Download ppt - Hall A - Jefferson Lab

PQE: The search for Pentaquark
partner states at Jefferson Lab Hall A,
E04-012
An update to the Hall A Collaboration
Paul E. Reimer
 What were we looking for?
 How did we look?
 What did we find?
(with help from all of my collaborators, especially
Y. Qiang and O. Hanson and their talks at
PANIC05 and Hadron05).
Argonne National Laboratory is managed by
The University of Chicago for the U.S. Department of Energy
Physics Today, Sept 2003
Chiral Soliton Model
Diakonov, Petrov and Polyakov,
Z. Phys. A 359, 305 (1997)
 All baryons are rotational excitations of a
rigid object.
 Reproduces mass splittings in lowest baryon
octet and decuplet.
PRL 91 (2003) 012002-1
 Predict mass splittings (equal) and widths.
M ¼ 1530 MeV
 < 15 MeV
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
SPRing-8 LEPS
 Apply to 3-flavor, 5-quark states.
 Anti-decuplet of states
 1 “free” parameter—fixed by identifying the
Jp = (1/2)+ N(1710) explicitly with nonstrange, non-exotic state in anti-decuplet
Corners are manifestly exotic—
with an unpaired antiquark!
2
Physics Today, Sept 2003
+ partner states
 E04-012 was approved to search for
partner states to the + pentaquark.
 Antidecuplet, non-exotic states
– From Soliton Model, mass is set by
M = M+ + (1-s) £ 107 MeV/c2
– N* and 0
 Isospin Partners (Capstick 2003)
– Narrow width in terms of
isospin-violating strong decays
– Predicts set of narrow, exotic
partners
– ++
 Narrow, Low mass, states of
specific strangeness
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
3
Hall A Experiment E04-012
Reaction
Mass Range
p(e,e0 K+)0 1550-1810 MeV/c2
p(e,e0 +)N* 1600-1830 MeV/c2
p(e,e0 K-)++ 1500-1600 MeV/c2
 Beam Energy: 5 GeV/c (Proposed 6 GeV/c)




Spectr. Angle: 6± (left and right w/septa)
Spectr. Momenta: 1.8 to 2.5 GeV/c
hQ2i ¼ 0.1 (GeV/c)2
In C-M  K( )¼ 6± (7±) K()¼ 40 (30) msr
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
4
Kinematics
Calibration settings
Kin
E0
Spect. Mom. (GeV)
Central Missing Mass
Purpose
Left (K/)
Right (e)
K

1, 2 5.0
2.29
2.50
0.899
0.994
Neutron
3
5.0
2.22
2.50
1.123
1.14
(1116)
4
5.0
2.10
2.00
1.523
1.585
(1520)
14
5.0
0.55
1.85
2.094
2.359
RICH Eff.
++ settings
Kin
E0
Spect. Mom. (GeV)
Central Missing Mass
Left (K/)
Right (e)
K

Purpose
8
5.0
2.10
2.00
1.523
1.585
++
9
5.0
1.93
2.00
1.611
1.680
++
17
5.0
2.06
2.00
1.550
1.613
++
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
5
Kinematics
0, N0 Settings
Kin
E0
Spect. Mom. (GeV)
Central Missing Mass
Left (K/)
Right (e)
K

Purpose
5
5.0
1.93
2.00
1.611
1.680
0, N*
6
5.0
1.93
1.93
1.648
1.718
0, N*
7
5.0
1.90
1.70
1.778
1.851
0, N*
10
5.0
1.93
1.83
1.700
1.770
0, N*
11
5.0
1.93
1.89
1.622
1.691
0, N*
12
5.0
1.93
2.02
1.600
1.669
0, N*
13
5.0
1.89
1.85
1.713
1.785
0, N*




