Thu·Sep 17, 2015Thursday·September 17, 2015

1. 01*

   Centrality-dependent modification of jet-production rates in deuteron-gold collisions at $\sqrt{s_{NN}}$=200 GeV

   A. Adare · C. Aidala · N.N. Ajitanand · Y. Akiba · H. Al-Bataineh · J. Alexander · M. Alfred · A. Angerami · K. Aoki · N. Apadula · Y. Aramaki · H. Asano and 473 other authors

   Jet production rates are measured in $p$$+$$p$ and $d$$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the $R=0.3$ anti-$k_t$ algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multi-wire proportional chambers, and the jet transverse momentum ($p_T$) spectra are corrected for the detector response. Spectra are reported for jets with $12<p_T<50$ GeV/$c$, within a pseudorapidity acceptance of $\left|\eta \right|<0.3$. The nuclear-modification factor ($R_{d\mathrm{Au}}$) values for 0\%--100\% $d$$+$Au events are found to be consistent with unity, constraining the role of initial state effects on jet production. However, the centrality-selected $R_{d\mathrm{Au}}$ values and central-to-peripheral ratios ($R_{\mathrm{CP}}$) show large, $p_T$-dependent deviations from unity, which challenge the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei.

   nucl-exPRL(2016)·98 citations
2. 02*

   Single electron yields from semileptonic charm and bottom hadron decays in Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV

   A. Adare · C. Aidala · N.N. Ajitanand · Y. Akiba · R. Akimoto · J. Alexander · M. Alfred · K. Aoki · N. Apadula · Y. Aramaki · H. Asano · E.C. Aschenauer and 421 other authors

   The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy-flavor production in minimum bias Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy-flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks due to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au$+$Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in $p$$+$$p$ collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV and find the fractions to be similar within the large uncertainties on both measurements for $p_T>4$ GeV/$c$. We use the bottom electron fractions in Au$+$Au and $p$$+$$p$ along with the previously measured heavy flavor electron $R_{AA}$ to calculate the $R_{AA}$ for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region $3<p_T<4$ GeV/$c$.

   nucl-exPRC(2016)·81 citations
3. 03*

   Dielectron production in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV

   A. Adare · C. Aidala · N.N. Ajitanand · Y. Akiba · R. Akimoto · J. Alexander · M. Alfred · H. Al-Ta'ani · A. Angerami · K. Aoki · N. Apadula · Y. Aramaki and 436 other authors

   We present measurements of $e^{+}{e}^{-}$ production at midrapidity in Au$+$Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ($m_{ee}<$ 5 GeV/$c^2$) and pair transverse momentum ($p_T$ $<$ 5 GeV/$c$), for minimum bias and for five centrality classes. The \ee yield is compared to the expectations from known sources. In the low-mass region ($m_{ee}=0.30$--0.76 GeV/$c^2$) there is an enhancement that increases with centrality and is distributed over the entire pair \pt range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\pm 0.4(\mathrm{stat})\pm 0.4(\mathrm{syst})\pm 0.2^{\mathrm{model}}$ or to $1.7\pm 0.3(\mathrm{stat})\pm 0.3(\mathrm{syst})\pm 0.2^{\mathrm{model}}$ for minimum bias collisions when the open-heavy-flavor contribution is calculated with {\sc pythia} or {\sc mc@nlo}, respectively. The inclusive mass and $p_T$ distributions as well as the centrality dependence are well reproduced by model calculations where the enhancement mainly originates from the melting of the $\rho$ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region ($m_{ee}$ = 1.2--2.8 GeV/$c^2$), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

   nucl-exPRC(2016)·111 citations
4. 04*

   Background subtraction methods for precision measurements of di-hadron and jet-hadron correlations in heavy ion collisions

   Natasha Sharma🇺🇸 · Joel Mazer🇺🇸 · Meghan Stuart🇺🇸 · Christine Nattrass🇺🇸

   Di-hadron correlations and jet-hadron correlations are frequently used to study interactions of the Quark Gluon Plasma with the hard partons that form jets. The existing background subtraction methods for these studies depend on several assumptions and independent measurements of the Fourier coefficients of the combinatorial background. In this paper, we present two background subtraction methods which use the observation that the near-side correlation signal is negligible for large separations between the associated particle and the trigger. The combinatorial background is fit in this background-dominated region. Including the reaction plane dependence of the raw correlation improves these results. To test the accuracy of these methods, a simple model is used to simulate di-hadron and jet-hadron correlations with a combinatorial background similar to that observed in the data. The true signal is compared to the extracted signal. The results are compared to results from two variants of the Zero-Yield-At-Minimum (ZYAM) method. We test these methods for mid-peripheral and central collisions and for di-hadron and jet-hadron correlations. These methods are more precise than the ZYAM method with fewer assumptions about the shape and level of the combinatorial background, even in central collisions where the experimental resolution on the measurement of the reaction plane dependence is poor. These methods will allow more accurate studies of modifications of the away-side jet and will be particularly useful for studies of jet-hadron correlations, where the combinatorial background is poorly constrained from previous studies.

