- 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

300

350

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

300

350

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.

- Yuji Tsuchimoto - QM2004 -18

Next step

Merge remain statistics ( ~50% ) Tune electron ID finely Analyze /

These will show at JPS (March)