Results of KEKPS E325 experiment. Introduction E325 Experiment Results of data analysis r/w e + e  spectra f e + e  spectra f K + K  spectra nuclear massnumber dependences of f e + e  & f K + K  Summary. F.Sakuma , RIKEN. Physics Motivation.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Results of KEKPS E325 experiment
F.Sakuma, RIKEN
Physics Motivation
Quark Mass
chiral symmetry restoration
effective mass
in QCD vacuum
mu≒md≒300MeV/c2
ms≒500MeV/c2
bare mass
mu≒md≒5MeV/c2
ms≒150MeV/c2
chiral symmetry breaking
How we can detect such a quark mass change?
at very high temperature or density, the chiral symmetry is expected to restore
W.Weise
NPA553,59 (1993)
even at normal nuclear density, the chiral symmetry is expected to restore partially
Vector Meson Modification
dropping mass
m*/m=0.8 (r=r0)
m*/m=10.16r/r0 for r/w
m*/m=10.03r/r0 for f
Lattice Calc.
width broadening
1GeV> for r, 45MeV for f (r=r0)
22MeV for f (r=r0)
33MeV for f (r=r0)
Vector Meson, r/w/f
r/w meson
16% 130MeV/c2
f meson
2~4% 2040MeV/c2
no other resonance nearby
⇒sensitive to the mass
spectrum change
T.Hatsuda, S.H.Lee,
Phys. Rev. C46(1992)R34.
Expected Modified Mass Spectra in e+e
bglab~1
e
e
e
p
p
r/w/f
r/w/f
e
outside decay
inside decay
+
m*/m=10.16r/r0
w
f
m*/m=10.02r/r0
r
Experimental Results on the Inmedium Mass and Width of the r, w and f meson
R.S.Hayano and T.Hatsuda, arXiv:0812.1702 [nuclex]
the majority of experiments does not
find evidence for a mass shift.
[CBELSA/TAPS, arXiv:1005.5694]
our report is
minority report!?
confirmation
@ JPARC E16
KEKPS E325 Experiment
Measurements
x6 statistics in K+K
Invariant Mass ofe+e, K+K
in 12GeV p+Ar,w,f+X reactions
slowly moving vector mesons (plab~2GeV/c)
large probability
to decay inside a nucleus
Beam
Primary proton beam
(~109/spill/1.8s)
Target
Very thin targets
(X/lI=0.2/0.05%,
X/X0=0.4/0.5% for C/Cu)
8
Detector Setup
Forward LG Calorimeter
Start Timing Counter
Hodoscope
Rear LG Calorimeter
Aerogel Cherenkov
Side LG Calorimeter
Forward TOF
Barrel Drift Chamber
B
0.81Tm
Cylindrical DC
Rear Gas Cherenkov
Vertex DC
Front Gas Cherenkov
M.Sekimoto et al., NIM, A516, 390 (2004).
1m
12GeV proton beam
E325 Spectrometer
front view
top view
beam
beam
Spectrometer Performance
M = 496.8±0.2 (MC 496.9) MeV/c2
σ = 3.9±0.4 (MC 3.5) MeV/c2
M = 1115.71±0.02 (MC 1115.52) MeV/c2
σ = 1.73±0.04 (MC 1.63) MeV/c2
K0sp+p
L pp
－Data
－MC
－Data
－MC
[counts / 2MeV/c2]
[counts / 0.5MeV/c2]
mass resolution for fmeson decays
fe+e : 10.7 MeV/c2
fK+K : 2.1 MeV/c2
Observed Invariant Mass Spectra
C
Cu
w(783)
w(783)
counts/10MeV/c2
counts/10MeV/c2
e+e
f(1020)
f(1020)
C
Cu
f(1020)
f(1020)
counts/4MeV/c2
counts/4MeV/c2
K+K
K+K
threshold
M.Naruki et al., PRL, 96 092301 (2006).
e+e Invariant Mass Spectra
counts/10MeV/c2
(~70% of total data)
by the detector acceptance
C
w(783)
f(1020)
fit the spectra with known sources
Fitting with known sources
(multiple scattering, energy loss, external bremsstrahlung,
chamber resolution,
detector acceptance, etc.)
by the event mixing method
components is determined
by the fitting
estimated spectrum using GEANT4
fe+e
experimental effects
+
internal radiative correction
relativistic
BreitWigner
Fitting Results
Cu
C
c2/dof=159/140
c2/dof=150/140
the excess over the known hadronic sources on the low mass side of w peak has been observed.
the region 0.600.76GeV/c2 is excluded from the fit, because the fit including this region results in failure at 99.9% C.L..
