New Detector Design for Combined Measurements

of Omega MesonKazuki UtsunomiyaKyoichiro Ozawa, Yosuke Watanabe, Shinichi Masumoto, Yusuke Komatsu, Tamotsu Sato, - The University of TokyoSatoshi Yokkaichi, Kazuya Aoki, - RIKENTomoya Tsuji, - CNS, The University of Tokyo

October 17, 2009 KE0002

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Contents

Combined measurements of w meson mass

Main two detectors• Neutron counter• Gamma-ray detector

Summary

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Combined Measurements of w

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“ORIGIN OF HADRON MASS”Meson mass modification in nucleusNuclear bound state

XnA w

0

Neutron Counter- Missing mass of w.- w initial condition is restricted.Gamma-ray Detector- Invariant mass of w.

Hadron Hall @ J-PARC

1.8 GeV/c momentum

w mesons are almost

stopped.

Main Two Detectors

Gamma-ray DetectorCsI(Tl) calorimerter

Neutron CounterTOF type Scintillator

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Target

Neutrons

Charged Particles

1.8GeV 7m

Flight path

n

140cm

100cm

n60cm

21cm

60cm

Neutron Counter48 PMTs

Hamamatsu H2431-5024 scintillators

Saint-Gobain Crystals BC408 (600 x 100 x 30mm)

4 iron plates

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Required performance• Time resolution : less or equal 80 psec• Neutron Efficiency : 30%

Double-end readout.

6 scintillators – 4 layers.

~5deg. neutron acceptance.

wStopped

7mTime-Of-Flight (TOF)

.deg0n ~1.8GeV/c

Expected performanceTime resolution : 55 psec

Beam test using electron beam at Fuji test beam line (KEK) and at Kakuriken (Tohoku Univ.).

Neutron efficiency : 25.6%(Scintillator and 1cm thick iron plates, 4 layers)Monte Carlo simulation using

the FLUKA package.

6Missing mass spectrum can be measured.

Missing mass spectrum of w

MeV/c2

Mass of w782.65

703.24Δ1.9%

Neu

tron

det

ectio

n effi

cien

cy

Gamma-ray Detector768 CsI(Tl) crystalsPIN photodiode readout12 muon holes for T-violation experiment

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[NIM A 440 (2000) 151]

The detector was used at KEK E246 experiment.

Under upgrading for T-violation experiment(E06) at J-PARC.

This detector will be reused and be customized for our combined measurements.

4 of 75%

Simulation for w mass reconstructionHow does the invariant mass of w meson look like?1. Make a simulation code to reproduce an existing

experiment data. [NIM A 440 (2000) 151] [NIM A 494 (2002) 318]

2. Run a simulation for w meson mass reconstruction.

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Our experiment Existing experimentw 0

0K

Mass of 0

• Energy resolution• Angular resolution• Shower leak

Evaluate by

Simulation

Simulation check by existing data

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Existing experiment data

Simulation for kaon

235.7MeV5.2%

234.7MeV4.9%

123.4MeV/c2

8.0%

127.2MeV/c2

6.9%

Opening angle Energy of 0 Invariant mass of 0Reproducing of an existing experiment data is very well.

w mass reconstruction

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A large tail is caused by muon hole effects. With cut

MeV/c2

All event

MeV/c2

w 0

Away from hole

Energy of

Mass of 0

Fiducial cut

Tail cut

Combined measurements of w

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The mass modification and the nuclear bound state can be measured with these two detectors.

MeV/c2MeV/c2MeV/c2

9% Shifted mass event

Invariantmass method

Missingmass method

Mass of w782.65

SummaryThe missing mass spectrum can be measured by neutron

counter.The invariant mass spectrum can be measured by gamma-ray

detector without w mass tail.Using these two detectors, the w mass modification in

nucleus and the nuclear bound state can be measured.

Out lookOur proposal will be discussed at J-PARC 9th PAC meeting,

January 15 – 17, 2010.Construct the spectrometer!!

12Shall we collaborate?

BACK UP

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Comparison betweensimulation and existing experimentOpening angle between two gamma-rays

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Existing experiment

Simulation

67.7 deg.

Left: All event.Right: Energy cut for small opening angle.

1.01.021

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EEEE

Reproducing opening angle is very well.

Comparison betweensimulation and existing experimentEnergy of 0

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Existing experiment

Simulation

242.5MeV4.1%

Left: All event.Right: Away from muon holes.

Reproducing energy of 0 is very well.

235.7MeV5.2%

234.7MeV4.9%

242.2MeV4.1%

Comparison betweensimulation and existing experimentInvariant mass of 0

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Existing experiment

Simulation

128.0MeV/c2

7.0%123.4MeV/c2

8.0%

127.2MeV/c2

6.9%133.0MeV/c2

5.6%

Left: All event.Right: Away from muon holes.

Reproducing mass of 0 is very well.

Fiducial cut and pion mass tail cut

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Pion mass tail cut

Fidu

cial

cut

With or without muon hole

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Muon hole No muon hole

Muon hole effect