Fri·Jan 8, 2016Friday·January 8, 2016

1. 01*

   Jet Shapes in Dijet Events at the LHC in SCET

   Andrew Hornig🇺🇸 · Yiannis Makris🇺🇸 · Thomas Mehen🇺🇸

   We consider the class of jet shapes known as angularities in dijet production at hadron colliders. These angularities are modified from the original definitions in e+e- collisions to be boost invariant along the beam axis. These shapes apply to the constituents of jets defined with respect to either k_T-type (anti-k_T, C/A, and k_T) algorithms and cone-type algorithms. We present an SCET factorization formula and calculate the ingredients needed to achieve next-to-leading-log (NLL) accuracy in kinematic regions where non-global logarithms are not large. The factorization formula involves previously unstudied "unmeasured beam functions," which are present for finite rapidity cuts around the beams. We derive relations between the jet functions and the shape-dependent part of the soft function that appear in the factorized cross section and those previously calculated for e+e- collisions, and present the calculation of the non-trivial, color-connected part of the soft-function to O(\alpha_s). This latter part of the soft function is universal in the sense that it applies to any experimental setup with an out-of-jet p_T veto and rapidity cuts together with two tagged jets and it is independent of the choice of jet (sub-)structure measurement. In addition, we implement the recently introduced soft-collinear refactorization to resum logarithms of the jet size, valid in the region of non-enhanced non-global logarithm effects. While our results are valid for all 2 \to 2 channels, we compute explicitly for the qq' \to qq' channel the color-flow matrices and plot the NLL resummed differential dijet cross section as an explicit example, which shows that the normalization and scale uncertainty is reduced when the soft function is refactorized. For this channel, we also plot the jet size R dependence, the p_T^{\rm cut} dependence, and the dependence on the angularity parameter a.

   hep-phJHEP(2016)·60 citations
2. 02*

   Long-Lived Staus and Displaced Leptons at the LHC

   Jared A. Evans🇺🇸 · Jessie Shelton🇺🇸

   As the majority of LHC searches are focused on prompt signatures, specific long-lived particles have the potential to be overlooked by the otherwise systematic new physics programs at ATLAS and CMS. While in many cases long-lived superparticles are now stringently constrained by existing exotic searches, we point out that the highly motivated model of gauge mediation with staus as the next-to-lightest superparticle (NLSP) has received less attention. We recast LHC searches for heavy stable charged particles, disappearing tracks, and opposite-flavor leptons with large impact parameters to assess current constraints on a variety of spectra that contain an NLSP stau, and find that portions of the parameter space motivated by naturalness are still experimentally unexplored. We additionally note a gap in the current experimental search program: same-flavor leptons with large impact parameters evade the suite of existing searches for long-lived objects. This gap is especially noteworthy as vetoes on displaced leptons in prompt new physics searches could be systematically discarding such events. We discuss several motivated models that can exhibit same-flavor displaced leptons: gauge mediation with co-NLSP sleptons, extended gauge mediation, R-parity violation, and lepton-flavored dark matter that freezes in during a matter-dominated era of the early universe. To address this gap, we propose a straightforward extension of the CMS search for leptons with large impact parameters, and project sensitivity to these scenarios at 13 TeV. Throughout this analysis, we highlight several methods whereby LHC searches for exotic long-lived objects could potentially improve their sensitivity to the displaced leptons originating from gauge mediation and beyond.

   hep-phJHEP(2016)·106 citations
3. 03*

   Triplet-Quadruplet Dark Matter

   Tim M.P. Tait🇺🇸 · Zhao-Huan Yu🇨🇳

   We explore a dark matter model extending the standard model particle content by one fermionic $SU(2{)}_L$ triplet and two fermionic $SU(2{)}_L$ quadruplets, leading to a minimal realistic UV-complete model of electroweakly interacting dark matter which interacts with the Higgs doublet at tree level via two kinds of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum of the dark sector consists of three Majorana fermions, three singly charged fermions, and one doubly charged fermion, with the lightest neutral fermion ${\chi }_1^0$ serving as a dark matter candidate. A typical spectrum exhibits a large degree of degeneracy in mass between the neutral and charged fermions, and we examine the one-loop corrections to the mass differences to ensure that the lightest particle is neutral. We identify regions of parameter space for which the dark matter abundance is saturated for a standard cosmology, including coannihilation channels, and find that this is typically achieved for $m_{{\chi }_1^0}\sim 2.4\mathrm{TeV}$. Constraints from precision electroweak measurements, searches for dark matter scattering with nuclei, and dark matter annihilation are important, but leave open a viable range for a thermal relic.

   hep-phJHEP(2016)·33 citations
4. 04*

   The 750GeV diphoton excess: who introduces it?

