1

Measurement of vector mesons in
nuclei: J-PARC E16 experiment
Satoshi Yokkaichi(RIKEN Nishina Center)●physics–

dilepton spectra●

precedent experiment E325●

proposed experiment E16●

status & schedule of construction●

summary

Collaboration
RIKEN
KEK

S.Yokkaichi, H. En'yo, F. Sakuma
K.Aoki, K.Ozawa, R. Muto, Y.Morino
S. Sawada, M. Sekimoto
U-Tokyo
Y.Komatsu, S.Masumoto, K.Kanno,
W.Nakai, Y.Obara, T.Shibukawa, H.Murakami
RCNP
T.N.Takahashi
CNS, U-Tokyo H. Hamagaki Kyoto-U M. Naruki
Hiroshima-U K. Shigaki
JASRI A. Kiyomichi

HHIQCD2015 2015Mar05 S.Yokkaichi

2spectral change of vector mesons●

hadron as the elementary excitation of QCD vacuum––

elementary excitation on a ground state : changed when the ground state is changed●

change of excitation reflects the vacuum●

condensed matter examples

hadroninc spectral function could be changed in the hot and/or dense matter, different
vaccum on the QCD phase diagram●●

various theoretical calculations

vector meson : dilepton decay–

spectral function probed by virtual photon–

experimentally, smaller final-state interaction is expected–many dilepton measurements have been performed in the world–●

in hot matter : high-energy HI collision●in dense matter ( nuclei ) : γ+A, p+A reactions

φ meson is simple (while cross section is smaller)●

isolated and narrow resonance unlike the ρ and ω mesons case (ρ/ω interfere, etc)●

spectra is related ms <ss>ρ

HHIQCD2015 2015Mar05 S.YokkaichiIn hadronic matter : vector
meson spectra in dense
nuclear matter (theory)

3

Klingle,Kaiser,Weise[NPA 624(97)527]

density ρ = ρ0/2 , ρ0ρPost & Mosel [NPA699(02)169]

ω
ρ-mesondensity ρ = ρ0hadronic matter, changing density ρ,
excited by induced proton / γ / HI,
mass spectrum is measured by dilepton.

φ

HHIQCD2015 2015Mar05 S.Yokkaichi

QCD phase diagram

4

normal nucleiµ

HHIQCD2015 2015Mar05 S.Yokkaichi

5dilepton measurements in different vacuum
vector mesons in HI-collisions have beenmeasured through the dilepton spectrain relation to the chiral symemtry restoration

In hot and dense matter,
spectral modification ofvector mesons (dilepton
invariant mass) are
observed in many
experiments

PHENIX/STARCERES/NA60
HADES/CBM
DLS/HADES
E325/E16
TAPS/CLASµHHIQCD2015 2015Mar05 S.Yokkaichi

observed dilepton spectra in the world

6“low mass enhancement"
below the ω meson peakin HI collisionsand HADES p+Nbchange of φ meson isobserved only by KEK-PS
E325 w/ best mass resolution& high statistics

PHENIX
NA60

CLAS

E325
φ

E325
DLS/HADES
ρ/ω
E325/E16
TAPS/CLAS

HADESµHHIQCD2015 2015Mar05 S.Yokkaichi

Dilepton spectrum in Heavy Ion Collision●

7

CERES@SPS : (PLB666(2008)425)–

S/B = 1/22 @ mee > 0.2 GeV/c2–“cocktail” with the thermal statistical modelraw data

bkg subtracted

resonance subtracted

HHIQCD2015 2015Mar05 S.Yokkaichi

8

HADES 3.5GeV/c pp and pNb[PLB715(2012)304](zoomed)Slow:
Pee < 0.8 GeV/c

Fast :
Pee > 0.8 GeV/c●

Slow:
Pee < 0.8 GeV/c

Excess in the slow component
in the p+Nb data
HHIQCD2015 2015Mar05 S.Yokkaichi

9CLAS-G7(PRC78(2008)015201)●●

2

γ+A → V → e+e-

H

no anomaly for p >0.8GeV/c : while
collisional broadening exist

C

Fe+Ti

BKG subtracted

PRC78(2008)015201

HHIQCD2015 2015Mar05 S.Yokkaichi

Dilepton spectra measured at KEK-PS E325

M. Naruki et al.,PRL 96 (2006) 092301
R.Muto et al.,PRL 98 (2007) 042501
●

C

10

ω(783)At the lower energy,●

better S/N●smaller production cross section●

possibly simpler environment

φ(1020)(T=0, no time evolution)

