results of kek-ps e325 experiment

Results of KEK-PS E325 Results of KEK-PS E325 experimentexperiment

Results of KEK-PS E325 Results of KEK-PS E325 experimentexperiment

•Introduction

•E325 Experiment

•Results of data analysis

e+e- spectra

e+e- spectra

K+K- spectra

nuclear mass-number dependences of e+e- & K+K-

•Summary

F.Sakuma, RIKEN

2

effective mass in QCD vacuum

　 mu m≒ d 300MeV/c≒ 2

ms 500MeV/c≒ 2

chiral symmetry breaking

Quark MassQuark Mass

bare massmu m≒ d 5MeV/c≒ 2

ms 150MeV/c≒ 2

How we can detect such a quark mass change? How we can detect such a quark mass change?

Physics Motivation

chiral symmetry restoration

even at normal nuclear density, the chiral symmetry is

expected to restore partially

at very high temperature or density, the chiral symmetry is

expected to restore

W.WeiseNPA553,59 (1993)

3

Vector Meson Modificationdropping massdropping mass

width broadeningwidth broadening

Brown & Rho (’91) m*/m=0.8 (=0)Hatsuda & Lee (’92) m*/m=1-0.160 for m*/m=1-0.030 for Muroya, Nakamura & Nonaka (’03) Lattice Calc.

Klingl, Kaiser & Weise (’97&98) 1GeV> for , 45MeV for (=0)Oset & Ramos (’01) 22MeV for (=0)Cabrera & Vicente (’03) 33MeV for (=0)

4

mesonmeson

Vector Meson,

T.Hatsuda, S.H.Lee,Phys. Rev.

C46(1992)R34.

mass decreases16% 130MeV/c2

large production cross-sectioncannot distinguish &

mesonmesonmass decreases

2~4% 20-40MeV/c2

small production cross-sectionnarrow decay width (=4.3MeV/c2), no other resonance nearby　　　⇒ sensitive to the mass spectrum change

5

Expected Modified Mass Spectra in e+e-

p

e

e p

e

e

outside　decay inside　decay

m*/m=1-0.160

small FSI in e+e- decay channeldouble peak (or tail-like) structure

m*/m=1-0.020

lab~1

second peak is caused by inside-nucleus decayinside-nucleus decay

depends on the nuclear size & meson velocity

enhanced for larger nuclei & slower meson

　　 Invariant massInvariant mass AttenuationAttenuation

　　 KEK-PS KEK-PS E325E325

Jlab Jlab CLAS g7CLAS g7 CBELSA/TAPSCBELSA/TAPS Jlab Jlab

CLAS g7CLAS g7Spring8 Spring8

LEPSLEPS

ReactionReaction pA　12　GeVA　0.6　-　3.8　GeV

A　0.7　-　2.5　GeV A　0.6　-　3.8　GeV

A　1.5　-　2.5　GeV

MomentuMomentumm

0　>　0.5　GeV/c

p　>　0.8　GeV/c

p　<　0.5　GeV/c

0.4　<　p　<　1.7　GeV/c

p　>　0.8　GeV/c

1.1　<　p　<　2.2　GeV/c

　 m　　0 　 　

m(0)/m　=　-9%

broadening 　 　 　 　

no　broadening

m　　0?

(0)　=　130-

150MeV/c2　

　 　→N　　70mb

m(0)/m　=　-3.4%

　N　　20mb

N　　35mb

(0)/　　15MeV/c2

　 　 　→　(0)　　45　MeV/c2

→(0)　　80　MeV/c2

6

Experimental Results on the In-medium Mass and Width of the ,

and mesonR.S.Hayano and T.Hatsuda, arXiv:0812.1702 [nucl-ex]

our report is minority report!?

confirmation@ J-PARC E16

7

KEK-PS E325 Experiment

88

KEK-PS E325 Experiment

Very thin targets(X/I=0.2/0.05%, X/X0=0.4/0.5% for C/Cu)

History of E325’93 proposed’96 construction start

NIM,A457 581(’01).NIM,A516 390(’04).

’97 first K+K- data’98 first e+e- data

: PRL,86 5019(’01).

’99~’02 x100 statistics in e+e-

: PRL,96 092301('06).ee: PRL,98 042501(’07).: PR,C75 025201(’06).

x6 statistics in K+K-

KK: PRL,98 152302(’07).

