Nuclear Theory·nucl-th

Tuesday·November 23, 2021

13 papers—5 primary·8 cross-listed

06
Towards testing the magnetic moment of the tau at one part per million
Andreas Crivellin🇨🇭 · Martin Hoferichter🇨🇭 · J. Michael Roney🇨🇦
If physics beyond the Standard Model (BSM) explains the $4.2 σ$ difference between the Standard-Model and measured muon anomalous magnetic moment, $a_{μ}$ , minimal flavor violation predicts a shift in the analog quantity for the $τ$ lepton, $a_{τ}$ , at the $1 0^{- 6}$ level, and even larger effects are possible in generic BSM scenarios such as leptoquarks. We show that this produces equivalent BSM deviations in the Pauli form factor, $F_{2} (s)$ , at $s = (10 GeV)^{2}$ , and report the first complete two-loop prediction of $Re F_{2}^{eff} (100 GeV^{2}) = - 268.77 (50) \times 1 0^{- 6}$ for resonant $τ$ -pair production in $e^{+} e^{-} \to Υ (n S) \to$ $τ^{+} τ^{-}$ , $n = 1, 2, 3$ . $Re F_{2}^{eff}$ can be measured from $e^{-}$ -helicity-dependent transverse and longitudinal asymmetries in $τ$ -pair events, which requires a longitudinally polarized $e^{-}$ beam. We discuss how Belle II asymmetry measurements could probe $a_{τ}^{BSM}$ at $1 0^{- 6}$ , assuming such a polarization upgrade of the SuperKEKB $e^{+} e^{-}$ collider, and conclude by outlining the next steps to be taken in theory and experiment along this new avenue for exploring realistic BSM effects in $a_{τ}$ .
↳ hep-phhep-exnucl-exnucl-thPRD(2022)·66 citations
07
Evidence for Nonlinear Gluon Effects in QCD and their $A$ Dependence at STAR
STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · A. Aitbaev · I. Alekseev and 384 other authors
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di- $π^{0}$ s produced at forward pseudorapidities ( $2.6 < η < 4.0$ ) in $p$ + $p$ , $p +$ Al, and $p +$ Au collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back $π^{0}$ pairs in $p +$ Al and $p +$ Au collisions compared to the $p$ + $p$ data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in $p +$ Au relative to $p +$ Al collisions exhibits a dependence of the saturation scale, $Q_{s}^{2}$ , on the mass number, $A$ . A linear scaling of the suppression with $A^{1/3}$ is observed with a slope of $- 0.09$ $\pm$ $0.01$ .
↳ nucl-exhep-exhep-thnucl-thPRL(2022)·40 citations
08
A New Model of Intranuclear Neutron-Antineutron Transformations in $_{8}^{16}$ O
J. L. Barrow🇺🇸 · A. S. Botvina🇷🇺 · E. S. Golubeva🇷🇺 · J-M. Richard🇫🇷
There has been much work in recent years pertaining to viability studies for the intranuclear observation of neutron-antineutron transformations. These studies begin firstly with the design and implementation of an event generator for the simulation of this rare process, where one hopes to retain as much of the underlying nuclear physics as possible in the initial state, and then studying how these effects may perturb the final state observable particles for detector efficiency studies following simulated reconstruction. There have been several searches for intranuclear neutron-antineutron transformations, primarily utilizing the $_{8}^{16}$ O nucleus, and completed within large underground water Cherenkov detectors such as Super-Kamiokande. The latest iteration of a generator is presented here for use in such an experiment. This generator includes several new features, including a new radial (position) annihilation probability distribution and related intranuclear suppression factor for $_{8}^{16}$ O, as well as a highly general, modern nuclear multifragmentation model with photonic de-excitations. The latter of these may allow for improved identification of the signal using large underground detectors such as Super-Kamiokande and the future Hyper-Kamiokande, potentially increasing the overall signal efficiencies of these rare searches. However, it should be noted that certain fast photonic de-excitations may be washed out by $π^{0}$ decays to photons. These new features implemented in these $n ˉ$ \isotope[15][8]{O} simulations increase the overall physical realism of the model, and are easily portable to other future searches such as to extranuclear $n ˉ_{6}^{12}$ C for the ESS NNBAR experiment, as well as intranuclear $n ˉ_{18}^{39}$ Ar used in DUNE.
↳ hep-exhep-phnucl-thPRC(2022)·5 citations
09
Lattice QCD at nonzero temperature and density
G. Aarts🇬🇧 · C. Allton🇬🇧 · S. Hands🇬🇧 · B. Jäger🇩🇰 · S. Kim🇰🇷 · M.P. Lombardo🇮🇹 · A.A. Nikolaev🇬🇧 · S.M. Ryan🇮🇪 · J.-I. Skullerud🇮🇪
We discuss some selected recent developments in the field of lattice QCD at nonzero temperature and density, describing in particular the transition from the hadronic gas to the quark-gluon plasma, as seen in simulations using Wilson fermions.
↳ hep-latnucl-thJ.Phys.Conf.Ser.(2022)·2 citations
10
Effective Field Theories and Lattice QCD for the X Y Z frontier
Nora Brambilla🇩🇪
