omega%20meson%20in%20nucleus,%20experimental%20study

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omega meson in nucleus, experimental study

• K. Ozawa
• (Univ. of Tokyo)

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Contents

• Physics motivation for w meson
• Experimental approaches
• Previous experiments
• Proposed experiment at J-PARC
• Summary

Collaboration with, or helped by Prof. R.S.
Hayano, Prof. H. Nagahiro, Prof. S.
Hirenzaki, K. Utsunomiya, S. Masumoto, Y.
Komatsu, Y. Watanabe I need more helps from you!
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Hadrons in QCD

• hadron can be undestood as
• excitation of QCD vacuum

Precise measurements of hadron property at
nuclear medium can provide QCD information

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

Mass GeV
Modification of vector meson mass is expected,
even at nuclear density.
Figure by Prof. V. Metag
Id like to focus on vector mesons, such as w.
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Experimental approaches

• Meson spectroscopy

• Direct measurements of mass spectra

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Results from LEPS
Chiral 05 N. Muramatsu
There some hints of a bound state.
Missing mass resolution of 30MeV/c2 is expected.
Forward measurements are essential.
Large statistics data and further analysis are
waited.
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Results from CBELSA/TAPS
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 results II
Large w width in nuclei due to w-N interaction.
M. Kotulla et al, PRL 100 (2008) 192302
Essential Focus on Small momentum Issue Yield
estimation of decays
60 MeV/c2 even at stopped w.
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Proposed experiment
Two measurements at the same time.

• Meson spectroscopy
• Direct measurements of mass spectra

Clear measurements in small momentum! Bound w
state search
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J-PARC

• Beam Energy 50GeV
• (30GeV for Slow Beam)
• Beam Intensity 3.3x1014ppp, 15mA
• (21014ppp, 9mA)

Hadron Hall
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Hadron hall
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Reaction and Beam momentum
Stopped w meson
Generate w meson using p beam. Emitted neutron is
detected at 0?. Decay of w meson is detected.
If p momentum is chosen carefully, momentum
transfer will be 0.
To generate stopped modified w meson, beam
momentum is 1.8 GeV/c. (K1.8 can be used.) As a
result of KEK-E325, 9 mass decreasing (70
MeV/c2) can be expected. Focus on forward
(2).
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Note Forward measurements

• Forward proton
• Good
• High mass resolution
• High efficiency
• Bad
• No separation between proton and p beam.
  Triggering generated protons is too hard.
• Forward 12will be excluded.
• Forward neutron
• Good
• 0 degree measurements
• Bad
• Need long TOF for high resolution
• Low efficiency lt 30

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Experimental setup

• p-p ? wn _at_ 1.8 GeV/c
• ? p0 g
• ? gg
• Target Carbon 6cm
• Small radiation loss
• Clear calculation of w bound state
• Ca, Nb, LH2 are under consideration.
• Neutron Detector
• Flight length 7m
• 60cm x 60 cm (2)
• Gamma Detector
• Assume T-violations
• 75 of 4p
• SKS for charge sweep

Neutron
Beam
Gamma Detector
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Neutron Measurement
Timing resolution Beam test is done at Tohoku
test line Timing resolution of 80 ps is achieved
(for charged particle). It corresponds to mass
resolution of 22 MeV/c2.
Neutron Efficiency Iron plate (1cm t) is placed
to increase neutron efficiency. Efficiency is
evaluated using a hadron transport code,
FLUKA. Neutron efficiency of 25 can be achieved.
We can not see a clear bound peak. At this
moment, there is no beam line at J-PARC to have
enough TOF length and beam energy
Bound region
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Gamma detector
CsI EMCalorimeter T-violations one is assumed.
Obtained p meson spectra for stopped K decays
(D.V. Dementyev et al., Nucl. Instrum. Meth.
A440(2000), 151)
Assumed Energy Resolution
Muon holes should be filled by additional
crystals. Acceptance for w is evaluated as 90.
Fast simulation is tuned to reproduce existing
data.
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Decay Yield Evaluation
Based on measured crosssection 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))
H. Nagahiro et al calculation based on the cross
section and known nuclear effects. Assumed
potential is consistent with w absorption in
nucleus.
Production cross section 0.02 mb/sr (CM) _at_ ?s
2.0 GeV 0.17 mb/sr (Lab) _at_ ?s 2.0 GeV Beam
intensity 107 / spill, 6 sec spill length Neutron
Detector acceptance Dq 2(60 cm x 60 cm _at_
7m) Gamma Detector acceptance 90 for w Radiation
loss in target 11 Survival probability in
final state interaction
60 Beam Time 100
shifts Branching Ratio 1.3
8.9
Total
No interact
Interact w nuclei
Large width 60 MeV/c2
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Results for three potentials
Generation of w
H. Nagahiro et al
Large abs. No int.
Large abs. Large int.
Decay of w (Invariant Mass)
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Final Spectrum
One can select bound region as Energy of w lt E0,
which is measured by the forward neutron counter.
Bound region
Including Background Main background is 2p0
decays and 1g missing
Strong kin. effects
Invariant Mass spectrum for the bound region
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Mass Correlation

• Invariant Mass VS Missing Energy
• Non-correlated model

Correlated model
Correlation analysis will useful for reducing
kinematical effects.
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Issue

• Its hard to find a bound state peak using
  forward neutron measurements at J-PARC due to a
  limited hadron hall space at this moment.
• Note proton measurements are also hard.
• Effects of relatively large angle to form a bound
  state
• Effects of beam spread and halo for a trigger.
• When we focus on mass modification of w meson
  in nucleus, large nucleus should be used.
• In addition, we can measure a large mass width
  (absorption cross section) of w in nucleus in
  small momentum range.

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Summary

• Hadrons can be understood as a excitation of QCD
  vacuum and carried vacuum information.
• Experimental efforts are underway to investigate
  this physics. Some results are already reported.
• Still, there are problems to extract physics
  information.
• New experiments for obtaining further physics
  information is being proposed.
• Measurement with stopped mesons
• Measurement of bound states