Download - 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
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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)
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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)
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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
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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
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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
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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
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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).
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E325 Spectrometer
front view
top viewbeam
beam
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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
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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
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Result of e+e-
M.Naruki et al., PRL, 96 092301 (2006).
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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
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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
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• 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
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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
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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
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Result of e+e-
R.Muto et al., PRL, 98 042501 (2007).
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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)
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<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
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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.
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• 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
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<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
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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.
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Result of K+K-
F.Sakuma et al., PRL, 98 152302 (2007).
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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
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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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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
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Result of nuclear mass-number
dependences of e+e- & K+K-
F.Sakuma et al., PRL, 98 152302 (2007).
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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
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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
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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
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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.
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* 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-
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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.
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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