HHIQCD2015 2015Mar05 S.Yokkaichi

11

Expected Invariant mass spectra in ee●

smaller FSI in e+e- decay channel●

double peak (or tail-like) structure :●second peak is made by inside-nucleus
decay (modified meson) : amount
depend on the nuclear size andmeson velocity●

could be enhanced for slower
mesons & larger nuclei

longer-life meson(ω & φ )cases : Schematic picture
inside decay(modified)outside decay(natural)+=

expected
to be observed

HHIQCD2015 2015Mar05 S.Yokkaichi

12E325 observed the meson modifications●●in the e+e- channel
below the ω and φ, statistically significant excesses over the
known hadronic sources including experimental effects
PRL96(06)092301

ω (783)Cu

φ (1020)Cu
βγ <1.25

PRL98(07)042501

HHIQCD2015 2015Mar05 S.Yokkaichi

Fitting results (ρ/ω )χ2/dof=161/140

C13

χ2/dof=154/140

Cu1) excess at the low-mass side of ω
To reproduce the data by the fitting, we have to exclude the excess region : 0.60-0.76 GeV

2) ρ meson component seems to be vanished. ( ρ/ω =1.0±0.2 in a former
experiment)

HHIQCD2015 2015Mar05 S.Yokkaichi

e e spectra of φ meson (divided by βγ )14

+ -βγ<1.25 (Slow)

1.25<βγ<1.75

1.75<βγ (Fast)

HHIQCD2015 2015Mar05 S.Yokkaichi

e e spectra of φ meson (divided by βγ )15

+ -βγ<1.25 (Slow)

1.75<βγ (Fast)

1.25<βγ<1.75

only slow/Cu is not reproduced in 99% C.L.
HHIQCD2015 2015Mar05 S.Yokkaichi

16Discussion : modification parameter●

MC type model analysis to include thenuclear size/meson velocity effects●

generation point : uniform for φ meson●●from the measured A-dependence●

measured momentum distribution●

Woods-Saxon density distribution●

decay in-flight : linearly dependent on
the density of the decay point●

dropping mass:M(ρ)/M(0) = 1 – k1 (ρ/ρ0)●

width broadening: Γ(ρ)/Γ(0) = 1 + k2 (ρ/ρ0)

consistent result with the predictions by
Hatsuda & Lee (k1 ) , Oset & Lamos (Γ)

k1 = 0.034 +−0.006
0.007 For φ, 3.4% mass reduction (35MeV)
t ot
+1.8
3.6 times width broadening(15MeV) at ρ0
k 2 = 2.6−1 .2
HHIQCD2015 2015Mar05 S.Yokkaichi

17

Modified shape of φ●Cu, βγ <1.25,●

best fit values of k1 and k2

HHIQCD2015 2015Mar05 S.Yokkaichi

18Discussion (ρ/ω)
Free param.: - scales of background and hadron components for each C & Cu
- modification parameter k for ρ and ω is common to C & Cu

From the fit : k=0.092 ± 0.002: ~ 9 % reduced at normal nuclear density
ρ/ω production ratio : 0.7± 0.1 (C), 0.9±0.2 (Cu) : ... ρ meson returns.
Note: if kω is assumed to be 0 (i.e. not modified), kρ could be smaller.
HHIQCD2015 2015Mar05 S.Yokkaichi

19Remark on the model fitting●

constraint at right side of peak–

Introducing the width broadening(x2 & x3) are rejected by thisconstraint–

prediction of ' ρ mass increasing'is also not allowed.

●

ρ (ω) decay inside nucleus :46%(5%) for C, 61%(10%) for Cu–●

used spectrum is the sum of themodified and not-modified
components.
momentum dependence of mass
shift is not included.( But typical p=1.5GeV/c)

used
inside(modified) spectra

outsideω+=ρ
HHIQCD2015 2015Mar05 S.Yokkaichimeasured production CS of ω & φ●values for the CM backward●

consistent w/ the former
measurement for ρ meson by
Blobel (PLB48(1974)73)●20

PRC 74(2006)025201
JAM: nuclear cascade code

Nuclear dependence αφ = 0.937
corresponds to about σφN=3.7mb(Sibirtsev et.al. EPJA 37(2008)287)●●

additional Γ=12 MeV for 2 GeV/cφ (β=0.9) : consistent with
Γ=15+8-5 MeV (i.e. k2=2.6+1.8-1.2)

Remark:σ(Α)=σ0∗Αααω = 0.710 ± 0.021(stat.) ± 0.037(syst.)
αφ = 0.937 ± 0.049(stat.) ± 0.018(syst.)

