Fri·Apr 1, 2016Friday·April 1, 2016

1. 01*

   Relating $\hat{q}$, $\eta /s$ and $\Delta E$ in an expanding Quark-Gluon Plasma

   Alejandro Ayala🇲🇽 · Isabel Dominguez🇲🇽 · Jamal Jalilian-Marian🇺🇸 · Maria Elena Tejeda-Yeomans🇲🇽

   We use linear viscous hydrodynamics to describe the energy and momentum deposited by a fast moving parton in a quark gluon plasma. This energy-momentum is in turn used to compute the probability density for the production of soft partons by means of the Cooper-Frye formula. We use this probability density to render manifest a relation between the average transverse momentum given to the fast moving parton from the medium $\hat{q}$, the entropy density to shear viscosity ratio $\eta /s$ and the energy lost by the fast moving parton $\Delta E$ in an expanding medium under similar conditions to those generated in nucleus-nucleus collisions at the LHC. We find that $\hat{q}$ increases linearly with $\Delta E$ for both trigger and away side partons that have been produced throughout the medium. On the other hand, $\eta /s$ is more stable with $\Delta E$. We also study how these transport coefficients vary with the geometrical location of the hard scattering that produces the fast moving partons. The behavior of $\hat{q}$, with $\Delta E$ is understood as arising from the length of medium the parton traverses from the point where it is produced. However, since $\eta /s$ is proportional to the ratio of the length of medium traversed by the fast parton and the average number of scatterings it experiences, it has a milder dependence on the energy it loses. This study represents a tool to obtain a direct connection between transport coefficients and the description of in-medium energy loss within a linear viscous hydrodynamical evolution of the bulk.

   hep-phnucl-thPRC(2016)·18 citations
2. 02*

   Factorization for groomed jet substructure beyond the next-to-leading logarithm

   Christopher Frye🇺🇸 · Andrew J. Larkoski🇺🇸 · Matthew D. Schwartz🇺🇸 · Kai Yan🇺🇸

   Jet grooming algorithms are widely used in experimental analyses at hadron colliders to remove contaminating radiation from within jets. While the algorithms perform a great service to the experiments, their intricate algorithmic structure and multiple parameters has frustrated precision theoretic understanding. In this paper, we demonstrate that one particular groomer called soft drop actually makes precision jet substructure easier. In particular, we derive a factorization formula for a large class of soft drop jet substructure observables, including jet mass. The essential observation that allows for this factorization is that, without the soft wide-angle radiation groomed by soft drop, all singular contributions are collinear. The simplicity and universality of the collinear limit in QCD allows us to show that to all orders, the normalized differential cross section has no contributions from non-global logarithms. It is also independent of process, up to the relative fraction of quark and gluon jets. In fact, soft drop allows us to define this fraction precisely. The factorization theorem also explains why soft drop observables are less sensitive to hadronization than their ungroomed counterparts. Using the factorization theorem, we resum the soft drop jet mass to next-to-next-to-leading logarithmic accuracy. This requires calculating some clustering effects that are closely related to corresponding effects found in jet veto calculations. We match our resummed calculation to fixed order results for both $e^{+}{e}^{-}\to$ dijets and $pp\to Z+j$ events, producing the first jet substructure predictions (groomed or ungroomed) to this accuracy for the LHC.

   hep-phJHEP(2016)·184 citations
3. 03*

   On the MSSM Higgsino mass and fine tuning

   Graham G. Ross🇬🇧 · Kai Schmidt-Hoberg🇩🇪 · Florian Staub🇨🇭

   It is often argued that low fine tuning in the MSSM necessarily requires a rather light Higgsino. In this note we show that this need not be the case when a more complete set of soft SUSY breaking mass terms are included. In particular an Higgsino mass term, that correlates the $\mu -$term contribution with the soft SUSY-breaking Higgsino masses, significantly reduces the fine tuning even for Higgsinos in the TeV mass range where its relic abundance means it can make up all the dark matter.

