Yu. T. Kiselev

Measurement of the in-medium phi-meson width in proton-nucleus collisions

The production of φ mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the φ → KK decay using the COSY-ANKE magnetic spectrometer. The φ meson production cross section follows a target mass dependence of A in the momentum region of 0.6–1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium φ width is about an order of magnitude larger than its free value.

Momentum dependence of the phi-meson nuclear transparency

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.

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→ppφ cross section from that of non-φ production. The differential spectra show that higher partial waves represent the majority of the pp→ppφ total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave φp enhancement near threshold. The non-φ 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.

EVIDENCE FOR ANTIKAON MASS MODIFICATION IN PROTON-NUCLEUS COLLISIONS

Yields of K+ and K− mesons from proton-nucleus collisions at the subthreshold energy range were measured. Kaons produced at 10.5° with momentum 1.28 GeV/c were detected by a beam-line focusing hadron spectrometer (FHS). The parameters of the Folding model were fixed by the best fit to the K+ data. Calculation with normal antikaon mass underestimates the experimental cross section of K− production by a factor of 2.5. In-medium antikaon mass was found to be 0.6-0.85 of its vacuum mass depending on the parametrization of the total cross section for K− production in pN collisions.

Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.

Non-resonant kaon pair production and medium effects in proton-nucleus collisions

We study the non-resonant (non-ϕ) production of KK +− pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag and Au targets within the collision model, based on the nuclear spectral function, for incoherent primary proton– nucleon and secondary pion–nucleon creation processes. The model takes into account the initial proton and final kaon absorption, target nucleon binding and Fermi motion as well as nuclear mean-field potential effects on these processes. We calculate the antikaon momentum dependences of the exclusive absolute and relative KK +− pair yields in the acceptance window of the ANKE magnetic spectrometer, used in a recent experiment performed at COoler SYnchrotron (COSY), within the different scenarios for the antikaon–nucleus optical potential. We demonstrate that the above observables are strongly sensitive to this potential. Therefore, they can be useful to help determine the K − optical potential from the direct comparison of the results of our calculations with the data from the respective ANKE-at-COSY experiment. We also show that the pion–nucleon production channels dominate in the lowmomentum K − , K + production in the considered kinematics and, hence, they have to be accounted for in the analysis of these data.

Experimental study of the subthreshold production of K+-mesons in proton-nucleus collisions

Energy dependence of the differential cross sections for the production of K+-mesons with a momentum of 1.28 GeV/c (c is the speed of light) by protons incident on Be, Al, Cu, and Ta nuclei was measured for energies both above and below the K+-meson production threshold in pp collisions. Evidence is given for the dominance of the mechanism of direct production in the experiment. The characteristics of momentum distribution are determined for nucleons in the Be and Al nuclei up to 650 MeV/c. The data cannot be described in the model of nuclear spectral function.

Near-threshold J/Ψ production in proton–nucleus collisions

We study the J/Ψ production from nuclei near the kinematic threshold within the collision model, based on the nuclear spectral function, for incoherent primary proton–nucleon charmonium creation processes. The model takes into account the initial proton and final J/Ψ absorption, target nucleon binding and Fermi motion, the formation length of J/Ψ mesons as well as the effect of their nuclear mean-field potential on these processes. We calculate the A-dependences of the absolute and relative (transparency ratio) charmonium yields as well as its excitation function within the different scenarios for the J/ΨN absorption cross-section, for the J/Ψ formation length and for J/Ψ in-medium modification. We demonstrate that the former observables, on the one hand, are not practically affected by the charmonium formation length effects and, on the other hand, they are appreciably sensitive to the genuine J/ΨN absorption cross-section at beam energies of interest, which means that these observables can be useful to ...

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 a laboratory angle of 10.5°, 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 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.

φ-meson production and the in-medium φ-width in proton-nucleus collisions

The production of φ-mesons in collisions of 2.83 GeV protons with C, Cu, Al, and Au targets has been measured with the ANKE magnetic spectrometer at the Cooler Synchrotron COSY. The φ-mesons were detected at small angles via their K+K− decay. The measured target mass dependence of the production cross section can be related to the in-medium φ width. First comparisons with model calculations suggest a significant broadening of the φ-width relative to its vacuum value of 4.3 MeV/c2.