Mon·Jul 25, 2016Monday·July 25, 2016

1. 01*

   On the challenge of estimating diphoton backgrounds at large invariant mass

   J.F. Kamenik🇸🇮 · G. Perez🇮🇱 · M. Schlaffer🇮🇱 · A. Weiler🇩🇪

   Diphoton searches at high invariant mass are an integral part of the experimental high energy frontier. Using the analyses of the 750\,GeV diphoton resonance as a case study, we examine the methodology currently employed by the experimental analyses in estimating the dominant standard model backgrounds. We assess the dependence of the significance associated with the excess on the background modeling. In particular, we show that close to the high energy tails of the distributions, estimates of the jet faking backgrounds relying on functional extrapolations or Monte Carlo estimates of the challenging photon-jet contributions introduce a large uncertainty. Analyses with loose photon cuts, low photon $p_T$ cuts and those susceptible to high photon rapidity regions are especially affected. Given that diphoton-based searches beyond 1\,TeV are highly motivated as discovery modes, these considerations are relevant and applicable in the future. We first consider a physics-driven deformation of the shape of the diphoton faking photon-jet spectrum by next-to-leading order effects combined with a rapidity and transverse momentum dependent fake rate. We show that the resulting local significance of the excess is reduced due to such a deformation. Then using a simple, but more general, ansatz to modify the contribution of the jet faking backgrounds at high invariant masses but keeping the inclusive and differential sample purities within experimental uncertainty estimates, we demonstrate that the originally reported local 750\,GeV excess significances could have been overestimated by more than one standard deviation. We furthermore cross-check our analysis by comparing fit results based on the smaller 2015 and the larger 2016 LHC datasets. Finally we employ our methodology on the complete 13\,TeV LHC dataset to asses the systematics involved in the current diphoton searches beyond the TeV region.

   hep-phEPJC(2017)·4 citations
2. 02*

   Astrophysical Constraints on Singlet Scalars at LHC

   Mark P. Hertzberg🇺🇸 · Ali Masoumi🇺🇸

   We consider the viability of new heavy gauge singlet scalar particles at colliders such as the LHC. Our original motivation for this study came from the possibility of a new heavy particle of mass ~ TeV decaying significantly into two photons at colliders, such as LHC, but our analysis applies more broadly. We show that there are significant constraints from astrophysics and cosmology on the simplest UV complete models that incorporate such new particles and its associated collider signal. The simplest and most obvious UV complete model that incorporates such signals is that it arises from a new singlet scalar (or pseudo-scalar) coupled to a new electrically charged and colored heavy fermion. Here we show that these new fermions (and anti-fermions) would be produced in the early universe, then form new color singlet heavy mesons with light quarks, obtain a non-negligible freeze-out abundance, and remain in kinetic equilibrium until decoupling. These heavy mesons possess interesting phenomenology, dependent on their charge, including forming new bound states with electrons and protons. We show that a significant number of these heavy states would survive for the age of the universe and an appreciable number would eventually be contained within the earth and solar system. We show that this leads to detectable consequences, including the production of highly energetic events from annihilations on earth, new spectral lines, and, spectacularly, the destabilization of stars. The lack of detection of these consequences rules out such simple UV completions, putting pressure on the viability of such new particles at LHC. To incorporate such a scalar would require either much more complicated UV completions or even further new physics that provides a decay channel for the associated fermion.

