106 research outputs found
Phenomenological analysis of K+ meson production in proton-nucleus collisions
Total and differential cross sections from literature, on the production of
K+ mesons in pA interactions at projectile energies between T=0.8 and 2.9 GeV,
covering the transition across the free nucleon-nucleon threshold at 1.58 GeV,
have been investigated. From the target-mass dependence of the production cross
sections no evidence for the expected change of the dominant reaction mechanism
from two-step to direct kaon production was found. At T=1.0 GeV the A
dependences of the total cross sections and of the most recent data from
COSY-Juelich, differential cross sections measured under forward angles, are
strongly different. The invariant K+ production cross sections show an overall
exponential scaling behavior with the squared four-momentum transfer between
the beam proton and the produced K+ meson for t< -0.05 GeV^2 independent of the
beam energy and emission angle. The data from COSY-Juelich reveal a strongly
different t dependence in the region of t>0 GeV^2. Further data at forward
angles and different beam energies should be taken in order to explore this
region of kinematically extreme conditions.Comment: 9 Pages, 11 Figure
Measurement of the isospin-filtering dd -> 4He K+ K- reaction at Q=39 MeV
The total cross section for the dd -> 4He K+ K- reaction has been measured at
a beam momentum of 3.7 GeV/c, corresponding to an excess energy of 39 MeV,
which is the maximum possible at the Cooler Synchrotron COSY-J\"{u}lich. A
deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed
inside the storage ring, have been employed in this investigation. We find a
total cross section of sigma(tot) < 14 pb, which brings into question the
viability of investigating the dd -> 4He a0(980) reaction as a means of
studying isospin violation.Comment: Five pages with three eps figure
Subthreshold and near-threshold kaon and antikaon production in proton-nucleus reactions
The differential production cross sections of K^+ and K^- mesons have been
measured at the ITEP proton synchrotron in p+Be, p+Cu collisions under lab
angle of 10.5^0, respectively, at 1.7 and 2.25, 2.4 GeV beam energies. A
detailed comparison of these data with the results of calculations within an
appropriate folding model for incoherent primary proton-nucleon, secondary
pion-nucleon kaon and antikaon production processes and processes associated
with the creation of antikaons via the decay of intermediate phi mesons is
given. We show that the strangeness exchange process YN->NNK^- gives a small
contribution to the antikaon yield in the kinematics of the performed
experiment. We argue that in the case when antikaon production processes are
dominated by the channels with KK^- in the final state, the cross sections of
the corresponding reactions are weakly influenced by the in-medium kaon and
antikaon mean fields.Comment: 24 pages. accepted for publication at J.Phys.
The Evaluation of V_{ud}, Experiment and Theory
The value of the V_{ud} matrix element of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix can be derived from nuclear superallowed beta decays, neutron decay, and
pion beta decay. We survey current world data for all three. Today, the most
precise value of V_{ud} comes from the nuclear decays; however, the precision
is limited not by experimental error but by the estimated uncertainty in
theoretical corrections. Experimental uncertainty does limit the neutron-decay
result, which, though statistically consistent with the nuclear result, is
approximately a factor of three poorer in precision. The value obtained for
leads to a result that differs at the 98% confidence level from the
unitarity condition for the CKM matrix. We examine the reliability of the small
calculated corrections that have been applied to the data, and assess the
likelihood of even higher quality nuclear data becoming available to confirm or
deny the discrepancy. Some of the required experiments depend upon the
availability of intense radioactive beams. Others are possible today.Comment: 21 pages, 1 figure, LaTe
Evidence of kaon nuclear and Coulomb potential effects on soft K+ production from nuclei
The ratio of forward K+ production on copper, silver and gold targets to that
on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as
a function of the kaon momentum p_K using the ANKE spectrometer at
COSY-Juelich. The strong suppression in the ratios observed for p_K<200-250
MeV/c can be ascribed to a combination of Coulomb and nuclear repulsion in the
K+A system. This opens a new way to investigate the interaction of K+-mesons in
the nuclear medium. Our data are consistent with a K+A nuclear potential of
V_K~20 MeV at low kaon momenta and normal nuclear density. Given the
sensitivity of the data to the kaon potential, the current experimental
precision might allow one to determine V_K to better than 3 MeV.Comment: 9 pages, 3 figures; changed conten
a0+(980)-resonance production in pp->dK+Kbar0 reactions close to threshold
The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46
MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected
coincident dK+ pairs about 1000 events with a missing Kbar0 were identified,
corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat)
+/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly
analyzed and reveal s-wave dominance between the two kaons, accompanied by a
p-wave between the deuteron and the kaon system. This is interpreted in terms
of a0+(980)-resonance production.Comment: 4 pages, 4 figures; accepted by Phys. Rev. Let
The energy dependence of the pp->K+ n Sigma+ reaction close to threshold
The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has
been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and
2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from
Sigma+ production so that their measurement allows the total cross section for
the reaction to be determined. The results obtained are completely consistent
with the values extracted from the study of the K+-proton correlation spectra
obtained in the same experiment. These spectra, as well as the inclusive K+
momentum distributions, also provide conservative upper limits on the Sigma+
production rates. The measurements show a Sigma+ production cross section that
varies roughly like phase space and, in particular, none of the three
experimental approaches used supports the anomalously high near-threshold
pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys.
Lett. B 643, 251 (2006)].Comment: Submitted to PR
Kaon Pair Production in Proton--Proton Collisions
The differential and total cross sections for kaon pair production in the
pp->ppK+K- reaction have been measured at three beam energies of 2.65, 2.70,
and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Juelich
accelerator. These near-threshold data are separated into pairs arising from
the decay of the phi-meson and the remainder. For the non-phi selection, the
ratio of the differential cross sections in terms of the K-p and K+p invariant
masses is strongly peaked towards low masses. This effect can be described
quantitatively by using a simple ansatz for the K-p final state interaction,
where it is seen that the data are sensitive to the magnitude of an effective
K-p scattering length. When allowance is made for a small number of phi events
where the K- rescatters from the proton, the phi region is equally well
described at all three energies. A very similar phenomenon is discovered in the
ratio of the cross sections as functions of the K-pp and K+pp invariant masses
and the identical final state interaction model is also very successful here.
The world data on the energy dependence of the non-phi total cross section is
also reproduced, except possibly for the results closest to threshold.Comment: 12 two-column pages, 12 figures, 1 tabl
The production of K+K- pairs in proton-proton collisions at 2.83 GeV
Differential and total cross sections for the pp -> ppK+K- reaction have been
measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic
spectrometer. Detailed model descriptions fitted to a variety of
one-dimensional distributions permit the separation of the pp -> pp phi cross
section from that of non-phi production. The differential spectra show that
higher partial waves represent the majority of the pp -> pp phi total cross
section at an excess energy of 76 MeV, whose energy dependence would then seem
to require some s-wave phi-p enhancement near threshold. The non-phi data can
be described in terms of the combined effects of two-body final state
interactions using the same effective scattering parameters determined from
lower energy data.Comment: 12 pages, 12 figures, 3 table
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