by factor ~2
this behavior is same as inclusive K yield at Au+Au
see posters by D.Pal(Spectra9) and C.F.Maguire(Strange14) for KK data
PHENIX Preliminary (d+Au)PHENIX Final (Au+Au)
- Yuji Tsuchimoto - QM2004 -16
Slope
T=326 94(stat) 53%(syst) MeV Those are agreed within error
see posters by D.Pal(Spectra9) and C.F.Maguire(Strange14) for KK data
PHENIX Preliminary (d+Au)PHENIX Final (Au+Au)
- Yuji Tsuchimoto - QM2004 -17
Summary
• I obtained • dN/dy=.056.015(stat) 50%(syst) and• T=326 94(stat) 53%(syst) MeV
of in e+e- mode at sNN = 200GeV d+Au collisions
• Those are consistent with results of K+K- mode within error bars.
increases from dAu to AuAu by factor ~2.
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