1. 液体重水素標的を用いた+バリオン光生成の研究
JPS 29 Mar. 2006
液体重水素標的を用いた+バリオン光生成の研究
村松　憲仁
大阪大学　核物理研究センター
For the LEPS Collaboration

2. 阪大RCNP　村松憲仁，中野貴志，A，D.S.Ahn，郡英輝, 藤原守,
堀田智明， 堀江圭都, 與曽井優
甲南大　 秋宗秀俊
釜山大　 J.K.Ahn
東北大核理研　石川貴嗣, 清水肇
京大理　 今井憲一, 新山雅之, 藤村寿子, 宮部学
JASRI　 大橋裕二, 伊達伸, 依田哲彦
Academia Sinica　D.S.Oshuev, W.C.Chang
東大CNS　 木野幸一
阪大理 　阪口篤志, 菅谷頼仁
千葉大　 椎野祐樹
東北大理 住浜水季
NSCLMSU R.G.T.Zegers
宮崎大 戸井裕也, 松田達郎
Ohio Univ. K.Hicks, 三部勉
名古屋大 福井崇時
防衛大 松村徹
Univ. of Saskatchewan C.Rangacharyulu
他SPring-8/LEPS Collaboration

3. Contents Introduction (+ Status) d+(1520) - BG estimation
- Signal-like behavior
- Cross section measurement
Summary & Prospects

4. Pentaquark Status @ EINN 2005
Group Signal Backgr. Significance
publ. Comments
SPring s 3.2s
SPring s
SAPHIR s 5.2s
DIANA s 3.4s
CLAS(d) s 4.4s
CLAS(p) s 4.7s
  s
HERMES  3.6s
ZEUS  s
COSY  s
SVD  s
SVD s Improved analysis
NA  s
H  s
SPring s L*(K+n)
STAR 2, , s Q++ candidate
s/ b+s
G11 CLAS-p
G10 CLAS-d
? BELLE Q+
? BABAR
This slide summarizes the remaining evidence for any pentaquark. The new CLAS results eliminated two signals one on hydrogen and one on deuterium. The two non-Theta+ signals at H1 and NA49 are highly questionable and contradict later results from ZEUS and HERA-B with higher sensitivity.
Finally, the very new CLAS data on deuterium, presented here for the first time, should be confronted with the LEPS deuterium results from SPring8 which have lower statistics.
On the side favoring pentaquark signal is some positive news: The SVD-2 improved analysis gives many more events with high significance. SprinG8 claims a signal in L*(K+n) with 5s, and there is a signal of a doubly charged Q++ from STAR at RHIC. X5
HERA-B, CDF, COMPASS
ZEUS, FOCUS, BABAR
Q0c
From EINN05

5. CLAS upper limits p+K0 <2 nb vs. SAPHIR 300 nb / 50 nb
d+K-p <450 pb
But acceptance coverage is very different
from LEPS (forward region). ↓
+ is not killed.

6. LEPS LD2 runs Collected Data (LH2 and LD2 runs)
Dec.2000 – June 2001　LH2 50 mm　~5×1012 photons
　　　　　　　 published data
May 2002 – Apr 2003　LH2 150 mm　~1.4×1012 photons　　
Oct – June 2003　LD2 150 mm　~2×1012 photons
#neutrons × #photons in K＋K－ detection mode
　　 LD2 runs = 5mm-thick STC in short LH2 runs × ~5
K－p detection mode w/o Fermi correction :γd→＋K－p

7. Laser Electron Photon (LEP) Beam
－8 GeV electronｓ in SPring nm Ar laser (3.5eV）
⇒ GeV photons (Backward Compton Scattering)
－Photon Flux ~106　cps, Photon Energy Resolution ~10 MeV
－Charged particle spectrometer with forward acceptance
－PID from momentum and time-of-flight measurements
TOF
Dipole Magnet
　0.7　Tesla
Target
Start Counter
DC2
DC3
DC1
SVTX
AC(n=1.03)
PWO measurement
tagged 

8. K－p detection mode ＋ is identified by pK－ missing mass from
deuteron. ⇒ No Fermi correction is needed.
Inclusive (n / p reaction + rescattering, or other mechanism) γ ＋ p K－ n
(1520) p

9. Event selections in K－p mode
K＋ mass : 0.40 – 0.62 GeV/c2
Λ(1520) : 1.50 – 1.54 GeV/c2
Non-resonant
KKp + p + …
γp→K－pKπ
π－ mis-ID
as K－
MMp(γ,K－p) GeV/c2
M(K－p) GeV/c2
Events with Λ(1520) production were selected.
E > 1.75 GeV was also applied.

