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

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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

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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

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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

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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

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• 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

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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%

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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.

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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 ）

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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 %

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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

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H. Nagahiro et al

2366 2755 938

Generation of

Decay of (Invariant Mass)

Large abs.No int.

Large abs.Large int.

Final SpectrumFinal Spectrum

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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

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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.

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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

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