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

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

Result of e+e- analysis Result of e+e- analysis Result of K+K- analysis A dependence of KK/ee

Future Plan

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

Megumi Naruki, KEK, 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. 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)

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KEK-PS E325 experimentKEK-PS E325 experimentWe measureInvariant Mass of e+e-, K+K-

in 12GeV p + A + Xslowly moving (plab~2GeV/c ）

larger probability to decay inside nucleus

Beamprimary proton beam(~109/spill/1.8s)

Targetinteraction 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 PRL, 86, 5019 (2001)

’99~’02 x100 statistics in e+e- PRL, 96, 092301 (’06) ee PRL, 98, 042501 (‘07) : PRC, 75, 025201 (‘06)

x6 statistics in K+K-

KK: PRL, 98, 152302 (’07)

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Detector SetupDetector Setup

12GeV proto

n

beam

Forward LG Calorimeter

Rear LG Calorimeter

Side LG Calorimeter

Front Gas Cherenkov

Rear Gas Cherenkov

Barrel DC

Cylindrical DC

Vertex DC

B0.81Tm

Hodoscope

Aerogel Cherenkov

Forward TOF

Start Timing Counter

1m

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

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Experimental EffectsExperimental Effects

Resonance 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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1g/cm2 1g/cm2

C Cu

421 ,, ZBackgroundZBremshAV

Experimentalists face to reality - E325 simulation- e+e-

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

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Spectrometer PerformanceSpectrometer Performance p -

Mass spectra are well reproduced by the simulation

Ks + -

M =496.8±0.3(MC 496.9±0.1) MeV/c2

= 3.9±0.4(MC 3.5±0.1) MeV/c2

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

= 1.73±0.02(MC 1.62±0.01) MeV/c2)

Expected mass resolution for = 10.7MeV/c2

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Invariant Mass Spectrum of e+e-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- 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)

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

NN0.04(stat.)+0.09(sys.) NN0.10(stat.)+0.21(sys.)

C Cu

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

ratio is consistent with zero. 95%C.L. allowed regions:

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Invariant Mass Spectrum of e+e-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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e+e- Invariant Mass Distributionse+e- 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 bg dependenceTo see bg 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 mass spectra of f e+e-Invariant mass spectra of f e+e-

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

Lar

ge

Nu

cleu

sS

mal

l N

ucl

eus

Rejected at 99% confidence level PRL 98(2007)042501

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Model Calculationw/ medium modification

e

e

m*/m 1 – k1 1 – k1

*/ 1 + 0 /0 1 + k2 /0

generation pointsurface uniform

=0.710±0.021 =0.937±0.049

momentum dist. measured

density 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) (k2:5~10)

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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 densityMass modification at finite density

Hatsuda & Lee PRC46(1992)R34

Oset & Ramos

Cabrera & Vicente

nuclear mass number dependencenuclear mass number dependence

• Mass number dependence α: 0A A

0.710 ±0.021 ±0.037

0.937 ±0.049 ±0.018

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

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Fit Results of Model CalculationFit 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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Width BroadeningWidth Broadening

C Cu

k1 = 0.08 k2 = 1

the best fit values are; k1 = 9.2 ± 0.6% k2 <0.32(90%C.L.) （ Preliminary)

events[/10MeV/c2] events[/10MeV/c2]

「 GeV/c2] 「 GeV/c2]

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Invariant spectra of e+e

fit with modified M.C. ( k1=0.034, k2=2.6 )

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)

Lar

ge

Nu

cleu

sS

mal

l N

ucl

eus

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

0

Fit Results of model calculationm*/m = 1 – k1 0, * = 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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K+K Invariant Mass SpectraK+K Invariant Mass Spectra

from 2001 run dataC & Cu targetsacceptance uncorrectedfit with

– simulated mass shape of (evaluated as same as )– combinatorial background obtained by the event mixing method

examine the mass shape as a function of

coun

ts/4

MeV

/c2

C

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Fitting Results of K+K Fitting Results of K+K <1.7 (Slow) 1.7<<2.2 2.2< (Fast)

Lar

ge

Nu

cleu

sS

mal

l N

ucl

eus

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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Kinematical Distributions of observed Kinematical Distributions of observed

the detector acceptance is different between e+e- and K+K-

very limited statistics for K+K- in <1.25 where the modification is observed in e+e-

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

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Partial Decay Width of eePartial Decay Width of ee

: T.Hatsuda, S.H.Lee,Phys. Rev. C46(1992)R34.

