The DIRAC experiment at CERN investigated in the reaction
p(24GeV/c)+Ni the particle pairs K+K−,π+π− and ppˉ with relative momentum Q in the pair system less than 100 MeV/c.
Because of background influence studies, DIRAC explored three subsamples of
K+K− pairs, obtained by subtracting -- using time-of-flight (TOF) technique
-- background from initial Q distributions with K+K− sample fractions
more than 70\%, 50\% and 30\%. The corresponding pair distributions in Q and
in its longitudinal projection QL were analyzed first in a Coulomb model,
which takes into account only Coulomb final state interaction (FSI) and
assuming point-like pair production. This Coulomb model analysis leads to a
K+K− yield increase of about four at QL=0.5 MeV/c compared to 100 MeV/c.
In order to study contributions from strong interaction, a second more
sophisticated model was applied, considering besides Coulomb FSI also strong
FSI via the resonances f0(980) and a0(980) and a variable distance r∗
between the produced K mesons. This analysis was based on three different
parameter sets for the pair production. For the 70\% subsample and with best
parameters, 3680±370K+K− pairs was found to be compared to 3900±410K+K− extracted by means of the Coulomb model. Knowing the efficiency
of the TOF cut for background suppression, the total number of detected
K+K− pairs was evaluated to be around 40000±10%, which agrees with
the result from the 30\% subsample. The K+K− pair number in the 50\%
subsample differs from the two other values by about three standard deviations,
confirming -- as discussed in the paper -- that experimental data in this
subsample is less reliable