10. K－p missing mass in 1.50<M(pK－)<1.54 GeV/c2
preliminary
5 MeV bins
Θ＋ signal？
~1.53 GeV/c2
MMd(γ,K－p) GeV/c2
preliminary
3 MeV bins
MMd(γ,K－p) GeV/c2

11. Fluctuation or not ? Important to understand BG shape reliably
Quasi-Free BG = K(1520) + p + Non-resonant KKp + …
MC-based & real data-based BG estimations
Non-resonant
KKp
(1520) 
Fermi-corrected
MMp(,p)
M(pK-) GeV/c2 [LH2]
M(KK) GeV/c2 [LH2] 
(1520)
M(pK-) GeV/c2 [LD2]
M(KK) GeV/c2 [LD2]

12. MC-based BG estimation by using LH2 data
- BGs were simulated by including Fermi motion. (MC ~ 20 x real data)
- Kinematics at CMS were adjusted to real LH2 data.
 ‘Filters’ in ECMS, CMS(pK－), CMS(proton), PCMS(proton), PCMS(K－)
- Non-resonant KKp ⇒ K+* ⇒ p were adjusted step by step.
K*
KKp p
M(pK－) GeV/c2
M(KK) GeV/c2

13. 2 test of MC to LH2 data in MMd(,pK－) distribution
1.50<M(pK－)<1.54 GeV/c2 (Signal region)
(1+2+3) – GeV
2 = ndf = 30
prob. = 0.275
(1) – GeV
2 = ndf = 10
prob. = 0.123
(2) – GeV
2 = ndf = 10
prob. = 0.824
(3) – GeV
2 = ndf = 10
prob. = 0.223
(1)
(2)
(3)
MMd(,pK－) GeV/c2

14. M(pK－) distribution in LD2
Fermi motion is turned on in MC.
Preliminary
Extra events, which are
not seen in LH2 data
　　　　　　↓
Kinematical filters were
made from LD2 data
outside the signal region.
KKp
K* p
M(pK－) GeV/c2

15. MMd(,pK－) in (1520) region [LD2 data]
1.50<M(pK－)<1.54 GeV/c2 +
Preliminary
Preliminary
1.6 GeV bump
MMd(,pK－) GeV/c2
MMd(,pK－) GeV/c2
Conservative statistical significance ~ 4
Gaussian fit (temporary) ⇒ mass ~1.53 GeV/c2, width ~10 MeV

16. MMd(,pK－) below/above (1520) region [LD2]
M(pK－)<1.50 GeV/c2
M(pK－)>1.54 GeV/c2
small excess
Preliminary
Preliminary
MMd(,pK－) GeV/c2
MMd(,pK－) GeV/c2

17. Real data-based BG estimation (Sideband subtraction method)
LH2 * *
Non-resonant BGs + p
M(K－p) GeV/c2
M(K－p) GeV/c2
- Non-resonant BGs +  p : Deduced by
0.4 x [1.45<M(K－p)<1.50 or 1.54<M(K－p)<1.59 GeV/c2]
- K(1520) : LH2 data after sideband subtraction
Linearity was checked by comparing
two independent sideband regions.

18. K－p missing mass spectrum
K(1520) fit to all MMd(,pK－) region
- BG level : 6.5% more.
- c2/ndf=2.8
* fitted in MM<1.52 GeV/c2 +
preliminary
preliminary
1.6 GeV bump
Counts/5 MeV
Counts/5 MeV *
from sidebands
MMd(γ,K－p) GeV/c2
MMd(γ,K－p) GeV/c2

19. Comparisons of the two methods
Two methods in BG estimation (Complementary)
Sideband method Filtering method
Any BG involved realistically Not affected by statistics
Affected by LH2 statistics Possibility of Model variations
* may be slightly under-estimated

20. MMd(pK－) in different M(pK-) gates around (1520) mass
10 MeV/c2
20 MeV/c2
(Standard)
The peak structure
looks associated with
(1520) production.
S/N ratio gets lower
by widening M(pK-)
gate, but the peak
height looks constant.
MMd(γ,K－p) GeV/c2
MMd(γ,K－p) GeV/c2
50 MeV/c2
100 MeV/c2
MMd(γ,K－p) GeV/c2
MMd(γ,K－p) GeV/c2

21. Photon energy dependence
Eg > 2.1 GeV
Eg < 2.1 GeV
Counts/5 MeV
MMd(,pK－) GeV/c2
+ is seen in both lower and higher energy regions.

22. 1.6 GeV bump & higher M(pK) tail in LD2
ECMS<2.18
ECMS<2.10
2.10<ECMS
<2.18
MMd(,pK－) GeV/c2
M(pK－) GeV/c2
M(pK－) GeV/c2
2.18<ECMS
<2.26
2.26<ECMS
2.18<ECMS
MMd(,pK－) GeV/c2
M(pK－) GeV/c2
M(pK－) GeV/c2
1.6 GeV bump: n contribution? Hyperon-spectator nucleon interaction?
pion association?
Higher M(pK) tail : n contribution? Proton-neutron interaction?

23. Summary Confirmation of + by using LD2 data
with K－p mode in MMd(,pK－) spectrum
- Two methods in BG shape estimation (MC-based &
sideband method) are complementary.
GeV/c2 peak (~4σ,preliminary) GeV/c2 bump
associated with (1520) production
- Signal-like behavior
[different M(pK－) gates, E dependence]

24. Prospects
Differential cross section is being measured. Luminosity(LD2) ~0.6 pb-1.
Planning to take another data sets with LD2 target and forward spectrometer this year. Tagger update is necessary. Photon beam intensity will be twice by injecting two lasers.
Time Projection Chamber is being prepared to increase acceptance coverage. CLAS region can be covered.
Started to discussing about constructing new beamline at SPring-8. Upgrades of beam intensity and energy are expected. 4π detector with good resolutions are under considerations.