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omega meson omega meson in nucleus, in nucleus,
experimental studyexperimental studyK. Ozawa K. Ozawa
(Univ. of Tokyo)(Univ. of Tokyo)
ContentsContents
• Physics motivation for meson • Experimental approaches• Previous experiments• Proposed experiment at J-PARC• Summary
2009/2/22 NQCD symposium, K. Ozawa 2
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!
Hadrons in QCDHadrons in QCDM
ass
[GeV
]
• 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.
many experimental and theoritical efforts to search for and study in-medium modifications of hadrons
2009/2/22 3NQCD symposium, K. Ozawa
Figure by Prof. V. Metag
I’d like to focus on vector mesons, such as .
Experimental approaches
– Direct measurements of mass spectra
Emitted Proton Neutronp
Nucleon Hole
Target
Decay
Meson
– Meson spectroscopy
2009/9/18 4PUHF WS, K. Ozawa
Results from LEPSResults from LEPS
2009/2/22 NQCD symposium, K. Ozawa 5
Chiral ’05N. 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.
Results from CBELSA/TAPSResults from CBELSA/TAPS
disadvantage:
• 0-rescattering
advantage:
• 0 large branching ratio (8 %)
• no -contribution ( 0 : 7 10-4)
p
A + X
0
2ppm
D. Trnka et al., PRL 94 (2005) 192203after background subtraction
%.mm 03
TAPS, TAPS, 00 with with +A+A
2009/2/22 NQCD symposium, K. Ozawa 6m = m0 (1 - /0) for = 0.13
TAPS results IITAPS results II
2009/2/22 NQCD symposium, K. Ozawa 7
M. Kotulla et al, PRL 100 (2008) 192302
Large width in nuclei due to -N interaction.
60 MeV/c2 even at stopped .
Essential:Focus on Small momentumIssue:Yield estimation of decays
Proposed experimentProposed experiment
Emitted Neutron
Nucleon Hole
Target
0 decay
– Meson spectroscopy– Direct measurements of mass spectra
2009/2/22 8NQCD symposium, K. OzawaClear measurements in small momentum!Bound state search
Two measurements at the same time.
J-PARCJ-PARC
2009/2/22 NQCD symposium, K. Ozawa 9
• Beam Energy : 50 GeV(30GeV for Slow
Beam)• Beam Intensity: 3.3x1014ppp, 15A
(2×1014ppp, 9A)
Hadron Hall
2009/2/22 NQCD symposium, K. Ozawa
Hadron hallHadron hallNP-HALL
56m(L)×60m(W)
10
Reaction and Beam momentumReaction and Beam momentum
2009/2/22 NQCD symposium, K. Ozawa 11
Stopped meson
n
A + N+X
0
2ppm
To generate stopped modified 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°).
Generate meson using beam.Emitted neutron is detected at 0.Decay of meson is detected.
If momentum is chosen carefully, momentum transfer will be ~ 0.
m
om
entu
m [
GeV
/c]
0.2
0.4
0 2 4 momentum [GeV/c]
0
Note: Forward measurementsNote: Forward measurements• Forward proton
– Good• High mass resolution• High efficiency
– Bad• No separation between proton and beam.
Triggering generated protons is too hard.• Forward 1~2°will be excluded.
• Forward neutron– Good
• 0 degree measurements– Bad
• Need long TOF for high resolution• Low efficiency < 30%
2009/2/22 NQCD symposium, K. Ozawa 12
2009/2/22 13NQCD symposium, K. Ozawa
Experimental setup-p n @ 1.8 GeV/c
0
Target: Carbon 6cmSmall radiation lossClear calculation of bound state Ca, Nb, LH2 are under consideration.
Neutron DetectorFlight length 7m60cm x 60 cm (~2°)
Gamma DetectorAssume T-violation’s 75% of 4
SKS for charge sweep
Beam Neutron
Gamma Detector
Neutron MeasurementTiming resolution
Beam test is done at Tohoku test lineTiming resolution of 80 ps is achieved (for charged particle).It corresponds to mass resolution of 22 MeV/c2.
2009/2/22 14NQCD symposium, K. Ozawa
Neutron EfficiencyIron 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.
Bound region
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
Gamma detectorCsI EMCalorimeter
T-violation’s one is assumed.( D.V. Dementyev et al., Nucl. Instrum. Meth. A440(2000), 151 )
2009/2/22 15NQCD symposium, K. Ozawa
Assumed Energy Resolution
Obtained meson spectra for stopped K decays
Muon holes should be filled by additional crystals.Acceptance for is evaluated as 90%.
Fast simulation is tuned to reproduce existing data.
Fast simulation is tuned to reproduce existing data.
Decay Yield EvaluationBased on measured crosssection of -p n for backward (G. Penner and U. Mosel, nucl-th/0111024,J. Keyne et al., Phys. Rev. D 14, 28 (1976))
Production cross section0.02 mb/sr (CM) @ s = 2.0 GeV 0.17 mb/sr (Lab) @ s = 2.0 GeV
Beam intensity107 / spill, 6 sec spill length
Neutron Detector acceptance = 2°(60 cm x 60 cm @ 7m)
Gamma Detector acceptance90% for
Radiation loss in target 11%Survival probability in final state interaction
60%Beam Time 100 shiftsBranching Ratio 1.3 % 8.9 %
2009/2/22 NQCD symposium, K. Ozawa 16
H. Nagahiro et al calculation based on the cross section and known nuclear effects.Assumed potential is consistent with absorption in nucleus.
Interact w nuclei
No interact
Total
Large width ~ 60 MeV/c2
% 26.1*
0,
*
totalabstotal
Results for three potentialsResults for three potentials
2009/2/22 NQCD symposium, K. Ozawa 17
H. Nagahiro et al
2366 2755 938
Generation of
Decay of (Invariant Mass)
Large abs.No int.
Large abs.Large int.
Final SpectrumFinal Spectrum
2009/2/22 NQCD symposium, K. Ozawa 18
Including Background: Main background is 2 decays and 1 missing
Bound region
One can select bound region as Energy of < E0, which is measured by the forward neutron counter.
Invariant Mass spectrum for the bound region
Strong kin. effects
““Mass” CorrelationMass” Correlation
2009/2/22 NQCD symposium, K. Ozawa 19
Invariant Mass VS Missing EnergyNon-correlated model
Correlated model
Correlation analysis will useful for reducing kinematical effects.
IssueIssue• It’s 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 meson in nucleus, large nucleus should be used.– In addition, we can measure a large mass
width (absorption cross section) of in nucleus in small momentum range.
2009/2/22 NQCD symposium, K. Ozawa 20
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
2009/2/22 NQCD symposium, K. Ozawa 21