   hep-phPLB(2016)·39 citations
4. 04*

   Novel kinematics from a custodially protected diphoton resonance

   Jack H. Collins🇺🇸 · Csaba Csaki🇺🇸 · Jeff Asaf Dror🇺🇸 · Salvator Lombardo🇺🇸

   We study a simple, well-motivated model based on a custodial symmetry which describes the tree-level production of a 750 GeV diphoton resonance from a decay of a singly produced vector-like quark. The model has several novel features. The identification of the resonance as an SU(2)${}_R$ triplet provides a symmetry explanation for suppression of its decays to hh, WW, and gg. Moreover, the ratio of the 13 TeV to 8 TeV cross sections can be larger than single production of a 750 GeV resonance, reaching ratios of up to 7 for TeV scale vector-like quark masses. This eliminates any tension between the results from Run I and Run II diphoton searches. Lastly, we study the kinematics of our signal and conclude that the new production mechanism is consistent with available experimental distributions in large regions of parameter space but, depending on the mass of the new vector-like quarks, can be differentiated from the background with more statistics.

   hep-phhep-exPRD(2016)·12 citations
5. 05*

   Asymmetric Dark Matter Models and the LHC Diphoton Excess

   Mads T. Frandsen🇩🇰 · Ian M. Shoemaker🇺🇸

   The existence of dark matter (DM) and the origin of the baryon asymmetry are persistent indications that the SM is incomplete. More recently, the ATLAS and CMS experiments have observed an excess of diphoton events with invariant mass of about 750 GeV. One interpretation of this excess is decays of a new spin-0 particle with a sizable diphoton partial width, e.g. induced by new heavy weakly charged particles. These are also key ingredients in models cogenerating asymmetric DM and baryons via sphaleron interactions and an initial particle asymmetry. We explore what consequences the new scalar may have for models of asymmetric DM that attempt to account for the similarity of the dark and visible matter abundances.

   hep-phJCAP(2016)·16 citations
6. 06*

   The one loop corrections to the neutrino masses in BLMSSM

   Shu-Min Zhao🇨🇳 · Tai-Fu Feng🇨🇳 · Xing-Xing Dong🇨🇳 · Hai-Bin Zhang🇨🇳 · Guo-Zhu Ning🇨🇳 · Tao-Guo🇨🇳

   The neutrino masses and mixings are studied in the model which is the supersymmetric extension of the standard model with local gauged baryon and lepton numbers(BLMSSM). At tree level the neutrinos can obtain tiny masses through the See-Saw mechanism in the BLMSSM. The one-loop corrections to the neutrino masses and mixings are important, and they are studied in this work with the mass insertion approximation. We study the numerical results and discuss the allowed parameter space of BLMSSM. It can contribute to study the neutrino masses and to explore the new physics beyond the standard model(SM).

   hep-phNPB(2016)·9 citations
7. 07*

   Analytic pion form factor

   Earle L. Lomon🇺🇸 · Simone Pacetti🇮🇹

   The pion electromagnetic form factor and two-pion production in electron-positron collisions are simultaneously fitted by a vector dominance model evolving to perturbative QCD at large momentum transfer. This model was previously successful in simultaneously fitting the nucleon electromagnetic form factors (spacelike region) and the electromagnetic production of nucleon-antinucleon pairs (timelike region). For this pion case dispersion relations are used to produce the analytic connection of the spacelike and timelike regions. The fit to all the data is good, especially for the newer sets of time-like data. The description of high-$q^2$ data, in the time-like region, requires one more meson with $\rho$ quantum numbers than listed in the 2014 Particle Data Group review.

   hep-phPRD(2016)·8 citations
8. 08*

   KK Gravitons at LHC2

   Barry M. Dillon🇬🇧 · Veronica Sanz🇬🇧

   In this work we study constraints from new searches for heavy particles at the LHC on the allowed masses and couplings of a KK Graviton in a holographic composite Higgs model. Keeping new electroweak states heavy such that electroweak precision tests are satisfied, we control the mass of the lightest KK graviton using a brane kinetic term. With this we study KK graviton masses from 0.5-3 TeV. In our analysis we also employ Little Randall-Sundrum (RS) Models, characterised by a lower UV scale in the 5D model which in turn implies modified couplings to massless bulk fields. Viewing this scenario as a strongly coupled 4D theory with a composite Higgs boson, the KK graviton is interpreted as a composite spin-2 state and the varying UV scale corresponds to a varying intermediate scale between the cutoff of the low energy effective theory and the Planck scale. We find that KK gravitons with masses in the range 0.5-3 TeV are compatible with current collider constraints, where the most promising channels for detecting these states are the di-photon and ZZ channels. A detection is more likely in the little RS models, in which the dual gauge theory has a larger number of colours than in traditional RS models.

