Thu·Jan 14, 2021Thursday·January 14, 2021

1. 01*

   In-medium modification of dijets in PbPb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV

   CMS Collaboration

   Modifications to the distribution of charged particles with respect to high transverse momentum ($p_{\mathrm{T}}$) jets passing through a quark-gluon plasma are explored using the CMS detector. Back-to-back dijets are analyzed in lead-lead and proton-proton collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV via correlations of charged particles in bins of relative pseudorapidity and angular distance from the leading and subleading jet axes. In comparing the lead-lead and proton-proton collision results, modifications to the charged-particle relative distance distribution and to the momentum distributions around the jet axis are found to depend on the dijet momentum balance $x_j$, which is the ratio between the subleading and leading jet $p_{\mathrm{T}}$. For events with $x_j$ $\approx$ 1, these modifications are observed for both the leading and subleading jets. However, while subleading jets show significant modifications for events with a larger dijet momentum imbalance, much smaller modifications are found for the leading jets in these events.

   ↳ hep-exnucl-exJHEP(2021)·43 citations
2. 02*

   Unexpectedly enhanced $\alpha$-particle preformation in ${}^{48}$Ti probed by the $(p,p\alpha )$ reaction

   Yasutaka Taniguchi🇯🇵 · Kazuki Yoshida🇯🇵 · Yohei Chiba🇯🇵 · Yoshiko Kanada-En'yo🇯🇵 · Masaaki Kimura🇯🇵 · Kazuyuki Ogata🇯🇵

   The formation of $\alpha$ particle on nuclear surface has been a fundamental problem since the early age of nuclear physics. It strongly affects the $\alpha$ decay lifetime of heavy and superheavy elements, level scheme of light nuclei, and the synthesis of the elements in stars. However, the $\alpha$-particle formation in medium-mass nuclei has been poorly known despite its importance. Here, based on the ${}^{48}\mathrm{Ti}(p,p\alpha {)}^{44}\mathrm{Ca}$ reaction analysis, we report that the $\alpha$-particle formation in a medium-mass nucleus ${}^{48}\mathrm{Ti}$ is much stronger than that expected from a mean-field approximation, and the estimated average distance between $\alpha$ particle and the residue is as large as 4.5 fm. This new result poses a challenge of describing four nucleon correlations by microscopic nuclear models.

   ↳ nucl-thnucl-exPRC(2021)·21 citations
3. 03*

   The $\mathbf{sQ}\bar{\mathbf{q}}\bar{\mathbf{q}}$ $(\mathbf{q}=\mathbf{u},\mathbf{d};\mathbf{Q}=\mathbf{c},\mathbf{b})$ tetraquarks in the chiral quark model

   Gang Yang🇨🇳 · Jialun Ping🇨🇳 · Jorge Segovia🇪🇸

   The low-lying $sQ\bar{q}\bar{q}$ $(q=u,d,Q=c,b)$ tetraquark states with $J^P=0^{+}$, $1^{+}$ and $2^{+}$, and in the isoscalar and isovector sectors, are systematically investigated in the framework of real- and complex-scaling range of a chiral quark model, whose parameters have been fixed in advance describing hadron, hadron-hadron and multiquark phenomenology, and thus all results presented here are pure predictions. Each tetraquark configuration, compatible with the quantum numbers studied, is taken into account; this includes meson-meson, diquark-antidiquark and K-type arrangements of quarks with all possible color wave functions in four-body sector. Among the different numerical techniques to solve the Schrödinger-like 4-body bound state equation, we use a variational method in which the trial wave function is expanded in complex-range Gaussian basis functions, because its simplicity and flexibility. Several compact bound states and narrow resonances are found in both charm-strange $cs\bar{q}\bar{q}$ and bottom-strange $bs\bar{q}\bar{q}$ tetraquark sectors, most of them as a product of the strong coupling between the different channels. The so-called $X_{0,1}(2900)$ signals, recently found by the LHCb collaboration, are unstable in our formalism with several candidates in the single-channel computations.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2021)·41 citations
4. 04*