   hep-phastro-ph.COhep-thJCAP(2017)·10 citations
3. 03*

   NLO+NLL Collider Bounds, Dirac Fermion and Scalar Dark Matter in the B-L Model

   Michael Klasen🇩🇪 · Florian Lyonnet🇺🇸 · Farinaldo S. Queiroz🇩🇪

   Baryon and lepton numbers being accidental global symmetries of the Standard Model (SM), it is natural to promote them to local symmetries. However, to preserve anomaly freedom, only combinations of B-L are viable. In this spirit, we investigate possible dark matter realizations in the context of the $U(1{)}_{B-L}$ model: (i) Dirac fermion with unbroken B-L; (ii) Dirac fermion with broken B-L; (iii) scalar dark matter; (iv) two component dark matter. We compute the relic abundance, direct and indirect detection observables and confront them with recent results from Planck, LUX-2016, and Fermi-LAT and prospects from XENON1T. In addition to the well known LEP bound $M_{Z^{\prime }}/g_{BL}\gtrsim 7$ TeV, we include often ignored LHC bounds using 13 TeV dilepton (dimuon+dielectron) data at next-to-leading order plus next-to-leading logarithmic accuracy. We show that, for gauge couplings smaller than $0.4$, the LHC gives rise to the strongest collider limit. In particular, we find $M_{Z^{\prime }}/g_{BL}>8.7$ TeV for $g_{BL}=0.3$. We conclude that the NLO+NLL corrections improve the dilepton bounds on the $Z^{\prime }$ mass and that both dark matter candidates are only viable in the $Z^{\prime }$ resonance region, with the parameter space for scalar dark matter being fully probed by XENON1T. Lastly, we show that one can successfully have a minimal two component dark matter model.

   hep-phastro-ph.COhep-exEPJC(2017)·95 citations
4. 04*

   Vacuum polarization and quadrupole corrections to the hyperfine splitting of P-states in muonic deuterium

   A.P. Martynenko🇷🇺 · V.V. Sorokin (Samara U.)🇷🇺

   On the basis of quasipotential approach in quantum electrodynamics we calculate vacuum polarization and quadrupole corrections in first and second orders of perturbation theory in hyperfine structure of P-states in muonic deuterium. All corrections are presented in integral form and evaluated analytically and numerically. The obtained results can be used for the improvement of the transition frequencies between levels 2P and 2S.

   hep-phquant-phJ.Phys.B(2017)·2 citations
5. 05*

   Second Stop and Sbottom Searches with a Stealth Stop

   Hsin-Chia Cheng🇺🇸 · Lingfeng Li🇺🇸 · Qin Qin🇺🇸

   The top squarks (stops) may be the most wanted particles after the Higgs boson discovery. The searches for the lightest stop have put strong constraints on its mass. However, there is still a search gap in the low mass region if the spectrum of the stop and the lightest neutralino is compressed. In that case, it may be easier to look for the second stop since naturalness requires both stops to be close to the weak scale. The current experimental searches for the second stop are based on the simplified model approach with the decay modes ${\tilde{t}}_2\to {\tilde{t}}_{1}Z$ and ${\tilde{t}}_2\to {\tilde{t}}_{1}h$. However, in a realistic supersymmetric spectrum there is always a sbottom lighter than the second stop, hence the decay patterns are usually more complicated than the simplified model assumptions. In particular, there are often large branching ratios of the decays ${\tilde{t}}_2\to {\tilde{b}}_{1}W$ and ${\tilde{b}}_1\to {\tilde{t}}_{1}W$ as long as they are open. The decay chains can be even more complex if there are intermediate states of additional charginos and neutralinos in the decays. By studying several MSSM benchmark models at the 14 TeV LHC, we point out the importance of the multi-$W$ final states in the second stop and the sbottom searches, such as the same-sign dilepton and multilepton signals, aside from the traditional search modes. The observed same-sign dilepton excesses at LHC Run 1 and Run 2 may be explained by some of our benchmark models. We also suggest that the vector boson tagging and a new kinematic variable may help to suppress the backgrounds and increase the signal significance for some search channels. Due to the complex decay patterns and lack of the dominant decay channels, the best reaches likely require a combination of various search channels at the LHC for the second stop and the lightest sbottom.

