Nuclear Experiment·nucl-ex
9 papers—7 primary·2 cross-listed·reconstructed*
These conferences proceedings summarize the experimental findings obtained in small collision systems at the LHC, as presented in the special session on "QGP in small systems?" at the Quark Matter 2015 conference. (The arXiv version is significantly longer than the printed proceedings, with more details and a short discussion.)
M. Bazzi🇮🇹 · G. Beer🇨🇦 · G. Bellotti🇮🇹 · C. Berucci🇦🇹 · A.M. Bragadireanu🇷🇴 · D. Bosnar🇭🇷 · M. Cargnelli🇦🇹 · C. Curceanu🇮🇹 · A.D. Butt🇮🇹 · A. d'Uffizi🇮🇹 · C. Fiorini🇮🇹 · F. Ghio🇮🇹 and 20 other authors
We measured the -series X-rays of the exotic atom in the SIDDHARTA experiment with a gaseous hydrogen target of 1.3 g/l, which is about 15 times the of hydrogen gas. At this density, the absolute yields of kaonic X-rays, when a negatively charged kaon stopped inside the target, were determined to be 0.012 for and 0.043 for all the -series transitions . These results, together with the KEK E228 experiment results, confirm for the first time a target density dependence of the yield predicted by the cascade models, and provide valuable information to refine the parameters used in the cascade models for the kaonic atoms.
P. Cabanelas · J. Cruz · M. Fonseca · A. Henriques · F. Lourenço · H. Luís · J. Machado · J. Pires Ribeiro · A. Sánchez-Benítez · P. Teubig · P. Velho · M. Zarza-Moreno · D. Galaviz · A.P. Jesus
We have studied the high energy gamma-rays produced in the reaction F(p,)O for incident proton energies from 1.5 to 4.0 MeV over NaF/Ag and CaF/Ag thin targets in two different sets of data. Gamma-rays were detected with a High Purity Ge detector with an angle of 130 with respect to the beam axis. The cross-sections for the high energy gamma-rays of 6.129, 6.915 and 7.115 MeV have been measured for the whole group between 5 and 7.2 MeV with accuracy better than 10\%. A new energy range was covered and more points are included in the cross-sections data base expanding the existing set of data. Results are in agreement with previous measurements in similar conditions.
S. Y. Ryu🇯🇵 · J. K. Ahn🇰🇷 · T. Nakano🇯🇵 · D. S. Ahn🇯🇵 · S. Ajimura🇯🇵 · H. Akimune🇯🇵 · Y. Asano · W. C. Chang🇹🇼 · J. Y. Chen🇹🇼 · S. Date🇯🇵 · H. Ejiri🇯🇵 · H. Fujimura🇯🇵 and 60 other authors
The - interference effect in the reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between and production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when pairs are observed at forward angles, but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the GeV bump structure in forward differential cross sections for photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange and rescattering processes via other hyperon states.
M. J. Bales🇺🇸 · R. Alarcon🇺🇸 · C. D. Bass🇺🇸 · E. J. Beise🇺🇸 · H. Breuer🇺🇸 · J. Byrne🇬🇧 · T. E. Chupp🇺🇸 · K. J. Coakley🇺🇸 · R. L. Cooper🇺🇸 · M. S. Dewey🇺🇸 · S. Gardner🇺🇸 · T. R. Gentile🇺🇸 and 6 other authors
The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335 0.00005 [stat] 0.00015 [syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14~keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582 0.00023 [stat] 0.00062 [syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.
D. Rimal · D. Adikaram · B.A. Raue · L.B. Weinstein · J. Arrington · W.K. Brooks · M. Ungaro · K.P. Adhikari · Z. Akbar · S. Anefalos Pereira · R.A. Badui · J. Ball and 133 other authors
[Background] The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments show a significant disagreement that grows with the squared four momentum transfer (). Calculations have shown that the two measurements can be largely reconciled by accounting for the contributions of two-photon exchange (TPE). TPE effects are not typically included in the standard set of radiative corrections since theoretical calculations of the TPE effects are highly model dependent, and, until recently, no direct evidence of significant TPE effects has been observed. [Purpose] We measured the ratio of positron-proton to electron-proton elastic-scattering cross sections in order to determine the TPE contribution to elastic electron-proton scattering and thereby resolve the proton electric form factor discrepancy. [Methods] We produced a mixed simultaneous electron-positron beam in Jefferson Lab's Hall B by passing the 5.6 GeV primary electron beam through a radiator to produce a bremsstrahlung photon beam and then passing the photon beam through a convertor to produce electron/positron pairs. The mixed electron-positron (lepton) beam with useful energies from approximately 0.85 to 3.5 GeV then struck a 30-cm long liquid hydrogen (LH) target located within the CEBAF Large Acceptance Spectrometer (CLAS). By detecting both the scattered leptons and the recoiling protons we identified and reconstructed elastic scattering events and determined the incident lepton energy. A detailed description of the experiment is presented.
R. Thies · A. Heinz · T. Adachi · Y. Aksyutina · J. Alcantara-Núñes · S. Altstadt · H. Alvarez-Pol · N. Ashwood · T. Aumann · V. Avdeichikov · M. Barr · S. Beceiro-Novo and 110 other authors
Background: Models describing nuclear fragmentation and fragmentation-fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool to reach the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from 10,12-18C and 10-15B isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent dataset. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic 10,12-18C and 10-15B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that EPAX is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data have allowed for a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.
Philipp Gubler🇮🇹 · Wolfram Weise🇩🇪
A detailed analysis of the lowest two moments of the meson spectral function in vacuum and nuclear matter is performed. The consistency is examined between the constraints derived from finite energy QCD sum rules and the spectra computed within an improved vector dominance model, incorporating the coupling of kanonic degrees of freedom with the bare meson. In the vacuum, recent accurate measurements of the cross section allow us to determine the spectral function with high precision. In nuclear matter, the modification of the spectral function can be described by the interactions of the kaons from with the surrounding nuclear medium. This leads primarily to a strong broadening and an asymmetric deformation of the meson peak structure. We confirm that, both in vacuum and nuclear matter, the zeroth and first moments of the corresponding spectral functions satisfy the requirements of the finite energy sum rules to a remarkable degree of accuracy. Limits on the strangeness sigma term of the nucleon are examined in this context. Applying our results to the second moment of the spectrum, we furthermore discuss constraints on four-quark condensates and the validity of the commonly used ground state saturation approximation.
Horst Lenske🇩🇪 · Xu Cao🇨🇳 · Madhumita Dhar🇩🇪 · Theodoros Gaitanos🇬🇷 · Radhey Shyam🇮🇳
The production of strangeness on the nucleon and hyperon and hypernuclear production in heavy ion collisions at relativistic energies and in antiproton annihilation on nuclei is discussed. The reaction process is described by transport theory with focus on channels and a comparison of different model interactions. The interactions of hyperons in nuclear matter is investigated in a novel SU(3) approach. An outlook to the sector and physics is given.
* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.