Fri·Aug 14, 2020Friday·August 14, 2020

1. 01*

   A New Extraction of Pion Parton Distributions in the Statistical Model

   Claude Bourrely🇫🇷 · Franco Buccella🇮🇹 · Jen-Chieh Peng🇺🇸

   We present a new analysis to extract pion's parton distribution functions (PDFs) in the framework of the statistical model. Starting from the statistical model framework first developed for the spin-1/2 nucleon, we apply appropriate modifications taking into account the spin-0 nature of pion and the isospin and charge-conjugation symmetry properties. This results in a significant reduction of the number of parameters compared to a recent work to extract pion's PDFs. Using ${\pi }^{-}$-induced Drell-Yan data to determine the parameters of this statistical model approach, we show that a good description of these experimental data with Next-to-Leading order QCD calculations can be obtained. Good agreement between the calculations and the ${\pi }^{+}/{\pi }^{-}$ Drell-Yan cross section ratio data, not included in the global fit, has confirmed the predictive power of these new pion PDFs.

   hep-phhep-exPLB(2021)·13 citations
2. 02*

   On the creation of charged massless fermion pair by a photon in crossed electromagnetic field

   V.R. Khalilov🇷🇺

   Creation of charged massless fermion pair by a photon in external constant crossed electromagnetic field is considered. For this we use the expression of elastic scattering amplitude (EAS) of photon in the one-loop approximation of massive quantum electrodynamics obtained earlier and calculate its massless limit. We assume that the imaginary part of EAS of photon describes the total probability of charged massless fermion pair creation in external electromagnetic field. Photon emission by a charged massless fermion is also studied in constant crossed electromagnetic field. We obtain the total probability of photon emission calculating elastic scattering amplitude of charged massive fermion in the electromagnetic field in the massless limit.

   hep-phquant-ph0 citations
3. 03*

   Dynamical grooming at work: from p+p to Pb+Pb

   Alba Soto-Ontoso🇺🇸

   We present a quantitative comparison between two grooming techniques: SoftDrop (SD) and Dynamical Grooming (DyG), in terms of the resilience of their associated observables to the underlying event, hadronization and pileup in proton-proton collisions at $\sqrt{s}=13$ TeV. For that purpose, we study the groomed momentum fraction, $z_g$, in QCD jets along with boosted W tagging. In addition, we obtain the groomed momentum angle, $R_g$, within several jet quenching Monte-Carlo models in order to asses the sensitivity of SD and DyG observables to quark-gluon plasma (QGP) effects in heavy-ion collisions.

   hep-phhep-exnucl-exPoS(2021)·4 citations
4. 04*

   Sum rule for the Compton amplitude and implications for the proton-neutron mass difference

   J. Gasser (U. Bern, AEC)🇨🇭 · H. Leutwyler (U. Bern, AEC)🇨🇭 · A. Rusetsky (U. Bonn, BCTP)🇩🇪

   The Cottingham formula expresses the leading contribution of the electromagnetic interaction to the proton-neutron mass difference as an integral over the forward Compton amplitude. Since quarks and gluons reggeize, the dispersive representation of this amplitude requires a subtraction. We assume that the asymptotic behaviour is dominated by Reggeon exchange. This leads to a sum rule that expresses the subtraction function in terms of measurable quantities. The evaluation of this sum rule leads to $m_{QED}^{p-n}=0.58\pm 0.16\text{mbox}MeV$.

   hep-phhep-latnucl-thEPJC(2020)·28 citations
5. 05*

   Particle Production in AgAg Collisions at $E_{\mathrm{Kin}}=1.58A$ GeV within a Hadronic Transport Approach

   Jan Staudenmaier🇩🇪 · Natey Kübler🇩🇪 · Hannah Elfner🇩🇪

   Heavy-ion collisions at low beam energies explore the high density regime of strongly-interacting matter. The dynamical evolution of these collisions can be successfully described by hadronic transport approaches. In March 2019, the HADES collaboration has taken data for AgAg collisions at $E_{\mathrm{Kin}}=1.58A$ GeV and in this work, we provide predictions for particle production and spectra within the Simulating Many Accelerated Strongly-interacting Hadrons (SMASH) approach. The multiplicities and spectra of strange and non-strange particles follow the expected trends as a function of system size. In particular, in AuAu collisions, much higher yields of double-strange baryons were observed experimentally than expected from a thermal model. Therefore, we incorporate a previously suggested mechanism to produce $\Xi$ baryons via rare decays of high mass $N^{\ast }$ resonances and predict the multiplicities. In addition, we predict the invariant mass spectrum for dilepton emission and explore the most important sources of dileptons above 1 GeV, that are expected to indicate the temperature of the medium. Interestingly, the overall dilepton emission is very similar to the one in AuAu collisions at $1.23A$ GeV, a hint that the smaller system at a higher energy behaves very similar to the larger system at lower beam energy.