Fitting Results (BG subtracted)
events[/10MeV/c2]
events[/10MeV/c2]
Cu
C
r/w ratios are consistent with zero !
r/w = 0.0±0.03(stat.)±0.09(sys.)
0.0±0.04(stat.)±0.21(sys.)
r/w=1.0±0.2 in former experiment (p+p, 1974)
the origin of the excess is modified r mesons
Simple Model Calculation
e
e
p
r/w
Cu
C
r=4.1fm
r=2.3fm
hemisphere of target nucleus
Fitting Results by the Simple Model
m*/m = 1  0.092r/r0
r/w = 0.7±0.1
r/w = 0.9±0.2
Cu
C
the excesses for C and Cu are well reproduced by the model including the mass modification.
Contours for r/w and k
simultaneously fitted.
k = 0.092±0.002
r/w = 0.7±0.1 (C)
0.9±0.2 (Cu)
mass of r/w meson decreases by 9% at normal nuclear density.
R.Muto et al., PRL, 98 042501 (2007).
fe+e Invariant Mass Spectra
(evaluated as same as r/w)
f(1020)
examine the mass shape as a function of bg (=p/m)
(anomaly could be enhanced for slowly moving mesons)
Fitting Results
1.75<bg (Fast)
bg<1.25 (Slow)
1.25<bg<1.75
Small Nucleus
Large Nucleus
Rejected at 99% confidence level
Amount of Excess
A significant enhancement is seen in the Cu data, in bg<1.25
the excess is attributed to the f 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.
excluded from
the fitting
Simple Model Calculation
p
f
Simple model like r/w case, except for
(no theoretical basis)
G*e+e/G*tot=Ge+e/Gtot
to increase the decay probability in a nucleus
Fitting Results by the Simple Model
m*/m = 1  0.034r/r0, G*/G = 1 + 2.6r/r0
1.75<bg (Fast)
bg<1.25 (Slow)
1.25<bg<1.75
Small Nucleus
Large Nucleus
well reproduce the data, even slow/Cu
Contours for k1 and k2 of fe+e
Pole Mass Shift
M*/M = 1–k1r/r0
Width Broadening
G*/G = 1+k2r/r0
simultaneously fitted.
F.Sakuma et al., PRL, 98 152302 (2007).
fK+K Invariant Mass Spectra
C
(evaluated as same as r/w)
by the event mixing method
counts/4MeV/c2
f(1020)
examine the mass shape as a function of bg
Fitting Results
2.2<bg (Fast)
bg<1.7 (Slow)
1.7<bg<2.2
Small Nucleus
Large Nucleus
Massspectrum changes are NOT statistically significant
However, impossible to compare fe+e with fK+K, directly
Kinematical Distributions of observed f
the histograms for fK+K are scaled by a factor ~3
Summary of Shape Analysis
m*/m = 1 – k1r/r0, G*/G = 1 + k2r/r0
m(r)/m(0)
fit result f
1
0.9
fit result r/w
0.8
prediction
0.7
0 0.5 1
r/r0
syst. error is not included
F.Sakuma et al., PRL, 98 152302 (2007).
Vector Meson, f
2~4% 2040MeV/c2
⇒ sensitive to the mass spectrum
change
(QK+K=32MeV/c2)
f mass
K+K
threshold
simple example
GfK+K becomes small
GfK+K becomes large
r0:normal nuclear density
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 MassNumber Dependence a
NfK+K /Nfe+e changes also
(A1!=A2)

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 MassNumber Dependence a
bg
rapidity
pT
bg
averaged
(0.13+/0.12)
afK+K and afe+e are consistent
Discussion onGfK+K and Gfe+e
We attempt to obtain the upper limit of the GfK+K and Gfe+emodification
The constraint on the GfK+Kmodificationis obtained from the K+Kspectra by comparing with the MC calculation.
Theoretical predictions
width broadening is expected to be up to ~x10
(Klingl, Kaiser & Weise, etc.)
Discussion onGfK+K and Gfe+e
broadening of Gfe+e
broadening of GfK+K
the first experimental limits assigned to the
inmedium broadening of the partial decay widths
Summary
calculations which take HatsudaLee prediction into
account.
the bg region in which we see the excess in the e+e mode.
broadenings for both the fe+e and fK+K decay
channels.
KEKPS E325 Collaboration (2007)
RIKEN Nishina Center
H.Enyo(*), F. Sakuma, T. Tabaru, S. Yokkaichi
KEK
J.Chiba, M.Ieiri, R.Muto, M.Naruki, O.Sasaki, M.Sekimoto, K.H.Tanaka
KyotoUniv.
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