Transcript Investigation of the nuclear medium property via f meson

New Frontiers in QDC 2010
-Exotic Hadron Systems and Dense Matter –
Mini Symposium on Exotic hadrons
Feb/23/2010
f meson
nucleus atatJ-PARC
phi
mesoninproduction
JPARC
Hiroaki Ohnishi
RIKEN
This talk is based on
the submitted proposal to J-PARC
Introduction
My personal questions
 What is the meaning of mass ?
 What is the meaning of mass in nuclear media?
i.e. If mass reduction of vector meson exist,
what is the meaning?
 Is there any clear relations between
Chiral order parameter <qq>
mass reduction of mesons in nuclear media
f meson in nuclear media

why are we focusing on f meson?
 Quark content : ~100% ss
 Mass shift on f meson in nuclear matter is directly
connecting (?) to the in medium change of
strange quark condensate <ss> (or gluon condensate?)
Direct access to the chiral symmetry restoration
in the strangeness sector can be possible via f meson
 f meson in nuclear media will give us unique information
on strange content of nucleon and nuclear matter
f mesons in nuclear media
- theoretical situation
 Mass of vector meson in nuclear media will be
decreasing when density increasing (QCD Sum rule)
(if no width broadening ?)
T. Hatsuda, H. Shiomi and H. Kuwabara
Prog. Theor. Phys. 95(1996)1009
 Very small mass shift but
significant broadening
of decay width
(Chiral SU(3) ….)
NPA 624(1997)527
f mesons in nuclear media
- experimental situation
 mass shift (~3%) of f meson
have been observed by KEK-PS E325.
( with the width getting 3.6 times
bigger then the width in vacuum)
- PRL 98(2007)04501
 photo production of f meson from Li, C, Al, and Cu at
LEPS/SPRING-8
 sfN in nuclear media getting much bigger (~35 mb) than in free space
( huge width broadening ) - PLB608(2005)215
 f meson production in 158 GeV/c
~2GeV/c
In-In collisions at CERN/SPS (NA60)
 mass shift and width broadening
are not identified in hot nuclear matter
(within detector resolution)
- EPJ C64(2009)1-18
What is really happening on f meson in nuclear media
Considering mass reduction
in nuclear media
 Strong attractive force exist between KbarN
This is confirmed by measurement of 2p->1s x-ray energy in Kaonic
hydrogen atom
M.Iwasaki et al.,
PRL78 (1997) 3067
2p
1s
G = 407 eV
DE = -323 eV
-8.6 keV
only Coulomb int.
 The strong attraction between
KbarN lead to the conclusion of
mass reduction of Kbar(K-)
in nuclear media.
Mass reduction = attractive force exist ???
= attractive potential
?
Nucl.Phys.A617(1997)449
f-N bound state?
 f-N bound state has already been discussed in year 2000,
however totally independent starting point.
 Meson-Nucleon bound state with “QCD van der Waals” attractive force
(Originally this idea is developed for the discussion of hc-N bound state)
Binding energy obtained with this analysis is 1.8 MeV/n.
Assume : BEA = BEN x A 2/3 ( like the case of hyper nucleus )
binding energy for Copper nucleus (for example) ~ 28 MeV.
f-N bound state?
 Results from Chiral SU(3) quark model
Experiment to search for such
bound state has been performed,
(at CLAS),But no experimentally evidence
for existence of such (quasi-) bound state
Goal of the experiment
 Question is how to measure mass shift which
can be compared with theoretical prediction??
 f-meson bound state
 measurement of binding energy
and width
(J-PARC P29)