   nucl-exPRC(2016)·25 citations
5. 05*

   The current evaluation of Vud

   J.C. Hardy🇺🇸 · I.S. Towner🇺🇸

   The Vud element of the Cabibbo-Kobayashi-Maskawa matrix can be determined from several different experimental approaches: either 0+-to-0+ superallowed nuclear beta decays, neutron decay, nuclear mirror decays, or pion beta decay. Currently all give consistent results but, because the nuclear superallowed value has an uncertainty at least a factor of seven less than all other results, it dominates the result. A new survey of world superallowed-decay data establishes the Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better; and all 14 are statistically consistent with one another. This very robust data set yields the result Vud = 0.97417(21), the value we recommend.

   nucl-exhep-phnucl-th0 citations
6. 06*

   Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

   Yu.T. Kiselev🇷🇺 · M. Hartmann🇩🇪 · A. Polyanskiy🇩🇪 · E.Ya. Paryev🇷🇺 · S. Barsov🇷🇺 · M. Buescher🇩🇪 · S. Dymov🇷🇺 · R. Gebel🇯🇵 · V. Hejny🇩🇪 · A. Kacharava🇩🇪 · I. Keshelashvili🇨🇭 · B. Lorentz🇩🇪 and 14 other authors

   The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.

   nucl-exnucl-thPRC(2015)·6 citations
7. 07*

   Identification of new transitions and mass assignments of levels in ${}^{143-153}$Pr

   E. H. Wang🇺🇸 · A. Lemasson🇫🇷 · J. H. Hamilton🇺🇸 · A. V. Ramayya🇺🇸 · J. K. Hwang🇺🇸 · J. M. Eldridge🇺🇸 · A. Navin🇫🇷 · M. Rejmund🇫🇷 · S. Bhattacharyya🇮🇳 · S. H. Liu🇺🇸 · N. T. Brewer🇺🇸 · Y. X. Luo🇺🇸 and 16 other authors

   The previously reported levels assigned to 151,152,153Pr have recently been called into question regarding their mass assignment. The above questioned level assignments are clarified by measuring g-transitions tagged with A and Z in an in-beam experiment in addition to the measurements from 252Cf spontaneous fission (SF) and establish new spectroscopic information from $N=84$ to $N=94$ in the Pr isotopic chain. The isotopic chain 143-153Pr has been studied from the spontaneous fission of 252Cf by using Gammasphere and also from the measurement of the prompt g-rays in coincidence with isotopically-identified fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced using 238U beams on a 9Be target at energies around the Coulomb barrier. The g-g-g-g data from 252Cf (SF) and those from the GANIL in-beam A- and Z-gated spectra were combined to unambiguously assign the various transitions and levels in 151,152,153Pr and other isotopes. New transitions and bands in 145,147,148,149,150Pr were identified by using g-g-g and g-g-g-g coincidences and A and Z gated g-g spectra. The transitions and levels previously assigned to 151,153Pr have been confirmed by the (A,Z) gated spectra. The transitions previously assigned to 152Pr are now assigned to 151Pr on the basis of the (A,Z) gated spectra. Two new bands with 20 new transitions in 152Pr and one new band with 7 new transitions in 153Pr are identified from the g-g-g-g coincidence spectra and the (A,Z) gated spectrum. In addition, new g-rays are also reported in 143-146Pr. New levels of 145,147-153Pr have been established, reliable mass assignments of the levels in 151,152,153Pr have been reported and new transitions have been identified in 143-146Pr showing the new avenues that are opened by combining the two experimental approaches.

   nucl-exPRC(2015)·20 citations
8. 08*

   Unravelling Medium Effects in Heavy Ion Collisions with Zeal

   Rajiv Gavai🇮🇳 · Ambar Jain🇮🇳 · Rishi Sharma🇮🇳

   We propose a new observable, called zeal, to analyze events with jets in heavy ion collisions. The observable measures how a thermal medium affects the multiplicity and distribution of energetic particles in a jet. Using few known models for energy loss and jet quenching, we demonstrate its capability to distinguish the physics of these models.

   ↳ hep-phhep-exnucl-ex3 citations
9. 09*

   Observation of long-range elliptic anisotropies in $\sqrt{s}=$13 and 2.76 TeV $pp$ collisions with the ATLAS detector

   ATLAS Collaboration

   ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, $\Delta \varphi$, and pseudorapidity, $\Delta \eta$, in $\sqrt{s}$=13 and 2.76 TeV $pp$ collisions at the LHC using charged particles measured in the pseudorapidity interval $|\eta |$<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at $\Delta \varphi \sim 0$ that extends over a wide range of $\Delta \eta$, which has been referred to as the "ridge". Per-trigger-particle yields, $Y(\Delta \varphi )$, are measured over 2<$|\Delta \eta |$<5. For both collision energies, the $Y(\Delta \varphi )$ distribution in all multiplicity intervals is found to be consistent with a linear combination of the per-trigger-particle yields measured in collisions with less than 20 reconstructed tracks, and a constant combinatoric contribution modulated by $\cos (2\Delta \varphi )$. The fitted Fourier coefficient, $v_{2,2}$, exhibits factorization, suggesting that the ridge results from per-event $\cos (2\varphi )$ modulation of the single-particle distribution with Fourier coefficients $v_2$. The $v_2$ values are presented as a function of multiplicity and transverse momentum. They are found to be approximately constant as a function of multiplicity and to have a $p_{\mathrm{T}}$ dependence similar to that measured in $p$+Pb and Pb+Pb collisions. The $v_2$ values in the 13 and 2.76 TeV data are consistent within uncertainties. These results suggest that the ridge in $pp$ collisions arises from the same or similar underlying physics as observed in $p$+Pb collisions, and that the dynamics responsible for the ridge has no strong $\sqrt{s}$ dependence.

