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3 E325 experiment slowly moving ( p lab ~2GeV/c ) larger probability to decay inside nucleus primary proton beam ~10 9 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, (‘06). ee nucl-ex/ : PRC, 75, (‘06) x6 statistics in K + K - KK : nucl-ex/ beam B
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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.