Γφ=15MeV at mφ=985MeV isconsistent with Oset & Ramos(NPA679(2001)616)
HHIQCD2015 2015Mar05 S.Yokkaichi

21J-PARC E16●

Systematic measurements of the spectralchange of φ (and ρ/ω ) in nuclei throught the e+echannel with highest statistics (100000 φ) & best
mass resolution (5 MeV) in the world
–

–

–

●

confirm the results of precedent exp. KEK-PS
E325, establish the spectral change of φ/ρ/ω
in nuclei w/ higher statistics
nuclear matter size dependence (H,E16C, Cu, Pb) : double-peak shape forthe very slowly-moving φ mesons inlarger nuclei

Precedent exp. E325

φ (1020)Cu
βγ <1.25

PRL98(07)042501

first measurement of the momentum
dependence (dispersion relation) in
nuclear matter

New spectrometer is required to collecthigh statistics, to cope with the 10MHz
interactions at the target w/ 30 GeV
primary proton beam of ~1010 pps

Momentum
Nuclear dependence dependence
HHIQCD2015 2015Mar05 S.Yokkaichitheory: spectral modification of φ at ρ

22parametrize the predicted spectral change with m & Γ
φ meson in vacuumm = 1019.456 MeV

Γ= 4.26 MeV

KEK-PS E325 experiment
PRL 98 (2007) 042501∆m = −35(28~41) MeV

15 (10~23) MeV

Hatsuda & Lee
PRC 46 (1992) R34∆m = −(12-44)MeV

not estimatedKlingl, Waas, Weise
PLB 431(1998) 254∆m < − 10MeV∼45 MeV

Oset & Ramos
NPA 679 (2001) 616∆m < − 10MeV∼22 MeV @ m=1020∼16 MeV @ m=985

Cabrera & Vacas
PRC 67 (2004) 045203∆m = − 8MeV

∼30 MeV @ m=1020

OR01
KWW98

HHIQCD2015 2015Mar05 S.Yokkaichi

expected shape w/ various parametersβγ<0.5E325

βγ<0.50.5<βγ<1.25

OR-01∆m : −35 MeV ∆m : −10 MeV
Γ : 15 MeV Γ : 15 MeV-

0.5<βγ<1.25

23

Cu

KWW-98∆m : −35 MeV ∆m : −10 MeV
Γ : 50 MeV
Γ : 50 MeV

using the parameters,
spectra are approximatedwith the relativistic BreitWigner shape including
experimental mass
resolution

Pb

●

Cu

Pb
HHIQCD2015 2015Mar05 S.Yokkaichi

expected shape w/ various parametersβγ<0.5E325

0.5<βγ<1.25

βγ<0.524

0.5<βγ<1.25

OR-01∆m : −35 MeV ∆m : −10 MeV
Γ : 15 MeV Γ : 15 MeV

Cu

KWW-98-∆m : −35 MeV ∆m : −10 MeV
Γ : 50 MeV
Γ : 50 MeV

blue: decays inside thehalf-density radius of
nuclei in the MC

Pb

Cu

;

Pb
HHIQCD2015 2015Mar05 S.Yokkaichi

25velocity and nuclear size dependence●

velocity dependence of excesses ('modified' component)●

E325 only one data point for φ (slow/Cu) has significant excess

excessregionHHIQCD2015 2015Mar05 S.Yokkaichi

26velocity and nuclear size dependence●

velocity dependence of excesses ('modified' component)●

E325 only one data point for φ (slow/Cu) has significant excess●

systematic study : all the data should be explained the interpretation modelPb

x 100 stat.

proton- establish the modification
HHIQCD2015 2015Mar05 S.Yokkaichi

27velocity and nuclear size dependence●

velocity dependence of excesses ('modified' component)●

E325 only one data point for φ (slow/Cu) has significant excess●

systematic study : all the data should be explained the interpretation model

Pb

proton- establish the modification- check the interpretation model with shape analysis
HHIQCD2015 2015Mar05 S.Yokkaichi
for each histogramdispersion relation (mass VS momentum)
●

●

28

prediction for φ by
S.H.Lee(p<1GeV/c)current E325 analysis
neglects the dispersion(limited by the statistics)

HHIQCD2015 2015Mar05 S.Yokkaichi

dispersion relation (mass VS momentum)
●

●

29

prediction for φ by
S.H.Lee(p<1GeV/c)current E325 analysis
neglects the dispersion(limited by the statistics)

HHIQCD2015 2015Mar05 S.Yokkaichi

dispersion relation (mass VS momentum)●

30

prediction for φ by
S.H.Lee(p<1GeV/c)●current E325 analysis
neglects the dispersion(limited by the statistics)●

In E16, momentumdependent k1(p), can be
deducedHHIQCD2015 2015Mar05 S.Yokkaichi

dispersion relation (mass VS momentum)●

prediction for φ by
S.H.Lee(p<1GeV/c)●●●current E325 analysis
neglects the dispersion(limited by the statistics)