   hep-phhep-exJHEP(2016)·14 citations
6. 06*

   Cosmological relaxation and high scale inflation

   Tetsutaro Higaki🇯🇵 · Naoyuki Takeda🇯🇵 · Yusuke Yamada🇯🇵

   We study whether the relaxion mechanism solves the Higgs hierarchy problem against a high scale inflation or a high reheating temperature. To accomplish the mechanism, we consider the scenario that the Higgs vacuum expectation value is determined after inflation. We take into account the effects of the Hubble induced mass and thermal one in the dynamics of the relaxion.

   hep-phastro-ph.COhep-thPRD(2017)·11 citations
7. 07*

   Heavy axion in asymptotically safe QCD

   Archil Kobakhidze🇦🇺

   Assuming QCD exhibits an interacting fixed-point behaviour in the ultraviolet regime, I argue that the axion can be substantially heavier than in the conventional case of asymptotically free QCD due to the enhanced contribution of small size instantons to its mass.

   hep-phhep-th24 citations
8. 08*

   Tuning of the Charged Hadrons Multiplicities for Deep Inelastic Interactions in NEUT

   Christophe Bronner🇯🇵 · Mark Hartz🇯🇵

   We describe a procedure to tune the charged hadron multiplicities for deep inelastic events produced by the NEUT neutrino interaction generator. This tuning uses a model based on Koba-Nielsen-Olesen scaling, whose parameters are obtained by fitting multiplicity data from deuterium bubble chamber experiments. After tuning, the multiplicities of the events generated by NEUT are found to be in good agreement with the measurements from the bubble chamber experiments.

   hep-phhep-exJPS Conf.Proc.(2016)·8 citations
9. 09*

   Relations among pionic decays of spin-1 mesons from an SU(4)$\times$U(1) emergent symmetry in QCD

   Hiroki Nishihara🇯🇵 · Masayasu Harada🇯🇵

   Motivated by recent results by lattice analysis, we assume that the spin-1 mesons of $\left(\rho ,\omega ,a_1,{\rho }^{\prime },{\omega }^{\prime },b_1,f_1,h_1\right)$ make a representation of $16$ of U(4) emergent symmetry in two-flavor QCD when the chiral symmetry is not broken. We study the decay properties of the spin-1 mesons by using a chiral model with an SU(4)$\times$U(1) hidden local symmetry. We first show that, since the SU(4) symmetry is spontaneously broken together with the chiral symmetry, each coupling of the interaction among one pion and two spin-1 mesons is proportional to the mass difference of the relevant spin-1 mesons similarly to the Goldberger-Treiman relation. In addition, some of one-pion couplings are related with each other by the SU(4) symmetry. We further show that there is a relation among the mass of ${\rho }^{\prime }$ meson, the ${\rho }^{\prime }\pi \pi$ coupling and the ${\rho }^{\prime }$-photon mixing strength as well as the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin relation for the $\rho$ meson. From the relations, we give numerical predictions such as ratios of the spin-1 meson decay widths, which are compared with future experiments for testing the existence of the U(4) emergent symmetry.

   hep-ph0 citations
10. 10*

    Entangling Higgs production associated with a single top and a top-quark pair in the presence of anomalous top-Yukawa coupling

