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.
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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.
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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.
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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-)
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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.
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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.
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The elementary cross section: nQ+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.
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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.
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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.
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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.
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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
dQ+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 dQ+, 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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