   hep-phPRD(2017)·46 citations
9. 09*

   Thermal Model Description of Collisions of Small Nuclei

   H. Oeschler🇩🇪 · J. Cleymans🇿🇦 · B. Hippolyte🇫🇷 · K. Redlich🇵🇱 · N. Sharma🇮🇳

   The dependence of particle production on the size of the colliding nuclei is analysed in terms of the thermal model using the canonical ensemble. The concept of strangeness correlation in clusters of sub-volume $V_c$ is used to account for the suppression of strangeness. A systematic analysis is presented of the predictions of the thermal model for particle production in collisions of small nuclei. The pattern of the maxima of strange-particles-to-pion ratios as a function of beam energy is quite special, as they do not occur at the same beam energy and are sensitive to system size. In particular, the $\Lambda /{\pi }^{+}$ ratio shows a clear maximum even for small systems while the maximum in the K${}^{+}/{\pi }^{+}$ ratio is less pronounced

   hep-phnucl-th14 citations
10. 10*

    A QCD analysis of CMS inclusive differential Z production data at sqrt(s) = 8 TeV

    Rajdeep M Chatterjee🇮🇳 · Monoranjan Guchait🇮🇳 · Ringaile Placakyte🇩🇪

    The parton distribution functions (PDFs) of the proton are one of the essential ingredients to describe physics processes at hadron colliders. The Z boson production data at the LHC have a potential to constrain PDFs, especially the gluon distribution. In this study the CMS measurement of the inclusive double differential Z boson production cross section in terms of transverse momentum and rapidity are compared to the next-to-leading order theory predictions at the center-of-mass energy of sqrt(s)=8 TeV with an integrated luminosity of 19.71 inverse femtobarns. In addition, the sensitivity of this measurement to PDFs is studied within the framework of the HERAFitter. A moderate improvement to the gluon distribution is observed at the Bjorken x ~ 0.1 region. However, in order to obtain further improvement to the gluon distribution in the global fits, the higher-order theory calculations accessible via fast techniques are necessary.

    hep-phPRD(2016)·4 citations
11. 11*

    Influence of jets and decays of resonances on the triangular flow in ultrarelativistic heavy-ion collisions

    J. Crkovska🇫🇷 · J. Bielcik🇨🇿 · L. Bravina🇳🇴 · B.H. Brusheim Johansson🇳🇴 · E. Zabrodin🇳🇴 · G. Eyyubova🇷🇺 · V.L. Korotkikh🇷🇺 · I.P. Lokhtin🇷🇺 · L.V. Malinina🇷🇺 · S.V. Petrushanko🇷🇺 · A.M. Snigirev🇷🇺

    Triangular flow $v_3$ of identified and inclusive particles in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV is studied as a function of centrality and transverse momentum within the \textsc{hydjet++} model. The model enables one to investigate the influence of both hard processes and final-state interactions on the harmonics of particle anisotropic flow. Decays of resonances are found to increase the magnitude of the $v_3(p_{\mathrm{T}})$ distributions at $p_{\mathrm{T}}\ge 2$ GeV/$c$ and shift their maxima to higher transverse momenta. The $p_{\mathrm{T}}$-integrated triangular flow, however, becomes slightly weakened for all centralities studied. The resonance decays also modify the spectra towards the number-of-constituent-quark scaling fulfillment for the triangular flow, whereas jets are the main source of the scaling violation at the energies available at the CERN Large Hadron Collider (LHC). Comparison with the corresponding spectra of elliptic flow reveals that resonance decays and jets act in a similar manner on both $v_3(p_{\mathrm{T}})$ and $v_2(p_{\mathrm{T}})$ behavior. Obtained results are also confronted with the experimental data on differential triangular flow of identified hadrons, ratio $v_3^{1/3}(p_{\mathrm{T}})/v_2^{1/2}(p_{\mathrm{T}})$ and $p_{\mathrm{T}}$-integrated triangular flow of charged hadrons.