’02 completed

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

MeasurementsMeasurements

BeamBeam

TargetTarget

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

in 12GeV p+A,,+X reactions

slowly moving vector mesons (plab~2GeV/c)

large probability large probability to decay inside a nucleusto decay inside a nucleus

9

Detector Setup

12GeV proto

n

beam

Forward LG Calorimeter

Rear LG Calorimeter

Side LG Calorimeter

Front Gas Cherenkov

Rear Gas Cherenkov

Barrel Drift Barrel Drift ChamberChamber

Cylindrical Cylindrical DCDC

Vertex Vertex DCDC

B0.81Tm

Hodoscope

Aerogel Cherenkov

Forward TOF

Start Timing Counter

1m

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

10

E325 Spectrometer

front view

top viewbeam

beam

11

M = 496.8±0.2 (MC 496.9) MeV/c2

σ = 3.9±0.4 (MC 3.5) MeV/c2

K0s

+- p-

－ Data

－ MC

M = 1115.71±0.02 (MC 1115.52) MeV/c2

σ = 1.73±0.04 (MC 1.63) MeV/c2

[co

un

ts /

2M

eV

/c2]

[co

un

ts /

0.5

Me

V/c

2 ]

Spectrometer Performance

－ Data

－ MC

mass resolution for -meson decayse+e- : 10.7 MeV/c2

K+K- : 2.1 MeV/c2

12

C Cu

co

unts

/10M

eV

/c2

coun

ts/1

0Me

V/c

2

Observed Invariant Mass Spectra

C Cu

ee++ee--

KK++KK-- coun

ts/4

MeV

/c2

coun

ts/4

MeV

/c2

K+K- threshold

13

Result of e+e-

M.Naruki et al., PRL, 96 092301 (2006).

14

Ccounts/10MeV/c2

e+e- Invariant Mass Spectra

from 2002 run data (~70% of total data)

C & Cu targets

acceptance uncorrected

M<0.2GeV/c2 is suppressed by the detector acceptance

fit the spectra with known sources

resonance–e+e-, 0e+e-, e+e-

– relativistic Breit-Wigner shape (with internal radiative corrections)– nuclear cascade code JAM gives momentum distributions– experimental effects are estimated through the Geant4 simulation (multiple scattering, energy loss, external bremsstrahlung, chamber resolution, detector acceptance, etc.)

background– combinatorial background obtained by the event mixing method

fit parameter– relative abundance of these components is determined by the fitting

Fitting with known sources

estimated spectrum using

GEANT4

experimental effects

+internal radiative

correction

e+e-

relativisticBreit-

Wigner

16

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

C Cu

the region 0.60-0.76GeV/c2 is excluded from the fit, because the fit including this region results in failure at 99.9% C.L..

2/dof=159/140 2/dof=150/140

Fitting Results

ratios are consistent with zero != 0.0±0.03(stat.)±0.09(sys.) 0.0±0.04(stat.)±0.21(sys.)

=1.0±0.2 in former experiment (p+p, 1974) the origin of the excess is modified mesons

Fitting Results (BG subtracted)events[/10MeV/c2] events[/10MeV/c2]

C Cu

18

• pole mass: m*/m = 1-k0 (Hatsuda-Lee formula)

• generated at surface of incident

hemisphere of target nucleus

– ~2/3 [PR, C75 025201 (2006).]

– decay inside a nucleus:

• nuclear density distribution : Woods-Saxon

• mass spectrum: relativistic Breit-Wigner Shape

• no width modification

p

e

e

C Cu

52% 66%

5% 10%

Cu Cr=4.1fm r=2.3fm

Simple Model Calculation

19

the excesses for C and Cu are well reproduced by the model including the mass modification.

m*/m = 1 - 0.092 0

C Cu

Fitting Results by the Simple Model

= 0.7±0.1 = 0.9±0.2

20

mass of meson decreases by 9% at normal nuclear density.

Contours for and k

Best-Fit values are k = 0.092±0.002 = 0.7±0.1 (C) 0.9±0.2 (Cu)

C and Cu data are simultaneously fitted.

free parameters– production ratio – shift parameter k

21

Result of e+e-

R.Muto et al., PRL, 98 042501 (2007).

22

e+e- Invariant Mass Spectra

from 2001 & 2002 run data

C & Cu targets

acceptance uncorrected

fit with– simulated mass shape of (evaluated as same as )– polynomial curve background

examine the mass shape as a function of (=p/m)(anomaly could be enhanced for slowly moving mesons)

23

<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

Fitting Results

24

Amount of ExcessAmount of Excess

excluded from the fitting

A significant enhancement is seen in the Cu data, in <1.25

the excess is attributed to the mesons which decay inside a nucleus and are modified

To evaluate the amount the excess Nexcess, fit again excluding the excess region (0.95~1.01GeV/c2) and integrate the excess area.

