1. Medium modifications on vector meson in 12GeV p+A reactions
Kyoto Univ.a , KEKb, RIKENc, CNS Univ. of Tokyod,
Megumi Naruki, KEK, Japan
J. 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. Mutob, 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)
Result of r/we+e- analysis
Result of fe+e- analysis
Result of fK+K- analysis
A dependence of GKK/Gee
Future Plan

2. larger probability to decay inside nucleus
KEK-PS E325 experiment
We measure
Invariant Mass of e+e-, K+K-
in 12GeV p + A  r, w, f + X
slowly moving r,w,f (plab~2GeV/c）
larger probability to decay inside nucleus
Beam
primary proton beam
(~109/spill/1.8s)
Target
interaction length
0.2%/0.05% (C/Cu)
radiation length:
0.4/0.5%(C/Cu)
History
’93 proposed
’96 construction start
NIM, A457, 581 (2001)
NIM, A516, 390 (2004)
’97 first K+K- data
’98 first e+e- data
r/w: PRL, 86, 5019 (2001)
’99~’02
x100 statistics in e+e-
r/w: PRL, 96, (’06)
f ee: PRL, 98, (‘07)
a : PRC, 75, (‘06)
x6 statistics in K+K-
f KK: PRL, 98, (’07)

3. Forward LG Calorimeter
Detector Setup
M.Sekimoto et al., NIM, A516, 390 (2004).
Hodoscope
Aerogel Cherenkov
Forward TOF
Start Timing Counter
Forward LG Calorimeter
Rear LG Calorimeter
Side LG Calorimeter
Barrel DC B
0.81Tm
Cylindrical DC
Front Gas Cherenkov
Rear Gas Cherenkov 1m
12GeV proton beam
Vertex DC

4. Experimental Effects
Resonance Shape : Breit-Wigner + internal radiative correction
experimental effect estimated by Geant4 simulation
– energy loss, mass resolution, mass acceptance etc.
detector simulation for f
Blue histogram : Detector Simulation
Red line : Breit-Wigner (gaussian convoluted) fitting result
Experimental effects are fully taken into account
we fit the data by the simulated shape, which fully includes the experimental effect

5. Experimentalists face to reality - E325 simulation- e+e-
KEK-E325 Target
material
beam (p/spill)
Interaction length(%)
radiation length(%) C
0.64x109
0.2% (0.18g/cm2)
0.4%
Cu X4
0.05% (0.07g/cm2) X4
0.5% X4
1g/cm2 C Cu

6. Spectrometer Performance
L  p p-
Ks  p+ p-
M =496.8±0.3(MC 496.9±0.1) MeV/c2
s = ±0.4(MC ±0.1) MeV/c2
M = ±0.02(MC ±0.01) MeV/c2
(s = ±0.02(MC ±0.01) MeV/c2)
Mass spectra are well reproduced by the simulation
Expected mass resolution for f = 10.7MeV/c2

7. Invariant Mass Spectrum of e+e-
we+e-
we+e- C Cu
fe+e-
fe+e-
we examine how well the data are reproduced with known hadronic sources & combinatorial background

8. Invariant Mass Spectrum of e+e-
we+e-
we+e- Cu C
c2/dof=161/140
c2/dof=154/140
f e+e-
f e+e-
the excess over the known hadronic sources on the low mass side of w peak has been observed.

9. Invariant Mass Spectrum of e+e- (background subtracted)Cu
r/w ratio is consistent with zero. 95%C.L. allowed regions:
Nr/Nw<0.04(stat.)+0.09(sys.)
Nr/Nw<0.10(stat.)+0.21(sys.)
most of r decay in nucleus due to their short lifetime; t ~ 1.3fm

10. Invariant Mass Spectrum of e+e-
we+e-
we+e- C Cu
fe+e-
fe+e-
we examine how well the data are reproduced with known hadronic sources & combinatorial background

11. e+e- Invariant Mass DistributionsC Cu f f
[GeV/c2]
[GeV/c2]
fit with MC shape & quadratic curve
a hint on the spectrum of Cu data.
longer lifetime; t~50fm  kinematical dependence

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

13. Invariant mass spectra of f e+e-
bg<1.25 (Slow)
1.25<bg<1.75
1.75<bg (Fast)
Small Nucleus
Large Nucleus
Rejected at 99% confidence level
PRL 98(2007)042501