    Jung Chang🇹🇼 · Kingman Cheung🇹🇼 · Jae Sik Lee🇰🇷 · Chih-Ting Lu🇹🇼

    The ATLAS and CMS collaborations observed a mild excess in the associated Higgs production with a top-quark pair ($t\bar{t}h$) and reported the signal strengths of ${\mu }_{tth}^{\mathrm{ATLAS}}=1.81\pm 0.80$ and ${\mu }_{tth}^{\mathrm{CMS}}=2.75\pm 0.99$ based on the data collected at $\sqrt{s}$= 7 and 8 TeV. Although, at the current stage, there is no obvious indication whether the excess is real or due to statistical fluctuations, here we perform a case study of this mild excess by exploiting the strong entanglement between the associated Higgs production with a single top quark ($thX$) and $t\bar{t}h$ production in the presence of anomalous top-Yukawa coupling. As well known, $t\bar{t}h$ production only depends on the absolute value of the top-Yukawa coupling. Meanwhile, in $thX$ production, this degeneracy is lifted through the strong interference between the two main contributions which are proportional to the top-Yukawa and the gauge-Higgs couplings, respectively. Especially, when the relative sign of the top-Yukawa coupling with respect to the gauge-Higgs coupling is reversed, the $thX$ cross section can be enhanced by more than one order of magnitude. We perform a detailed study of the influence of $thX$ production on $t\bar{t}h$ production in the presence of the anomalous top-Yukawa coupling and point out that it is crucial to include $thX$ production in the analysis of the $t\bar{t}h$ data to pin down the sign and the size of the top-Yukawa coupling in future. While assuming the Standard Model (SM) value for the gauge-Higgs coupling, we vary the top-Yukawa coupling within the range allowed by the current LHC Higgs data. We consider the Higgs decay modes into multileptons, $b\bar{b}$ and $\gamma \gamma$ putting a particular emphasis on the same sign dilepton events. We also discuss ...

    hep-phhep-exJHEP(2017)·6 citations
11. 11*

    Parity-violating $\pi NN$ coupling constant from the flavor-conserving effective weak chiral Lagrangian

    Chang Ho Hyun🇰🇷 · Hyun-Chul Kim🇰🇷 · Hee-Jung Lee🇰🇷

    We investigate the parity-violating pion-nucleon-nucleon coupling constant $h_{\pi NN}^1$, based on the chiral quark-soliton model. We employ an effective weak Hamiltonian that takes into account the next-to-leading order corrections from QCD to the weak interactions at the quark level. Using the gradient expansion, we derive the leading-order effective weak chiral Lagrangian with the low-energy constants determined. The effective weak chiral Lagrangian is incorporated in the chiral quark-soliton model to calculate the parity-violating $\pi NN$ constant $h_{\pi NN}^1$. We obtain a value of about $10^{-7}$ at the leading order. The corrections from the next-to-leading order reduce the leading order result by about 20~\%.

    hep-phPLB(2017)·5 citations
12. 12*

    Fluctuations and the QCD Phase Diagram

    Volker Koch🇺🇸 · Adam Bzdak🇵🇱

    In this contribution we will discuss how the study of various fluctuation observables may be used to explore the phase diagram of the strong interaction. We will briefly summarize the present study of experimental and theoretical research in this area. We will then discuss various corrections and issues which need to be understood and applied for a meaningful comparison of experimental measurements with theoretical predictions. This contribution is dedicated to Andrzej Bialas on the occasion of his $80^{\mathrm{th}}$ birthday.

    hep-phActa Phys.Polon.B(2016)·5 citations
13. 13*

    Bayes-factor of the ATLAS diphoton excess

    Andrew Fowlie🇦🇺

    We present a calculation of Bayes-factors for the digamma resonance ($ϝ$) versus the SM in light of ATLAS 8 TeV 20.3/fb, 13 TeV 3.2/fb and 13 TeV 15.4/fb data, sidestepping any difficulties in interpreting significances in frequentist statistics. We matched, wherever possible, parameterisations in the ATLAS analysis. We calculated that the plausibility of the $ϝ$ versus the Standard Model increased by about eight in light of the 8 TeV 20.3/fb and 13 TeV 3.2/fb ATLAS data, somewhat justifying interest in $ϝ$ models. All told, however, in light of 15.4/fb data, the $ϝ$ was disfavoured by about 0.7.

    hep-phhep-exphysics.data-anEur.Phys.J.Plus(2017)·5 citations
14. 14*

    Limit on Lorentz-Invariance- and CPT-Violating Neutron Spin Interactions Using a ${}^3$He-${}^{129}$Xe Comagnetometer

    Fabian Allmendinger🇩🇪 · Ulrich Schmidt🇩🇪 · Werner Heil🇩🇪 · Sergej Karpuk🇩🇪 · Yuri Sobolev🇩🇪

