η photoproduction from proton

Photoproduction of η meson
from proton at LEPS2
2014/2/20
Toshikazu Hashimoto @Kyoto Univ.
1
Physics Motivation
The 𝑁 ∗ family are
predicted in quark
model,
but large number of
them haven't been
identified
experimentally so far.
Particle Data Group 2012
2
feature of 𝜂N channel
• 𝜂 production probes
only 𝑁 ∗ contribution
(not Δ∗ ).
• 𝜂 has 𝑠𝑠 components.
→we expect strong
coupling to 𝑁 ∗ which
have large s𝑠 components.
−
1 2 S11(1535)
+
3 2 P13(1720)
−
5 2 D15(2070)
A. Sarantev , CPC2009, 33(12)
3
𝜂 photoproduction from proton at LEPS
• Backward-angle 𝜂 photoproduction
(−1 < cos Θ𝑐𝑚 < −0.6)
• 1.6 GeV < 𝐸𝛾 < 2.4 GeV
• 𝜂 was measured in the missing-mass spectrum for 𝛾𝑝 → 𝑝𝑋
p
𝜂
𝛾
4
M. Sumihama et al., PRC80,052201
result of LEPS experiment
bump structure exist
above 2GeV ?
M. Sumihama et al., PRC80,052201
5
comparison to other experiment
descrepancy between LEPS
and CLAS exists.
→ reconfirm at LEPS2
𝑁 ∗ ? or reaction mechanism?
V. Crede et al., PRC80,055202
6
M. Williams et al., PRC80,045213
Beam Asymmetry
•
𝑑𝜎
𝑑Ω
=
𝑑𝜎
𝑑Ω 0
𝛾
1 − 𝑃𝛾 Σ cos 2𝜙
p
𝜙
𝜂
𝑃𝛾 : incident photon polarization
Σ : Beam Asymmetry
𝜙 : azimutial orientation of reaction plane to beam polarization
ELSA
coherent
breamstrahlung
•
LEPS2
•
•
polarization
~ 10%
𝐸𝛾 =1250 ～
1340 MeV
D. Elsner et al., EPJA 33,147
D. Elsner et al., EPJ A 33,147
𝜂 photoproduction
•
differential cross
section oscillate.
This amplitude is
𝑃𝛾 Σ.
polarization 50~ 90%
Spin-dependent
amplitude can be
measured.
High 𝑃𝛾 is necessary
for precise study of Σ
Beam Polarization
LEPS2
backward compton
polarization ~ 10%
polarization 60~ 90%
D. Elsner et al., EPJA 33,147
ELSA
coherent
breamstrahlung
LEPS2 Beamline
e-
𝐸𝛾 1.3～3.0GeV
Beam Intensity ～10Mcps
9
Experimental setup
x
y
z
𝛾
𝛾
𝜂
p
target
𝛾
BGO EGG
Drift Chamber
TOF wall
z = 1.5m
z = 4.0m
RPC
10
z = 12.5m
BGOEGG
x
9 backward
layers
y
13 forward layers
z
144°
𝛾
𝛾
𝜂
p
𝛾
BGO EGG
• 1320 BGO crystals
• egg-like shape
• 60 crystals/layer
TOF counter
Drift Chamber
z = 1.5m
z = 4.0m
RPC
11
z = 12.5m
Target,CDC,Scinti
x
Target
• target is LiquidH2.
y
z
𝛾
Cylindrical Drift Chamber
𝛾
𝜂
𝛾
BGO EGG
• covering 13°~160° in polar
angle.
p
Scintilation counter
• surrounding CDC.
• detecting charged particles
Drift Chamber
TOF wall
z = 1.5m
z = 4.0m
RPC
12
z = 12.5m
FDC
BGO
𝛾𝑝 → 𝜂𝑝
x
•
•
•
•
Forward Drift Chamber
y
z
𝛾
p
𝜂
𝛾
effective area is
𝜙1280mm 𝛾
covering 24° in polar
angle
1.5m from target
BGOresolution
EGG
angular
is
0.5°
Drift Chamber
TOF wall
z = 1.5m
z = 4.0m
RPC
13
z = 12.5m
TOF wall
𝛾𝑝 → 𝜂𝑝
𝛾
•
•
•
•
𝜂
𝛾
p
𝛾
covering 7°~24° in polar angle
4.0m from target
timing resolution is 60ps (KEK)
BGO EGG
timing resolution is 175psDrift
(RS)Chamber
z = 1.5m
TOF wall
z = 4.0m
RPC
14
z = 12.5m
RPC
3.2 m
2m
•
•
•
•
•
𝛾 resolution is 50 ps
time
𝛾 target
12.5 m from
vertical length is 2m
horizontal length is 3.2m
BGO EGG7° in polarDrift
covering
angle
Chamber
z = 1.5m
TOF wall
z = 4.0m
RPC
15
z = 12.5m
MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
𝛾s is detected with BGO egg.
Forward Proton is detected with FDC and TOF.
Sideway Proton is detected with CDC and Scintilator.
𝜂 → 3𝜋 0 → 6𝛾
𝑃γ lab [GeV/c]
𝑃γ lab [GeV/c]
𝜂 → 2𝛾
BGOEGG area
𝜃γ lab [deg]
BGOEGG area
16
𝜃γ lab [deg]
MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
𝛾s is detected with BGO egg.
Forward Proton is detected with FDC and TOF.
Sideway Proton is detected with CDC and Scintilator.