   ↳ hep-exnucl-exPRL(2016)·555 citations
10. 10*

    $\bar{p}p$ annihilation into $\bar{D}D$ meson pair within an effective Lagrangian model

    R. Shyam🇮🇳 · H. Lenske🇩🇪

    We study the charmed meson pair (${\bar{D}}^0{D}^0$ and $D^{-}{D}^{+}$) production in $\bar{p}p$ annihilation within an effective Lagrangian model that has only the baryon-meson degrees of freedom and involves the physical hadron masses. The reaction amplitudes include terms corresponding to the t-channel ${\Lambda }_c^{+}$, ${\Sigma }_c^{+}$ and ${\Sigma }_c^{++}$ baryon exchanges and the s-channel excitation, propagation and decay of the $\Psi$(3770) resonance into the charmed mesons. The initial- and final-state distortion effects have been accounted for by using a simple eikonal approximation-based procedure in the same way as was done in our previous study of the $\bar{p}p\to {\bar{\Lambda }}_c^{-}{\Lambda }_c^{+}$ reaction within a similar model. The ${\bar{D}}^0{D}^0$ production reaction is dominated by the ${\Lambda }_c^{+}$ baryon exchange process, and the corresponding total cross sections are predicted to be in the range of 0.18 - 0.7 $\mu$b for antiproton beam momenta varying between threshold and 20 $GeV/c$. The $\Psi$(3770) resonance contributions have a large influence on the differential cross sections of the $D^{-}{D}^{+}$ production reaction.

    ↳ hep-phhep-exnucl-exnucl-thPRD(2016)·12 citations
11. 11*

    Effect of Delta potential on the pion-/pion+ ratio in heavy-ion collisions at intermediate energies

    Wen-Mei Guo🇨🇳 · Gao-Chan Yong🇨🇳 · Wei Zuo🇨🇳

    Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, effects of $\Delta$ resonance potential on the free n/p and ${\pi }^{-}/{\pi }^{+}$ ratios in the central collision of ${}^{197}Au{+}^{197}Au$ at beam energies of 200 and 400 MeV/A are studied. It is found that the effect of $\Delta$ potential on the ratio of pre-equilibrium free $n/p$ is invisible. The effect of $\Delta$ isovector potential on the kinetic energy integrating ratio of ${\pi }^{-}/{\pi }^{+}$ may be observable only at lower incident beam energies and with stiffer symmetry energy. The strength of the $\Delta$ isoscalar potential affects the height of the ${\pi }^{-}/{\pi }^{+}$ ratio around the Coulomb peak but does not affect the kinetic energy integrating ratio of ${\pi }^{-}/{\pi }^{+}$. In heavy-ion collisions at intermediate energies, relating to the question of non-conservation of energy on $\Delta$ or $\pi$ productions, one can replace the $\Delta$ potential by nucleon isoscalar potential especially a soft symmetry energy is employed.

    ↳ nucl-thnucl-exPRC(2015)·17 citations
12. 12*

    FPGA-based trigger system for the Fermilab SeaQuest experiment

    Shiuan-Hal Shiu🇺🇸 · Jinyuan Wu🇺🇸 · Randall Evan McClellan🇺🇸 · Ting-Hua Chang🇹🇼 · Wen-Chen Chang🇹🇼 · Yen-Chu Chen🇹🇼 · Ron Gilman🇺🇸 · Kenichi Nakano🇯🇵 · Jen-Chieh Peng🇺🇸 · Su-Yin Wang

    The SeaQuest experiment (Fermilab E906) detects pairs of energetic {\mu}+ and {\mu}- produced in 120 GeV/c proton-nucleon interactions in a high rate environment. The trigger system consists of several arrays of scintillator hodoscopes and a set of field-programmable gate array (FPGA) based VMEbus modules. Signals from up to 96 channels of hodoscope are digitized by each FPGA with a 1-ns resolution using the time-to-digital convertor (TDC) firmware. The delay of the TDC output can be adjusted channel-by-channel in 1-ns steps and then re-aligned with the beam RF clock. The hit pattern on the hodoscope planes is then examined against pre-determined trigger matrices to identify candidate muon tracks. Information on the candidate tracks is sent to the 2nd-level FPGA-based track correlator to find candidate di-muon events. The design and implementation of the FPGA-based trigger system for SeaQuest experiment are presented.

    ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2015)·7 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.