Pentaquark Q+ search experiment at J-PARC
M. Moritsu( Kyoto University RCNP, Osaka University )
for the J-PARC E19 collaboration
Baryons2013 @ Glasgow, 2013/06/24
Contents
1. Introduction2. J-PARC E19 experiment– Overview of the experiment– New result of E19-2nd run
3. Summary
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J-PARC E19 Collaboration
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Pentaquark search
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• Genuine exotic hadron (uuddsbar )• M = ~1540 MeV/c2 (decay Q+ KN)
Situation is still controversial ...
Pentaquark Q+
Historical background• Q+ pentaquark was first predicted by Diakonov et al. in 1997.• SPring8/LEPS group reported the evidence for Q+ in 2003.• Dozen experimental groups published supporting evidence for the Q+,• followed by a number of experiments with no evidence.
Physics Motivation• Distinctive feature of Q+ pentaquark
– Need some mechanism to suppress decay.
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Narrow Width
Meson-Baryon molecule Diquark structure(Need quark rearrangement for KN decay)
( < a few MeV )
Useful tool to understand low energy QCD dynamics !!
R.Jaffe, F.Wilczek (2003)
Our Approach ( J-PARC E19 )
1. Pion induced reaction– Complementary to photo-production (LEPS/CLAS).– Expect sizable production cross section. => High statistics
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p- + p → K- + Q+
2. High resolution missing mass spectroscopy– K1.8 beam line & SKS = DM < 2 MeV (FWHM)
2.6s
KEK-PS E522Miwa et al., PLB 635, 72.
DM ~ 13.4 MeV
(FWHM)
Previous experiment
Our Approach ( J-PARC E19 )
1. Pion induced reaction– Complementary to photo-production (LEPS/CLAS).– Expect sizable production cross section. => High statistics
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p- + p → K- + Q+
2. High resolution missing mass spectroscopy– K1.8 beam line & SKS = DM < 2 MeV (FWHM)
Conclusive result by higher sensitivity !!
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Experimental setup
J-PARC K1.8
p- beam
1.92/2.00 GeV/c
Dedicated to the (p,K) reaction spectroscopy
History of E19
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Comment Beam Momentum
Beam intensity
p’s on Target
2009/10 ~ K1.8 beam line & detector commissioning start
2010/10-111st RUN
examine the 2.6s bump structure observed in E522
1.92 GeV/c
1.0 M /spill
7.8 x 1010
2012/022nd RUN
new data at the highest beam momentum at K1.8
2.00 GeV/c
1.7 M /spill
8.7 x 1010
This presentation
Shirotori et al., PRL 109, 132002 (2012).• Q+ Peak was not observed.• We concluded that E522 bump was not the signal
by 10 times higher sensitivity.
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Note on Q+ decay width
PV Fs 500MeV
PV Fc 1800MeV
1800 2000 2200 2400 26000
2
4
sqrt(s) [MeV]
s [m
b]
Jp=1/2+, G +Q = 1MeV
Theoretical calculations :T. Hyodo et al., PRC 72, 055202 (2005),
PTP 128, 523 (2012).
plab=2.0 GeV/c
plab= 1.92 GeV/c
• Higher beam momentum provides higher sensitivity.
2.0 GeV/c ( = Max. of K1.8 B.L.) Even if no peak, stronger
constraint on the Q+ decay width will be obtained.
s-channel dominance GQ g∝ 2
KNQ ∝ s
Result of the E19-2nd run
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SKS spectrometer
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K
Scattered particle M2
pp
M2 [GeV2]
SKS system : pK
PID counters– Timing counter– Aerogel Cherenkov (K/p) : n=1.05– Lucite Cherenkov (K/p) : n=1.49Tracking– MWDCs : 3 mm pitch– DCs : 10 mm pitch, 2m×1m size
Good momentum reconstruction and PID !!
We can separate only K very clearly.
Example of analysis 1
Vertex-ZVertex-(X vs Y)
Vertex Reconstruction
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LH
2 T
arge
t ce
ll
f67.8 × 120 mm
pK
Target cell is clearly identified !!
Consistent with horizontally oblate beam shape.
window window
Beam
LH2 targetEmpty target (scaled)
Example of analysis 2
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Consistency check with previous exp.
p+ + p → K+ + S+ @ 1.37 GeV/c Missing mass resolution: DMS = 1.92 MeV
(FWHM)– Equivalent to the 1st run.
Cf.) 1.86±0.08 MeV @ E19-1st
S+ Missing Mass
DM = 1.92 ±0.05 MeV
p+ + p → K+ + S+ @ 1.37 GeV/c
S+
E19-2nd
Preliminary
Preliminary
DMQ = 1.74 MeV (FWHM)
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p+ + p → K+ + S+ @ 1.37 GeV/c Missing mass resolution: DMS = 1.92 MeV
(FWHM)– Equivalent to the 1st run.
Cf.) 1.86±0.08 MeV @ E19-1st
S+ Differential Cross Section
Preliminary
Differential cross section– Almost consistent with 1st run
and reference data.– Good understanding of
efficiencies and acceptance.
p+ + p → K+ + S+ @ 1.37 GeV/c
Consistency Check OK
Consistency check with previous exp.