Exotic states have been predicted before and after the advent of QCD. In the last decades they have been observed at accelerator experiments in the sector with two heavy quarks, at or above the quarkonium strong decay threshold and called X Y Z states. These states offer a unique possibility for investigating the dynamical properties of strongly correlated systems in QCD. I will show how an alliance of nonrelativistic effective field theories and lattice can allow us to address these states in QCD. In particular I will explain what are the opportunities and challenges of lattice QCD in this respect and which new tools should be developed.
↳ hep-lathep-phhep-thnucl-thPoS(2022)·13 citations
11
Modulation of pulse profile as a signal for phase transitions in a pulsar core
Partha Bagchi🇨🇳 · Biswanath Layek🇮🇳 · Anjishnu Sarkar🇮🇳 · Ajit M. Srivastava🇮🇳
We calculate detailed modification of pulses from a pulsar arising from the effects of phase transition induced density fluctuations on the pulsar moment of inertia. We represent general statistical density fluctuations using a simple model where the initial moment of inertia tensor of the pulsar (taken to be diagonal here) is assumed to get random additional contributions for each of its component which are taken to be Gaussian distributed with certain width characterized by the strength of density fluctuations $ϵ$ . Using sample values of $ϵ$ , (and the pulsar deformation parameter $η$ ) we numerically calculate detailed pulse modifications by solving Euler's equations for the rotational dynamics of the pulsar. We also give analytical estimates which can be used for arbitrary values of $ϵ$ and $η$ . We show that there are very specific patterns in the perturbed pulses which are observable in terms of modulations of pulses over large time periods. In view of the fact that density fluctuations fade away eventually leading to a uniform phase in the interior of pulsar, the off-diagonal components of MI tensor also vanish eventually. Thus, the modification of pulses due to induced wobbling (from the off-diagonal MI components) will also die away eventually. This allows one to distinguish these transient pulse modulations from the effects of any wobbling originally present. Further, the decay of these modulations in time directly relates to relaxation of density fluctuations in the pulsar giving valuable information about the nature of phase transition occurring inside the pulsar.
↳ astro-ph.HEhep-phnucl-exnucl-thMNRAS(2022)·5 citations
12
Upcgen: a Monte Carlo simulation program for dilepton pair production in ultra-peripheral collisions of heavy ions
Nazar Burmasov🇷🇺 · Evgeny Kryshen🇷🇺 · Paul Buehler🇦🇹 · Roman Lavicka🇦🇹
Ultra-peripheral collisions (UPCs) of heavy ions can be used as a clean environment to study two-photon induced interactions such as dilepton pair photoproduction. Recently, precise data on lepton pair production in UPCs were obtained by the ATLAS experiment at the LHC where significant deviations, of up to 20%, from available theoretical predictions were observed. In this work, we present a Monte Carlo event generator, Upcgen, that implements a refined treatment of the photon flux allowing us to improve the agreement with ATLAS data at large dilepton rapidities. Besides, the new generator offers a possibility to study photon polarization effects and set arbitrary values of the lepton anomalous magnetic moment that can be used in the future studies of tau g-2 via ditau production measurements in UPCs.
↳ hep-phnucl-exnucl-thComput.Phys.Commun.(2022)·27 citations
13
Stability of Classical Chromodynamic Fields
Sylwia Bazak🇵🇱 · Stanislaw Mrowczynski🇵🇱
A system of gluon fields generated at the earliest phase of relativistic heavy-ion collisions can be described in terms of classical fields. Numerical simulations show that the system is unstable but a character of the instability is not well understood. With the intention to systematically study the problem, we analyze a stability of classical chromomagnetic and chromoelectric fields which are constant and uniform. We consider the Abelian configurations discussed in the past where the fields are due to the single-color potentials linearly depending on coordinates. However, we mostly focus on the nonAbelian configurations where the fields are generated by the multi-color non-commuting constant uniform potentials. We derive a complete spectrum of small fluctuations around the background fields which obey the linearized Yang-Mills equations. The spectra of Abelian and nonAbelian configurations are similar but different and they both include unstable modes. We briefly discuss the relevance of our results for fields which are uniform only in a limited spatial domain.
↳ hep-phhep-thnucl-thPRD(2022)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE