Nuclear Theory·nucl-th

Monday·November 16, 2015

14 papers—6 primary·8 cross-listed

07
Prompt double $J / ψ$ production in proton-proton collisions at the LHC
S. P. Baranov🇷🇺 · Amir H. Rezaeian🇨🇱
We provide a detailed study of prompt double $J / ψ$ production within the non-relativistic QCD (NRQCD) framework in proton-proton collisions at the LHC. We confront the recent LHC data with the results obtained at leading-order (LO) in the NRQCD framework within two approaches of the collinear factorization and the $k_{T}$ -factorization. We show that the LHCb data are consistent with the $k_{T}$ -factorized LO NRQCD results. We show that the full LO NRQCD formalism cannot describe the recent CMS data, with about one order of magnitude discrepancy. If the CMS data are confirmed, this indicates rather large higher-order corrections for prompt double $J / ψ$ production. We provide various predictions which can further test the NRQCD-based approach at the LHC in a kinematic region that LO contributions dominate. We also investigate long-range in rapidity double $J / ψ$ correlations. We found no evidence of a ridge-like structure for double $J / ψ$ production in proton-proton collisions at the LHC up to subleading $α_{s}^{6}$ accuracy.
↳ hep-phhep-exnucl-thPRD(2016)·35 citations
08
Searching for Axion Dark Matter in Atoms: Oscillating Electric Dipole Moments and Spin-Precession Effects
Benjamin M. Roberts🇦🇺 · Yevgeny V. Stadnik🇦🇺 · Victor V. Flambaum🇦🇺 · Vladimir A. Dzuba🇦🇺
We propose to search for axion dark matter via the oscillating electric dipole moments that axions induce in atoms and molecules. These moments are produced through the intrinsic oscillating electric dipole moments of nucleons and through the $P, T$ -violating nucleon-nucleon interaction mediated by pion exchange, both of which arise due to the axion-gluon coupling, and also directly through the axion-electron interaction. Axion dark matter may also be sought for through the spin-precession effects that axions produce by directly coupling to fermion spins.
↳ physics.atom-phhep-phnucl-th2 citations
09
Searching for Scalar Dark Matter in Atoms and Astrophysical Phenomena: Variation of Fundamental Constants
Yevgeny V. Stadnik🇦🇺 · Benjamin M. Roberts🇦🇺 · Victor V. Flambaum🇦🇺 · Vladimir A. Dzuba🇦🇺
We propose to search for scalar dark matter via its effects on the electromagnetic fine-structure constant and particle masses. Scalar dark matter that forms an oscillating classical field produces `slow' linear-in-time drifts and oscillating variations of the fundamental constants, while scalar dark matter that forms topological defects produces transient-in-time variations of the constants of Nature. These variations can be sought for with atomic clock, laser interferometer and pulsar timing measurements. Atomic spectroscopy and Big Bang nucleosynthesis measurements already give improved bounds on the quadratic interaction parameters of scalar dark matter with the photon, electron, and light quarks by up to 15 orders of magnitude, while Big Bang nucleosynthesis measurements provide the first such constraints on the interaction parameters of scalar dark matter with the massive vector bosons.
↳ hep-phastro-ph.COnucl-thphysics.atom-ph2 citations
10
Predictions for 5.023 TeV Pb+Pb collisions at the LHC
H. Niemi🇩🇪 · K. J. Eskola🇫🇮 · R. Paatelainen🇪🇸 · K. Tuominen🇫🇮
We compute predictions for various low-transverse-momentum bulk observables in $s_{N N} = 5.023$ TeV Pb+Pb collisions at the LHC from the event-by-event next-to-leading-order perturbative-QCD + saturation + viscous hydrodynamics ("EKRT") model. In particular, we consider the centrality dependence of charged hadron multiplicity, flow coefficients of the azimuth-angle asymmetries and correlations of event-plane angles. The centrality dependencies of the studied observables are predicted to be very similar to those at 2.76 TeV, and the magnitudes of the flow coefficients and event-plane angle correlations are predicted to be close to those at 2.76 TeV. The flow coefficients may, however, offer slightly more discriminating power on the temperature dependence of QCD matter viscosity than the 2.76 TeV measurements. Our prediction for the multiplicity in the 0-5\% centrality class, obtained using the two temperature-dependent shear-viscosity-to-entropy ratios that give the best overall fit to RHIC and LHC data is $d N_{ch} / d η_{∣ η ∣ \leq 0.5} = 1876 \dots 2046$ . We also predict a power-law increase from 200 GeV Au+Au collisions at RHIC to 2.76 and 5.023 TeV Pb+Pb collisions at the LHC, $d N_{ch} / d η_{∣ η ∣ \leq 0.5} \propto s^{0.164 \dots 0.174}$ .