DMQ = 1.74 MeV (FWHM)
E19-2nd Preliminary
Analysis Result of E19-2nd run
• No peak structure was observed.• Upper limit on differential cross section averaged from 2 to 15 deg:
< 0.28 mb/sr @ 1.50 – 1.57 GeV/c2
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p- + p → K- + X @ pp = 2.0 GeV/c
An example of fitting result @ 1.535 GeV/c2
Fitting results of each mass and Upper limit (90%C.L.)
Upper limit on decay width
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• 0.61 MeV for ½+• 3.7 MeV for ½-
gKNQ
• Considering about theoretical uncertainty (coupling scheme and form factor), we chose the most conservative case as the upper limit.
GQ g∝ 2KNQ ∝ s
T. Hyodo et al., PTP 128, 523 (2012).
Upper Limit on GQ for JPQ
Summary• J-PARC E19 is a pentaquark Q+ search experiment with
high statistics and high resolution.– p- p → K- Q+ reaction– J-PARC K1.8 B.S. and SKS
• New result of E19-2nd run was presented. – Consistency with the 1st run was checked. O.K.– Q+ missing mass resolution of 1.74 MeV was evaluated.– No peak structure was observed in MM spectrum.– Upper limit for Q+ production cross section was obtained to be
0.28 mb/sr @ 1.50 – 1.57 GeV/c2
– This corresponds to upper limit on Q+ decay width of 0.61 and 3.7 MeV for JP = ½+ and ½-, respectively.
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BACKUPS
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1st run result of E19
• No prominent peak structure• Upper limit: < 0.26 mb/sr
@ 1.51-1.55 GeV/c2
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p- + p → K- + X @ 1.92 GeV/c
E19-1stdatabackground(sim.)
s-channel dominance GQ g∝ 2
KNQ ∝ sUpper limit of decay width
• 0.72 MeV for ½+• 3.1 MeV for ½-
Shirotori et al., PRL 109, 132002 (2012).
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Comparison with background simulation
Simulation with measured cross section using angular distributions• f production : uniform (S-wave)• L(1520) : 1+cos∝ 2qcm (D-wave)
BG reactions• p- p → fn→K- K+ n(s = 30±8 mb)
• p- p → L(1520) K0
→K- K0 p(s = 21±5 mb)
• p- p →K- K+ n• p- p →K- K0 p(s ~25 mb)
O. I. Dahl et al . Phys. Rev. B 163, 1377 (1967).(Bubble chamber data)
Cut condition : NpK = 1
2 < q < 15 deg Vertex-(X2+Y2) < 252 mm2
-60 < Vertex-Z < 60 mm0.15 < m2 < 0.4 GeV2
c2 cut : Local tracking c2 < 20 (BcOut c2 < 10)SKS, K18 tracking c2 < 30
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Previous experiments at KEK-PSE522 : p- p → K- Q+ @ 1.92 GeV/c E559 : K+ p → p+ Q+ @ 1.20 GeV/c
K. Miwa et al., PLB 635, 72 (2006).
K. Miwa et al., PRC 77, 045203 (2008).
2.6s
Bump structure (2.6s) Not enough to claim the existence
Upper limit: s < 3.9 mb (90% C.L.)
No peak structure Upper limit: s < 3.5 mb/sr (90% C.L.)
p--induced
K+-induced
Prev. Exp.
1.53 GeV
Positive Results (~2005)LEPS DIANA CLAS-d
HERMES
ITEP
COSY-TOF
ZEUS
SVD
SAPHIR
CLAS-p
4.33.43.2 5.1
3.6
4.93.6
4~5
4.74.4
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[CAUTION]Significances ware recalculated by significance = S/√(S+B) or S/dS
Positive Results (updated)LEPS
DIANA
HERMES
ITEP
ZEUS
SVD
CLAS-p
5.55.1
3.6
4.93.6
4~6
5.825
CLAS-d< 0.3 nb
COSY-TOF< 0.15 mb Some confirmed their evidence,
but others did not...[CAUTION]Significances ware recalculated by significance = S/√(S+B) or S/dS
Negative Results26
FOCUS
BABAR
SPHINXCDF
BES
BELLE
LEP
HERA-B
HyperCP
PHENIX (Q-)_
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J-PARC Hadron facility
High-p
K1.1BR
K1.8BR
K1.8
Primaryproton beam
T1 target
KL
GC BH1BC1 BC2
K1.8 Beam Spectrometer
SKS Spectrometer
MS2
Q10 Q11
Q12
Q13
D4
SDC3SDC4 TOF
LC
AC1AC2
SDC2SDC1
BC4BC3 BH2
Target
2009 Oct
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2011 Sep.
Injection angle : 30 15 deg.• Higher-momentum acceptance.• For future experiments.
Rotation of SKS
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Recovery from the earthquake
Setup difference of 1st and 2nd run
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E19-1st run (2010) E19-2nd run (2012)
30 deg.
injection
15 deg.injection