Wed·Sep 30, 2015Wednesday·September 30, 2015

1. 01*

   Nucleon Resonance Transition Formfactors

   I. G. Aznauryan🇦🇲 · V. D. Burkert🇺🇸 · V. I. Mokeev🇺🇸

   We discuss recent results from CLAS on electromagnetic resonance transition amplitudes and their dependence on the distance scale ($Q^2$). From the comparison of these results with most advanced theoretical calculations within QCD-based approaches there is clear evidence that meson-baryon contributions are present and important at large distances, i.e. small $Q^2$, and that quark core contributions dominate the short distance behavior.

   nucl-exhep-lathep-phnucl-th1 citation
2. 02*

   A study of transverse momentum distributions of jets produced in p-p, p-\bar p, d-Au, Au-Au, and Pb-Pb collisions at high energies

   Hua-Rong Wei🇨🇳 · Fu-Hu Liu🇨🇳

   The transverse momentum distributions of jets produced in p-p, p-\bar p, d-Au, Au-Au, and Pb-Pb collisions at high energies with different selected conditions are analyzed by using a multi-source thermal model. The multi-component (mostly two-component) Erlang distribution used in our description is in good agreement with the experimental data measured by the STAR, D0, CDF II, ALICE, ATLAS, and CMS Collaborations. Related parameters are extracted from the transverse momentum distributions and some information on different interacting systems are obtained. In the two-component Erlang distribution, the first component has usually two or more sources which are contributed by strong scattering interactions between two quarks or more quarks and gluons, while the second component has mostly two sources which are contributed by harder head-on scattering between two quarks.

   nucl-exhep-exhep-phnucl-thAdv.High Energy Phys.(2015)·1 citation
3. 03*

   On pseudorapidity distribution and speed of sound in high energy heavy ion collisions based on a new revised Landau hydrodynamic model

   Li-Na Gao🇨🇳 · Fu-Hu Liu🇨🇳

   We propose a new revised Landau hydrodynamic model to study systematically the pseudorapidity distributions of charged particles produced in heavy ion collisions over an energy range from a few GeV to a few TeV per nucleon pair. The interacting system is divided into three sources namely the central, target, and projectile sources respectively. The large central source is described by the Landau hydrodynamic model and further revised by the contributions of the small target/projectile sources. In the calculation, to avoid the errors caused by an unapt conversion or non-division, the rapidity and pseudorapidity distributions are obtained respectively. The modeling results are in agreement with the available experimental data at relativistic heavy ion collider (RHIC), large hadron collider (LHC), and other energies for different centralities. The value of square speed of sound parameter in different collisions has been extracted by us from the widths of rapidity distributions. Our results show that, in heavy ion collisions at RHIC and LHC energies, the central source undergoes through a phase transition from hadronic gas to quark-gluon plasma (QGP) liquid phase; meanwhile, the target/projectile sources remain in the state of hadronic gas. The present work confirms that the QGP is of liquid type rather than that of a gas. The whole region of participants undergoes through a mixed phase consisting of a large quantity of (>90%) QGP liquid and a small quantity of (<10%) hadronic gas.

   nucl-exhep-exhep-phnucl-thAdv.High Energy Phys.(2015)·18 citations
4. 04*

   Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at $\sqrt{\text{s}}$ = 13 TeV

   ALICE Collaboration

   The pseudorapidity ($\eta$) and transverse-momentum ($p_{\mathrm{T}}$) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy $\sqrt{s}$ = 13 TeV. The pseudorapidity distribution in $|\eta |<$ 1.8 is reported for inelastic events and for events with at least one charged particle in $|\eta |<$ 1. The pseudorapidity density of charged particles produced in the pseudorapidity region $|\eta |<$ 0.5 is 5.31 $\pm$ 0.18 and 6.46 $\pm$ 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 $<$ $p_{\mathrm{T}}$ $<$ 20 GeV/c and $|\eta |<$ 0.8 for events with at least one charged particle in $|\eta |<$ 1. The correlation between transverse momentum and particle multiplicity is also investigated by studying the evolution of the spectra with event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators.

   nucl-exhep-exPLB(2016)·216 citations
5. 05*

   Measurement of an excess in the yield of J/$\psi$ at very low $p_{\mathrm{T}}$ in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   We report on the first measurement of an excess in the yield of J/$\psi$ at very low transverse momentum ($p_{\mathrm{T}}<0.3$ GeV/$c$) in peripheral hadronic Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/$\psi$ in the rapidity range $2.5<y<4$ reaches about 7 (2) in the $p_{\mathrm{T}}$ range 0-0.3 GeV/$c$ in the 70-90% (50-70%) centrality class. The J/$\psi$ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/$\psi$ is the underlying physics mechanism. If confirmed, the observation of J/$\psi$ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the Quark-Gluon Plasma.

