Wed·Sep 19, 2018Wednesday·September 19, 2018

1. 01*

   Impact of QCD jets and heavy-quark production in cosmic-ray proton atmospheric showers up to 10${}^{20}$ eV

   David d'Enterria🇨🇭 · Tanguy Pierog🇩🇪 · Guanhao Sun🇨🇭

   The PYTHIA 6 Monte Carlo (MC) event generator, commonly used in collider physics, is interfaced for the first time with a fast transport simulation of a hydrogen atmosphere, with the same density as air, in order to study the properties of extended atmospheric showers (EAS) produced by cosmic ray protons with energies E${}_{CR}\approx 10^{14}$--$10^{20}$ eV. At variance with the hadronic MC generators (EPOS-LHC, QGSJET, and SIBYLL) commonly used in cosmic-rays physics, PYTHIA includes the generation of harder hadronic jets and heavy (charm and bottom) quarks, thereby producing higher transverse momentum final particles, that could explain several anomalies observed in the data. The electromagnetic, hadronic, and muonic properties of EAS generated with various settings of PYTHIA 6, tuned to proton-proton data measured at the LHC, are compared to those from EPOS-LHC, QGSJET 01, QGSJET II, and SIBYLL 2.1. Despite their different underlying parton dynamics, the characteristics of the EAS generated with PYTHIA 6 are in between those predicted by the rest of MC generators. The only exceptions are the muonic components at large transverse distances from the shower axis, where PYTHIA predicts more activity than the rest of the models. Heavy-quark production, as implemented in this study for a hydrogen atmosphere, does not seem to play a key role in the EAS muon properties, pointing to nuclear effects as responsible of the muon anomalies observed in the air-shower data.

   ↳ astro-ph.HEhep-exhep-phnucl-ex+1ApJ(2019)·15 citations
2. 02*

   Weak radius of the proton

   C. J. Horowitz🇺🇸

   The weak charge of the proton determines its coupling to the $Z^0$ boson. The distribution of weak charge is found to be dramatically different from the distribution of electric charge. The proton's weak radius $R_W=1.545\pm 0.017$ fm is 80\% larger than its charge radius $R_{ch}\approx 0.84$ fm because of a very large pion cloud contribution. This large weak radius can be measured with parity violating electron scattering and may provide insight into the structure of the proton, various radiative corrections, and possible strange quark contributions.

   ↳ nucl-thhep-phnucl-exPLB(2019)·7 citations
3. 03*

   Open heavy-flavour measurements with ALICE at the LHC

   Fabio Colamaria (for the ALICE Collaboration)🇮🇹

   Heavy quarks are produced in the early stages of ultra-relativistic heavy-ion collisions, and their number is preserved throughout the subsequent evolution of the system. Therefore, they constitute ideal probes for characterising the Quark--Gluon Plasma (QGP) medium and for the study of its transport properties. In particular, heavy quarks interact with the partonic constituents of the plasma, losing energy, and are expected to be sensitive to the medium collective motion induced by its hydrodynamical evolution. In pp collisions, the measurement of heavy-flavour hadron production provides a reference for heavy-ion studies, and allows also testing perturbative QCD calculations in a wide range of collision energies. Similar studies in p--Pb collisions help in disentangling cold nuclear matter effects from modifications induced by the presence of a QGP medium, and are also useful to investigate the possible existence of collective phenomena also in this system. The ALICE detector provides excellent performances in terms of particle identification and vertexing capabilities. Hence, it is fully suited for the reconstruction of charmed mesons and baryons and of electrons from heavy-flavour hadron decays at central rapidity. Furthermore, the ALICE muon spectrometer allows reconstructing heavy-flavour decay muons at forward rapidity. A review of the main ALICE results on open heavy flavour production in pp, p--Pb and Pb--Pb collisions is presented. Recent, more differential measurements are also shown, including azimuthal correlations of heavy-flavour particles with charged hadrons in p--Pb collisions, and D-meson tagged-jet production in p--Pb and Pb--Pb collisions.

   ↳ hep-exnucl-exEPJ Web Conf.(2018)·0 citations
4. 04*

   Final-state interactions of the Higgs boson in quark-gluon matter

   David d'Enterria🇨🇭 · Constantin Loizides🇺🇸

   In the first version of this paper \cite{dEnterria:2018bqi}, we presented a study of the final-state interactions of the Higgs boson in the hot and dense quark-gluon systems produced in pp, pPb, and PbPb collisions at CERN LHC and FCC energies. By computing the leading-order diagrams of the Higgs-parton scattering cross sections in perturbative QCD, and by embedding the produced Higgs bosons in an expanding quark-gluon medium modeled with 2D+1 viscous hydrodynamics with various QCD equations of state, we presented estimates of the expected scalar boson yields as functions of transverse momentum $p_{\mathrm{T}}^H$, and produced medium space-time size. A moderate suppression of the scalar boson yields was predicted due to medium-enhanced $H\to gg,q\bar{q}$ decays, in detriment of the $H\to \gamma \gamma ,4\ell$ channels that are typically used to observe the Higgs particle. After our work appeared, J. Ghiglieri and U. Wiedemann \cite{Ghiglieri:2019lzz} have presented thermal-field-theory calculations that indicate that the $H\to gg,q\bar{q}$ partial decays widths remain basically unaffected by interactions with surrounding partons in the kinematic range of relevance of our study. Such a theoretical result, in contradiction with our estimates, has brought us to revisit our calculations and to realize of the quantitative importance of thermal virtual corrections, neglected in our first work, that are as large as the real ones and of opposite sign. Such virtual corrections significantly reduce the Higgs-parton "absorption" cross sections originally computed in Ref. \cite{dEnterria:2018bqi}, and make the Higgs boson suppression negligible in the kinematic regime considered.

   ↳ hep-phhep-exnucl-exnucl-th13 citations
5. 05*

   The GRIFFIN Facility for Decay-Spectroscopy Studies at TRIUMF-ISAC

   A.B. Garnsworthy🇨🇦 · C.E. Svensson🇨🇦 · M. Bowry🇨🇦 · R. Dunlop🇨🇦 · A.D. MacLean🇨🇦 · B. Olaizola🇨🇦 · J.K. Smith🇺🇸 · F.A. Ali🇨🇦 · C. Andreoiu🇨🇦 · J.E. Ash🇺🇸 · W.H. Ashfield🇺🇸 · G.C. Ball🇨🇦 and 92 other authors

   Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency $\gamma$-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF's Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) $\gamma$-ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2019)·40 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.