Hadron Physics with Photon
Beam at LEPS/ LEPS2

Takashi Nakano (RCNP, Osaka Univ.)	

1	

HHIQCD2015, March 3rd, 2015	

Outline	LEPS
• Overview• Some recent results
LEPS2• Physics Motivation• Overview
Summary	2	

• First experimentOperated since 2000.	

3	

Laser Electron Photon beamline at SPring-8

Photon tagging and experiment

Timing and position of a scattered electron is measured at acounting rate of ~1 M /sec.
•••Eγ ≥1.5 GeV : about 40% of (0<Eγ<Emax) photons
For incident photon number normalization
For trigger : rate ~ 100 /secBackward-Compton Scattered
Photon8 GeV electrons in SPring-8 + 350nm(260nm) laserè maximum 2.4 GeV(2.9 GeV) photon
Laser Power ~6 W è Photon Flux ~1 Mcps
Eγ measured by tagging a recoil electron è Eγ>1.4 GeV, ΔEγ ~10 MeV
Laser linear polarization 95-100% ⇒ Highly polarized γ beamLinear Polarization of γ beam

PWO measurement

taggedphoton energy [MeV]

5photon energy [GeV]Setup of LEPS
Detectors

Only FWD spectrometer±20°x ±10°61.5

Setup of LEPS
Detectors

1.5E // BPolarized HD target will be ready soon.

7γ

Linearly Polarized Photons	
(1) Natural parity(1)γ

Vector K* (2) Unnatural parity(2)

HyperonDecayed Particles

8	p

Exchangedparticle

Scaler κ exchange inΣ+ production	

9	K : Pseudoscalar meson à unnatural exchange
κ: Scalar meson à natural exchange

Parity Spin Asymmetry	
PRL 108, 092001 (2012)	

w/ κ-exchange
Y. Oh and H. Kim,
PRC 74, 015208 (2006)
w/o κ-exchange	⇒ Consistent with κ(800) meson exchange.

10	

Dominance of natural-parity exchange is indicated at forward angles.

Kaonic nuclei search
K/K*γπ+	π	p

NπK

K0	

direct K-exchange
is forbiddenin (π+,Κ+) reaction.

N11nVirtualK, K*

Κ+	Physics motivation	
• K-N interaction is strongly attractive (I=0).
weakly attractive (I=1).
à KNN bound state (K-pp, K-pn, K-nn)
the strongest bound state	• K-pp• Theory: B.E. = 20 - 120 MeV, Γ=60 – 110 MeV• Experiment : FINUDA (B.E. =115 MeV, Γ = 67MeV)
DISTO(B.E. =103 MeV, Γ = 118MeV)

12	

K-pp search via γ + d à K+ + π- + X	
21.5(a)Λ1.511Σ	 0.52.2 2.25 2.3 2.35 2.4n	Λ*/Σ*0.501.8

Upper limit of cross section (95% C.L.)	

SearchRegion

1.92

2.1 2.2K-pp
threshold

2.3

2.4 2.5 2.6 2.7
MMd(K+π-) [GeV/c2]

Upper Limit of K-pp production(d2σ/dcosΘlabK+dcosΘlabπ-[μb])d3σ/dcosΘlabK+dcosΘlabπ-/dM(μb / 20 [MeV/c2])

MM(K+π-)	

3.5
3(b)

2.5

Γ = 20 MeV
Γ = 60 MeV
Γ = 100 MeV

2
1.5
10.502.22 2.24 2.26 2.28

2.3

2.32 2.34 2.36MMd(K+π-) [GeV/c2]

So far, no peak was observed in From
inclusive
likelihood
modes.ratio method;
Search region 2.22 – 2.36 GeV/c2
We will try to detect decay products.
Γ = 20 MeV : 0.17 - 0.55 µb→ cannotLargerbe
acceptance,
Significant peakobserved. LEPS2.	
Γ = 60 MeV : 0.55 - 1.7 µb
à ~ 10% of Q.F. processes 	Γ = 100 MeV : 1.1 - 2.9 µb~10% of Q.F.13	
processes	Prediction of the Θ+ Baryon
ud  sD. Diakonov, V. Petrov, and M. Polyakov,Z. Phys. A 359 (1997) 305.

••••

Exotic: S=+1
Low mass: 1530 MeV
Narrow width: < 15 MeV
Jp=1/2+14

M = [1890-180*Y] MeV

Previous result	γ d →K+K-pn reaction	
・Data taken in 2002-2003.
・2.0<Eγ<2.4 GeV.
・Significance of 5.1σ from shape analysis.
(Δ(-2lnL) with/without signal)
・Mass=1524±2＋3MeV/c2.