   nucl-exPRL(2016)·177 citations
6. 06*

   The $Q_{weak}$ Experiment: First Determination of the Weak Charge of the Proton

   Manolis Kargiantoulakis🇺🇸

   The $Q_{weak}$ Collaboration has completed a challenging measurement of the parity-violating asymmetry in elastic electron-proton ($\vec{e}$p) scattering at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The initial result reported here is extracted from the commissioning part of the experiment, constituting about 4% of the full data set. The parity-violating asymmetry at a low momentum transfer $Q^2$=0.025 GeV${}^2$ is $A_{ep}$ = -279 $\pm$ 35 (stat) $\pm$ 31 (syst) ppb, which is the smallest and most precise asymmetry ever measured in $\vec{e}$p scattering. This result allowed the first determination of the weak charge of the proton $Q_W^p$ from a global fit of parity-violating elastic scattering (PVES) results from nuclear targets, where earlier data at higher $Q^2$ constrain uncertainties of hadronic structure. The value extracted from the global fit is $Q_W^p$ (PVES) = 0.064 $\pm$ 0.012, in agreement with the standard model prediction $Q_W^p$ (SM) = 0.0710 $\pm$ 0.0007. The neutral weak charges of up and down quarks are extracted from a combined fit of the PVES results with a previous atomic parity violation (APV) measurement on ${}^{133}$Cs. The analysis of the full $Q_{weak}$ data is ongoing and expected to yield a value for the asymmetry within 10 ppb of precision. Because of the suppression of $Q_W^p$, such a high precision measurement will place significant constraints to models of physics beyond the standard model.

   nucl-ex0 citations
7. 07*

   Di-Jet Imbalance Measurements in Central Au+Au Collisions at $\sqrt{s_{NN}}=200$ GeV from STAR

   Kolja Kauder (for the STAR Collaboration)🇺🇸

   The STAR collaboration reports the first measurements of the transverse momentum asymmetry $A_J$ of di-jet pairs in central gold-gold collisions and minimum bias proton-proton collisions at $\sqrt{s_{NN}}=200$ GeV at RHIC. We focus on anti-$k_T$ di-jets with a leading jet $p_T>20$ GeV/$c$ and a subleading jet $p_T>10$ GeV/$c$, with a constituent cut of 2 GeV/$c$, which reduces the effect of the underlying heavy-ion background. We examine the evolution of $A_J$ while reclustering these same di-jets with a lower constituent cut of 200 MeV/$c$. For the low $p_T$ constituent cut with a resolution parameter of $R=0.4$, the balance between the di-jets is restored to the level of p+p collisions which indicates the lost energy observed for di-jets with a constituent cut of $p_T^{\text{Cut}}>2$ GeV/$c$ is recovered. Further variations of $R$ and the constituent \pT-cutoff indicate that the lost energy is redistributed in the form of soft particles, accompanied by a broadening of the jet structure.

   nucl-exNucl.Part.Phys.Proc.(2016)·3 citations
8. 08*

   Self-similarity of strangeness production in pp collisions at RHIC

   M. Tokarev (1) · I. Zborovsky (2) ((1) Veksler and Baldin Laboratory of High Energy Physics, Joint Institute for Nuclear Research, Dubna, Moscow region, Russia (2) Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Rez, Czech Republic)

   New experimental data on transverse momentum spectra of strange particles (KS0, K-, K*, phi,...) produced in pp collisions at sqrt s = 200 GeV obtained by the STAR and PHENIX collaborations at RHIC are analysed in the framework of z-scaling approach. Scaling properties of the data z-presentation are illustrated. Self-similarity of strange particle production is discussed. A microscopic scenario of constituent interactions developed within the z-scaling approach is used to study constituent energy loss, proton momentum fraction and recoil mass in dependence on the transverse momentum, strangeness, and mass of the inclusive particle. The obtained results can be useful for understanding strangeness origin, for searching for new physics with strange probes and can serve as a benchmark for complex analyses of self-similar features of strange production in heavy ion collisions.