14. Model Calculation w/ medium modification
r/w e f
dropping mass: M(r)/M(0) = 1 – k1 (r/r0) (Hatsuda & Lee)
width broadening: G(r)/G(0) = 1 + k2 (r/r0) (k2:5~10)
r, w f
m*/m
1 – k1 r/wr/r0
1 – k1f r/r0
G*/G
1 + 0* r/r0
1 + k2 r/r0
generation point
surface
uniform
a=0.710±0.021
a=0.937±0.049
momentum dist.
measured
density distribution
Woods-Saxon, radius: C:2.3fm/Cu:4.1fm

15. Mass modification at finite densityr w f
Hatsuda & Lee PRC46(1992)R34
dropping mass
Brown-Rho scaling (’91)
m*/m = 0.8 at r = r0
QCD Sum Rule by Hatsuda & Lee (’92)
m*/m = r/r0 for r/w
m*/m = r/r0 for f
Lattice Calc. by Muroya, Nakamura & Nonaka(’03)
width broadening (at r0)
Klingl, Kaiser, Weise (’97-8)
G*/G~10 for r/w/f
Rapp & Wambach (’99) : G*r/Gr ~2
Oset & Ramos (’01) : DGf = 22MeV
Cabrera & Vicente (’03) : DGf = 33MeV
Oset & Ramos r
Cabrera & Vicente

16. nuclear mass number dependencew
0.710 ±0.021 ±0.037 f
0.937 ±0.049 ±0.018
T. Tabaru et al. Phys. Rev. C74 (2006)

17. Fit Results of Model Calculation
m*/m = r/r0 C Cu
[GeV/c2]
[GeV/c2]
the excesses for both C and Cu are well reproduced by the model including the 9% mass decrease at r0.

18. C Cu Width Broadening k1 = 0.08 k2 = 1
events[/10MeV/c2]
events[/10MeV/c2] C Cu
「GeV/c2]
「GeV/c2]
the best fit values are; k1 = 9.2 ± 0.6% k2 <0.32(90%C.L.)
（Preliminary)

19. Invariant spectra of fe+e- fit with modified M. C. ( k1=0. 034, k2=2
bg<1.25 (Slow)
1.25<bg<1.75
1.75<bg (Fast)
Small Nucleus
Large Nucleus

20. Fit Results of model calculation m. /m = 1 – k1 r/r0, G
Fit Results of model calculation m*/m = 1 – k1 r/r0, G*/G = 1 + k2 r/r0
Contours for k1 and r/w
Contours for k1 and k2 of fe+e-
Best Fit Values
r, w f k1
9.2 ± 0.2% % k2
0 (fixed)
r/w
0.7 ± 0.1 (C)
0.9 ± 0.2 (Cu) - 1
0.9
0.8
0.7
fit result f
m(r)/m(0)
fit result r/w
The data were well reproduced with the model;
mr/w decreases by 9%,
mf decreases by 3% and
Gf increases by at r0
prediction
r/r0
syst. error is not included

21.  examine the mass shape as a function of bg
fK+K- Invariant Mass Spectra C
from 2001 run data
C & Cu targets
acceptance uncorrected
fit with
simulated mass shape of f
(evaluated as same as r/w)
combinatorial background obtained by the event mixing method
counts/4MeV/c2
f(1020)
 examine the mass shape as a function of bg

22. modification is not statistically significant
Fitting Results of fK+K-
bg<1.7 (Slow)
1.7<bg<2.2
2.2<bg (Fast)
Small Nucleus
Large Nucleus
modification is not statistically significant
Our statistics in the K+K- decay mode are very limited in the bg region in which we find the excess in the e+e- mode

23. the histograms for fK+K- are scaled by a factor ~3
Kinematical Distributions of observed f
the detector acceptance is different between e+e- and K+K-
very limited statistics for fK+K- in bg<1.25 where the modification is observed in fe+e-
the histograms for fK+K- are scaled by a factor ~3

24. Partial Decay Width of f; GKK/Gee
mass decreases
2~4%  20-40MeV/c2
narrow decay width (G=4.3MeV/c2)
　⇒ sensitive to the mass spectrum
modification
small decay Q value
(QK+K-=32MeV/c2)
⇒ the branching ratio is
sensitive to f or K modification
f mass
K+K-
threshold
r0:normal nuclear density
for example…
f mass decreases
 GfK+K- becomes small
K mass decreases
 GfK+K- becomes large
f : T.Hatsuda, S.H.Lee,
Phys. Rev. C46(1992)R34.
K : H.Fujii, T.Tatsumi,
PTPS 120(1995)289.

