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