ü It should be reproducible.
ü It should appear in M(nK+).
ü It should not appear in M(nK-) nor in M(pK+).

15	If the peak is real,	Results of Inclusive Analysis	New datacontains 2.6 times morestatistics than the previousdata.

New data
previous data
χ2/ndf=56.4/66
K.S test 58.8%

16	

・Blind analysis: Cuts are pre-determined. ・Two data sets are normalized by the entry.
・In total, two data sets are consistent.
・Narrow strong structure is not seen in
the signal region.
Fluctuation?
・The significance is ~ 2σ if we
Exclusive analysis
Human bias?
perform the same shape analysis as
Over/under-estimation?	
the previous analysis.

Exclusive Analysis	
K-­‐	K+	γ	d	K-­‐	K+	γ	n	  p	spectator	d	p	  spectator	

0.3~0.8 GeV/c	Λ(1520), φ, ...	

Θ+, φ, ...	

n	Proton detection by using dE/dx in Start Counter	p	K-	K+	K-	K+	p	

or	

K-	
K+	

Proton not tagged(Proton rejected)	

Proton tagged (ε ~60%)	

KKn and a part of KKp	KKp only	
Signal enhancement isseen in proton rejected
events.
should be associatedwith γn reaction.	

p/n ratio:
1.6 before proton rejection
0.6 after proton rejection	

18	n	

Pid = (Measured energy loss in SC)– (Expectation of KK)– (Half of expectation of proton)1. dE/dx-based
exclusive analysis	
Proton rejection efficiency
becomes 60%→90% by
selecting downstream oftarget	
p	Efficiency	Two methods to reduce “leaked” proton BG	

K-	“leaked” proton BG	

2. MC-based exclusive analysis	
・ Proton contribution is estimated byfitting realistic MC distributions toproton-tagged spectra.
・ The estimated leaked proton
contributions are subtracted from full
data sample (without z-vertex).		

M(pK-)	
χ2/ndf = 34.4/37 	
φ and non-resonant KK
Λ(1520)Λ(1405)
Summed19	K+	

M(nK-) distribution	
üThe peak did not appear in M(nK-)	

subtracted	20	n and p(leaked)	

M(nK+) with two methods	
80
70
60
50
4030
20
100

1.4

1.45

1.5

1.55

1.6

1.65

1.7

1.75

1.8

1.85

1.9

M(nK+) (GeV/c2)

21	Counts/12.5 MeV

MC-based exclusive events	 dE/dX-based exclusive events	M(nK+) with two methods	

MC-based exclusive events	 dE/dX-based exclusive events	
80
70
60
50
4030
20
100

1.4

1.45

1.5

1.55

1.6

1.65

1.7

1.75

1.8

1.85

1.9

22	

Subtract proton contribution.	

M(nK+) with two methods	

MC-based exclusive events	 dE/dX-based exclusive events	
8020070

17560

150
12550

100

4075

3050

2025

10

1.4

1.45

1.5

1.55

1.6

1.65

1.7

1.75

1.8

1.85

1.9

0

1.4

1.45

1.5

1.55

1.6

1.65

1.7

1.75

1.8

1.85

1.9

Overlay with normalization by entry	
23	0

24

Large Start Counter
to improve proton tag/rejection efficiency.	

After φexclusion	

450

400

proton detection efficiency

Counts	Proton detection
efficiency	
350

300

250

200

150

10.9
0.8
0.7
0.6
0.5
0.4
0.3

100

○ : New setup (2013 – 2014)● : Old setup (2006 – 2007)	

0.2
50

0

0.1
0.98

1

1.02

1.04

1.06

1.08

1.1

M(K+K-) [GeV/c2]	

0-1100-1050-1000-950-900
lower limit of vertex position [mm]We have just finished data taking with the new setup. 	
Data with new setup! Data with old setup

LEPS2 Facility
Backward Compton Scattering

8 GeV electron
Recoil electron(Tagging)

10 times high intensity：	
Multi laser injection &Laser beam shaping

Laser
LEP
(GeV γ -ray)Large 4π spectrometer based on
BNL-E949 detector system.
Better resolutions are expected.

26	

Best emittance⇒ photon beam
does not spreadDivergence of LEP beam
LEPS2BL31LEPS
BL33<σx’ >=14 µrad.

e- àe- àReaction region(30m)<σx’ >=58 µrad.