   Hao Zhang🇺🇸

   Recently, both ATLAS and CMS collaborations report an excess at 750GeV in the diphoton invariant mass spectrum at 13TeV LHC. If it is a new scalar produced via loop induced gluon-gluon fusion process, it is important to know what is the particle in the loop. In this work, we investigate the possibility of determine the fraction of the contribution from the standard model top-quark in the loop.

   hep-phhep-exPRD(2016)·41 citations
5. 05*

   The Diphoton and Diboson Excesses in a Left-Right Symmetric Theory of Dark Matter

   Asher Berlin🇺🇸

   We explore the possibility that the recently reported diphoton excess at ATLAS and CMS can be accommodated within a minimal extension of a left-right symmetric model. Our setup is able to simultaneously explain the Run 2 diphoton and Run 1 diboson excesses, while providing a standard thermal freeze-out of weak-scale dark matter. In this scenario, the 750 GeV neutral right-handed Higgs triplet is responsible for the diphoton excess. Interactions of this state with the neutral and charged components of dark matter multiplets provide the dominant mechanisms for production and decay. A striking signature of this model is the additional presence of missing energy in the diphoton channel.

   hep-phhep-exPRD(2016)·62 citations
6. 06*

   Compendium of Models from a Gauge U(1) Framework

   Ernest Ma (UC Riverside and HKUST/JCIAS)🇺🇸

   A gauge U(1) framework was established in 2002 to extend the supersymmetric standard model. It has many possible realizations. Whereas all have the necessary and sufficient ingredients to explain the possible 750 GeV diphoton excess, observed recently by the ATLAS Collaboration at the Large Hadron Collider (LHC), they differ in other essential aspects. A compendium of such models is discussed.

   hep-phMod.Phys.Lett.A(2016)·12 citations
7. 07*

   Spin Polarized versus Chiral Condensate in Quark Matter at Finite Temperature and Density

   H. Matsuoka (Kochi Univ., Japan)🇯🇵 · Y. Tsue (Kochi Univ., Japan)🇯🇵 · J. da Providencia (Univ. de Coimbra, Portugal)🇵🇹 · C. Providencia (Univ. de Coimbra, Portugal)🇵🇹 · M. Yamamura (Kansai Univ., Japan)🇯🇵 · H. Bohr (Danish Technical Univ., Denmark)🇩🇰

   It is shown that the spin polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasinio-type model as a low energy effective theory of quantum chromodynamics. It is indicated within this low energy effective model that the chiral symmetry is broken again by the spin polarized condensate as increasing the quark number density, while the chiral symmetry restoration occurs in which the chiral condensate disappears at a certain density.

   hep-phnucl-thPTEP(2016)·11 citations
8. 08*

   Comparisons of electric charge and axial charge meson cloud distributions in the PCQM

   X. Y. Liu🇹🇭 · K. Khosonthongkee🇹🇭 · A. Limphirat🇹🇭 · Y. Yan🇹🇭

   The meson cloud distributions in $r$-space are extracted from the nucleon electromagnetic and axial form factors which are derived in the perturbative chiral quark model. The theoretical results indicate that the electric charge and axial charge distributions of the three-quark core are the same, the magnetic charge distributions of the meson cloud and three-quark core are more or less in the same region and peak at distances of around 2 $\mathrm{Ge}{\mathrm{V}}^{-1}$, but the axial charge meson cloud distributes mainly inside the three-quark core.

   hep-phnucl-thSci.Rep.(2017)·5 citations
9. 09*

   Upsilon suppression in the Schrödinger-Langevin approach

   Pol Bernard Gossiaux🇫🇷 · Roland Katz🇫🇷

   We treat the question of bottomonia suppression in ultrarelativistic heavy ion collisions (URHIC) as a dynamical open quantum problem, tackled for the first time using the Schrödinger-Langevin equation. Coupling this equation to the EPOS2 event generator, predictions are made for the nuclear modification factor of ${\rm Y}(1S)$ and ${\rm Y}(2S)$.

   hep-phhep-exquant-phNPA(2016)·16 citations
10. 10*

    Strangeness Production in AA and pp Collisions

    P.Castorina🇮🇹 · H.Satz🇩🇪

    Boost-invariant hadron production in high energy collisions occurs in causally disconnected regions of finite space-time size. As a result, globally conserved quantum numbers (charge, strangeness, baryon number) are conserved locally in spatially restricted correlation clusters. Their size is determined by two time scales: the equilibration time specifying the formation of a quark-gluon plasma, and the hadronization time, specifying the onset of confinement. The expected values for these scales provide the theoretical basis for the suppression observed for strangeness production in elementary interactions ($pp$, $e^{+}{e}^{-}$) below LHC energies. In contrast, the space-time superposition of individual collisions in high energy heavy ion interactions leads to higher energy densities, resulting in much later hadronization and hence much larger hadronization volumes. This largely removes the causality constraints and results in an ideal hadronic resonance gas in full chemical equilibrium. In the present paper, we determine the collision energies needed for that; we also estimate when $pp$ collisions reach comparable hadronization volumes and thus determine when strangeness suppression should disappear there as well.