    We performed a search for a Lorentz-invariance- and CPT-violating coupling of the ${}^3$He and ${}^{129}$Xe nuclear spins to posited background fields. Our experimental approach is to measure the free precession of nuclear spin polarized ${}^3$He and ${}^{129}$Xe atoms using SQUID detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the co-located spin samples. As a result we obtain an upper limit on the equatorial component of the background field ${\tilde{b}}_{\perp }^n<8.4\cdot 10^{-34}$ GeV (68\% C.L.). Furthermore, this technique was modified to search for an electric dipole moment (EDM) of ${}^{129}$Xe.

    hep-phphysics.atom-ph1 citation
15. 15*

    Singularity-free Next-to-leading Order $\Delta S=1$ Renormalization Group Evolution and ${ϵ}_K^{\prime }/{ϵ}_K$ in the Standard Model and Beyond

    Teppei Kitahara🇩🇪 · Ulrich Nierste🇩🇪 · Paul Tremper🇩🇪

    The standard analytic solution of the renormalization group (RG) evolution for the $\Delta S=1$ Wilson coefficients involves several singularities, which complicate analytic solutions. In this paper we derive a singularity-free solution of the next-to-leading order (NLO) RG equations, which greatly facilitates the calculation of ${ϵ}_K^{\prime }$, the measure of direct $CP$ violation in $K\to \pi \pi$ decays. Using our new RG evolution and the latest lattice results for the hadronic matrix elements, we calculate the ratio ${ϵ}_K^{\prime }/{ϵ}_K$ (with ${ϵ}_K$ quantifying indirect $CP$ violation) in the Standard Model (SM) at NLO to ${ϵ}_K^{\prime }/{ϵ}_K=(1.06\pm 5.07)\times 10^{-4}$, which is $2.8\sigma$ below the experimental value. We also present the evolution matrix in the high-energy regime for calculations of new physics contributions and derive easy-to-use approximate formulae. We find that the RG amplification of new-physics contributions to Wilson coefficients of the electroweak penguin operators is further enhanced by the NLO corrections: If the new contribution is generated at the scale of 1-10 TeV, the RG evolution between the new-physics scale and the electroweak scale enhances these coefficients by 50-100 %. Our solution contains a term of order ${\alpha }_{EM}^2/{\alpha }_s^2$, which is numerically unimportant for the SM case but should be included in studies of high-scale new-physics.

    hep-phhep-exJHEP(2016)·78 citations
16. 16*

    Neutrino mass from M Theory SO(10)

    Bobby S. Acharya🇬🇧 · Krzysztof Bozek🇬🇧 · Miguel Crispim Romão🇬🇧 · Stephen F. King🇬🇧 · Chakrit Pongkitivanichkul🇬🇧

    We study the origin of neutrino mass from $SO(10)$ arising from $M$ Theory compactified on a $G_2$-manifold. This is linked to the problem of the breaking of the extra $U(1)$ gauge group, in the $SU(5)\times U(1)$ subgroup of $SO(10)$, which we show can achieved via a (generalised) Kolda-Martin mechanism. The resulting neutrino masses arise from a combination of the seesaw mechanism and induced R-parity breaking contributions. The rather complicated neutrino mass matrix is analysed for one neutrino family and it is shown how phenomenologically acceptable neutrino masses can emerge.

    hep-phhep-thJHEP(2016)·10 citations
17. 17*

    Sensitivity of EAS measurements to the energy spectrum of muons

    J. Espadanal🇵🇹 · L. Cazon🇵🇹 · R. Conceição🇵🇹

    We have studied how the energy spectrum of muons at production affects some of the most common measurements related to muons in extensive air shower studies, namely, the number of muons at the ground, the slope of the lateral distribution of muons, the apparent muon production depth, and the arrival time delay of muons at ground. We found that by changing the energy spectrum by an amount consistent with the difference between current models (namely EPOS-LHC and QGSjet-II.04), the muon surface density at ground increases $5\%$ at $20^{\circ }$ zenith angle and $17\%$ at $60^{\circ }$ zenith angle. This effect introduces a zenith angle dependence on the reconstructed number of muons which might be experimentally observed. The maximum of the muon production depth distribution at $40^{\circ }$ increases $\sim 10{\text{ g/cm}}^2$ and $\sim 0{\text{ g/cm}}^2$ at $60^{\circ }$, which, from pure geometrical considerations, increases the arrival time delay of muons. There is an extra contribution to the delay due to the subluminal velocities of muons of the order of $\sim 3$ ns at all zenith angles. Finally, changes introduced in the logarithmic slope of the lateral density function are less than 2%.

