Wed·Nov 16, 2016Wednesday·November 16, 2016

1. 01*

   Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment

   B.S. Henderson🇺🇸 · L.D. Ice🇺🇸 · D. Khaneft🇩🇪 · C. O'Connor🇺🇸 · R. Russell🇺🇸 · A. Schmidt🇺🇸 · J.C. Bernauer🇺🇸 · M. Kohl🇺🇸 · N. Akopov🇦🇲 · R. Alarcon🇺🇸 · O. Ates🇺🇸 · A. Avetisyan🇦🇲 and 58 other authors

   The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, $R_{2\gamma }$, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of $\approx 20°$ to $80°$. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved GEM and MWPC detectors at $12°$, as well as symmetric Møller/Bhabha calorimeters at $1.29°$. A total integrated luminosity of 4.5~fb${}^{-1}$ was collected. In the extraction of $R_{2\gamma }$, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of $R_{2\gamma }$, presented here for a wide range of virtual photon polarization $0.456<ϵ<0.978$, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.

   nucl-exPRL(2017)·126 citations
2. 02*

   Recent results from the NA61/SHINE strong interaction physics programme

   Evgeny Andronov (for the NA61/SHINE Collaboration)🇷🇺

   The main physics goals of the NA61/SHINE programme on strong interactions are the study of the properties of the onset of deconfinement and the search for signatures of the critical point of strongly interacting matter. For this purpose a scan of the two dimensional phase diagram ($T$-${\mu }_B$) is being performed at the SPS by measurements of hadron production in nucleus-nucleus collisions as a function of collision energy and system size. This contribution presents intriguing results on the energy dependence of hadron spectra and yields in inelastic p+p and centrality selected Be+Be and Ar+Sc collisions. In particular, the energy dependence of the signals of deconfinement, the "horn", "step" and "kink", and new results on fluctuations and correlations are shown and compared with the corresponding data of other experiments and model predictions.

   nucl-exEPJ Web Conf.(2017)·0 citations
3. 03*

   Target and beam-target spin asymmetries in exclusive pion electroproduction for $Q^2>1$ GeV${}^2$. II. $ep\to e{\pi }^{0}p$

   P.E. Bosted · A. Kim · K.P. Adhikari · D. Adikaram · Z. Akbar · M.J. Amaryan · S. Anefalos Pereira · H. Avakian · R.A. Badui · J. Ball · I. Balossino · M. Battaglieri and 144 other authors

   Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive ${\pi }^0$ electroproduction reaction ${\gamma }^{\ast }p\to p{\pi }^0$, expanding an analysis of the ${\gamma }^{\ast }p\to n{\pi }^{+}$ reaction from the same experiment. The results were obtained from scattering of 6 GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Lab. The kinematic range covered is $1.1<W<3$ GeV and $1<Q^2<6$ GeV${}^2$. Results were obtained for about 5700 bins in $W$, $Q^2$, \cthcm, and ${\varphi }^{\ast }$. The beam-target asymmetries were found to generally be greater than zero, with relatively modest \phicmsp dependence. The target asymmetries exhibit very strong \phicmsp dependence, with a change in sign occurring between results at low $W$ and high $W$, in contrast to ${\pi }^{+}$ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but significant differences are seen at higher $W$. When combined with cross section measurements, as well as ${\pi }^{+}$ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.

   nucl-exPRC(2017)·12 citations
4. 04*

   Charmed particles production in pA-interactions at 70 GeV

   V. Ryadovikov (for the SVD collaboration)🇷🇺

   The results of the SERP-E-184 experiment at the U-70 accelerator (IHEP, Protvino) are presented. Interactions of the 70 GeV proton beam with carbon, silicon and lead targets were studied to detect decays of charmed $D^0$, ${\bar{D}}^0$, $D^{+}$, $D^{-}$ mesons and ${\Lambda }_c^{+}$ baryon near their production threshold. Measurements of lifetimes and masses have shown a good agreement with PDG data. The inclusive cross sections of charm production and their A-dependencies have been obtained. The yields of these particles are compared with the theoretical predictions and the data of other experiments. The measured cross section of the total open charm production $\sigma (c\bar{c})=7.1\pm 2.3(stat)\pm 1.4(syst)$ $\mu$b/nucleon at the collision c.m. energy $\surd s$ = 11.8 GeV is well above the QCD model predictions. The contributions of different kinds of charmed particles to the total cross section of the open charm production in proton-nucleus interactions vary with energy.

   ↳ hep-exnucl-exEPJ Web Conf.(2016)·0 citations
5. 05*

   Measurement of the pi^0 -> e^+e^-gamma Dalitz decay at the Mainz Microtron

   P. Adlarson · F. Afzal · P. Aguar-Bartolomé · Z. Ahmed · C. S. Akondi · J. R. M. Annand · H. J. Arends · K. Bantawa · R. Beck · H. Berghäuser · M. Biroth · N. S. Borisov and 85 other authors

   The Dalitz decay pi^0 -> e^+e^-gamma has been measured in the gamma p -> pi^0 p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the pi^0 electromagnetic transition form factor, a_pi = 0.030+/-0.010_tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of a_pi is lower than in previous results based on the pi^0 -> e^+e^-gamma decay.

   ↳ hep-exnucl-exPRC(2017)·44 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.