p-p??n?????? ???????? ?????????

1
p-p??n???????????????????????

• ??????????

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Motivation

• hadron can be undestood as
• excitation of QCD vacuum

Precise measurements of hadron property at
nuclear medium can provide QCD information
Modification of vector meson mass is expected,
even at nuclear density.
Mass GeV

• many experimental and theoritical efforts
• to search for and study in-medium modifications
  of hadrons

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Two approaches

• Meson spectroscopy

• Direct measurements of mass spectra

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Mass spectra

• Situation is not so simple, several theories and
  models predict spectral function of vector mesons
  (r, w, f).
• Lowering of in-medium mass
• Broadening of resonance

?- meson
r- meson
F. Klingl et al. NPA 624 (1997) 527
NPA 650 (1999) 299
R. Rapp and J. Wambach, EPJA 6 (1999) 415
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Mass spectra (contd)
M. Lutz et al. , Nucl. Phys. A 706 (2002) 431
P. Muehlich et al. , Nucl. Phys. A 780 (2006) 187
?
?
?
structure in spectral function due to coupling
to baryon resonances
structure due to coupling to S11,P13 resonances
To distinguish several physics processes
experimentally, Measurements at exclusive
condition are important.
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KEK E325, r/w? ee-
w?ee-
the excess over the known hadronic sources on the
low mass side of w peak has been observed both in
Carbon and Cupper target.
Cu
mr m0 (1 - ? ?/?0) for ? 0.09
The excess for both C and Cu are well reproduced
by the model including the 9 mass decrease at r0.
CLAS claims no
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Positive experimental result
TAPS, w ? p0g with gA
D. Trnka et al., PRL 94 (2005) 192203
advantage p0g large branching ratio (8 )
no ?-contribution (? ? ?0? 7 ? 10-4)
disadvantage p0-rescattering
m? m0 (1 - ? ?/?0) for ? 0.13
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TAPS, Updated analysis
refined analysis requiring recoil proton and p-?
coplanarity
w
Strange Peak is seen. It exists on heavier
targets. It does NOT exist in higher momentum
region.
Its still preliminary result and under
investigation.
Its gone after further analysis. Information by
M. Naruki at workshop
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Missing mass spectroscopy
Energy level of bound state has information about
interaction between nucleus and meson.
Theoretical prediction for w bound states
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Example p bound state
K. Suzuki et al., Phys. Rev. Let., 92(2004) 072302

• bound state is observed in
• Sn(d, 3He) pion transfer reaction.

Reduction of the chiral order parameter,
fp(r)2/fp20.64 at the normal nuclear density,
r r0 is indicated.
Y. Umemoto et al., Phys. Rev. C62(2004) 024606
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New experiment _at_ J-PARC

• Meson spectroscopy

• Direct measurements of mass spectra

Simultaneous measurement!
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Kinematics
0.4
Neutron q dependence
Mass dependence (Mw 783 MeV/c2)
1.2
w momentum GeV/c2
q 10?
0.8
0.2
-100 MeV/c2
q 5?
-50 MeV/c2
0.4
q 0?
DM 0 MeV/c2
0
0

• Almost stopped w mesons are created.

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0 degree measurement
R.E. Chrien et al., Phys. Rev. Let., 60 (1988)
2595
Li
C
O
Al
Negative results for h Measurements _at_ 15
H. Nagahiro et al, Calculation for 12C(g, p)11Bw
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Final state interaction
disadvantage p0-rescattering
no distortion by pion rescattering expected in
mass range of interest further reduced by
requiring T?gt150 MeV
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Beam line
Beam Momentum 2.0 GeV/c K1.8 or High Momentum
Beam line
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Spectrometer

• p-p ? wn _at_ 2.0 GeV/c
• ? p0 g
• ? gg
• Target Carbon 1cm
• Neutron Detector
• Flight length 7m
• Gamma Detector
• Borrow from
• T-violation
• Charged Track sweep
• SKS?

Neutron
Beam
Gamma Detector
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Neutron Detector
Neutron Detector Scintillation counter or
Resistive Plate To achieve 30 MeV/c2 of missing
mass resolution, 80 ps timing resolution is
required 7 m flight path 30 MeV/c2 20 m flight
path 8.9 MeV/c2
cf proton SKS 1.3 GeV/c 100 bending
0.17 2.0 GeV/c 36 bending 0.47 missing
mass resolution _at_ w mass 8 MeV/c2
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Gamma detector
CsI EMCalorimeter Borrow from T-violation
experiment Mass resolution
?E/E 1 /vE
?E/E 3 /vE
DE/E 2.8 _at_ 200MeV (?E/E 1.7 /vE ? ) (D.V.
Dementyev et al., Nucl. Instrum. Meth.
A440(2000), 151)
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Yield Estimation
Summary plot of p-p ? wn for backward w (G.
Penner and U. Mosel, nucl-th/0111024, J. Keyne et
al., Phys. Rev. D 14, 28 (1976))
0.14 mb/sr _at_ ?s 1.8 GeV same cross section is
assumed. Beam intensity 107 / spill, 3 sec spill
length) Neutron Detector acceptance Dq 1(30
cm x 30 cm _at_ 7m Gamma Detector acceptance 75
for single, 42 for triple Branching Ratio 8.9
Optimistic obtained yield is 31650
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Summary

• New experiment for exploring hadron mass property
  in nuclear medium is being proposed.
• K1.8 beam line can be used. High momentum beam
  line is suitable.
• Proposed experiment aims performing two
  measurements simultaneously. The experiment seems
  feasible, at least not impossible.

Next tasks for proposal

• Background and trigger should be considered
  carefully.
• Quasi free reaction
• p-p ? p0n
• 2 p0 ? 4 g (1 gamma missing)
• Detector RD should be done soon.

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Thanks

• R.S. Hayano (University of Tokyo)
• Y. Kuroda, A. Ishida, T. Ichikawa
• K. Itahashi, H. Ohnishi, H. Outa, M. Iwasaki, T.
  Suzuki, F. Sakuma, S. Yokkaichi (RIKEN)
• T. Takahashi (KEK)
• H. Nagahiro (RCNP)
• S. Hirenzaki (Nara W University)