0:normal nuclear density

mass decreases2~4% 20-40MeV/c2

narrow decay width (=4.3MeV/c2) 　⇒ sensitive to the mass spectrum modification

small decay Q value (QK+K-=32MeV/c2)

⇒ the branching ratio is sensitive to or K modification

K+K-

threshold

for example…for example… mass decreases

K+K- becomes small K mass decreases

K+K- becomes large

K : H.Fujii, T.Tatsumi,PTPS 120(1995)289.

mass

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K+K-K+K-//e+ee+e and Nuclear Mass-Number and Nuclear Mass-Number Dependence Dependence

K+K-K+K-//e+ee+e and Nuclear Mass-Number and Nuclear Mass-Number Dependence Dependence

K+K-/e+e- increases in a nucleus NK+K- /Ne+e- becomes largeThe lager modification is expected in the larger nucleus

K+K- becomes larger than e+e-

The difference of is expected to be enhanced in slowly moving mesons

1A A A

)/ln(/)(

)(/

)(

)(ln 21

2

2

1

1 AAA

A

A

A

ee

KK

ee

KK

eeKK

(A1>A2)

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Results of Nuclear Mass-Number Results of Nuclear Mass-Number Dependence Dependence

Results of Nuclear Mass-Number Results of Nuclear Mass-Number Dependence Dependence

averaged(0.14+/-0.12)

K+K- and e+e- are consistent

rapidity pT

possible modification of the decay widths is discussed

= -K+K- e+e-

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

=

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* 0tot 0

* 00

* 00

1 ,

1 ,

1

KK K K K

ee e e e

k

k

k

1. The values of expected are obtained by the MC.– mesons are uniformly produced in a nucleus and decayed

according to the values of kK and ke.2. The measured provides constraints on kK and ke.

Discussion on K+K- and e+e-Discussion on K+K- and e+e-

we expect ktot ~ kK since the meson mainly decays into KK as long as such decays are kinematically allowed.

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 peak and BG.– From the MC, we estimate the ratio of the number of mesons decayed inside to

outside Nin/Nout (inside = the half-density radius of the Woods-Saxon dist.).– When the surpluses are assumed as the -meson decayed inside a nucleus, we

obtain the constraint on kK by comparing Nsurplus/N with Nin/Nout.

Discussion on andeeDiscussion on andee

excluded from the fitting

surplus

Nsurplus/N = 0.044+/-0.037+/-0.058 (C) 0.076+/-0.025+/-0.043 (Cu)

Cu Cu

MC

kK

~ N

surp

lus/

N

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

dataN

in/N

ou

t

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nuclear mass number dependence of

ee

nuclear mass number dependence of

ee

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

F. Sakuma,Phys. Rev. Lett., 98 (2007) 152302

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

kK = 1.4±1.1(stat.)±2.1(syst.)• The measured provides

constraints on kK and ke.

colored contour : MC

)(

)(/

)(

)(ln

1

2

1

2

A

A

A

A

ee

ee

KK

KKeeKK

)/(1 /

)/(1 /

)/(1/

00*

00*

00*

tottottot

eeeee

KKKKK

k

k

k

J-PARC Facility

Nuclear Transmutation

J-PARC = Japan Proton Accelerator Research Complex

3 GeV Synchrotron(25 Hz, 1MW)

Hadron Beam FacilityMaterials and Life Science

Experimental Facility

Neutrino to Kamiokande

50 GeV Synchrotron(0.75 MW)

500 m

Linac(330m)

J-PARC E16 Electron pair spectrometer

to explore the chiral symmetry in QCD

high momentum beam line

Hadron Hall 50-GeV PS

T1 Target

Beam Dump

Switch Yard A-Line

Split Point T0 Target

E16

J-PARC E16 Electron pair spectrometer

to explore the chiral symmetry in QCD

107 interaction (10 X E325) 1010 protons/spill with 0.1% interaction length target GEM TrackereID : Gas Cherenkov　 　 + Lead GlassLarge Acceptance (5 X E325)

primary proton beam at high momentum beam line　　　　　　　 + large acceptance electron spectrometer

velocity dependencenuclear number dependence (p Pb)centrality dependence　 systematic study of mass modification

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SummarySummaryWe 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.