↳ hep-phnucl-thPRC(2016)·107 citations
11
Strong Multi-step Interference Effects in 12C(d,p) to the 9/2+ State in 13C
N. Keeley · K. W. Kemper · K. Rusek
The population of the 9.50 MeV 9/2+ resonance in 13C by single neutron transfer reactions is expected to be dominated by the two-step route through the 12C 2+ (4.44 MeV) state, with another possible contribution via the strongly excited 3- (9.64 MeV) resonance in 12C. However, we find that a good description of the angular distribution for population of this state via the 12C(d,p)13C reaction is only possible when both direct 0+ x g_9/2 and two-step (via the 4.44 MeV 12C 2+ state) 2+ x d_5/2 paths are included in a coupled reaction channel calculation. While the calculated angular distribution is almost insensitive to the presence of the two-step path via the 9.64 MeV 12C 3- resonance, despite a much greater contribution to the wave function from the 3- x f_7/2 configuration, its inclusion is required to fit the details of the experimental angular distribution. The very large interference between the various components of the calculations, even when these are small, arises through the ``kinematic'' effect associated with the different transfer routes.
↳ nucl-exnucl-thPRC(2015)·5 citations
12
Higher order effective interactions and effective bosonized model for 2-N particle states
Fabio L. Braghin🇧🇷
In this work, an effective fermion model with particular higher order interactions given by: $I_{I I} = \sum_{n}^{N} g_{2^{n}} (ψ ˉ_{a} ψ_{a})^{2^{n}}$ , for finite $N$ , is investigated by means of the auxiliary field method by taking into account 2 $n$ -particle states as proposed in Ref. [1]. The bosonized model was found to exhibit an approximate symmetry when expanded for weak field fluctuations around the mean field solutions. In the present work, the role of the mean field solutions for the corresponding auxiliary fields is investigated. With the integration of fermions, the resulting determinant is expanded in a polynomial boson model in the weak field approximation and the approximate symmetry found for this series does not appear if the boson mean fields are set to zero.
↳ hep-phhep-thnucl-thEPJ Web Conf.(2016)·0 citations
13
On $γ N \to γ ρ N^{'}$ at large $γ ρ$ invariant mass
R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇫🇷 · S. Wallon🇫🇷
Photoproduction of a pair of particles with large invariant mass is a natural extension of collinear QCD factorization theorems which have been much studied for deeply virtual Compton scattering and deeply virtual meson production. We consider the case where the wide angle Compton scattering subprocess $γ (q q ˉ) \to γ ρ$ factorizes from generalized parton distribution. At dominant twist, separating the transverse (respectively longitudinal) polarization of the $ρ$ meson allows one to get access to chiral-odd (respectively chiral-even) GPDs. This opens a new way to the extraction of these elusive transversity GPDs.
↳ hep-phhep-exnucl-exnucl-th2 citations
14
Experiment summary
Andrea Rossi (Padua University & INFN)🇮🇹
The measurement of the production of particles coming from hard scattering processes covers a fundamental role in the characterization of the system formed in heavy-ion collisions, allowing to probe the microscopic processes underlying the interaction of high energy partons with the medium. An impressive amount of measurements related to jet, quarkonia, open heavy flavor, and electroweak signal production in nucleus-nucleus as well as p(d)-nucleus collisions was delivered by experiments at RHIC and LHC in past years. In these proceedings, the main experimental results presented during the Hard Probes conference are summarized.
↳ hep-exhep-phnucl-exnucl-thNucl.Part.Phys.Proc.(2016)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE