Wed·Dec 6, 2017Wednesday·December 6, 2017

1. 01*

   Azimuthal anisotropy in Cu+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV

   STAR Collaboration: L. Adamczyk🇵🇱 · J. R. Adams🇺🇸 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · N. N. Ajitanand🇺🇸 · I. Alekseev🇷🇺 · D. M. Anderson🇺🇸 · R. Aoyama🇯🇵 · A. Aparin🇷🇺 · D. Arkhipkin🇺🇸 and 341 other authors

   The azimuthal anisotropic flow of identified and unidentified charged particles has been systematically studied in Cu+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV for harmonics $n=$ 1-4 in the pseudorapidity range $|\eta |<1$. The directed flow in Cu+Au collisions is compared with the rapidity-odd and, for the first time, the rapidity-even components of charged particle directed flow in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200~GeV. The slope of the directed flow pseudorapidity dependence in Cu+Au collisions is found to be similar to that in Au+Au collisions, with the intercept shifted toward positive $\eta$ values, i.e., the Cu-going direction. The mean transverse momentum projected onto the spectator plane, $⟨p_x⟩$, in Cu+Au collision also exhibits approximately linear dependence on $\eta$ with the intercept at about $\eta \approx -0.4$, closer to the rapidity of the Cu+Au system center-of-mass. The observed dependencies find natural explanation in a picture of the directed flow originating partly due the "tilted source" and partly due to the rapidity dependent asymmetry in the initial density distribution. Charge-dependence of the $⟨p_x⟩$ was also observed in Cu+Au collisions, indicating an effect of the initial electric field created by charge difference of the spectator protons in two colliding nuclei. The rapidity-even component of directed flow in Au+Au collisions is close to that in Pb+Pb collisions at $\sqrt{s_{{}_{NN}}}$ = 2.76 TeV, indicating a similar magnitude of dipole-like fluctuations in the initial-state density distribution. Higher harmonic flow in Cu+Au collisions exhibits similar trends to those observed in Au+Au and Pb+Pb collisions and is qualitatively reproduced by a viscous hydrodynamic model and a multi-phase transport model. For all harmonics with $n\ge 2$ we observe an approximate scaling of $v_n$ with the number of constituent quarks.

   nucl-exPRC(2018)·46 citations
2. 02*

   Physics perspectives with AFTER@LHC (A Fixed Target ExpeRiment at LHC)

   L. Massacrier🇫🇷 · M. Anselmino🇮🇹 · R. Arnaldi🇮🇹 · S.J. Brodsky🇺🇸 · V. Chambert🇫🇷 · C. Da Silva🇺🇸 · J.P. Didelez🇫🇷 · M.G. Echevarria🇮🇹 · E.G. Ferreiro🇪🇸 · F. Fleuret🇫🇷 · Y. Gao🇨🇳 · B. Genolini🇫🇷 and 29 other authors

   AFTER@LHC is an ambitious fixed-target project in order to address open questions in the domain of proton and neutron spins, Quark Gluon Plasma and high-$x$ physics, at the highest energy ever reached in the fixed-target mode. Indeed, thanks to the highly energetic 7 TeV proton and 2.76 A.TeV lead LHC beams, center-of-mass energies as large as $\sqrt{s_{NN}}$ = 115 GeV in pp/pA and $\sqrt{s_{NN}}$ = 72 GeV in AA can be reached, corresponding to an uncharted energy domain between SPS and RHIC. We report two main ways of performing fixed-target collisions at the LHC, both allowing for the usage of one of the existing LHC experiments. In these proceedings, after discussing the projected luminosities considered for one year of data taking at the LHC, we will present a selection of projections for light and heavy-flavour production.

   ↳ hep-exnucl-exEPJ Web Conf.(2018)·11 citations
3. 03*

   Performance of a MICROMEGAS-based TPC in a high-energy neutron beam

   Lucas Snyder🇺🇸 · Brett Manning🇺🇸 · Nathaniel S. Bowden🇺🇸 · Jeremy Bundgaard🇺🇸 · Robert J. Casperson🇺🇸 · Daniel A. Cebra🇺🇸 · Timothy Classen🇺🇸 · Dana L. Duke🇺🇸 · Joshua Gearhart🇺🇸 · Uwe Greife🇺🇸 · Christian Hagmann🇺🇸 · Michael Heffner🇺🇸 and 18 other authors

   The MICROMEGAS (MICRO-MEsh GAseous Structure) charge amplification structure has found wide use in many detection applications, especially as a gain stage for the charge readout of Time Projection Chambers (TPCs). Here we report on the behavior of a MICROMEGAS TPC when operated in a high-energy (up to 800 MeV) neutron beam. It is found that neutron-induced reactions can cause discharges in some drift gas mixtures that are stable in the absence of the neutron beam. The discharges result from recoil ions close to the MICROMEGAS that deposit high specific ionization density and have a limited diffusion time. For a binary drift gas, increasing the percentage of the molecular component (quench gas) relative to the noble component and operating at lower pressures generally improves stability.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·7 citations
4. 04*

   Precise Neutron Lifetime Measurement with a Solenoidal Coil

   Naoyuki Sumi🇯🇵 · Hidetoshi Otono🇯🇵 · Tamaki Yoshioka🇯🇵 · Kenji Mishima🇯🇵 · Yasuhiro Makida🇯🇵

   The neutron lifetime, $\tau$ = 880.2 $\pm$ 1.0 sec , is an important parameter for particle physics and cosmology. There is, however, an 8.4 sec (4.0$\sigma$) deviation between the measured value of the neutron lifetime using two methods : one method counts neutrons that survive after some time, while the other counts protons resulting from neutron beta decay. A new method is being implemented at J-PARC / MLF / BL05 using a pulsed cold neutron beam. A Time Projection Chamber (TPC) records both the electrons from neutron beta decay and protons from the neutron-${}^3$He capture reactions in order to estimate the neutron flux. Electron background signals require the largest correction and are source of uncertainty for this experiment. A solenoidal magnetic field can greatly reduce this background. The TPC drift region must be divided into three region in this case. A prototype detector was developed to study the multi drift layer TPC. The status of a study using a prototype detector is reported in this paper.

   ↳ physics.ins-detnucl-exJPS Conf.Proc.(2018)·4 citations
5. 05*

   Diffuse axion-like particle searches

   Hendrik Vogel🇺🇸 · Ranjan Laha🇩🇪 · Manuel Meyer🇺🇸

   We propose a new method to search for axion-like particles (ALPs) based on the gamma-rays produced concomitant with high-energy astrophysical neutrinos. The existence of high-energy neutrinos implies production of gamma-rays in the same sources. Photons can convert into ALPs in the sources' magnetic fields, and will travel as ALPs through extragalactic space. Back-conversion in the Milky Way's magnetic field leads to a diffuse anisotropic high-energy photon flux that existing and upcoming gamma-ray detectors, like HAWC, CTA, and LHAASO can detect. This method probes unexplored ALP parameter space, with LHAASO being realistically sensitive to couplings above $10^{-11}\mathrm{Ge}{\mathrm{V}}^{-1}$ and masses up to $3\times 10^{-6}\mathrm{eV}$ in ten years. Our technique also explores viable ALP dark matter parameter space.

   ↳ hep-phastro-ph.COastro-ph.HEhep-ex+1PoS(2019)·35 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.