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Medium modifications on vector meson in 12GeV p+A reactions

Introduction Result of e+e- analysis Result of e+e- analysis Result of K+K- analysis

Kyoto Univ.a , KEKb, RIKENc, CNS Univ. of Tokyod,

Megumi Naruki, RIKEN, JapanJ. Chibab, H. En’yoc, Y. Fukaoa, H. Funahashia, H. Hamagakid, M. Ieirib,

M. Ishinoe, H. Kandaf , M. Kitaguchia, S. Miharae, K. Miwaa, T. Miyashitaa,

T. Murakamia, R. Mutoc, T. Nakuraa, K. Ozawad, F. Sakumaa, O. Sasakib,

M. Sekimotob, T. Tabaruc, K.H. Tanakab, M. Togawaa, S. Yamadaa,

S. Yokkaichic, Y. Yoshimuraa

(KEK-PS E325 Collaboration)

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dropping mass• Brown-Rho scaling (’91)

– m*/m = 0.8 at = • QCD Sum Rule by Hatsuda & Lee (’92)

– m*/m = 1 - 0.16 for – m*/m = 1 - 0.03 0 for

• Lattice Calc. by Muroya, Nakamura & Nonaka(’03)

width broadening (at 0)• Klingl, Kaiser, Weise (’97-8)

~ for • Rapp & Wambach (’99):

~2• Oset & Ramos (’01) : 22MeV • Cabrera & Vicente (’03) : 33MeV

Mass modification at finite density

Hatsuda & Lee PRC46(1992)R34

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E325 experiment

• slowly moving (plab~2GeV/c ）

larger probability to decay inside nucleus

• primary proton beam ~109 ppp• thin targets: 0.2%/0.05% (C/Cu) radiation length: 0.4/0.5%(C/Cu)

Invariant Mass of e+e-, K+K-

in 12GeV p + A + X History’93 proposed’96 construction start NIM, A457, 581 (2001). NIM, A516, 390 (2004).

’97 first K+K- data’98 first e+e- data PRL, 86, 5019 (2001).

’99~’02 x100 statistics in e+e- PRL 96, 092301 (‘06). ee nucl-ex/0511019 : PRC, 75, 025201 (‘06)

x6 statistics in K+K-

KK : nucl-ex/0606029

beam

B

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Invariant Mass Spectrum of e+e-

C Cu

we examine how well the data are reproduced with known hadronic sources & combinatorial background

e+e-

e+e- e+e-

e+e-

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Invariant Mass Spectrum of e+e-

C Cu

the excess over the known hadronic sources on the low mass side of peak has been observed.

e+e- e+e-

e+e- e+e-

/dof

/dof

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Invariant Mass Spectrum of e+e- (background subtracted)

NN=0.0±0.02(stat.)±0.2(sys.) 0.0±0.04(stat.)±0.3(sys.)

C Cu

most of decay in nucleus due to their short lifetime; ~ 1.3fm

ratio is consistent with zero

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Invariant Mass Spectrum of e+e-

C Cu

we examine how well the data are reproduced with known hadronic sources & combinatorial background

e+e-

e+e- e+e-

e+e-

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ee++ee-- Invariant Mass Distributions Invariant Mass Distributions

C Cu

[GeV/c2] [GeV/c2]• fit with MC shape & quadratic curve• a hint on the spectrum of Cu data.• longer lifetime; ~50fm kinematical dependence

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To see To see dependence dependenceSlowly moving mesons have a larger probability to decay inside the target nucleus.We divided the data into three by ( = p/m ); <1.25, 1.25<<1.75 and 1.75<.

distribution

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Invariant spectra of e+e-

<1.25 (Slow) 1.25<<1.75 1.75< (Fast)

Larg

e N

ucle

usSm

all N

ucle

us

Rejected at 99% confidence level nucl-ex/0511019

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Energy LossEnergy LossResonance Shape : Breit-Wigner + internal radiative correction experimental effect estimated by Geant4 simulation – energy loss, mass resolution, mass acceptance etc.

•Blue histogram : Detector Simulation

•Red line : Breit-Wigner (gaussian convoluted) fitting result

Experimental effects are fully taken into account

detector simulation for

we fit the data by the simulated shape,

which fully includes the experimental

effect

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Model Calculationw/ medium modification

ee

m*/m 1 – k1 1 – k1

*/ 1 1 + k2 /0

generation point surface uniform

PRC74(06)025201]

0.710±0.021 0.937±0.049

momentum dist. measureddensity distribution Woods-Saxon, radius: C:2.3fm/Cu:4.1fm

• dropping mass: M()/M(0) = 1 – k1 (/0) (Hatsuda & Lee)

• width broadening: ()/(0) = 1 + k2 (/0) (k2~10 (Klingl et.al ))

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Fit Results of Model Calculation

the excesses for both C and Cu are well reproduced by the model including the 9% mass decrease at 0.

m*/m = 1 - 0.092

C Cu

[GeV/c2] [GeV/c2]

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Invariant spectra of e+e-

fit with modified M.C. ( k1=0.034, k2=2.6 )<1.25 (Slow) 1.25<<1.75 1.75< (Fast)

Larg

e N

ucle

usSm

all N

ucle

us

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Fit Results of model calculationm*/m = 1 – k1 */ = 1 + k2 /0

The data were well reproduced with the model;

m decreases by 9%,m decreases by 3% andincreases by 3.6 at 0

Best Fit Values

k1 9.2 ± 0.2% 3.4+0.6-0.7%

k2 0 (fixed) 2.6+1.8-1.2

0.7 ± 0.1 (C)0.9 ± 0.2 (Cu)

-

Contours for k1 and k2 of e+e-

syst. error is not included

prediction

0 0.5 1 0

1

0.9

0.8

0.7

fit result

fit result

m(

)/m(0

)

Contours for k1 and

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Fitting Results of K+K-

<1.7 (Slow) 1.7<<2.2 2.2< (Fast)La

rge

Nuc

leus

Smal

l Nuc

leus

modification is not statistically significantOur statistics in the K+K- decay mode are very limited in the region in which we find the excess in the e+e- mode

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nuclear mass number dependence of nuclear mass number dependence of K+K-K+K- / / e+e-e+e-

the first experimental limits of the in-medium broadening of the partial decay widths

F. Sakuma, nucl-ex/0606029

• kK/e was obtained from the amount of excess.

kK = 2.0±1.1(stat.)±2.2(syst.)• The measured provides

constraints on kK and ke.

colored contour : MC

)()(

/)()(

ln1

2

1

2

AA

AA

ee

ee

KK

KKeeKK

)/(1 /

)/(1 /

)/(1/

00*

00*

00*

tottottot

eeeee

KKKKK

k

k

k

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SummaryWe have observed the excess over the known hadronic sources at the low-mass side of . Obtained ratio indicates that the excess is mainly due to the modification of .We also observed the excess at the low-mass side of , only at the low region of Cu data.The data were well reproduced by the model calculation based on the mass modification. The fit results show that; : the massdecreases by 9% at .:the mass decreases by 3%, and the width increases by a factor of 3.6 at .

The mass modification is not statistically significant for the K+K- invariant mass distributions.The observed nuclear mass-number dependences of e+e- and K+K- are consistent. – We have obtained limits on the in-medium decay width broadenings

for both the e+e- and K+K- decay channels.