Mon·Mar 1, 2021Monday·March 1, 2021

1. 01*

   Measurement of beauty and charm production in pp collisions at $\sqrt{s}=5.02$ TeV via non-prompt and prompt D mesons

   ALICE Collaboration

   The $p_{\mathrm{T}}$-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity ($|y|<0.5$) in proton--proton collisions at $\sqrt{s}=5.02\mathrm{TeV}$. The data sample used in the analysis corresponds to an integrated luminosity of $(19.3\pm 0.4)\mathrm{n}{\mathrm{b}}^{-1}$. D mesons were reconstructed from their decays ${\mathrm{D}}^0\to {\mathrm{K}}^{-}{\pi }^{+}$, ${\mathrm{D}}^{+}\to {\mathrm{K}}^{-}{\pi }^{+}{\pi }^{+}$, and ${\mathrm{D}}_{\mathrm{s}}^{+}\to \varphi {\pi }^{+}\to {\mathrm{K}}^{-}{\mathrm{K}}^{+}{\pi }^{+}$ and their charge conjugates. Compared to previous measurements in the same rapidity region, the cross sections of prompt ${\mathrm{D}}^{+}$ and ${\mathrm{D}}_{\mathrm{s}}^{+}$ mesons have an extended $p_{\mathrm{T}}$ coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, depending on $p_{\mathrm{T}}$, allowing for a more precise determination of their $p_{\mathrm{T}}$-integrated cross sections. The results are well described by perturbative QCD calculations. The fragmentation fraction of heavy quarks to strange mesons divided by the one to non-strange mesons, $f_{\mathrm{s}}/(f_{\mathrm{u}}+f_{\mathrm{d}})$, is compatible for charm and beauty quarks and with previous measurements at different centre-of-mass energies and collision systems. The $\mathrm{b}\overline{\mathrm{b}}$ production cross section per rapidity unit at midrapidity, estimated from non-prompt D-meson measurements, is $\mathrm{d}{\sigma }_{\mathrm{b}\overline{\mathrm{b}}}/\mathrm{d}y{|}_{|y|<0.5}=34.5\pm 2.4(stat.{)}_{-2.9}^{+4.7}(tot.syst.)\mu \mathrm{b}$. It is compatible with previous measurements at the same centre-of-mass energy and with the cross section predicted by perturbative QCD calculations.

   nucl-exhep-exJHEP(2021)·154 citations
2. 02*

   New Physics Searches at the BESIII Experiment

   Shenjian Chen🇨🇳 · Stephen Lars Olsen🇨🇳

   The Standard Model (SM) of particle physics, comprised of the unified electro-weak (EW) and Quantum Chromodynamic (QCD) theories, accurately explains almost all experimental results related to the micro-world, and has made a number of predictions for previously unseen particles, most notably the Higgs scalar boson, that were subsequently discovered. As a result, the SM is currently universally accepted as the theory of the fundamental particles and their interactions. However, in spite of its numerous successes, the SM has a number of apparent shortcomings including: many free parameters that must be supplied by experimental measurements; no mechanism to produce the dominance of matter over antimatter in the universe; and no explanations for gravity, the dark matter in the universe, neutrino masses, the number of particle generations, etc. Because of these shortcomings, there is considerable incentive to search for evidence for new, non-SM physics phenomena that might provide important clues about what a new, beyond the SM theory (BSM) might look like. Although the center-of-mass energies that BESIII can access are far below the energy frontier, searches for new, BSM physics are an important component of its research program. Here we describe ways that BESIII looks for signs of BSM physics by measuring rates for processes that the SM predicts to be forbidden or very rare, searching for non-SM particles such as dark photons, making precision tests of SM predictions, and looking for violations of the discrete symmetries $C$ and $CP$ in processes for which the SM-expectations are immeasurably small.

   ↳ hep-phhep-exnucl-exNatl.Sci.Rev.(2021)·10 citations
3. 03*

   Probing gluon spin-momentum correlations in transversely polarized protons through midrapidity isolated direct photons in $p^{\uparrow }+p$ collisions at $\sqrt{s}=200$ GeV

   U.A. Acharya · C. Aidala · Y. Akiba · M. Alfred · V. Andrieux · N. Apadula · H. Asano · B. Azmoun · V. Babintsev · N.S. Bandara · K.N. Barish · S. Bathe and 300 other authors

   Studying spin-momentum correlations in hadronic collisions offers a glimpse into a three-dimensional picture of proton structure. The transverse single-spin asymmetry for midrapidity isolated direct photons in $p^{\uparrow }+p$ collisions at $\sqrt{s}=200$ GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). Because direct photons in particular are produced from the hard scattering and do not interact via the strong force, this measurement is a clean probe of initial-state spin-momentum correlations inside the proton and is in particular sensitive to gluon interference effects within the proton. This is the first time direct photons have been used as a probe of spin-momentum correlations at RHIC. The uncertainties on the results are a fifty-fold improvement with respect to those of the one prior measurement for the same observable, from the Fermilab E704 experiment. These results constrain gluon spin-momentum correlations in transversely polarized protons.

   ↳ hep-exnucl-exPRL(2021)·26 citations
4. 04*

   Study of Drell-Yan dimuon production in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}=$ 8.16 TeV

   CMS Collaboration

   Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb${}^{-1}$. The differential cross section as a function of the dimuon mass is measured in the range 15-600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15-60 GeV and 60-120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum $p_{\mathrm{T}}$ and of a geometric variable ${\varphi }^{\ast }$ are measured, where ${\varphi }^{\ast }$ highly correlates with $p_{\mathrm{T}}$ but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions.

   ↳ hep-exnucl-exJHEP(2021)·38 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.