    hep-phnucl-thEPJA(2016)·10 citations
11. 11*

    750 GeV Di-photon excess at CERN LHC from a dark sector assisted scalar decay

    Subhaditya Bhattacharya🇮🇳 · Sudhanwa Patra🇮🇳 · Nirakar Sahoo🇮🇳 · Narendra Sahu🇮🇳

    We present a simple extension of the standard model (SM) to explain the diphoton excess, reported by CMS and ATLAS at CERN LHC. The SM is extended by a dark sector including a vector-like lepton doublet and a singlet of zero electromagnetic charge, which are odd under a $Z_2$ symmetry. These vector-like leptons assist the additional scalar, different from SM Higgs, to decay to di-photons of invariant mass around 750 GeV and thus explaining the excess observed at LHC. The admixture of neutral component of the vector-like lepton doublet and singlet constitute the dark matter component of the Universe. We show the relevant parameter space for correct relic density and direct detection of dark matter.

    hep-phJCAP(2016)·60 citations
12. 12*

    A 750 GeV Portal: LHC Phenomenology and Dark Matter Candidates

    Francesco D'Eramo🇺🇸 · Jordy de Vries🇳🇱 · Paolo Panci🇫🇷

    We study the effective field theory obtained by extending the Standard Model field content with two singlets: a 750 GeV (pseudo-)scalar and a stable fermion. Accounting for collider productions initiated by both gluon and photon fusion, we investigate where the theory is consistent with both the LHC diphoton excess and bounds from Run 1. We analyze dark matter phenomenology in such regions, including relic density constraints as well as collider, direct, and indirect bounds. Scalar portal dark matter models are very close to limits from direct detection and mono-jet searches if gluon fusion dominates, and not constrained at all otherwise. Pseudo-scalar models are challenged by photon line limits and mono-jet searches in most of the parameter space.

    hep-phastro-ph.COhep-exJHEP(2016)·85 citations
13. 13*

    Predicting the $\sin {\varphi }_S$ Transverse Single-spin Asymmetry of Pion Production at an Electron Ion Collider

    Xiaoyu Wang🇨🇳 · Zhun Lu🇨🇳

    We study the transverse single-spin asymmetry with a $\sin {\varphi }_S$ modulation in semi-inclusive deep inelastic scattering. Particularly, we consider the case in which the transverse momentum of the final state hadron is integrated out. Thus, the asymmetry is merely contributed by the coupling of the transversity distribution function $h_1(x)$ and the twist-3 collinear fragmentation function $\tilde{H}(z)$. Using the available parametrization of $h_1(x)$ from SIDIS data and the recent extracted result for $\tilde{H}(z)$, we predict the $\sin {\varphi }_S$ asymmetry for charged and neutral pion production at an Electron Ion Collider. We find that the asymmetry is sizable and could be measured. We also study the impact of the leading-order QCD evolution effect and find that it affects the $\sin {\varphi }_S$ asymmetry at EIC considerably.

    hep-phhep-exPRD(2016)·7 citations
14. 14*

    Probing the Small-$x$ Gluon Tomography in Correlated Hard Diffractive Dijet Production in DIS

    Yoshitaka Hatta🇯🇵 · Bo-Wen Xiao🇨🇳 · Feng Yuan🇺🇸

    We investigate the close connection between the quantum phase space Wigner distribution of small-$x$ gluons and the color dipole scattering amplitude, and propose to study it experimentally in the hard diffractive dijet production at the planned electron-ion collider. The angular correlation between the nucleon recoiled momentum and the dijet transverse momentum will probe the nontrivial correlation in the phase space Wigner distribution. This experimental study will not only provide us with three-dimensional tomographic pictures of gluons inside high energy proton, but also give a unique and interesting signal for the small-$x$ dynamics with QCD evolution effects.

    hep-phnucl-thPRL(2016)·206 citations
15. 15*

    Semi-elastic cross section for a scalar resonance of mass 750 GeV

    I. Sahin🇹🇷

    We assume that the recently reported excess over Standard Model expectations in the diphoton production is originated from a new scalar boson phi which interacts with photons through the coupling proportional to phi F^2. We obtain the cross section for semi-elastic production process pp-> p gamma p-> p phi q X by considering phi-photon-photon and phi-photon-Z couplings and discuss the constraints on the coupling parameters. We investigate the potential of the semi-elastic production process to probe phi-photon-photon and phi-photon-Z.

    hep-ph39 citations
16. 16*

    Light Sterile Neutrinos In Cosmology

    Stefano Gariazzo🇮🇹

    We briefly discuss the main effects of the presence of a Light Sterile Neutrino (LS$\nu$) in Cosmology and how its properties can be constrained by Cosmic Microwave Background (CMB) and other cosmological measurements.

