Nuclear Theory·nucl-th

Wednesday·December 20, 2017

8 papers—3 primary·5 cross-listed

04
A no-go theorem for non-standard explanations of the $τ \to K_{S} π ν_{τ}$ CP asymmetry
Vincenzo Cirigliano🇺🇸 · Andreas Crivellin🇨🇭 · Martin Hoferichter🇺🇸
The CP asymmetry in $τ \to K_{S} π ν_{τ}$ , as measured by the BaBar collaboration, differs from the Standard Model prediction by $2.8 σ$ . Most non-standard interactions do not allow for the required strong phase needed to produce a non-vanishing CP asymmetry, leaving only new tensor interactions as a possible mechanism. We demonstrate that, contrary to previous assumptions in the literature, the crucial interference between vector and tensor phases is suppressed by at least two orders of magnitude due to Watson's final-state-interaction theorem. Furthermore, we find that the strength of the relevant CP-violating tensor interaction is strongly constrained by bounds from the neutron electric dipole moment and $D$ - $D ˉ$ mixing. These observations together imply that it is extremely difficult to explain the current $τ \to K_{S} π ν_{τ}$ measurement in terms of physics beyond the Standard Model originating in the ultraviolet.
↳ hep-phhep-exnucl-thPRL(2018)·80 citations
05
Electromagnetic field effects on $Υ$ -meson dissociation in PbPb collisions at LHC energies
J. Hoelck🇩🇪 · G. Wolschin🇩🇪
We investigate the effect of the electromagnetic field generated in relativistic heavy-ion collisions on the dissociation of $Υ$ mesons. The electromagnetic field is calculated using a simple model which characterizes the emerging quark-gluon plasma (QGP) by its conductivity only. A numerical estimate of the field strength experienced by $Υ$ mesons embedded in the expanding QGP and its consequences on the $Υ$ dissociation is made. The electromagnetic field effects prove to be negligible compared to the established strong-interaction suppression mechanisms.
↳ hep-phnucl-thEPJA(2017)·18 citations
06
Fast neutrino flavor conversion: roles of dense matter and spectrum crossing
Sajad Abbar🇺🇸 · Huaiyu Duan (UNM)🇺🇸
The flavor conversion of a neutrino usually occurs at densities $≲ G_{F}^{- 1} ω$ , whether in the ordinary matter or the neutrino medium, and on time/distance scales of order $ω^{- 1}$ , where $G_{F}$ is the Fermi weak coupling constant and $ω$ is the vacuum oscillation frequency of the neutrino. In 2005 Sawyer and more recently both he and other groups have shown that neutrino flavor conversions can occur on scales much shorter than $ω^{- 1}$ in a very dense, anisotropic neutrino gas such as that in a core-collapse supernova or a binary neutron star merger. It has also been suggested that the fast neutrino flavor conversion require a crossing in the electron lepton number (ELN) angular distribution or spectrum. We study a few simple analytical models with which we elucidate the roles of the dense matter and the ELN spectrum crossing in neutrino fast flavor conversions. We show that a large matter density can induce fast neutrino flavor conversions in certain astrophysical scenarios such as at the early epoch of a core-collapse supernova.
↳ hep-phastro-ph.HEnucl-thPRD(2018)·93 citations
07
Gluon Shadowing in Heavy-Flavor Production at the LHC
Aleksander Kusina🇵🇱 · Jean-Philippe Lansberg🇫🇷 · Ingo Schienbein🇫🇷 · Hua-Sheng Shao🇫🇷
We study the relevance of experimental data on heavy-flavor [ $D^{0}$ , $J / ψ$ , $B \to J / ψ$ and $Υ (1 S)$ mesons] production in proton-lead collisions at the LHC to improve our knowledge of the gluon-momentum distribution inside heavy nuclei. We observe that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) provide a good overall description of the LHC data. We interpret this as a hint that these are the dominant ones. In turn, we perform a Bayesian-reweighting analysis for each particle data sample which shows that each of the existing heavy-quark(onium) data set clearly points --with a minimal statistical significance of 7 $σ$ -- to a shadowed gluon distribution at small $x$ in the lead. Moreover, our analysis corroborates the existence of gluon antishadowing. Overall, the inclusion of such heavy-flavor data in a global fit would significantly reduce the uncertainty on the gluon density down to $x ≃ 7 \times 1 0^{- 6}$ --where no other data exist-- while keeping an agreement with the other data of the global fits. Our study accounts for the factorization-scale uncertainties which dominate for the charm(onium) sector.
↳ hep-phhep-exnucl-exnucl-thPRL(2018)·170 citations
08
Illuminating the photon content of the proton within a global PDF analysis
Valerio Bertone🇳🇱 · Stefano Carrazza🇨🇭 · Nathan P. Hartland🇳🇱 · Juan Rojo🇳🇱
Precision phenomenology at the LHC requires accounting for both higher-order QCD and electroweak corrections as well as for photon-initiated subprocesses. Building upon the recent NNPDF3.1 fit, in this work the photon content of the proton is determined within a global analysis supplemented by the LUXqed constraint relating the photon PDF to lepton-proton scattering structure functions: NNPDF3.1luxQED. The uncertainties on the resulting photon PDF are at the level of a few percent, with photons carrying up to 0.5% of the proton's momentum. We study the phenomenological implications of NNPDF3.1luxQED at the LHC for Drell-Yan, vector boson pair, top quark pair, and Higgs plus vector boson production. We find that photon-initiated contributions can be significant for many processes, leading to corrections of up to 20%. Our results represent a state-of-the-art determination of the partonic structure of the proton including its photon component.
↳ hep-phhep-exnucl-thSciPost Phys.(2018)·292 citations

Affiliations

first authorsco-authorsvia INSPIRE

A no-go theorem for non-standard explanations of the τ→KS​πντ​ CP asymmetry

Electromagnetic field effects on Υ-meson dissociation in PbPb collisions at LHC energies

Fast neutrino flavor conversion: roles of dense matter and spectrum crossing

Gluon Shadowing in Heavy-Flavor Production at the LHC

Illuminating the photon content of the proton within a global PDF analysis

Affiliations

A no-go theorem for non-standard explanations of the $τ \to K_{S} π ν_{τ}$ CP asymmetry

Electromagnetic field effects on $Υ$ -meson dissociation in PbPb collisions at LHC energies