    hep-phnucl-exnucl-thPRC(2017)·23 citations
12. 12*

    $H\to \ell {\ell }^{\prime }$ in the Simplest Little Higgs Model

    Andrea Lami🇪🇸 · Pablo Roig🇲🇽

    Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the $H\to \tau \mu$ CMS hint and at the same time respect (as they do) the severe limits on $H\to \mu e$ inherited from the non-observation of $\mu \to e\gamma$. We compute the predictions of the Simplest Little Higgs Model for the $H\to \ell {\ell }^{\prime }$ decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) would, under reasonable assumptions, disfavor this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.

    hep-phhep-exPRD(2016)·36 citations
13. 13*

    Electron and muon anomalous magnetic dipole moment in a 3-3-1 model

    G. De Conto🇧🇷 · V. Pleitez🇧🇷

    We calculate, in the context of a 3-3-1 model with heavy charged leptons, constraints on some parameters of the extra particles in the model by imposing that their contributions to both the electron and muon $(g-2)$ factors are in agreement with experimental data up to 1$\sigma$-3$\sigma$. In order to obtain realistic results we use some of the possible solutions of the left- and right- unitary matrices that diagonalize the lepton mass matrices, giving the observed lepton masses and at the same time allowing to accommodate the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. We show that, at least up to 1-loop order, in the particular range of the space parameter that we have explored, it is not possible to fit the observed electron and muon $(g-2)$ factors at the same time unless one of the extra leptons has a mass of the order of 20-40 GeVs and the energy scale of the 331 symmetry to be of around 60-80 TeVs.

    hep-phJHEP(2017)·23 citations
14. 14*

    ASCR/HEP Exascale Requirements Review Report

    Salman Habib🇺🇸 · Robert Roser (HEP Leads)🇺🇸 · Richard Gerber🇺🇸 · Katie Antypas🇺🇸 · Katherine Riley🇺🇸 · Tim Williams🇬🇧 · Jack Wells🇺🇸 · Tjerk Straatsma (ASCR Leads)🇺🇸 · A. Almgren🇺🇸 · J. Amundson🇺🇸 · S. Bailey🇺🇸 · D. Bard🇺🇸 and 42 other authors

    This draft report summarizes and details the findings, results, and recommendations derived from the ASCR/HEP Exascale Requirements Review meeting held in June, 2015. The main conclusions are as follows. 1) Larger, more capable computing and data facilities are needed to support HEP science goals in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of the demand at the 2025 timescale is at least two orders of magnitude -- and in some cases greater -- than that available currently. 2) The growth rate of data produced by simulations is overwhelming the current ability, of both facilities and researchers, to store and analyze it. Additional resources and new techniques for data analysis are urgently needed. 3) Data rates and volumes from HEP experimental facilities are also straining the ability to store and analyze large and complex data volumes. Appropriately configured leadership-class facilities can play a transformational role in enabling scientific discovery from these datasets. 4) A close integration of HPC simulation and data analysis will aid greatly in interpreting results from HEP experiments. Such an integration will minimize data movement and facilitate interdependent workflows. 5) Long-range planning between HEP and ASCR will be required to meet HEP's research needs. To best use ASCR HPC resources the experimental HEP program needs a) an established long-term plan for access to ASCR computational and data resources, b) an ability to map workflows onto HPC resources, c) the ability for ASCR facilities to accommodate workflows run by collaborations that can have thousands of individual members, d) to transition codes to the next-generation HPC platforms that will be available at ASCR facilities, e) to build up and train a workforce capable of developing and using simulations and analysis to support HEP scientific research on next-generation systems.

    ↳ physics.comp-phastro-ph.COhep-exhep-lat+17 citations
15. 15*

    Collinear Superspace

    Timothy Cohen🇺🇸 · Gilly Elor🇺🇸 · Andrew J. Larkoski🇺🇸

    This letter provides a superfield based approach to constructing a collinear slice of $\mathcal{N}$ = 1 superspace. The strategy is analogous to integrating out anti-collinear fermionic degrees-of-freedom as was developed in the context of soft-collinear effective theory. The resulting Lagrangian can be understood as an integral over collinear superspace, where half the supercoordinates have been integrated out. The application to $\mathcal{N}$ = 1 super Yang-Mills is presented. Collinear superspace provides the foundation for future explorations of supersymmetric soft-collinear effective theory.