   ↳ hep-phnucl-exnucl-thJ.Phys.Conf.Ser.(2016)·4 citations
9. 09*

   A covariant model for the negative parity resonances of the nucleon

   G. Ramalho🇧🇷

   We present a model for the ${\gamma }^{\ast }N\to N^{\ast }$ helicity amplitudes, where $N$ is the nucleon and $N^{\ast }$ is a negative parity nucleon excitation, member of the $SU(6)$-multiplet $[70,1^{-}]$. The model combines the results from the single quark transition model for the helicity amplitudes with the results of the covariant spectator quark model for the ${\gamma }^{\ast }N\to N^{\ast }(1535)$ and ${\gamma }^{\ast }N\to N^{\ast }(1520)$ transitions. With the knowledge of the amplitudes $A_{1/2}$ and $A_{3/2}$ for those transitions we calculate three independent coefficients defined by the single quark transition model and make predictions for the helicity amplitudes associated with the ${\gamma }^{\ast }N\to N^{\ast }(1650)$, ${\gamma }^{\ast }N\to N^{\ast }(1700)$, ${\gamma }^{\ast }N\to \Delta (1620)$, and ${\gamma }^{\ast }N\to \Delta (1700)$ transitions. In order to facilitate the comparison with future experimental data at high $Q^2$, we provide also simple parametrizations for the amplitudes, compatible with the expected falloff at high $Q^2$.

   ↳ hep-phhep-exhep-latnucl-ex+1J.Phys.Conf.Ser.(2016)·0 citations
10. 10*

    Design, development and performance study of six-gap glass MRPC detectors

    Moon Moon Devi🇮🇳 · Naba K. Mondal🇮🇳 · B. Satyanarayana🇮🇳 · R.R. Shinde🇮🇳

    The Multigap Resistive Plate Chambers (MRPCs) are gas ionization detectors with multiple gas sub-gaps made of resistive electrodes. The high voltage (HV) is applied on the outer surfaces of outermost resistive plates only, while the interior plates are left electrically floating. The presence of multiple narrow sub--gaps with high electric field results in faster signals on the outer electrodes, thus improving the detector's time resolution. Due to their excellent performance and relatively low cost, the MRPC detector has found potential application in Time-of-Flight (TOF) systems. Here we present the design, fabrication, optimization of the operating parameters such as the HV, the gas mixture composition, and, performance of six--gap glass MRPC detectors of area 27cm $\times$ 27 cm, which are developed in order to find application as trigger detectors, in TOF measurement etc. The design has been optimized with unique spacers and blockers to ensure a proper gas flow through the narrow sub-gaps, which are 250 $\mu$m wide. The gas mixture consisting of R134A, Isobutane and SF${}_6$, and the fraction of each constituting gases has been optimized after studying the MRPC performance for a set of different concentrations. The counting efficiency of the MRPC is about 95% at $17.9$ kV. At the same operating voltage, the time resolution, after correcting for the walk effect, is found to be about $219$ ps.

    ↳ physics.ins-dethep-exnucl-exEPJC(2016)·9 citations
11. 11*

    On Extraction of Chemical Potentials of Quarks from Particle Transverse Momentum Spectra in High Energy Collisions

    Hong Zhao🇨🇳 · Fu-Hu Liu🇨🇳

    We present two methods to extract the chemical potentials of quarks in high energy collisions. The first method is based on the ratios of negatively/positively charged particles, and the temperatures extracted from the transverse momentum spectra of related hadrons are needed. The second method is based on the chemical potentials of some particles, and we also need the transverse momentum spectra of related hadrons. To extract the quark chemical potentials, we would like to propose experimental collaborations to measure simultaneously not only the transverse momentum spectra of anti-p, p, K^-, K^+, pion^-, and pion^+, but also those of D^-, D^+, B^-, and B^+ (even those of Delta^++, Delta^-, and Omega^-) in high energy nuclear collisions

    ↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2015)·9 citations
12. 12*

    Transverse momentum and pseudorapidity distributions of final-state particles and spatial structure pictures of interacting system in p-Pb collisions at \sqrt{s_{NN}}=5.02 TeV

    Fu-Hu Liu🇨🇳 · Hua-Rong Wei🇨🇳 · Roy A. Lacey🇺🇸

    The transverse momentum and pseudorapidity distributions of final-state particles produced in proton-lead (p-Pb) collisions at center-of-mass energy per nucleon pair \sqrt{s_{NN}}=5.02 TeV are studied in the framework of a multisource thermal model. Experimental results measured by the ALICE and CMS Collaborations are described by the Tsallis transverse momentum distribution and the two-cylinder pseudorapidity distribution. Based on the parameter values extracted from the transverse momentum and pseudorapidity distributions, some other quantities are extracted. Then, the structure pictures of interacting system at the stage of kinetic freeze-out in some spaces are obtained.

