Mon·Jul 28, 2014Monday·July 28, 2014

1. 01*

   Quasifree photoproduction of $\eta$ mesons off protons and neutrons

   A2 Collaboration at MAMI: D. Werthmüller🇨🇭 · L. Witthauer🇨🇭 · I. Keshelashvili🇨🇭 · P. Aguar-Bartolomé🇩🇪 · J. Ahrens🇩🇪 · J.R.M. Annand🇬🇧 · H.J. Arends🇩🇪 · K. Bantawa🇺🇸 · R. Beck🇩🇪 · V. Bekrenev🇷🇺 · A. Braghieri🇮🇹 · D. Branford🇬🇧 and 62 other authors

   Differential and total cross sections for the quasifree reactions $\gamma p\to \eta p$ and $\gamma n\to \eta n$ have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes $\eta \to 2\gamma$ and $\eta \to 3{\pi }^0\to 6\gamma$ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The $\eta$-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the $S_{11}(1535)$ resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy $W=(1670\pm 5)$ MeV with an intrinsic width of $\Gamma \approx 30$ MeV.

   nucl-exhep-exnucl-thPRC(2014)·83 citations
2. 02*

   Toward polarized antiprotons: Machine development for spin-filtering experiments

   C. Weidemann🇮🇹 · F. Rathmann🇩🇪 · H.J. Stein🇩🇪 · B. Lorentz🇩🇪 · Z. Bagdasarian🇬🇪 · L. Barion🇮🇹 · S. Barsov🇷🇺 · U. Bechstedt🇩🇪 · S. Bertelli🇮🇹 · D. Chiladze🇬🇪 · G. Ciullo🇮🇹 · M. Contalbrigo🇮🇹 and 45 other authors

   The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of $49.3$MeV in COSY. The implementation of a low-$\beta$ insertion made it possible to achieve beam lifetimes of ${\tau }_{\mathrm{b}}=8000$s in the presence of a dense polarized hydrogen storage-cell target of areal density $d_{\mathrm{t}}=(5.5\pm 0.2)\times 10^{13}atoms/c{\mathrm{m}}^2$. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent $\bar{p}p$ cross sections via spin filtering.

   ↳ physics.acc-phnucl-exPhys.Rev.ST Accel.Beams(2015)·33 citations
3. 03*

   Dielectron production in 200 GeV p+p and Au+Au collisions at STAR

   Yi Guo (for the STAR collaboration)

   Leptons do not interact strongly with the hot dense medium created in relativistic heavy ion collisions. They can escape the interaction region undistorted and thus carry direct information about the space-time evolution of the expanding system. In the low mass region (LMR, $0.3<M_{ee}<1.1$ GeV/$c^2$), dielectron mass spectra can provide the in-medium vector meson properties, while in the intermediate mass region (IMR, $1.1<M_{ee}<3$ GeV/$c^2$), the slope of dielectron transverse mass spectra is expected to have connection with the QGP temperature. In this paper, we present the centrality and $p_T$ dependence of the dielectron mass spectra measured in STAR experiment at RHIC. The data sets used in the analysis include large statistics samples collected during years 2010 for 200 GeV Au+Au collisions and 2012 for 200 GeV p+p collisions. In order to extract underlying physics, we will compare our results with model calculations.

   ↳ hep-exnucl-exJ.Phys.Conf.Ser.(2014)·5 citations

* 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.