PQE: The search for Pentaquark partner states at Jefferson Lab Hall A, E04-012
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Transcript of PQE: The search for Pentaquark partner states at Jefferson Lab Hall A, E04-012
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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).
26 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Chiral Soliton Model
Physics Today, Sept 2003
Corners are manifestly exotic—with an unpaired antiquark!
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.
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 non-strange, non-exotic state in anti-decuplet
Predict mass splittings (equal) and widths.
M ¼ 1530 MeV < 15 MeV
PRL 91 (2003) 012002-1
SP
Rin
g-8 L
EP
S
36 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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
Physics Today, Sept 2003
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
46 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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
56 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Kinematics
Calibration settingsKin 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.
++ settingsKin E0 Spect. Mom. (GeV) Central Missing Mass Purpose
Left (K/) Right (e) K
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 ++
66 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Kinematics0, N0 Settings
Kin E0 Spect. Mom. (GeV) Central Missing Mass Purpose
Left (K/) Right (e) K
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 ++)
76 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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
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
86 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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,e0+)Xaccidental
p(e,e0+)X
96 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Acceptance Correction—Matching Spectrometer settings
Total and 4 of the 8 spectra, corrected for efficiencies, effective charge and acceptance
106 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Missing Mass Calibration High resolution
missing mass = 1.5 MeV/c2
Missing Mass Uncertainty < 3 MeV/c2 (absolute)
116 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Parameters of (1520)
M(1520) = 1519.8§ 0.6 MeV/c2
= 16.6 § 1.5 MeV/c2Measured cross section at forward angle
126 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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 (2
b+s)
Test of significance (Where a is the integral of the diff. cross section of the hypothesized resonance)
Most significant peak, 2 ¼ -6
Resonance Search: 0
2 22
2 2
0,
0( )s b b
s b b
a
a
146 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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.
156 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Repeat experiment 1000 timesSimulated background spectra
with actual experimental statistics—i.e. randomly populate missing mass spectra taking acceptance weights into account.
Apply peak search algorithm.
Peak Significance: A frequentist approach
2Find largest 2 improvement in each spectrumUse 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
166 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
Upper Limits—How small is too small to be observed (heard)?
Repeat experiment 1000 timesAdd 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
176 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
N0 Upper Limits
p(e,e0 +)0
Probability of Real Peak < 50%For 0, least restrictive upper limit
at M=1.65, 1.68, 1.73, 1.86 GeV/c2
0 90% CL upper limit:
4 to 9 nb/sr for = 1 to 8 MeV/c2
186 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
++ 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
196 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting
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.