31

prediction for φ by
S.H.Lee(p<1GeV/c)current E325 analysis
neglects the dispersion(limited by the statistics)●●

In E16, momentumdependent k1(p), can be
deducedHHIQCD2015 2015Mar05 S.Yokkaichi

32

momentum dependence
many predictions are for the mesons at rest (p=0)
while measurements are p>0●●

extrapolation to p=0 if it is a simple dependence●

S.H.Lee (PRC57(98)927): m*/m0 = 1- k ρ/ρ0 for p<1GeV/c–

ρ/ω : k=0.16±0.06+(0.023±0.007)(p/0.5)2–φ●: k=0.15(±0.05)∗y +(0.0005±0.0002)(p/0.5)2

Post &Mosel●(NPA699(02)169)

ex

ate
r
o
p
tra

Harada & Sasaki(PRC80(09)054912)

a1

t

eV
G
3
o
●

/c

Kondratyuk et al.
(PRC58(98)1078)

ρρρ
HHIQCD2015 2015Mar05 S.Yokkaichi

33

E16 Detectors●~10 MHz interaction at the targets with ~5 GHz of 30GeV proton beam●

Tracking : GEM Tracker (3 layers of X&Y)–

5kHz/mm2 at the most forward, 100µm resolution(x) for 5MeV/c2 mass resolution●

Electron ID : Hadron Blind Detector(HBD) & lead glass EMC (LG)●Spectrometer Magnet : 1.77 T at the center, 0.78Tm for R=600 mm
Proposed Spectrometer

Plan View

Prototype Module

26 detector modules HHIQCD2015 2015Mar05 S.Yokkaichi

34

E16 : development & achieved performance
Hadron Blind Cherenkov Detector(HBD)

GEM Tracker

Lead-Glass EM Calorimeterpion suppression down
to ~0.1% is achieved
with the combination of
the two stage ofelectron-ID counters;
HBD & LG

position resolution 100 m
is achieved to keep the ~5
MeV mass resolution for the mesons.

The spectromter magnet should be reconstructed and located at the new Highmomentum beam line, which is underconstruction and completed in JFY 2016.

Experiment will start in early 2017.
HHIQCD2015 2015Mar05 S.Yokkaichi

35

Near future of the J-PARC Hadron hall

HHIQCD2015 2015Mar05 S.Yokkaichi

36High-p line in the J-PARC Hadron hall●High momentum line is under consturction
HHIQCD2015 2015Mar05 S.Yokkaichi

37High-p line in the J-PARC Hadron hall

E16 spectrometer●●

magnetreassemble isstarted in Feb.

High momentum line is under consturction
HHIQCD2015 2015Mar05 S.YokkaichiE16 Spectrometer Magnet
FM magnet in
the Hadron Hall38

new parts are deliveredin 2012 (by R. Muto)

coil
re-assemble with newparts (2015)
additional yoke

additional pole pieces

121229 S. Yokkaichi

39experimental area plan

SKS spectrometer
will be moved here

E16 spectrometer beam dump of High-p lline
HHIQCD2015 2015Mar05 S.Yokkaichi

40

E16 preparation status●

Basic performance of GTR/HBD/LG is confirmed–

Production of parts is started (GEM, R/O board) & LG●–●

Design of support frames will be completed till Mar.

Spectrometer magnet re-assemble–

by KEK, started 2015 Feb., 2-3 months–

after that, we will install LG, GTR and HBD in the magnet●●

parts for 6 GTR & 2 HBD, 8 LG modules will be ready in Mar.

target day is July 1st for the support structure delivery

R/O circuits–

GTR preamp is OK. HBD preamp w/SRS is also OK.
●

ready in Mar. for 8 modules–

GTR/HBD trigger ASD are in the test.

–

test of trigger logic circuits is also being tested.

–

Goal : ready for production by Mar. 2015

HHIQCD2015 2015Mar05 S.Yokkaichi

41

Summary●

dilepton spectra in medium have been meausred, and spectral
modification is observed in many experiments, including KEK-PS E325.

●

J-PARC E16 will measure the spectral change of vector mesons in nuclei
with the ee decay channel, using 30GeV proton beam at the newly
constructed high-momentum beam line in the J-PARC hadron hall.

●●confirm the observation by E325 and provide more systematic information of
the spectral modification (as nuclear-size dependence, momentum
dependence, etc) of vector mesons in the finite density matter.

●

preparation is underway and detector mass-production was started.

●

Staged goal of construction : 8 modules out of 26.

●

beamline construction is also on-going, possibly delayed to JFY2016.

calculation of spectral function of vector mesons in real nuclei (N/Z
asymmetric) with finite momentum is expected.

HHIQCD2015 2015Mar05 S.Yokkaichi