k pp bound state search at leps2...
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-
K− pp bound state search
at LEPS2 experiment
A. O. Tokiyasu
ELPH, Tohoku University
NSMAT2016 @ Tohoku Universiyt
21th. Nov. 2016
-
Index
2
1. Physics Motivation
2. LEPS2 experiment
3. Schedule
4. Summary
-
Kaonic nuclei
☆K-N interactionLow energy Kp scattering
Kaonic hydrogen level shift
(KEK-PS E228)
strongly attractive (I = 0)
☆Kaonic nucleiKaon bound states with a few nucleons
(Akaishi-Yamazaki prediction)
B.E. ~several tenth MeV
Phys. Rev. C 65, 044005 (2002)
Study on K-pp bound state
Information on K–N interactionIf K-N interaction is very strong,
Kaon condensation inside NS
KK
K
KK
K
K
K
Lect. Notes Phys. 578 (2001) 175-202
-
Previous experiment
Experiment Reaction B.E. G
FINUDA
(Italy, 2005)
stopped K-
on Li, C
115±6±4 MeV 67±14±3 MeV
DISTO
(France, 2010)
p + p K+ + L + p 105±2±5 MeV 118±8±10MeV
J-PARC E15
(Japan, 2015)
3He(K-, n )X
X = L + p
event enhancement below K-pp threshold
J-PARC E27
(Japan, 2015)
d(p+, K+)X 95+18-17+30
-21 MeV 162+87
-45+66
-78 MeV
Measured B.E. and G are inconsistent!
-
Threoretical prediction
0
50
100
150
200
250
300
-140 -120 -100 -80 -60 -40 -20 0
■ exp● Chiral● non-chiral
J-PARC E27
DISTO
FINUDA
Almost all theoretical models
predict the existence of
the K-pp bound state!
- B.E. and Γ depends on models.
- inconsistent with exp results.
but
-B.E. (MeV)
Γ (
MeV
)
Situation is still controversial…
Other experiments are awaited.
Ref. NPA914(2013)270
-
Search for K-pp in LEPS
g + d K+ + p- + X
g beam ( Eg = 1.5 – 2.4 GeV) by Backward Compton Scattering methods.
K+ p- were detected at forward angles (cosΘ > 0.95)
Peak Structures were searched for in missing mass spectrum.
-
K-pp search via g + d K+ + p- + X
1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.70
0.5
1
1.5
2
2.2 2.25 2.3 2.35 2.4
0.5
1
1.5
MMd(K+π-) [GeV/c2]
d3σ
/dco
sΘla
b
K+d
cosΘ
lab
π-/dM
(μb
/ 2
0 [
MeV
/c2])
K-pp
threshold
Search
Region
2.22 2.24 2.26 2.28 2.3 2.32 2.34 2.360
0.5
1
1.5
2
2.5
3
3.5
= 20 MeVΓ
= 60 MeVΓ
= 100 MeVΓ
Upp
er L
imit
of
K- p
p p
rod
uct
ion
(d2σ
/dco
sΘla
b
K+d
cosΘ
lab
π-[μ
b])
MMd(K+π-) [GeV/c2]
(a) (b)
From likelihood ratio method;
G = 20 MeV : 0.17 - 0.55 mb
G = 60 MeV : 0.55 - 1.7 mb
G = 100 MeV : 1.1 - 2.9 mb
n
L
S
L*/S*
Search region 2.22 – 2.36 GeV/c2
Significant peak cannot be observed.
MM(K+p-) Upper limit of cross section (95% C.L.)
~10% of Q.F. processes
-
Lesson from LEPS experiment
SPring-8/LEPS2 experiment!
☆1st search results by the photo-induced reaction.
☆
-
LEPS2 project
K-pp search
Θ+ search
Study of Λ(1405) K* photo-production
Missing resonance search
η’-nuclei search
meson photo-production mechanism
Y-N scattering
dark photon search
high intensity g beam large acceptance detector
New field in hadron physics
Large acceptance
spectrometer
5 – 120° (charged)40 – 110° (photon)
multi laser
injection
+
low emittance
e- beam
~107 cps(LEPS x10)
-
SPring-8/LEPS2
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
11
☆ Acceptance5 – 120° (charged particle)
30 – 110° (γ)
☆ Momentum measurement- sideway (50– 120°)
TPC Δp/p ~ 0.04 (1 GeV/c)
- forward (5 – 50°)DC Δp/p ~ 0.01 (1 GeV/c)
☆ Particle Identification3σ separation up to 2.7 GeV/c
- sideway (5 – 50°)RPC (TOF)
- middle (30 – 60°)AC, RPC
11
SC
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
12
12
SC
Scintillator + MPPC
Time Resolution σ ~ 200ps
TDC_ch [ch](1ch = 50 ps)800 900 1000 1100 1200 1300 1400
co
un
t/ch
0
20
40
60
80
100
120
140
160
TDC_Mean-TDC_RF w/ CorrectionTDC_Mean-TDC_RF w/ Correction
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
13
13
• R=655 mm, 24 layer• σrφ=150 μm, σz=2 mm
SC
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
14
14
SC
1.3m
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
15
15
SC
K/π
20 cm
20 cm 16
cm
4 cm
PMT
6.5 cm
6.5 cm
6 cm
4 cm
n=1.03, 1.05
Efficiency > 99% for π+/-
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
16
16
SC
200 cm
25 cm
gas tight body
preamp
Long RPC 200 mm
σ < 70 ps
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
17
17
SC
Lead + Scintillator :14.3 X0
ΔE/E ~ 20 %
(100 MeV)
-
LEPS2 spectrometer system
2.22 m
g
TPC DC
g counter RPC
AC
Magnet (BNL-E949)
B=1 T
18
18
SC
☆Data Acquisition system
- Software
DAQ-Middleware
- Trigger system
1 charged particle
(min bias trigger)
J-PARC MTM
-
K-pp bound state search at LEPS2
• Minimum bias trigger (1 charged particle hit)
Search in many reactions
19
-
K-pp bound state search at LEPS2
• Minimum bias trigger (1 charged particle hit)
Search in many reactions
– γ + d K-pp + K+ + π-
– γ + d K-pp + Ks
– γ + d K-pp + K*0
– γ + d K-pn + K+
20
-
K-pp bound state search at LEPS2
• Minimum bias trigger
Search in many reactions
• Highly polarized γ
Select exchanged particle in t-channel.
