Yi Qiang, The search for pentaquarks at JLab Hall A 1June 2006

The Search for PentaQuarks at Jefferson Lab Hall A: E04-012

Yi QiangMassachusetts Institute of Technology

for JLab E04-012 Collaboration

Hall A Collaboration Meeting, June 2006

Yi Qiang, The search for pentaquarks at JLab Hall A 2June 2006

PentaQuark Model Chiral Quark Soliton Model

(Diakonov et al., 1997) predicts an anti-decuplet of pentaquarks

Iso-spin Partners (Capstick et al., 2003): Narrow width in terms of isospin-violating strong decays

Following theoretical and experimental studies suggested:

– Narrow ( 1~8 MeV)– Low mass (Θ~1530 MeV)– (1 ) 107M M S MeV

Physics Today, Sept 2003

Corners are manifestly exotic—with an unpaired antiquark!

Spring-8 LE

PS

PRL 91 (2003) 012002-1

Yi Qiang, The search for pentaquarks at JLab Hall A 3June 2006

Hall A Experiment E04-012

( , ' )H e e K

10( , ' ) oH e e K

10( , ' ) oH e e N

1550 – 1810 MeV

1610 – 1880 MeV

1470 – 1590 MeV

15cm

Beam Energy: 5GeV

Left and Right HRS angle: 6°

Left HRS (hadron): 1.85 ~ 2.0 GeV/c

Right HRS (e): 1.89 ~ 2.10 GeV/c

Q2 : ~ 0.1 (GeV/c)2

* *

( )

:~ 8.5 2.9 , :~ 7.

:~ 38(32)

7 2.7CM CM

K

CMK msr

High Resolution and Statistics!

Yi Qiang, The search for pentaquarks at JLab Hall A 4June 2006

Particle Identification

Left HRS: Aerogel 1 & 2 Cheren

kov Counters; Ring Imaging Cheren

kov detector: RICH; Lead Glass Pion Reje

ctor.

Right HRS: Gas Cherenkov

RICH detector has very good Cherenkov angle resolution: ~ 6 mrad, which reduced pion contamination from kaon events to

less than 5 %

K

Freon Radiator (n=1.28)

CsI Pad Photocathode

MWPC

Yi Qiang, The search for pentaquarks at JLab Hall A 5June 2006

Coincidence System

TOF Resolution :

FWHM ≈ 600 ps

CT difference ~ 2 ns

Longitudinal target vertex resolution:

FWHM ≈ 2.5 cm

15 cm extended Target removes background by a factor of 2

Yi Qiang, The search for pentaquarks at JLab Hall A 6June 2006

Missing Mass Calibration

High Missing Mass Resolution

mm = 1.5 MeV

Mass Uncertainty < 3 MeV

Better than ANY previous experiment!

Yi Qiang, The search for pentaquarks at JLab Hall A 7June 2006

Combine Kinematics Settings Small momentum acceptance of HRS requires combined kinematics settings

Pure Counts in individual missing mass spectra was transformed into differential cross-section of virtual photoproduction in CMS:

The Combination was very smooth!

)( * hXpd

dCM

Yi Qiang, The search for pentaquarks at JLab Hall A 8June 2006

Γ=16.5 ± 1.7 MeV/c2

(PDG: 15.6 ± 1.0 MeV/c2)

01520Parameters of

*| ( ) 417 33 /CM

dp K nb sr

d

Yi Qiang, The search for pentaquarks at JLab Hall A 9June 2006

First glance of all three channels

No observation of significant narrow structure in any of them

Need further attempt to settle down the problem: Feldman-Cousins approach

Yi Qiang, The search for pentaquarks at JLab Hall A 10June 2006

Feldman-Cousins Approach A way which will automatically determ

ine confidential interval type: pure upper limit or interval

Test statistics: 0)|(

)|(ln2)()(2

XP

XPLLLL

bestbest

2

80%

90%

0

90% upper limit

80% interval

best

For each ordering of 2 will find out 2

90% (from M.C.):

Create 90% CL interval: the collection of satisfying

%90))()(( 290

2 P

)()( 290

2exp

Yi Qiang, The search for pentaquarks at JLab Hall A 11June 2006

Fit and Monte-Carlo

We selected four different fixed widths: 0.5, 2, 5, 10 MeV;

At each point of MX, we first determined the background level by fitting the side bands: both 20 MeV above and below the 90% resonance window;

Fix the background level, then fit in the resonance window with only cross-sectio

n varying and get 2exp()

1000 M.C. experiments with resonace

was generated to get 290%()

Compare 2exp() and 2

90%() to

get 90% CL interval 20 MeV side bands

90% Resonance window

Yi Qiang, The search for pentaquarks at JLab Hall A 12June 2006

Upper Limits0

10

Blue: upper limit

Red: lower limit

Green: 90% background flucuation

Maximum upper limit:

7 nb/sr ~ 17.5 nb/sr

*

10( , ) op K

Yi Qiang, The search for pentaquarks at JLab Hall A 13June 2006

Upper Limits0

10N

90% CL upper limit at that position ranges:

4.5 nb/sr ~ 10.5 nb/sr

for 0.5~10 MeV width

*

10( , ) op N

Yi Qiang, The search for pentaquarks at JLab Hall A 14June 2006

Upper Limits*( , )p K

90% CL upper limit at that position ranges:

3.0 nb/sr ~ 4.0 nb/sr

for 0.5~10 MeV width

Yi Qiang, The search for pentaquarks at JLab Hall A 15June 2006

Summary

There’s no significant narrow pentaquark structures observed in Hall A experiment E04-012;

All signals seen are consistent to statistical fluctuation. The maximum upper limits and ratio to (1520)

production are listed at a function of selected width.

(MeV/c2)

0.5 2.0 5.0 10.0Mass Range (MeV/

c2)

(nb/sr) 7.0 (1.7%) 9.0 (2.1%)13.0 (3.1

%)17.5 (4.2

%)1550 - 1810

(nb/sr) 4.5 (1.1%) 5.5 (1.3%) 6.0 (1.4%)10.5 (1.5

%)1610 - 1880

(nb/sr)

3.0 (0.7%) 3.5 (0.8%) 3.5 (0.8%) 4.0 (1.0%) 1480 - 1590

Yi Qiang, The search for pentaquarks at JLab Hall A 16June 2006

Thank you

Yi Qiang, The search for pentaquarks at JLab Hall A 17June 2006

CollaborationJ. Annand, J. Arrington, Y. Azimov, W. Bertozzi, C. M. Camacho, G. Cates,

J. P. Chen, S. Choi, E. Chudakov, F. Cusanno, K. de Jager, M. Epstein,

R. Feuerbach, J. Gomez, O. Gayou (run coordinator), F. Garibaldi,

R. Gilman, D. Hamilton, O. Hansen (analysis coordinator),

D. Higinbotham, T. Holmstrom, M. Iodice, X. Jiang, M. Jones, J. Lerose,

R. Lindgren, N. Liyanage, D. Margaziotis, P. Markowitz,

V. Mamyan (analysis guru), R. Michaels, Z. Mezianni, P. Monaghan,

V. Nelyubin, K. Paschke, E. Piasetzky, P. Reimer (co-spokesperson),

J. Reinhold, B. Reitz, R. Roche, Yi Qiang (Ph.D. student), A. Sarty,

A. Saha, E. Schulte, A. Shahinyan, R. Sheyor, J. Singh, I. Rachek

I. Strakovsky, R. Subedi, R. Suleiman, V. Sulkovsky,

B. Wojtsekhowski (contact and spokesperson), X. Zheng.

and the Hall A Collaboration