    ↳ hep-thhep-phPRD(2016)·6 citations
16. 16*

    Jet Substructure Classification in High-Energy Physics with Deep Neural Networks

    Pierre Baldi🇺🇸 · Kevin Bauer🇺🇸 · Clara Eng🇺🇸 · Peter Sadowski🇺🇸 · Daniel Whiteson🇺🇸

    At the extreme energies of the Large Hadron Collider, massive particles can be produced at such high velocities that their hadronic decays are collimated and the resulting jets overlap. Deducing whether the substructure of an observed jet is due to a low-mass single particle or due to multiple decay objects of a massive particle is an important problem in the analysis of collider data. Traditional approaches have relied on expert features designed to detect energy deposition patterns in the calorimeter, but the complexity of the data make this task an excellent candidate for the application of machine learning tools. The data collected by the detector can be treated as a two-dimensional image, lending itself to the natural application of image classification techniques. In this work, we apply deep neural networks with a mixture of locally-connected and fully-connected nodes. Our experiments demonstrate that without the aid of expert features, such networks match or modestly outperform the current state-of-the-art approach for discriminating between jets from single hadronic particles and overlapping jets from pairs of collimated hadronic particles, and that such performance gains persist in the presence of pileup interactions.

    ↳ hep-exhep-phPRD(2016)·228 citations
17. 17*

    Physics Accomplishments and Future Prospects of the BES Experiments at the BEPC Collider

    Roy A. Briere🇺🇸 · Frederick A. Harris🇺🇸 · Ryan E. Mitchell🇺🇸

    The cornerstone of the Chinese experimental particle physics program consists of a series of experiments performed in the tau-charm energy region. China began building e+e- colliders at the Institute for High Energy Physics in Beijing more than three decades ago. Beijing Electron Spectrometer, BES, is the common root name for the particle physics detectors operated at these machines. The development of the BES program is summarized and highlights of the physics results across several topical areas are presented.

    ↳ hep-exhep-phAnn.Rev.Nucl.Part.Sci.(2016)·10 citations
18. 18*

    Combined QCD and electroweak analysis of HERA data

    ZEUS Collaboration: H. Abramowicz🇮🇱 · I. Abt🇩🇪 · L. Adamczyk🇵🇱 · M. Adamus🇵🇱 · S. Antonelli🇮🇹 · V. Aushev🇺🇦 · O. Behnke🇩🇪 · U. Behrens🇩🇪 · A. Bertolin🇮🇹 · S. Bhadra🇨🇦 · I. Bloch🇩🇪 · E.G. Boos🇰🇿 and 114 other authors

    A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarisation of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.

    ↳ hep-exhep-phPRD(2016)·31 citations
19. 19*

    Mesonic Decay of Charm Hypernuclei ${\Lambda }_c^{+}$

    Sabyasachi Ghosh🇧🇷 · Carlos E. Fontoura🇧🇷 · Gastão Krein🇧🇷

    ${\Lambda }_c^{+}$ hypernuclei are expected to have binding energies and other properties similar to those of strange hypernuclei in view of the similarity between the quark structures of the strange and charmed hyperons, namely $\Lambda (uds)$ and ${\Lambda }_c^{+}(udc)$. One striking difference however occurs in their mesonic decays, as there is almost no Pauli blocking in the nucleonic decay of a charm hypernucleus because the final-state nucleons leave the nucleus at high energies. The nuclear medium nevertheless affects the mesonic decays of charm hypernucleus because the nuclear mean fields modify the masses of the charm hyperon. In the present communication we present results of a first investigation of the effects of finite baryon density on different weak mesonic decay channels of the ${\Lambda }_c^{+}$ baryon. We found a non-negligible reduction of the decay widths as compared to their vacuum values.

    ↳ nucl-thhep-phnucl-exEPJ Web Conf.(2016)·2 citations
20. 20*

    Dynamical Analysis of Anisotropic Inflation

    Mindaugas Karčiauskas🇫🇮

    Inflaton coupling to a vector field via the $f^2(\varphi )F_{\mu \nu }{F}^{\mu \nu }$ term is used in several contexts in the literature, such as to generate primordial magnetic fields, to produce statistically anisotropic curvature perturbation, to support anisotropic inflation and to circumvent the $\eta$-problem. Here, I perform dynamical analysis of such a system allowing for most general Bianchi I initial conditions. I also confirm the stability of attractor equilibrium points in phase-space directions that had not been investigated before.

    ↳ gr-qcastro-ph.COhep-phMod.Phys.Lett.A(2016)·19 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.