21
-
K-pp bound state search at LEPS2
• Highly polarized γ
Select exchanged particle in t-channel.
22
E g K*K
p
unatural parity ex.P= -(-1)J
kaons
Parity filter
(γ、K*0)
-
K-pp bound state search at LEPS2
• Minimum bias trigger
Search in many reactions
• Highly polarized γ
Select exchanged particle in t-channel.
• 4π Spectrometer for charged particles and γ
All decay particles will be detected
23
-
K-pp bound state search at LEPS2
• 4π Spectrometer
production and decay particles will be detected
24
K-pp Λ p
Σ p
Λ p π0
Σ p π0
non-mesonic decay mode
mesonic decay mode
-
K-pp bound state search at LEPS2
• Minimum bias trigger
Search in many reactions
• Highly polarized γ
Select exchanged particle in t-channel.
• 4π Spectrometer
production and decay particles will be detected
25
But…
The photo-production cross section is very small
How many yield is expected?
-
Yield estimation
• in case γ + d Ks0 + K-pp Ks
0 + Λ + p
• Y(K-pp)
= photon number
* target number
* cross section
* BR(YP)
* Acceptance
26
-
• in case γ + d Ks0 + K-pp Ks
0 + Λ + p
• Y(K-pp)
= photon number
2 * 1014
* target number
8 * 1023
* cross section
20 nb
* BR(YP)
10 %
* Acceptance
30 %27
☆Assumption 1:Λ(1405) door-way
K-pp / Λ(1405) ~ 1%
☆Assumption 2:σ (γ p K+ Λ(1405))
σ (γ p Ks Λ(1405))
10 7cps γ, 200 days (optimistic)
Yield estimation
-
• in case γ + d Ks0 + K-pp Ks
0 + Λ + p
• Y(K-pp)
= photon number
2 * 1014
* target number
8 * 1023
* cross section
20 nb
* BR(YP)
10 %
* Acceptance
30 %28
~103 ev / year
- differential cross section
(t-dep, Eγ-dep…)
reaction mechanism
- Polarization Observable
Spin, Parity
(under study)
Yield estimation
-
Schedule• 2016 Oct.
– Trigger Study
• 2016 Nov. Detector install
– SC, TPC, DC, AC, RPC (not full setup)
• 2016 Dec. Commissioning run start
– Performance check of Spectrometer by using the γp pπ+π- reaction
29
DC
e+/e-
veto AC
BeamProfile Monitor
K/π ID AC
SC
TPC
γ beamCH2
p
π-
π+DAQ
supported byKAKENHI No.15H00839新学術公募研究「実験と観測で解き明かす中性子星の核物質」
-
Summary
☆K-pp bound state is a good probe to extract the information on
the structure inside neutron stars.
☆ LEPS2 : 107 cps γ beam, 4π spectrometer
Search for K-pp bound state via various reactions.
(g + d Ks0 +X, g + d K*0 + X…)
☆ LEPS2 Commissioning run starts from 2016 Dec.
☆ Collaboration is open. Let’s work together!
30
-
Back UP
31
-
K-pn, K-pn search
2 2.1 2.2 2.3 2.4 2.5 2.6 2.70
0.2
0.4
0.6
2.2 2.25 2.3 2.35 2.40
0.2
0.4
0.6
0.8
MMd(K+π+) [GeV/c2]
d3σ
/dco
sΘla
b
K+d
cosΘ
lab
π+/d
M
(μ
b /
20
[M
eV/c
2])
K-nn
threshold
Search
Region
preliminary
2 2.1 2.2 2.3 2.4 2.5 2.6 2.70
0.5
1
1.5
2
2.2 2.25 2.3 2.350
0.5
1
1.5
K-pn
threshold
Search
Region
d2σ
/dco
sΘla
b
K+
-/dM
(μ
b /
10
[M
eV/c
2])
MMd(K+) [GeV/c2]
preliminary
- large background from QF process in the inclusive measurement.
- Identification of Final state is indispensable (KNN Y N)
K-pn search
via γ + d K+ + X
K-nn search
via γ + d K+ + π+ + X
32
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