25. GfK+K-/Gfe+e- and Nuclear Mass-Number Dependence a
GfK+K-/Gfe+e- increases in a nucleus
 NfK+K- /Nfe+e- becomes large
The lager modification is expected in the larger nucleus
(A1>A2)
afK+K- becomes larger than afe+e-
The difference of a is expected to be enhanced in slowly moving f mesons

26. - Results of Nuclear Mass-Number Dependence a Da=bg
rapidity pT
ae+e- with corrected for the K+K- acceptance =
Da= -
K+K-
e+e- bg
possible modification of the decay widths is discussed
averaged
(0.14+/-0.12)
afK+K- and afe+e- are consistent

27. Discussion on GfK+K- and Gfe+e-
we expect ktot ~ kK since the f meson mainly decays into KK as long as such decays are kinematically allowed.
The values of expected Da are obtained by the MC.
f mesons are uniformly produced in a nucleus and decayed according to the values of kK and ke.
The measured Da provides constraints on kK and ke.

28. Discussion on GfK+K- and Gfe+e-
3. The constraint on kK is obtained from the K+K- spectra.
In the K+K- spectra, we fit again excluding the region 0.987(=2mk) ~ 1.01GeV/c2.
We obtain a surplus over the f peak and BG.
From the MC, we estimate the ratio of the number of f mesons decayed inside to outside Nin/Nout (inside = the half-density radius of the Woods-Saxon dist.).
When the surpluses are assumed as the f-meson decayed inside a nucleus, we obtain the constraint on kK by comparing Nsurplus/Nf with Nin/Nout. Cu Cu
excluded from
the fitting
~ Nsurplus/Nf MC
Nin/Nout
surplus
data kK
Nsurplus/Nf = / / (C)
0.076+/ / (Cu)
kK=1.4+/-1.1+/-2.1 (C&Cu)

29. nuclear mass number dependence of
GfK+K- / Gfe+e-
colored contour : MC
1.4
kK/e was obtained from the amount of excess.
kK = 1.4±1.1(stat.)±2.1(syst.)
The measured Da provides constraints on kK and ke.
F. Sakuma,
Phys. Rev. Lett., 98 (2007)
the first experimental limits of the in-medium broadening of the partial decay widths

30. J-PARC Facility 500 m Hadron Beam Facility Materials and Life Science
Nuclear Transmutation
J-PARC = Japan Proton Accelerator Research Complex
3 GeV Synchrotron
(25 Hz, 1MW)
Hadron Beam Facility
Materials and Life Science
Experimental Facility
Neutrino to Kamiokande
50 GeV Synchrotron
(0.75 MW)
500 m
Linac
(330m)

31. J-PARC E16 Electron pair spectrometer to explore the chiral symmetry in QCD
high momentum beam line
Hadron Hall
50-GeV PS
A-Line
Switch Yard
E16
Split Point
T0 Target
T1 Target
Beam Dump

32. J-PARC E16 Electron pair spectrometer to explore the chiral symmetry in QCD
primary proton beam at high momentum beam line
　　　　　　　+ large acceptance electron spectrometer
107 interaction (10 X E325)
1010 protons/spill
with 0.1% interaction length target
 GEM Tracker
eID : Gas Cherenkov
　 　 + Lead Glass
Large Acceptance (5 X E325)
velocity dependence
nuclear number dependence (p  Pb)
centrality dependence
　 systematic study of mass modification

33. Summary
We have observed the excess over the known hadronic sources at the low-mass side of w. Obtained r / w ratio indicates that the excess is mainly due to the modification of r .
We also observed the excess at the low-mass side of f, only at the low bg region of Cu data.
The data were well reproduced by the model calculation based on the mass modification. The fit results show that;
r/w : the mass decreases by 9% at r0 .
f : the mass decreases by 3%,
and the width increases by a factor of 3.6 at r0.
The mass modification is not statistically significant for the K+K- invariant mass distributions.
The observed nuclear mass-number dependences of fe+e- and fK+K- are consistent.
We have obtained limits on the in-medium decay width broadenings for both the fe+e- and fK+K- decay channels.