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

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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-PSE325 Collaboration)

- Result of r/we+e- analysis
- Result of fe+e- analysis
- Result of fK+K-analysis
- A dependence of GKK/Gee
- Future Plan

KEK-PS E325 experiment

We measure

Invariant Mass ofe+e-, K+K-

in 12GeV p + Ar, w, f + X

- slowly movingr,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, 092301 (’06)
- f ee: PRL, 98, 042501 (‘07)
- a : PRC, 75, 025201 (‘06)

x6 statistics in K+K-

- fKK: PRL, 98, 152302 (’07)

Forward LG Calorimeter

Start Timing Counter

Hodoscope

Rear LG Calorimeter

Aerogel Cherenkov

Side LG Calorimeter

Forward TOF

B

0.81Tm

Rear Gas Cherenkov

Front Gas Cherenkov

M.Sekimoto et al., NIM, A516, 390 (2004).

Barrel DC

Cylindrical DC

1m

12GeV proton beam

Vertex DC

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

L p p-

Ks p+ p-

M =496.8±0.3(MC 496.9±0.1)MeV/c2

s = 3.9±0.4(MC 3.5±0.1)MeV/c2

M =1115.71±0.02(MC 1115.53±0.01)MeV/c2

(s = 1.73±0.02(MC 1.62±0.01)MeV/c2)

Mass spectra are well reproduced by the simulation

Expected mass resolution for f = 10.7MeV/c2

Invariant Mass Spectrum of e+e-

we+e-

we+e-

C

Cu

fe+e-

fe+e-

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

Invariant Mass Spectrum of e+e-

we+e-

we+e-

Cu

C

c2/dof=161/140

c2/dof=154/140

fe+e-

fe+e-

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

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

C

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

Invariant Mass Spectrum of e+e-

we+e-

we+e-

C

Cu

fe+e-

fe+e-

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

e+e- Invariant Mass Distributions

C

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

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

Invariant mass spectra of f e+e-

1.75<bg (Fast)

bg<1.25 (Slow)

1.25<bg<1.75

Small Nucleus

Large Nucleus

Rejected at 99% confidence level

PRL 98(2007)042501

Model Calculationw/medium modification

e

e

r/w

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)

Mass modification at finite density

r

w

f

Hatsuda & Lee PRC46(1992)R34

dropping mass

- Brown-Rho scaling (’91)
- m*/m = 0.8 atr = r0
- QCD Sum Rule by Hatsuda & Lee (’92)
- m*/m = 1 - 0.16 r/r0forr/w
- m*/m = 1 - 0.03 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

nuclear mass number dependence

- Mass number dependence α:

T. Tabaru et al. Phys. Rev. C74 (2006) 025201

Fit Results of Model Calculation

m*/m = 1 - 0.092r/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.

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)

Invariant spectra of fe+e-fit with modified M.C. ( k1=0.034, k2=2.6 )

1.75<bg (Fast)

bg<1.25 (Slow)

1.25<bg<1.75

Small Nucleus

Large Nucleus

Fit Results of model calculationm*/m = 1 – k1r/r0, G*/G = 1 + k2r/r0

Contours for k1 and r/w

Contours for k1 and k2 of fe+e-

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

Gfincreases by 3.6 at r0

prediction

0 0.5 1 r/r0

syst. error is not included

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

2.2<bg (Fast)

bg<1.7 (Slow)

1.7<bg<2.2

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

Kinematical Distributions of observed f

- the detector acceptance is different between e+e- and K+K-
- very limited statistics for fK+K- in bg<1.25 where the modification is observed in fe+e-

the histograms for fK+K- are scaled by a factor ~3

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

GfK+K- becomes small

- K mass decreases

GfK+K- becomes large

f : T.Hatsuda, S.H.Lee,

Phys. Rev. C46(1992)R34.

K : H.Fujii, T.Tatsumi,

PTPS 120(1995)289.

GfK+K-/Gfe+e- and Nuclear Mass-Number Dependence a

- GfK+K-/Gfe+e- increases in a nucleus

NfK+K- /Nfe+e- becomes large

- The lager modification is expected in the larger nucleus

(A1>A2)

- afK+K- becomes larger than afe+e-
- The difference of a is expected to be enhanced in slowly moving f mesons

Da=

e+e-

K+K-

ae+e- with corrected for the K+K- acceptance

possible modification of the decay widths is discussed

=

Results of Nuclear Mass-Number Dependence a

bg

rapidity

pT

bg

averaged

(0.14+/-0.12)

afK+K- and afe+e- are consistent

Discussion onGfK+K- and Gfe+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.

Discussion on GfK+K- and Gfe+e-

kK=1.4+/-1.1+/-2.1 (C&Cu)

- 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 = 0.044+/-0.037+/-0.058 (C)

0.076+/-0.025+/-0.043 (Cu)

nuclear mass number dependence of

GfK+K- / Gfe+e-

colored contour : MC

1.4

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) 152302

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

J-PARC Facility

Hadron Beam Facility

Materials and Life Science

Experimental Facility

Nuclear Transmutation

500 m

Neutrino to Kamiokande

3 GeV Synchrotron

(25 Hz, 1MW)

50 GeV Synchrotron

(0.75 MW)

Linac

(330m)

J-PARC = Japan Proton Accelerator Research Complex

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

T1 Target

T0 Target

Beam Dump

J-PARC E16 Electron pair spectrometer to explore the chiral symmetry in QCD

primary proton beam at high momentum beam line

+ large acceptanceelectron 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)

velocitydependence

nuclear number dependence (p Pb)

centrality dependence

systematic study of mass modification

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 massdecreases 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 fe+e- and fK+K- are consistent.

We have obtained limits on the in-medium decay width broadenings for both the fe+e- and fK+K- decay channels.

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