25

• pole mass: m*/m = 1-k10 (Hatsuda-Lee formula)

• width broadening: */= 1+k20

(no theoretical basis)– e+e- branching ratio is not changed

*e+e-/*tot=e+e-/tot

• uniformly generated in target nucleus

– ~1 [PR, C75 025201 (2006).]

– decay inside a nucleus (for <1.25):C Cu

3% 6%

Simple Model Calculation

p

Simple model like case, except for

to increase the decay probability

in a nucleus

26

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

Lar

ge

Nu

cleu

sS

mal

l N

ucl

eus

Fitting Results by the Simple Model

well reproduce the data, even slow/Cu

m*/m = 1 - 0.034 0, */ = 1 + 2.6 0

27

Pole Mass Shift M*/M = 1–k1/0

Width Broadening / = 1+k2/0

Best-Fit values are

C and Cu data are simultaneously fitted. free parameters

– parameter k1 & k2

Contours for k1 and k2 of e+e-

0.0060.007

1.81

t t2

1

2o

.

0.034

2.6k

k

mass of meson decreases by 3.4%width of meson increases by a factor of 3.6

at normal nuclear density.

28

Result of K+K-

F.Sakuma et al., PRL, 98 152302 (2007).

29

K+K- Invariant Mass Spectra

from 2001 run data

C & Cu targets

acceptance uncorrected

fit 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

Fitting ResultsFitting Results<1.7 (Slow) 1.7<<2.2 2.2< (Fast)

Lar

ge

Nu

cleu

sS

mal

l N

ucl

eus

Mass-spectrum changes are NOT statistically significantHowever, impossible to compare e+e- with K+K-, directly

31

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

32

Summary ofshape analysis

Summary of Shape Analysis

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)

-

syst. error is not included

prediction

1

fit result

fit result m()/m(0)

m*/m = 1 – k1 */ = 1 + k2 /0

0.9

0.8

0.70 0.5 1

33

34

Result of nuclear mass-number

dependences of e+e- & K+K-

F.Sakuma et al., PRL, 98 152302 (2007).

35

Vector Meson,

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

⇒ the branching ratio is sensitive to or K modification

K+K-

threshold

simple examplesimple example mass decreases

K+K- becomes smallK mass decreases

K+K- becomes large

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

mass

36

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

K+K-/e+e- changes in a nucleus NK+K- /Ne+e- changes alsoThe lager modification is expected in the larger nucleus

difference between K+K- and e+e-

could be founddifference of is expected to be enhanced in slowly moving mesons

1 2

1 21 2

ln ln

K K e e

K K K K

e e e e

N A N AA A

N A N A

(A1!=A2)

1A A A

37

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

averaged(0.13+/-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

=

We attempt to obtain the upper limit of the K+K- and e+e- modification

38

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

Theoretical predictionswidth broadening is expected to be

up to ~x10 (Klingl, Kaiser & Weise, etc.)

① The measured provides constraints on the K+K- and e+e- modification by comparing with the values of expected obtained from the MC.

② The constraint on the K+K- modification is obtained from the K+K- spectra by comparing with the MC calculation.

39

* 0tot 0

* 00

* 00

1 ,

1 ,

1

KK K K K

ee e e e

k

k

k

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

tot KWe expect k k since the meson mainly decays into KK as long as such decays are kinematically allowed.

the first experimental limits assigned to the

in-medium broadening of the partial decay widths

broadening of K+K-

bro

aden

ing

of

e+

e-

40

SummaryKEK PS-E325 measured e+e- and K+K- invariant mass distributions in 12GeV p+A reactions.

The significant excesses at the low-mass side of e+e- and e+e- peak have been observed.

→ These excesses are well reproduced by the simple model calculations which take Hatsuda-Lee prediction into account.

Mass spectrum changes are not statistically significant in the K+K- invariant mass distributions.

→ Our statistics in the K+K- decay mode are very limited in the region in which we see the excess in the e+e- mode.

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.

41

KEK-PS E325 Collaboration (2007)

RIKEN Nishina Center H.Enyo(*), F. Sakuma, T. Tabaru, S. Yokkaichi KEKJ.Chiba, M.Ieiri, R.Muto, M.Naruki, O.Sasaki, M.Sekimoto, K.H.Tanaka Kyoto-Univ. H.Funahashi, H. Fukao, M.Ishino, H.Kanda, M.Kitaguchi, S.Mihara, T.Miyashita, K. Miwa, T.Murakami, T.Nakura, M.Togawa, S.Yamada, Y.Yoshimura CNS,Univ.of Tokyo H.Hamagaki Univ.of Tokyo K. Ozawa

(*) spokesperson