ForwardK+Production in SubthresholdpACollisions at 1.0 GeV

Abstract

K1 -meson production in pA (A C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Jülich accelerator. The complete momentum spectrum of kaons emitted at forward angles, q # 12 ± , has been measured for a beam energy of T p 1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus. DOI: 10.1103/PhysRevLett.87.022301 PACS numbers: 25.40.Ve, 13.75.Cs, 29.40. -n A central topic of hadron physics is the influence of the nuclear medium on elementary processes. This question can be studied by measuring the production of mesons in nuclei using projectiles with energies below the threshold for free NN collisions (so-called subthreshold production). These processes necessarily involve cooperative effects of the nucleons inside the target nucleus. The investigation of K 1 production is particularly well suited for this purpose since the meson is relatively heavy so that its production requires strong medium effects. Furthermore, the K 1 scatters little in nuclear matter so that its final-state interactions are expected to be small. Proton-induced K 1 production at subthreshold energies has been studied at several accelerators. Total cross sections have been measured at the Petersburg Nuclear Physics Institute (PNPI) synchrocyclotron for targets between Be and Pb and projectile energies T p from 0.8 to 1.0 GeV [1]. The results were discussed in terms of different models [1][2][3][4][5], in particular, of single-or two-step reactions involving the creation of an intermediate pion. It was concluded that additional experimental data were needed for an unambiguous determination of the reaction mechanism and the extraction of the information on nuclearmedium effects. Inclusive differential cross sections for pA interactions have been studied at BEVALAC [6], SATURNE [7], and CELSIUS [8]. Partial momentum spectra have been obtained at laboratory emission angles of 10

Meson–nucleus potentials and the search for meson–nucleus bound states

“…The predictions of the theoretical approaches, outlined above, on kaon properties in dense matter can be tested by analyzing proton-nucleus and heavy-ion collision data on kaon spectra, excitation functions (see Section 3.4) and collective flow [34,99-101,112-115]. The latter observable was also recognised as Figure 16: The K + spectra from CBUU calculations (solid lines) in comparison to the data from the ANKE Collaboration [123,127] for p+C reactions at 1.0, 1.2, 1.5, 2.0 and 2.3 GeV . The calculations include both the momentum-dependent nucleon potential and a repulsive K + potential of +20 MeV at density ρ 0 .…”

Subthreshold and near-threshold kaon and antikaon production in proton–nucleus reactions

“…Until now, a lot of data on total [1] and double differential [2][3][4][5][6][7][8]18] K + production cross sections in proton-nucleus collisions at bombarding energies between 0.8 and 2.9 GeV has been collected. Whereas the experimental K + spectra have been taken [2,3,4,18] mostly at laboratory emission angles ≥ 15 • , only in two experiments [5,[6][7][8] the kaon yields have been obtained at forward angles (< 15 • ). In the experiment [6][7][8], K + mesons were measured at laboratory angles < 12 • and for momenta in the restricted range of 150-600 MeV/c, while in the experiment [5], kaons with an emission angle of 10.5 • and a fixed momentum of 1.28 GeV/c were detected.…”

“…Whereas the experimental K + spectra have been taken [2,3,4,18] mostly at laboratory emission angles ≥ 15 • , only in two experiments [5,[6][7][8] the kaon yields have been obtained at forward angles (< 15 • ). In the experiment [6][7][8], K + mesons were measured at laboratory angles < 12 • and for momenta in the restricted range of 150-600 MeV/c, while in the experiment [5], kaons with an emission angle of 10.5 • and a fixed momentum of 1.28 GeV/c were detected. In this respect, it is highly desirable and useful to measure differential K + production cross sections in pA interactions at beam energies below or close to the nucleon-nucleon threshold at forward emission angles and for the momenta ranging from ∼ 0.6 to ∼ 1.0-1.3 GeV/c, since such data in combination with the available differential data may help to shed light on the mechanism of subthreshold and near-threshold kaon creation in these interactions.…”

The legacy of the experimental hadron physics programme at COSY

“…The inclusive momentum spectrum of K + emitted at laboratory angles θ K < 12 • was measured for 1.0 GeV protons hitting C, Cu, and Au targets [206]. The experiment was carried out at ANKE using the delayed-veto technique on the range telescopes [19].…”

“…The experiment was carried out at ANKE using the delayed-veto technique on the range telescopes [19]. Each telescope covered a well-defined interval of K + momentum p K so that the 15 elements spanned the momentum range from 200 to 520 MeV/c [206]. There were typically 100 K + counts per telescope from a four-day run with a carbon target.…”