Search for the Q+ in photoproduction experiments at CLAS APS spring meeting (Dallas) April 22, 2006 Ken Hicks (Ohio University) for the CLAS Collaboration.
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Transcript Search for the Q+ in photoproduction experiments at CLAS APS spring meeting (Dallas) April 22, 2006 Ken Hicks (Ohio University) for the CLAS Collaboration.
Search for the Q+ in photoproduction
experiments at CLAS
APS spring meeting (Dallas)
April 22, 2006
Ken Hicks (Ohio University)
for the CLAS Collaboration
April 22, 2005
K. Hicks, Ohio U.
2
Analysis strategy for the
Q+ :
Independent analysis of several reactions by different groups;
K
Q+
d
detected final states
N
d p K K n; Q nK
d 0 K (0) n( p);Q nK , pKS0
d p K ; Q pKS0 ; KS0
" n" K K n; Q nK Fermi momentum
corrections
pK K
p K ; pp
p K
K K
Work on cross section upper limit estimate in other channels is in
progress. Requires acceptance simulations for each final state.
April 22, 2005
K. Hicks, Ohio U.
4
Comparison: earlier data
April 22, 2005
Restricted photon energy range
Two distributions statistically
consistent with each other:
26% c.l. for null hypothesis
from the Kolmogorov test
(two histograms are
compatible).
G10 mass distribution can be used
as a background for refitting the
published spectrum.
K. Hicks, Ohio U.
5
Fit to the MM(pK-) distributions
The same 3rd degree polynomial as a background in both fits (for g2a
function was scaled by x5.9).
For the fit to the g10 distribution Gaussian, the sigma was fixed to the
known CLAS resolution (determined from MC and fits to other peaks).
g10
g2a
-)
MM(pK
April 22, 2005
K. Hicks, Ohio U.
MM(pK-)
6
Missing momentum
(active neutron
cut)
g10: all photons E
low B-field
(2250 A)
high B-field
(3375 A)
g2a cut
0.2>GeV/c
M(nK+)
April 22, 2005
K. Hicks, Ohio U.
7
Cross section upper limit
d --> pK-K+n
upper limit from
counts above BG
(angle integrated).
M(nK+)
Upper limit as a
function of Q+ angle
for 1.52<M<1.56.
Same, for M=1.54
cos(Q*)
April 22, 2005
K. Hicks, Ohio U.
9
The elementary cross section: nQ+K(1520)
p
p
K-
K
n
n
K
(1520) is produced on the proton,
neutron is a spectator.
• A model for an
energetic spectator:
take the (1520)
production as a guide.
• The symmetry of
(1520) and Q+ is seen
below.
• Studies show the
spectator cut reduces
the cross section by a
factor of about 10.
• Upper limit n-->Q+Kestimated at 3-6 nb.
+ is produced on the neutron, proton is a spectator.
QApril
22, 2005
K. Hicks, Ohio U.
10
New subject: d --> Q+
• Two baryons in the final state:
– simpler kinematics
– no possibility of kinematic reflections
• --> p - is cleanly identified
– many topologies: Q+ --> nK+ used here
– neutron momentum should be significant
April 22, 2005
K. Hicks, Ohio U.
11
Mass Spectra (particle ID)
n
Missing mass
(= neutron mass)
for cut on peak.
MM(K+p-)
Invariant mass
(= mass)
for cut on n peak.
high statistics!
M(p-)
April 22, 2005
K. Hicks, Ohio U.
12
nK+ mass spectrum
No signal for the
Q+ is evident in
the full data.
These cuts were
made to enhance
Q+ production.
Still no signal.
April 22, 2005
M(nK+) K. Hicks, Ohio U.
13
Cross section upper limit
Upper limit at a given
mass (angle integrated).
M(nK+)
t (GeV2)
April 22, 2005
K. Hicks, Ohio U.
Upper limit for masses
(1.52<M<1.56) vs.
momentum transfer t.
Open/closed assume
different models of
Q+ production.
solid = phase spaced
open = Guzey et al.
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Summary of Deuterium Data
• A search for the Q+ in the photon-induced reactions using
photons with energies up to 3.6 GeV has been carried out
with the CLAS.
• The peak in the M(nK+) spectrum published earlier cannot be
reproduced. Also, no peak is found in the full data set (all E).
• The upper limit on the measured cross section in the reaction
dQ+pK-, with Pp>0.35 GeV/c, is about 0.3 nb (95% CL).
For the elementary (neutron) cross section, the limit is higher.
• A second search was done using the reaction dQ+, to the
exclusive final state p-K+n, but no Q+ peak is seen. Upper
limit is model dependent, especially at forward angles.
April 22, 2005
K. Hicks, Ohio U.
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