   Vorticity and Polarization in Heavy Ion Collisions: Hydrodynamic Models

   Iurii Karpenko🇨🇿

   Fluid dynamic approach is a workhorse for modelling collective dynamics in relativistic heavy-ion collisions. The approach has been successful in describing various features of the momentum distributions of hadrons produced in the heavy-ion collisions, such as $p_T$ spectra, flow coefficients $v_n$ etc. As such, the description of the phenomenon of polarization of $\Lambda$ hyperons in heavy-ion collisions has to be incorporated into the hydrodynamic approach. We start this chapter by introducing different definitions of vorticity in relativistic fluid dynamics. Then we present a derivation of the polarization of spin 1/2 fermions in the relativistic fluid. The latter is directly applied to compute the spin polarization of the $\Lambda$ hyperons, which are produced from the hot and dense medium, described with fluid dynamics. It is followed by a review of the existing calculations of global or local polarization of $\Lambda$ hyperons in different hydrodynamic models of relativistic heavy-ion collisions. We particularly focus on the explanations of the collision energy dependence of the global $\Lambda$ polarization from the different hydrodynamic models, the polarization component in the beam direction as well as on the origins of the global and local $\Lambda$ polarization.

   ↳ nucl-thnucl-ex14 citations
5. 05*

   Novel twist-three transverse-spin sum rule for the proton and related generalized parton distributions

   Yuxun Guo🇺🇸 · Xiangdong Ji🇺🇸 · Kyle Shiells🇺🇸

   We derive a new twist-3 partonic sum rule for the transverse spin of the proton, which involves the well-know quark spin structure function $g_T(x)=g_1(x)+g_2(x)$, the less-studied but known transverse gluon polarization density $\Delta G_T(x)$, and quark and gluon canonical orbital angular momentum densities associated with transverse polarization. This is the counter part of the sum rule for the longitudinal spin of the proton derived by Jaffe and Manohar previously. We relate the partonic canonical orbital angular momentum densities to a new class of twist-3 generalized parton distribution functions which are potentially measurable in deep-virtual exclusive processes. We also discuss in detail an important technicality related to the transverse polarization in the infinite momentum frame, i.e., separation of intrinsic contributions from the extrinsic ones. We apply our finding to the transverse-space distributions of partons, angular momentum, and magnetic moment, respectively, in a transversely polarized proton.

   ↳ hep-phhep-latnucl-exnucl-thNPB(2021)·36 citations
6. 06*

   Analysis methods for the first KATRIN neutrino-mass measurement

   M. Aker🇩🇪 · K. Altenmüller🇩🇪 · A. Beglarian🇩🇪 · J. Behrens🇩🇪 · A. Berlev🇷🇺 · U. Besserer🇩🇪 · B. Bieringer🇩🇪 · K. Blaum🇩🇪 · F. Block🇩🇪 · B. Bornschein🇩🇪 · L. Bornschein🇩🇪 · M. Böttcher🇩🇪 and 117 other authors

   We report on the data set, data handling, and detailed analysis techniques of the first neutrino-mass measurement by the Karlsruhe Tritium Neutrino (KATRIN) experiment, which probes the absolute neutrino-mass scale via the $\beta$-decay kinematics of molecular tritium. The source is highly pure, cryogenic T${}_2$ gas. The $\beta$ electrons are guided along magnetic field lines toward a high-resolution, integrating spectrometer for energy analysis. A silicon detector counts $\beta$ electrons above the energy threshold of the spectrometer, so that a scan of the thresholds produces a precise measurement of the high-energy spectral tail. After detailed theoretical studies, simulations, and commissioning measurements, extending from the molecular final-state distribution to inelastic scattering in the source to subtleties of the electromagnetic fields, our independent, blind analyses allow us to set an upper limit of 1.1 eV on the neutrino-mass scale at a 90\% confidence level. This first result, based on a few weeks of running at a reduced source intensity and dominated by statistical uncertainty, improves on prior limits by nearly a factor of two. This result establishes an analysis framework for future KATRIN measurements, and provides important input to both particle theory and cosmology.

   ↳ hep-exastro-ph.COnucl-exphysics.ins-detPRD(2021)·71 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.