    ↳ astro-ph.COhep-ph7 citations
17. 17*

    Summary of workshop on Future Physics with HERA Data

    A. Bacchetta🇮🇹 · J. Blümlein🇩🇪 · O. Behnke🇩🇪 · J. Dainton🇬🇧 · M. Diehl🇩🇪 · F. Hautmann🇬🇧 · A. Geiser🇩🇪 · H. Jung🇩🇪 · U. Karshon🇮🇱 · D. Kang🇺🇸 · P. Kroll🇩🇪 · C. Lee🇺🇸 and 21 other authors

    Recent highlights from the HERA experiments, Hermes, H1 and ZEUS, are reviewed and ideas for future analyses to fully exploit this unique data set are proposed. This document is a summary of a workshop on future physics with HERA data held at DESY, Hamburg at the end of 2014. All areas of HERA physics are covered and contributions from both experimentalists and theorists are included. The document outlines areas where HERA physics can still make a significant contribution, principally in a deeper understanding of QCD, and its relevance to other facilities. Within the framework of the Data Preservation in High Energy Physics, the HERA data have been preserved for analyses to take place over a timescale of 10 years and more. Therefore, although an extensive list of possibilities is presented here, safe storage of the data ensures that it can also be used in the far future should new ideas and analyses be proposed.

    ↳ hep-exhep-ph5 citations
18. 18*

    The gradient flow in $\lambda {\varphi }^4$ theory

    Kazuo Fujikawa🇯🇵

    A gradient flow equation for $\lambda {\varphi }^4$ theory in $D=4$ is formulated. In this scheme the gradient flow equation is written in terms of the renormalized probe variable $\Phi (t,x)$ and renormalized parameters $m^2$ and $\lambda$ in a manner analogous to the higher derivative regularization. No extra divergence is induced in the interaction of the probe variable $\Phi (t,x)$ and the 4-dimensional dynamical variable $\varphi (x)$ which is defined in renormalized perturbation theory. The finiteness to all orders in perturbation theory is established by power counting argument in the context of $D+1$ dimensional field theory. This illustrates that one can formulate the gradient flow for the simple but important $\lambda {\varphi }^4$ theory in addition to the well-known Yang-Mills flow, and it shows the generality of the gradient flow for a wider class of field theory.

    ↳ hep-lathep-phhep-thJHEP(2016)·21 citations
19. 19*

    How big are the smallest drops of quark-gluon plasma?

    Paul M. Chesler🇺🇸

    Using holographic duality, we present results for both head-on and off-center collisions of Gaussian shock waves in strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills theory. The shock waves superficially resemble Lorentz contracted colliding protons. The collisions results in the formation of a plasma whose evolution is well described by viscous hydrodynamics. The size of the produced droplet is $R\sim 1/T_{\mathrm{eff}}$ where $T_{\mathrm{eff}}$ is the effective temperature, which is the characteristic microscopic scale in strongly coupled plasma. These results demonstrate the applicability of hydrodynamics to microscopically small systems and bolster the notion that hydrodynamics can be applied to heavy-light ion collisions as well as some proton-proton collisions.

    ↳ hep-thgr-qchep-phnucl-thJHEP(2016)·75 citations
20. 20*

    Direct Evaluation of the Quark Content of Nucleons from Lattice QCD at the Physical Point

    A. Abdel-Rehim (The Cyprus Inst.)🇨🇾 · C. Alexandrou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · M. Constantinou (The Cyprus Inst.)🇨🇾 · K. Hadjiyiannakou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · K. Jansen (DESY-Zeuthen)🇩🇪 · Ch. Kallidonis (The Cyprus Inst.)🇨🇾 · G.Koutsou (The Cyprus Inst.)🇨🇾 · A. Vaquero Aviles-Casco (INFN, Milan)🇮🇹

    We evaluate the light, strange and charm scalar content of the nucleon using one lattice QCD ensemble generated with two degenerate light quarks with mass fixed to their physical value. We use improved techniques to evaluate the disconnected quark loops to sufficient accuracy to determine the strange and charm nucleon $\sigma$-terms. in addition to the light quark content ${\sigma }_{\pi N}$. We find ${\sigma }_{\pi N}$=$37.2(2.6){(}_{2.9}^{4.7})$ MeV ${\sigma }_s$=$41.1(8.2){(}_{5.8}^{7.8})$ MeV and ${\sigma }_c$=$79(21){(}_8^{12})$ MeV, where the first error is statistical and the second is the systematic error due to the determination of the lattice spacing, the assessment of finite volume and residual excited state effects.

    ↳ hep-lathep-phnucl-exnucl-thPRL(2016)·143 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.