the invariant mass study
of f ee in nucleus
(J-PARC E16)
This part is missing!!!
Origin of mass shift and contribution of
chiral symmetry restoration in the mass of vector meson
(need helps from theory..)
Experimental
method
How to identify f meson bound state
 Formation of f mesic nucleus will be identified with
missing mass analysis.
a
b
f
 Need to find good elementary process for
f meson production
 (p,K) reaction for hyper nucleus formation
 produced f meson momentum must be small
(up to a few hundred MeV/c)
How to produce f with low momentum
efficiently?
 f production via p(p,f)f
KEK-E325 reaction
f meson
 Very interesting production
process
 Momentum transfer ~ 200 MeV/c
bg distribution
 Double f meson production will be
dominant around threshold
( 0.9 GeV/c<p<1.4 GeV/c)
 Only less than 10% physical
background
~2GeV/c
f meson production cross section
Once we
one f meson in
will be 
smaller
thandetect
KEK E325,
reaction,
partner will also be
but usingthe
pbar,
could produce
mesonefficiently
slow f fmeson
 Missing mass spectroscopy can be
done with forward going f meson
How to produce f with low momentum
efficiently?
 Huge Background
However, once one can identify
third strangeness in the event,
then event sample will be
almost background free
f meson production with
anti-proton will be primary candidate
of the elementary process for
the f mesoic-nucleus production.
How to ensure f meson is really in
nucleus
 Let’s focusing on decay mode
 Mass of the f meson will be decreasing about 30 MeV.
 i.e. 1019 MeV – 30 MeV = 989 MeV ~ 2 x MKaon
Main decay mode for Φmeson, Φ→K+K-, will be suppress.
 However, Φ meson is in nucleus.
There are many nucleon surrounding them.
1019 MeV – 30 MeV + 938 MeV(proton)
＝ 1927 MeV > MKaon+MΛ
i.e. Φp→K+Λ will be a dominant decay mode,
if f meson is in nucleus. (This mode is not suppressed
by OZI role )
s
s
i.e. K+L in final state will be
a good signal to ensure
f meson in medium
Φ
s
u
p u
d
u
K+
s
uΛ
d
Concept for the experiment
Anti-proton
Nuclear
target
Reaction
f meson
bound
state
Decay
K+
L
Outgoing
f meson
Very recent theoretical progress
on f mesic nucleus
arXiv:1001.2235v1 [nucl-th] 13 Jan 2010
 Posibility of f mesic nuclei formation has been
discussed in this paper,
If attractive potential is strong enough,
some hope to see the peak? Structure
due to the bound state formation…
Concerning for the experiment
 pbar-p → ff reaction is really happening
in nucleus????
 f production process :
 Direct production process
p
p
f
f
 OZI rule viorated
 Anomalous large cross section
 This process can be expected even in nucleus.
 Kaon loop
 According to a theoretical calculation,
Kaon loop process contributes
2mb to 4mb of cross section.
p
u
u
d
s
s
s
u
p u
d
s
p
p
f
f
K
K
f
K
f
If such hadron loops are main component of ff
production, its process may suppress in nuclear
medium (??).
 Theoretical calculation or experimental evidence is important.
Probably we need to measure cross section of pbar-p → ff in light nucleus as 1st step
Detector concept
and
signal expected
Experimental method
How to produce and detect f mesic nucleus?
Slow
f meson
Anti
proton
L
K+
Φ
Fast
Φmeson
Φ
Bound
K+
K-
～0.3GeV/c
Nucleus
～１GeV/c
Φmesic nucleus
Missing mass using reconstructed
forward going f coincidence
with K+ and L from target
Momentum of f produced by this reaction
Just select f
produced to
180°in CM
If we choose pbar momentum = 1.0 – 1.3 GeV/c
momentum of the f will be 200 – 260 MeV/c
Conceptual design of the detector
 Large solid angle charged particle spectrometer
(with large gap dipole magnet)
Main spectrometer
CDC
ToF wall
Large acceptance for
forward going f meson
(for missing mass analysis)
Large solid angle for the
decay particles, K+ and L,
from f mesic nucleus
Target Region
K+
Kbeam
target
Target surrounded by
trigger counter
Conceptual design of the detector
Candidate of spectrometer magnet
ToF wall = Resistive Plate Chamber (RPC)
Target Region
• FOPI ToF Wall will be a model
• < 65 ps time resolution
• Working well under the magnetic field
target
beam
RIKEN 4th-cyclotron magnet
now used as historical monument
220 cm pole diameter
Aerogel cherenkov counter
• n~1.2 will be used
Typical event display
 p + Cu  f + fNi (Bf = 30 MeV)
 “f”+”p”  K+ + L
K+
~500 MeV/c
X [cm]
Detector simulation
using GEANT4 based on
conceptual detector design
is in progress
Y [cm]
( proton & f at rest )
 All decay processes are isotopic.
K~500 MeV/c
K+
~500 MeV/c
p~100 MeV/c P
~450 MeV/c
Y [cm]
Anyway, how the signal looks like?
If life is simple enough (I knew life is complicated)
Assumption in the simulation:
bound state with 30 MeV B.E. exist
Spectrometer missing mass resolution = 18 MeV (s)
Fermi momentum in nucleus is taking into account in
the simulation
 Gf in nucleus assumed to be broaden 10 time more
than natural width
Blue triangle: Missing mass spectra of unbound f
Red circle
Beam
Mass number
Carge number
Cross section (Z2/3 x spp ) [mb]
Target thickness [g/cm2]
Acceptance of forward KK
Acceptance of decay particle
Averaged Sticking probability
Analysis and DAQ efficiency
Expected yield/120 shift
Cu
106
63.5
29
23
2.0
5x10-2
8x10-2
0.13
0.7
~200
: Expected signals
C
106
12
6
7.9
2.0
5x10-2
8x10-2
0.13
0.7
~290
C2H4
106
1
1
2.4
2.0
7x10-2
3x10-2
N/A
0.7
610
Summary
 Based on the results reported by KEK-PS E325
(mass shift of f meson) strongly suggested that the
production of f mesic nucleus can be possible.
 The most promising elementary process for
the f mesic nucleus production will be pp→ff
channel.
 Naïve event rate estimation tells us that ~200 events
candidate for f mesic nucleus will be produce per 40
days,with beam intensity, 1x106/spill, for 1.1 GeV/c
anti-proton.