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

2

J-PARC E19 Collaboration

3

Pentaquark search

4

• 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.

5

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

6

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

7

p- + p → K- + Q+

2. High resolution missing mass spectroscopy– K1.8 beam line & SKS = DM < 2 MeV (FWHM)

Conclusive result by higher sensitivity !!

8

Experimental setup

J-PARC K1.8

p- beam

1.92/2.00 GeV/c

Dedicated to the (p,K) reaction spectroscopy

History of E19

9

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