Photoproduction of η meson from proton at LEPS2

2014/2/20Toshikazu Hashimoto @Kyoto Univ.

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Physics Motivation

Particle Data Group 2012

The family are predicted in quark model, but large number of them haven't been identified experimentally so far.

2

feature of N channel

• production probes only contribution (not ).

• has components.　→ we expect strong coupling to which have large components.

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A. Sarantev , CPC2009, 33(12)

S11(1535) P13(1720) D15(2070)

photoproduction from proton at LEPS

• Backward-angle photoproduction • 1.6• was measured in the missing-mass spectrum for

𝛾

p𝜂

M. Sumihama et al., PRC80,0522014

bump structure exist above 2GeV ?

M. Sumihama et al., PRC80,0522015

result of LEPS experiment

M. Williams et al., PRC80,045213V. Crede et al., PRC80,055202

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comparison to other experiment

descrepancy between LEPS and CLAS exists.→ reconfirm at LEPS2? or reaction mechanism?

Beam Asymmetry𝑑𝜎𝑑Ω=(𝑑𝜎𝑑Ω )

0{1− 𝑃𝛾

❑Σ cos (2𝜙 ) }

: incident photon polarization : Beam Asymmetry : azimutial orientation of reaction plane to beam polarization

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D. Elsner et al., EPJA 33,147

ELSA LEPS2coherent breamstrahlung

polarization

polarization

D. Elsner et al., EPJ A 33,147

• differential cross section oscillate.

• This amplitude is .• Spin-dependent

amplitude can be measured.

• High is necessary for precise study of

𝜙

𝛾

𝜂p

=1250 ～ 1340 MeV

photoproduction off proton

Beam Polarization

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D. Elsner et al., EPJA 33,147

ELSA

LEPS2

coherent breamstrahlung

polarization polarization

backward compton

LEPS2 Beamline

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e-

1.3 ～ 3.0GeVBeam Intensity ～ 10Mcps

Experimental setup

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Drift ChamberBGO EGG

𝜂𝛾 p𝛾

𝛾

TOF wall RPC

zx

y

target

z = 1.5m z = 4.0m z = 12.5m

11z = 1.5m z = 4.0m z = 12.5m

BGOEGG

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Drift ChamberBGO EGG

𝜂𝛾 p𝛾

𝛾

TOF counter RPC

• 1320 BGO crystals• egg-like shape• 60 crystals/layer

zx

y

13 forward layers9 backward layers

144°

12z = 1.5m z = 4.0m z = 12.5m

Target,CDC,Scinti

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Drift ChamberBGO EGG

𝜂𝛾 p𝛾

𝛾

TOF wall RPC

• target is LiquidH2.

• surrounding CDC.• detecting charged particles

Target

Scintilation counter

Cylindrical Drift Chamber

• covering in polar angle.

zx

y

zx

y

Forward Drift Chamber

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Drift ChamberBGO EGG

𝜂𝛾 p𝛾

𝛾

TOF wall RPC

𝛾𝑝→𝜂𝑝

• effective area is 1280mm

• covering in polar angle• 1.5m from target• angular resolution is

FDCBGO

13z = 1.5m z = 4.0m z = 12.5m

14z = 1.5m z = 4.0m z = 12.5m

TOF wall

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Drift ChamberBGO EGG

𝜂𝛾 p𝛾

𝛾

TOF wall RPC

𝛾𝑝→𝜂𝑝

• covering in polar angle• 4.0m from target• timing resolution is 60ps (KEK)• timing resolution is 175ps (RS)

RPC

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Drift ChamberBGO EGG

𝛾𝛾

TOF wall RPC

• time resolution is 50 ps• 12.5 m from target• vertical length is 2m• horizontal length is 3.2m• covering in polar angle

15z = 1.5m z = 4.0m z = 12.5m

2 m

3.2 m

s is detected with BGO egg.Forward Proton is detected with FDC and TOF.Sideway Proton is detected with CDC and Scintilator.