Tagging point

Reaction region(7.8m)
Tagging point

Better divergence à Better tagging resolution
Smaller beam size at long distanceΘ+ Search at LEPS2	γ‘n’γdudKp−duus+ΘKduu

d∗0dsuduKsdp+

Θdu−π+du0sKsdπ−+No Fermi motion πcorrection.
No φ background.

pK 	  	  invariant	  mass	(t-­‐channel	  K-­‐exchange	  is	  possible)	

s angular dependence of production rateK 	  in	  missing	  mass	
To measurelarge angle region, up to CLAS acceptance.

A large acceptance and better resolution detector is necessary.

28*

Two pole structure of Λ(1405)	

V.K. Magas, E. Oset and A. Ramos, PRL 95	

29D.	  Jido,	  et	  al.	  
NPA725(2003)	  K*(890) Λ(1405) photoproduction
with linearly polarized photon	γ	

E	K	
K*	
π	K-	Λ(1405)
Σ(1385)	
30p	

K*(890) Λ(1405) photoproduction
with linearly polarized photon	γ	

E	K	K*	π	K-	T.Hyodo et. al, PLB593	

Λ(1405)
Σ(1385)	
31p	

LEPS2 Detector

B=1 T : Δp/p ∼ 1% for θ >7°		
2.22 m

RMS=117 µm	

γ counter 	

RPC 	TOP 	TPC Prototype Residual	

RPC ToF time distribution	

γ	2.96 m	

DC	>3σ K/π separation @1.1 GeV/c2	32

TPC

Transport each disk

Installation of the E949 magnet (2011.Nev-Dec) 	

Open the roof of LEPS2 building	Insert each disk using 360t crane	Installation was finished after painting	γ counters were installed. (2012.June)	

Installation of the E949 magnet (2011.Nev-Dec) 	

Beam pipe (2012.May)	

37	

Exp. hall was constructed. (2010.Oct-2012Jan)	

Comparison of LEPS
and LEPS2	
LEPS2	

Beam Intensity (~2.4 GeV)	

2~3x106 (2 lasers)	

<107 (4 high-power lasers)	

Beam Intensity (~2.9 GeV)	

2~3x105 (2 lasers)	

<106 (4 high-power lasers)	

Polarization	

Linear/Circular	

Linear/Circular	Detector Area 	

42m2 x 3m(h)	

198m2 x 10m(h)	

Charged Particle
Acceptance	

0~30 degrees	

7~120 degrees	

Momentum Resolution	

0.5% (for 1-GeV kaon)	

1~1.5% (for 1-GeV kaon)	

Photon Coverage	

none	

30~110 degrees

38	LEPS	BGO-Egg : constructed@ ELPH, Tohoku U.	

Large acceptance photon detector (BGO-Egg)• 1320 BGO crystals• Covering 24o ~144o polar angle• 1.3% energy resolution for 1 GeV	

BGOegg calibration	
(a)	

36°	
target24°	

counts / 1 MeV	π0 (σ=6.7 MeV/c2)	

(b)	

η (σ=14.4 MeV/c2)	

2γ invariant mass (MeV/c2)	

• Obtained mass resolutions are consistent with MC simulation results.
• Timing resolution was measured to be 340 ps by checking π0→2γ.	

Experimental setup	γ + 12C -> η’ x 11B + p 	
Tagging counter	

Forward TOF	LEPS2 building	e-	γ

150 MeV	

144° 	

7° 	

24° 	

target	12.5m	

Drift Chamber	
Tracking	
H.Nagahiro et al.
PRC74(2006)45203

41	

Storage Ring	

BGOegg calorimeter	Experimental method	
γ + 12C	  -­‐>	  	  η’	  	  x	  11B	  +	  p	IdenLfy	  η’	  producLon	  by	  η	  tag	Search	  for	  a	  bound	  state		  2	  γ (39%)	

12.5m	  from	  the	  target		  3π0-­‐>6	  γ (33%)	

1m	

BGOegg	  calorimeter	

2m	

3.2m	

Vert	  :	  ±7°Hori:	  ±4°

Forward	  TOF	42	η	

2.4 GeV γ	0°

No shift	
ΔE=28MeV	bound	η tag (6γ)	
counts	

150MeV shift	ΔE=28MeV	bound	NJL model
calculation	

bound	-100	0100	
Eex-E0(MeV)	
H. Nagahiro	

Eex-E0(MeV)	

Secondary η	 multi π	

Eex-E0(MeV)	

Small background	
See signals in bound region	

43	

counts	

Expected energy spectrum	Summaryn LEPS

Kaonic nuclei search, updates on Θ+.
n LEPS2n x10 luminosity. ~10Mcps.
n Two different experimental setups.
n Solenoid spectrometern Θ+, Λ(1405)n BGO EGG + TOF
n Backward meson production from proton and nuclein BGO EGG experiment was started last year!
44n