𝜂 → 3𝜋 0 → 6𝛾
proton
go through
BGO
𝑃𝑝 lab [GeV/c]
𝑃𝑝 lab [GeV/c]
𝜂 → 2𝛾
FDC and TOF CDC and Scinti
area
area
𝜃𝑝 lab [deg]
proton
go through
BGO
FDC and TOF CDC and Scinti
area
area
𝜃𝑝 lab 17[deg]
Acceptance of η𝑝 detection is showed as function
of 𝜂 polar angle.
𝜂 → 3𝜋 0 → 6𝛾
Acceptance
𝛾+p
𝛾
measured in LEPS
experiment
cos 𝜃𝜂c.m.
branting ratio is 39%
average of Acc. is 0.26
0.39 * 0.26 = 0.10
Acceptance
𝜂 → 2𝛾
𝛾+p
𝛾
measured in LEPS
experiment
cos 𝜃𝜂c.m.
branting ratio is 33%
average of Acc. is 0.18
0.33* 0.18 = 0.06
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Yield estimation
Yield of 𝛾𝑝 → 𝜂𝑝 process
• 𝑑𝜎 𝑑Ω (𝛾𝑝 → 𝜂𝑝)~ 0.05 𝜇b/str : ref) M. Sumihama et al., PRC80,052201
• 4.0 cm LH2 target ⇒ 3.3 × 10−9 𝜇b−1
• Photon beam intensity ~1Mcps
⇒ 𝜂 generate
4.2 × 105 counts/month
• Assume 16% acceptance
⇒ yield ~60k counts/month
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MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
Signal
𝛾𝑝 → 𝜂𝑝
detect with FDC and TOF
(0.05 𝜇b/str )
detect with BGOEGG
𝛾𝛾
(br =39%)
3𝜋 0 → 6𝛾
(br =33%)
Background
𝛾𝑝 → 𝜋 0 𝜂𝑝
𝛾𝑝 → 𝜂′𝑝 → 𝜋𝜋𝜂𝑝
𝛾𝑝 → 𝜋 0 𝜋 0 𝑝
𝛾𝑝 → 𝜛𝑝 → 𝜋 0 𝛾𝑝
3 𝜇b
0.7 𝜇b
~10 𝜇b ?
5.5 𝜇b
I.Horn et al, PRL 101, 202002
V. Crede et al., PRC80,055202
M. Sumihama et al., PRC80,052201
J.Barth et al, EPJA 18, 117
20
MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
𝛾s invariant mass
select mass region of 𝜂
arbitrary
𝜂 mass cut
All
𝛾𝑝 → 𝜂𝑝 (2𝛾 and 6𝛾)
𝛾𝑝 → 𝜋 0 𝜂𝑝
𝛾𝑝 → 𝜂′𝑝 → 𝜋𝜋𝜂𝑝
𝛾𝑝 → 𝜋 0 𝜂𝑝 combinational
𝛾𝑝 → 𝜔𝑝 → 𝜋 0 𝛾 combinational
𝛾𝑝 → 𝜋 0 𝜋 0 𝑝 combinational
𝜎𝑀𝜂 : 20MeV/𝑐 2
cut region is ±3𝜎
main background is
𝜋 0 𝜋 0 and 𝜋 0 𝜂
𝛾𝑠 invariant mass [GeV/c2]
21
arbitrary
MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
"𝜂" missing mass
Δ𝐸𝛾 = 15MeV
p mass cut
All
𝛾𝑝 → 𝜂𝑝 (2𝛾 and 6𝛾)
𝛾𝑝 → 𝜋 0 𝜂𝑝
𝛾𝑝 → 𝜂′𝑝 → 𝜋𝜋𝜂𝑝
𝛾𝑝 → 𝜋 0 𝜂𝑝 combinational
𝛾𝑝 → 𝜔𝑝 → 𝜋 0 𝛾 combinational
𝛾𝑝 → 𝜋 0 𝜋 0 𝑝 combinational
𝜎𝑀𝑝 : 60MeV/𝑐 2
cut region is ±3𝜎
background decrease
to 4.1%
"𝜂" missing mass [GeV/c2]
22
MC simulation of 𝛾𝑝 → 𝜂𝑝 at 𝐸𝛾 = 2.4GeV
All
𝛾𝑝 → 𝜂𝑝 (2𝛾 and 6𝛾)
𝛾𝑝 → 𝜋 0 𝜂𝑝
𝛾𝑝 → 𝜂′𝑝 → 𝜋𝜋𝜂𝑝
𝛾𝑝 → 𝜋 0 𝜂𝑝 combinational
𝛾𝑝 → 𝜔𝑝 → 𝜋 0 𝛾 combinational
𝛾𝑝 → 𝜋 0 𝜋 0 𝑝 combinational
angle between 𝜂 and proton
𝜑𝜂c.m. − 𝜑𝑝c.m.
±3𝜎
𝜃𝜂c.m. + 𝜃𝑝c.m.
𝜑 cut
arbitrary
arbitrary
If reaction is two-body decay,
the equation holds.
𝜃𝜂c.m. = 180 − 𝜃𝑝c.m.
back to back
𝜑𝜂c.m. = 180 + 𝜑𝑝c.m.
𝜃 cut
±3𝜎
background decrease
to 1.1%
𝜙𝜂c.m. + 𝜙𝑝c.m. [deg]
23
𝜃𝜂c.m. + 𝜃𝑝c.m. [deg]
Summary
• 𝜂 production has the advantage of 𝑁 ∗ 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 𝜂
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.
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