Tasks
Event identification (/K separation, random rejection)
Acceptance correction between different separate
spectrometer settings
Mass calibration
Search for resonances (non-exotic 0, N*, and exotic ++)
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
6
PID and Coincidence System
Single Arm PID
 2 Aerogel thres. Cerenkov
counters n = 1.015, 1.055
 RICH n = 1.30
 Single arm pion reject. 3£104
 K/ ratio > 20
6 December 2005
Coincidence Time
 ToF resolution,
FWHM ¼ 0.60 ns
 Coincidence time difference
¼ 2 ns
Reaction Vertex Z
 FWHM ¼ 2.5 cm
 15 cm target reduces
background by factor of 2
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
7
Acceptance Correction
 Missing Mass acceptance is
proportional to the (diagonal)
length in the 2-D momentum
acceptance plot.
– e + p ! e0 + K§ + X
– MX ¼ const – Ee0 – EK
p(e,e0K+)X
accidental
p(e,e0K+)X
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
8
Acceptance Correction—Matching Spectrometer settings
Total and 4 of the 8 spectra, corrected for efficiencies, effective
charge and acceptance
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
9
Missing Mass Calibration
 High resolution
missing mass = 1.5 MeV/c2
 Missing Mass Uncertainty < 3 MeV/c2
(absolute)
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
10
Parameters of (1520)
 M(1520) = 1519.8§ 0.6 MeV/c2
  = 16.6 § 1.5 MeV/c2
6 December 2005
 Measured cross section at forward angle
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
11
Resonance Search: 0
 Within 50 MeV/c2 window, fit spectra
twice
1. Linear, “background” only fit (2b)
2. Linear + resonance
Breit-Wigner (fixed width of  = 1,
3, 5 MeV/c2) convoluted
w/Gaussian,  = 1.5 MeV/c2
detector resolution (2b+s)
 Test of significance (Where a is the
integral of the diff. cross section of the
hypothesized resonance)
2
2

a0



2
s b
b
  
,
2
2
(  s b  b ) a  0
 Most significant peak, 2 ¼ -6
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
12
Peak Significance: A frequentist approach
 Simulate smooth mass spectra (left)
 To achieve this, must consider acceptance/luminosity weight factors for 8
spectrometer settings, so randomly populate right distribution and weight
events just as in analysis.
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
14
Peak Significance: A
frequentist approach
Repeat experiment 1000 times
 Simulated background spectra
with actual experimental
statistics—i.e. randomly
populate missing mass spectra
taking acceptance weights into
account.
 Apply peak search algorithm.
2

 Find largest 2 improvement in each spectrum
 Use distribution of “greatest 2 improvement” to determine probability
such an improvement being a background fluctuation.
 For 0, =5 MeV, a 2 improvement of -6 corresponds to a < 55%
probability of not being a background fluctuation
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
15
Upper Limits—How small is too small
to be observed (heard)?
Repeat experiment 1000 times
 Add small resonance.
 How large must resonance be for search
procedure to find beam at 90% CL
p(e,e0 K )
+
0
 For 0, least restrictive upper limit at
M=1.72 GeV/c2
0
  90% CL upper limit:
8 to16 nb/sr for  = 1 to 8 MeV/c2
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
16
N0 Upper Limits
p(e,e0
 )N
+
0
 Probability of Real Peak < 50%
 For N0, least restrictive upper limit
at M=1.65, 1.68, 1.73, 1.86 GeV/c2
0
 N 90% CL upper limit:
4 to 9 nb/sr for  = 1 to 8
MeV/c2
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
17
++ Upper Limits
p(e,e0 K-)++
 Low statistics—switch to log
likelihood as estimator.
 Probability of Real Peak < 80%
 For ++, least restrictive upper limit
at M=1.57 GeV/c2
++
 90% CL upper limit:
3 to 6 nb/sr for  = 1 to 8
MeV/c2
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
18
Summary
 PQE/E04-012 has completed a high resolution search for narrow partner
states to the +.
 No strong signal is observed for the ++, 0 or N0
 All “bumps” are statistically consistent with the background.
6 December 2005
Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
19