    ↳ nucl-thhep-exhep-phnucl-exEPJA(2015)·4 citations
13. 13*

    On Productions of Net-baryons in Central Au-Au Collisions at RHIC Energies

    Ya-Hui Chen🇨🇳 · Guo-Xing Zhang🇨🇳 · Fu-Hu Liu🇨🇳

    The transverse momentum and rapidity distributions of net-baryons (baryons minus anti-baryons) produced in central gold-gold (Au-Au) collisions at 62.4 and 200 GeV are analyzed in the framework of a multisource thermal model. Each source in the model is described by the Tsallis statistics to extract the effective temperature and entropy index from the transverse momentum distribution. The two parameters are used as input to describe the rapidity distribution and to extract the rapidity shift and contribution ratio. Then, the four types of parameters are used to structure some scatter plots of the considered particles in some three-dimensional (3D) spaces at the stage of kinetic freeze-out, which are expected to show different characteristics for different particles and processes. The related methodology can be used in the analyzes of particle production and event holography, which are useful for us to better understand the interacting mechanisms.

    ↳ nucl-thhep-exhep-phnucl-exAdv.High Energy Phys.(2015)·5 citations
14. 14*

    The COHERENT Experiment at the Spallation Neutron Source

    COHERENT Collaboration: D. Akimov · P. An · C. Awe · P.S. Barbeau · P. Barton · B. Becker · V. Belov · A. Bolozdynya · A. Burenkov · B. Cabrera-Palmer · J.I. Collar · R.J. Cooper and 54 other authors

    The COHERENT collaboration's primary objective is to measure coherent elastic neutrino-nucleus scattering (CEvNS) using the unique, high-quality source of tens-of-MeV neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). In spite of its large cross section, the CEvNS process has never been observed, due to tiny energies of the resulting nuclear recoils which are out of reach for standard neutrino detectors. The measurement of CEvNS has now become feasible, thanks to the development of ultra-sensitive technology for rare decay and weakly-interacting massive particle (dark matter) searches. The CEvNS cross section is cleanly predicted in the standard model; hence its measurement provides a standard model test. It is relevant for supernova physics and supernova-neutrino detection, and enables validation of dark-matter detector background and detector-response models. In the long term, precision measurement of CEvNS will address questions of nuclear structure. COHERENT will deploy multiple detector technologies in a phased approach: a 14-kg CsI[Na] scintillating crystal, 15 kg of p-type point-contact germanium detectors, and 100 kg of liquid xenon in a two-phase time projection chamber. Following an extensive background measurement campaign, a location in the SNS basement has proven to be neutron-quiet and suitable for deployment of the COHERENT detector suite. The simultaneous deployment of the three COHERENT detector subsystems will test the $N^2$ dependence of the cross section and ensure an unambiguous discovery of CEvNS. This document describes concisely the COHERENT physics motivations, sensitivity and plans for measurements at the SNS to be accomplished on a four-year timescale.

    ↳ physics.ins-dethep-exnucl-ex108 citations
15. 15*

    How strange is pion electroproduction?

    Mikhail Gorchtein🇩🇪 · Hubert Spiesberger🇩🇪 · Xilin Zhang🇺🇸

    We consider pion production in parity-violating electron scattering (PVES) in the presence of nucleon strangeness in the framework of partial wave analysis with unitarity. Using the experimental bounds on the strange form factors obtained in elastic PVES, we study the sensitivity of the parity-violating asymmetry to strange nucleon form factors. For forward kinematics and electron energies above 1 GeV, we observe that this sensitivity may reach about 20\% in the threshold region. With parity-violating asymmetries being as large as tens p.p.m., this study suggests that threshold pion production in PVES can be used as a promising way to better constrain strangeness contributions. Using this model for the neutral current pion production, we update the estimate for the dispersive $\gamma Z$-box correction to the weak charge of the proton. In the kinematics of the Qweak experiment, our new prediction reads Re${\square }_{\gamma Z}^V(E=1.165\mathrm{GeV})=(5.58\pm 1.41)\times 10^{-3}$, an improvement over the previous uncertainty estimate of $\pm 2.0\times 10^{-3}$. Our new prediction in the kinematics of the upcoming MESA/P2 experiment reads Re${\square }_{\gamma Z}^V(E=0.155\mathrm{GeV})=(1.1\pm 0.2)\times 10^{-3}$.

    ↳ nucl-thhep-phnucl-exPLB(2016)·12 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.