   hep-phnucl-exnucl-thPRC(2021)·12 citations
6. 06*

   Renormalization Group Studies of Dense Relativistic Systems

   Jens Braun🇩🇪 · Timon Dörnfeld🇩🇪 · Benedikt Schallmo🇩🇪 · Sebastian Töpfel🇩🇪

   Dense relativistic matter has attracted a lot of attention over many decades now, with a focus on an understanding of the phase structure and thermodynamics of dense strong-interaction matter. The analysis of dense strong-interaction matter is complicated by the fact that the system is expected to undergo a transition from a regime governed by spontaneous chiral symmetry breaking at low densities to a regime governed by the presence of a Cooper instability at intermediate and high densities. Renormalization group (RG) approaches have played and still play a prominent role in studies of dense matter in general. In the present work, we study RG flows of dense relativistic systems in the presence of a Cooper instability and analyze the role of the Silver-Blaze property. In particular, we critically assess how to apply the derivative expansion to study dense-matter systems in a systematic fashion. This also involves a detailed discussion of regularization schemes. Guided by these formal developments, we introduce a new class of regulator functions for functional RG studies which is suitable to deal with the presence of a Cooper instability in relativistic theories. We close by demonstrating its application with the aid of a simple quark-diquark model.

   hep-phnucl-thPRD(2021)·37 citations
7. 07*

   First exotic hadron with open heavy flavor: $cs\bar{u}\bar{d}$ tetraquark

   Marek Karliner🇮🇱 · Jonathan L. Rosner🇺🇸

   The LHCb Collaboration has reported resonant activity in the channel $D^{+}{K}^{-}$, identifying two components: $X_0(2900)$ with $J^P=0^{+}$ at $2866\pm 7$ MeV, ${\Gamma }_0=57\pm 13$ MeV and $X_1(2900)$ with $J^P=1^{-}$ at $2904\pm 7$ MeV, ${\Gamma }_1=110\pm 12$ MeV. We interpret the $X_0(2900)$ component as a $cs\bar{u}\bar{d}$ isosinglet compact tetraquark, calculating its mass to be $2863\pm 12$ MeV. This is the first exotic hadron with open heavy flavor. The analogous $bs\bar{u}\bar{d}$ tetraquark is predicted at $6213\pm 12$ MeV. We discuss possible interpretations of the heavier and wider $X_1(2900)$ state and examine potential implications for other systems with two heavy quarks.

   hep-phhep-exPRD(2020)·93 citations
8. 08*

   A Composite Solution to the Neutron Bottle Anomaly

   Surjeet Rajendran🇺🇸 · Harikrishnan Ramani🇺🇸

   Measurements of the lifetime of neutrons trapped in a bottle have been consistently shorter than the lifetime measured in neutron beam experiments. With trapping potentials as low as 50 neV and neutron detectors located only at the top of the bottle, this discrepancy could be the result of the soft scattering of dark matter with neutrons. However, it is challenging to obtain the observed loss rate in conventional models of dark matter scattering. We show that this phenomenology is possible in composite models of dark matter where the soft scattering is from dark matter that has been captured and accumulated in the earth. This solution can be tested by placing more neutron detectors around the trap, providing better angular coverage. The phenomenology of soft scattering by trapped composite dark matter is generic and suggests new experimental directions that could be pursued to detect this large class of models.

   hep-phastro-ph.COhep-exPRD(2021)·25 citations
9. 09*

   A Statistical Analysis of the COHERENT Data and Applications to New Physics

   Peter B. Denton🇺🇸 · Julia Gehrlein🇺🇸

   The observation of coherent elastic neutrino nucleus scattering (CE$\nu$NS) by the COHERENT collaboration in 2017 has opened a new window to both test Standard Model predictions at relatively low energies and probe new physics scenarios. Our investigations show, however, that a careful treatment of the statistical methods used to analyze the data is essential to derive correct constraints and bounds on new physics parameters. In this manuscript we perform a detailed analysis of the publicly available COHERENT CsI data making use of all available background data. We point out that Wilks' theorem is not fulfilled in general and a calculation of the confidence regions via Monte Carlo simulations following a Feldman-Cousins procedure is necessary. As an example for the necessity of this approach to test new physics scenarios we quantify the allowed ranges for several scenarios with neutrino non-standard interactions. Furthermore, we provide accompanying code to enable an easy implementation of other new physics scenarios as well as data files of our results.