MC simulation of

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BGOEGG area BGOEGG area

𝜂→2𝛾 𝜂→3𝜋 0→6𝛾

[deg] [deg]

[GeV

/c]

[GeV

/c]

s is detected with BGO egg.Forward Proton is detected with FDC and TOF.Sideway Proton is detected with CDC and Scintilator.

MC simulation of

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𝜂→2𝛾 𝜂→3𝜋 0→6𝛾

[deg] [deg]

[GeV

/c]

[GeV

/c]

FDC and TOFarea

FDC and TOFarea

CDC and Scintiarea

CDC and Scintiarea

proton go through BGO

proton go through BGO

Acceptance of detection is showed as function of polar angle.

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cos𝜃𝜂 c .m.   cos𝜃𝜂 c .m.  

+ p

+ p

measured in LEPS experiment

measured in LEPS experiment

Acce

ptan

ce

Acce

ptan

ce

𝜂→2𝛾 𝜂→3𝜋 0→6𝛾

branting ratio is 39% branting ratio is 33%average of Acc. is 0.26 0.39 * 0.26 = 0.10

average of Acc. is 0.18 0.33* 0.18 = 0.06

Yield estimation

Yield ofprocess • ~ 0.05 /str : ref) M. Sumihama et al., PRC80,052201

• 4.0 cm LH2 target ⇒• Photon beam intensity ~1Mcps ⇒ generate counts/month• Assume 16% acceptance ⇒ yield ~60k counts/month

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MC simulation of

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Background

(0.05 /str )

(br =39%) (br =33%)

𝛾𝑝→𝜋 0𝜂𝑝𝛾𝑝→𝜂 ′𝑝→𝜋𝜋𝜂𝑝𝛾𝑝→𝜛𝑝→𝜋 0𝛾𝑝𝛾𝑝→𝜋 0𝜋 0𝑝

Signal detect with FDC and TOF

detect with BGOEGG

3 0.7

5.5 J.Barth et al, EPJA 18, 117

I.Horn et al, PRL 101, 202002

V. Crede et al., PRC80,055202

~10 M. Sumihama et al., PRC80,052201

MC simulation of

invariant mass [GeV/c2]

s invariant mass

select mass region of mass cut

𝛾𝑝→𝜋 0𝜂𝑝 (2 and 6)

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cut region is

main background is and

𝛾𝑝→𝜂 ′𝑝→𝜋 𝜋 𝜂𝑝 combinational combinational combinational

All

arbi

trar

y

MC simulation of

missing mass

p mass cut

missing mass [GeV/c2] 22

arbi

trar

y

𝛾𝑝→𝜋 0𝜂𝑝 (2 and 6)

𝛾𝑝→𝜂 ′𝑝→𝜋 𝜋 𝜂𝑝 combinational combinational combinational

All

background decrease to 4.1%

cut region is

Δ 𝐸𝛾=15MeV

MC simulation of angle between and protonIf reaction is two-body decay, the equation holds.

𝜃𝜂c . m .+𝜃𝑝 c .m.𝜑𝜂 c. m .−𝜑𝑝c . m.

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cut cut

[deg] [deg]

𝛾𝑝→𝜋 0𝜂𝑝 (2 and 6)

𝛾𝑝→𝜂 ′𝑝→𝜋 𝜋 𝜂𝑝 combinational combinational combinational

All

arbi

trar

y

arbi

trar

ybackground decrease to 1.1%

back to back

Summary• production has the advantage of resonance study.• A bump structure has been observed above 2.0GeV in total

energy in LEPS experiment, but this is not consistent with CLAS experiment.

• We are planning to measure diffrential cross section of photoproduction and beam asymmetry at LEPS2.

• We want to decide origin of bump structure,N* or production mechanism.

• 60k events/month in BGO experiment at LEPS2.• Background decrease to 1% by detecting proton with FDC and

TOF counter.• We will estimate background when proton is detected with CDC

and Scinti.• Data taking will be started in April. 24