    hep-phastro-ph.HEhep-exAstropart.Phys.(2017)·13 citations
18. 18*

    Towards the next generation of simplified Dark Matter models

    Andreas Albert🇩🇪 · Martin Bauer🇩🇪 · Oliver Buchmueller🇬🇧 · Jim Brooke🇬🇧 · David G. Cerdeno🇬🇧 · Matthew Citron🇬🇧 · Gavin Davies🇬🇧 · Annapaola de Cosa🇨🇭 · Albert De Roeck🇨🇭 · Andrea De Simone🇮🇹 · Tristan Du Pree🇬🇧 · John Ellis🇬🇧 and 14 other authors

    This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediator to include mixing with the Higgs boson. We show that this approach not only provides a better description of the underlying kinematic properties that a complete model would possess, but also offers the option of using this more realistic class of scalar mixing models to compare and combine consistently searches based on different experimental signatures. The second example outlines how a new physics signal observed in a visible channel can be connected to DM by extending a simplified model including effective couplings. This discovery scenario uses the recently observed excess in the high-mass diphoton searches of ATLAS and CMS for a case study to show that such a pragmatic approach can aid the experimental search programme to verify/falsify a potential signal and to study its underlying nature. In the next part of the White Paper we outline other interesting options for SDMM that could be studied in more detail in the future. Finally, we discuss important aspects of supersymmetric models for DM and how these could help to develop of more complete SDMM.

    ↳ hep-exhep-phPhys.Dark Univ.(2017)·78 citations
19. 19*

    Lattice operators for scattering of particles with spin

    S. Prelovsek🇸🇮 · U. Skerbis🇸🇮 · C.B. Lang🇦🇹

    We construct operators for simulating the scattering of two hadrons with spin on the lattice. Three methods are shown to give the consistent operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar, vector and nucleon. Explicit expressions for operators are given for all irreducible representations at lowest two relative momenta. Each hadron has a good helicity in the first method. The hadrons are in a certain partial wave L with total spin S in the second method. These enable the physics interpretations of the operators obtained from the general projection method. The correct transformation properties of the operators in all three methods are proven. The total momentum of two hadrons is restricted to zero since parity is a good quantum number in this case.

    ↳ hep-lathep-phJHEP(2017)·43 citations
20. 20*

    CP violation in the B system

    T. Gershon🇬🇧 · V.V. Gligorov🇫🇷

    The phenomenon of CP violation is crucial to understand the asymmetry between matter and antimatter that exists in the Universe. Dramatic experimental progress has been made, in particular in measurements of the behaviour of particles containing the b quark, where CP violation effects are predicted by the Kobayashi-Maskawa mechanism that is embedded in the Standard Model. The status of these measurements and future prospects for an understanding of CP violation beyond the Standard Model are reviewed.

    ↳ hep-exhep-phRept.Prog.Phys.(2017)·36 citations
21. 21*

    Laser Gyroscopes, Gravity, and the SME

    Nicholas Scaramuzza🇺🇸 · Jay D. Tasson🇺🇸

    In this contribution to the CPT'16 proceedings, we illustrate the potential use of ring-laser systems in searching for Lorentz violation in the framework of the Standard-Model Extension. We present expressions for the Lorentz-violating contribution to the ring-laser signal for a sample system and make sensitivity estimates for the GINGER project.

    ↳ gr-qchep-ph2 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.