   hep-phhep-exJHEP(2021)·52 citations
10. 10*

    Supervised Jet Clustering with Graph Neural Networks for Lorentz Boosted Bosons

    Xiangyang Ju🇺🇸 · Benjamin Nachman🇺🇸

    Jet clustering is traditionally an unsupervised learning task because there is no unique way to associate hadronic final states with the quark and gluon degrees of freedom that generated them. However, for uncolored particles like $W$, $Z$, and Higgs bosons, it is possible to approximately (though not exactly) associate final state hadrons to their ancestor. By labeling simulated final state hadrons as descending from an uncolored particle, it is possible to train a supervised learning method to create boson jets. Such a method much operates on individual particles and identifies connections between particles originating from the same uncolored particle. Graph neural networks are well-suited for this purpose as they can act on unordered sets and naturally create strong connections between particles with the same label. These networks are used to train a supervised jet clustering algorithm. The kinematic properties of these graph jets better match the properties of simulated Lorentz-boosted $W$ bosons. Furthermore, the graph jets contain more information for discriminating $W$ jets from generic quark jets. This work marks the beginning of a new exploration in jet physics to use machine learning to optimize the construction of jets and not only the observables computed from jet constituents.

    hep-phhep-exphysics.data-anPRD(2020)·55 citations
11. 11*

    Review of results on forward physics and diffraction by CMS

    Cristian Baldenegro (on behalf of the CMS Collaboration)🇺🇸

    Results by the CMS Collaboration on forward physics, diffraction, and physics in the small-$x$ limit of quantum chromodynamics (QCD), are presented. In particular, results on azimuthal angle decorrelations between two jets in events where two outermost jets are separated by a large rapidity interval are discussed. In addition, results based on the production of two jets separated by a large rapidity gap (interval void of radiation) are presented. These dijet production processes are expected to be sensitive to Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution effects. We highlight results on inclusive forward jet production and on exclusive vector meson production in proton-lead collisions, which access gluon densities in the small-$x$ and $Q^2$ where saturation effects may play a role. A summary of results on underlying event activity studies based on inclusive $Z$ boson production, charged particle spectra in minimum bias events, and energy density in forward pseudorapidities is presented. These studies provide valuable inputs for Monte Carlo event generator tuning, and test predictions based on perturbative and non-perturbative QCD techniques.

    ↳ hep-exhep-ph0 citations
12. 12*

    High-energy neutrino emission subsequent to gravitational wave radiation from supermassive black hole mergers

    Chengchao Yuan🇺🇸 · Kohta Murase🇺🇸 · Shigeo S. Kimura🇺🇸 · Péter Mészáros🇺🇸

    Supermassive black hole (SMBH) coalescences are ubiquitous in the history of the Universe and often exhibit strong accretion activities and powerful jets. These SMBH mergers are also promising candidates for future gravitational wave detectors such as Laser Space Inteferometric Antenna (LISA). In this work, we consider neutrino counterpart emission originating from the jet-induced shocks. The physical picture is that relativistic jets launched after the merger will push forward inside the premerger disk wind material, and then they subsequently get collimated, leading to the formation of internal shocks, collimation shocks, forward shocks and reverse shocks. Cosmic rays can be accelerated in these sites and neutrinos are expected via the photomeson production process. We formulate the jet structures and relevant interactions therein, and then evaluate neutrino emission from each shock site. We find that month-to-year high-energy neutrino emission from the postmerger jet after the gravitational wave event is detectable by IceCube-Gen2 within approximately five to ten years of operation in optimistic cases where the cosmic-ray loading is sufficiently high and a mildly super-Eddington accretion is achieved. We also estimate the contribution of SMBH mergers to the diffuse neutrino intensity, and find that a significant fraction of the observed very high-energy ($E_{\nu }\gtrsim 1$ PeV) IceCube neutrinos could originate from them in the optimistic cases. In the future, such neutrino counterparts together with gravitational wave observations can be used in a multimessenger approach to elucidate in greater detail the evolution and the physical mechanism of SMBH mergers.

    ↳ astro-ph.HEgr-qchep-phPRD(2020)·24 citations
13. 13*

    Holographic cosmology solutions of problems with pre-inflationary cosmology

    Horatiu Nastase🇧🇷

    In this paper we describe in detail how to solve the problems of pre-inflationary cosmology within the holographic cosmology model of McFadden and Skenderis \cite{McFadden:2009fg}. The solutions of the smoothness and horizon problems, the flatness problem, the entropy and perturbation problems and the baryon asymmetry problem are shown, and the mechanisms for them complement the inflationary solutions. Most of the paper is devoted to the solution of the monopole relic problem, through a detailed calculation of 2-loop correlators of currents in a toy model which we perform in $d$ dimensions, in order to extract its leading dependece on $g_{\mathrm{eff}}^2=g_{YM}^{2}N/q$ and find a dilution effect. Taken together with the fact that holographic cosmology gives as good a fit to CMBR as the standard paradigm of $\Lambda$ CDM with inflation, it means holographic cosmology extends the inflationary paradigm into new corners, explorable only through a dual perturbative field theory in 3 dimensions.

    ↳ hep-thgr-qchep-phJHEP(2020)·8 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.