# Presentation: 882755

## 槌本 裕二 Yuji Tsuchimoto
for PHENIX collaboration
tsuchimoto@bnl.gov

Experimental Quark Physics group
Hiroshima University, Japan

*for PHENIX collaboration*
*tsuchimoto@bnl.gov*
- Experimental Quark Physics group
- Hiroshima 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  -

## Motivation

- The chiral symmetry is partially restored at normal nuclear density.
- Mass modification of vector mesons is expected.

- Quark mass in vacuum
- mu ~ md ~ 5 MeV/c2
- ms ~ 100 MeV/c2

- Effective quark mass
- in 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  -

##  previous experiments

-  previous experiments

- KEK E325

- K.Ozawa et al.
- Observation of / Meson Modification in Nuclear Matter (Phys.Rev.Lett 86-22)

- _[G. ](http://www.slac.stanford.edu/spires/find/hep/wwwauthors?key=3675076)__[Agakichiev](http://www.slac.stanford.edu/spires/find/hep/wwwauthors?key=3675076)__[ et al.](http://www.slac.stanford.edu/spires/find/hep/wwwauthors?key=3675076)_
- 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](http://www.slac.stanford.edu/spires/find/hep/www?j=PHLTA,B422,405)_ )

- 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  -

## 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  -

## PHENIX detector

- RHIC : p+p, d+Au, Au+Au   sNN = 200GeV (500GeV for p+p)

- BBC → trigger/centrality/vertex
- PHENIX Central Arms can detect _electrons_, photons, hadrons within the same   region, || < 0.35 (||<0.38 for )
- Drift Chamber → pT
- EMC → energy
- RICH → electron ID

- - Yuji Tsuchimoto - QM2004  -

## Electron identification

- 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

- We used the following cuts.

- - Yuji Tsuchimoto - QM2004  -

## 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  -

## Conversion Rejection by invariant mass and PhiV

- 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

**Cut**

**Cut**

- PhiV

- - Yuji Tsuchimoto - QM2004  -

## 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

- Minimum bias triggered

- ERT triggered

- see poster by F.Kajihara(Instr4) about ERT trigger

- - Yuji Tsuchimoto - QM2004  -

## 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.

- - Yuji Tsuchimoto - QM2004  -

## 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  -

## Acceptance Correctionwith 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

- - Yuji Tsuchimoto - QM2004  -

## mT spectrum

- mT spectrum

- dN/dy=.056 .015(stat) 50%(syst)
- T=326 94(stat) 53%(syst) MeV

- PHENIX Preliminary

- - Yuji Tsuchimoto - QM2004  -

## mT spectra comparison with KK results

- mT spectra comparison with KK results

- Those points are agreed within error bars
- ee channel
- dN/dy=.056.015(stat) 50%(syst)
- T=32694(stat)53%(syst) MeV
- KK channel
- dN/dy = 0.04230.0063(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  -

## dN/dy / Nparticipant

- dN/dy / Nparticipant

- dN/dydAuee =.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  -

## 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  -

## 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.

- - Yuji Tsuchimoto - QM2004  -

## Next step

- Merge remain statistics ( ~50% )
- Tune electron ID finely
- Analyze /
- These will show at JPS (March)

- - Yuji Tsuchimoto - QM2004  -