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arXiv2013

CP-violating Phases in Active-Sterile Solar Neutrino Oscillations

Effects of CP-violating phases in active-sterile solar neutrino oscillations are discussed in a general scheme of 3+N_{s} mixing, without any constraint on the mixing between the three active and the N_{s} sterile neutrinos, assuming only a realistic hierarchy of neutrino mass-squared differences. A generalized Parke formula describing the neutrino oscillation probabilities inside the Sun is calculated. The validity of the analytical calculation and the probability variation due to the unknown CP-violating phases are illustrated with a numerical calculation of the evolution equation in the case of 3+1 neutrino mixing.

hep-ph↗
arXiv2013

Correlated, Precision Measurements of θ_{23} and $δ$ using only the Electron Neutrino Appearance Experiments

Precision measurement of the leptonic CP violating phase $δ$ will suffer from the, then surviving, large uncertainty of sin^2 θ_{23} of 10-20% in the experimentally interesting region near maximal mixing of θ_{23}. We advocate a new method for determination of both θ_{23} and $δ$ at the same time using only the ν_e and \barν_e appearance channels, and show that sin^2 θ_{23} can be determined automatically with much higher accuracy, approximately a factor of six, than \sin δ. In this method, we identify a new degeneracy for the simultaneous determination of θ_{23} and δ, the θ_{23} intrinsic degeneracy, which must be resolved in order to achieve precision measurement of these two parameters. Spectral information around the vacuum oscillation maxima is shown to be the best way to resolve this degeneracy.

hep-ph↗
arXiv2013

Improving the neutrino mass hierarchy identification with inelasticity measurement in PINGU and ORCA

Multi-megaton scale under ice and underwater detectors of atmospheric neutrinos with few GeV's energy threshold (PINGU, ORCA) open up new possibilities in the determination of neutrino properties, and in particular the neutrino mass hierarchy. With a dense array of optical modules it will be possible to determine the inelasticity, $y$, of the charged current $ν_μ$ events in addition to the neutrino energy $E_ν$ and the muon zenith angle $θ_μ$. The discovery potential of the detectors will substantially increase with the measurement of $y$. It will enable (i) a partial separation of the neutrino and antineutrino signals; (ii) a better reconstruction of the neutrino direction; (iii) the reduction of the neutrino parameters degeneracy; (iv) a better control of systematic uncertainties; (v) a better identification of the $ν_μ$ events. It will improve the sensitivity to the CP-violation phase. The three dimensional, $(E_ν, θ_μ, y)$, $ν_μ-$oscillograms with the kinematical as well as the experimental smearing are computed. We present the asymmetry distributions in the $E_ν- θ_μ$ plane for different intervals of $y$ and study their properties. We show that the inelasticity information reduces the effect of degeneracy of parameters by 30%. With the inelasticity, the total significance of establishing mass hierarchy may increase by 20% - 50%, thus effectively increasing the volume of the detector by factor 1.5 - 2.

hep-ph↗
arXiv2013

Probing the indefinite CP nature of the Higgs Boson through decay distributions in the process $e^+e^-\to t\bar{t}Φ$

The recently discovered scalar resonance at the LHC is now almost confirmed to be a Higgs Boson, whose CP properties are yet to be established. At the ILC with and without polarized beams, it may be possible to probe these properties at high precision. In this work, we study the possibility of probing departures from the pure CP-even case, by using the decay distributions in the process $e^+ e^- \to t \bar{t} Φ$, with $Φ$ mainly decaying into a $b\bar b$ pair. We have compared the case of a minimal extension of the SM case (Model I) with an additional pseudoscalar degree of freedom, with a more realistic case namely the CP-violating Two-Higgs Doublet Model (Model II) that permits a more general description of the couplings. We have considered the ILC with $\sqrt{s}=800$\,GeV and integrated luminosity of $300\, {\rm fb}^{-1}$. Our main findings are that even in the case of small departures from the CP-even case, the decay distributions are sensitive to the presence of a CP-odd component in Model II, while it is difficult to probe these departures in Model I unless the pseudoscalar component is very large. Noting that the proposed degrees of beam polarization increases the statistics, the process demonstrates the effective role of beam polarization in studies beyond the Standard Model. Further, our study shows that an indefinite CP Higgs would be a sensitive laboratory to physics beyond the SM.

hep-ph↗
arXiv2013

Proton (antiproton) elastic scattering at energies from FNAL to LHC in the tripole pomeron-odderon model

The model of elastic scattering amplitudes dominated by the triple (at $t=0$) pomeron pole suggested earlier is modified to confront to existing experimental data on $pp$ and $\bar pp$ total and differential cross sections at $\sqrt{s}\geq 19$ GeV and $|t|\leq 14.2$ GeV$^{2}$ including the newest TOTEM data. Predictions for the future TOTEM measurements at 13 and 14 TeV are given.

hep-ph↗
arXiv2013

The Constrained NMSSM with a 126 GeV Higgs boson: A global analysis

We present the first global analysis of the Constrained NMSSM that investigates the impact of the recent discovery of a 126 GeV Higgs-like boson, of the observation of a signal for BR(B_s->μ^+μ^-), and of constraints on supersymmetry from ~5/fb of data accumulated at the LHC, as well as of other relevant constraints from colliders, flavor physics and dark matter. We consider three possible cases, assuming in turn that the discovered Higgs boson is: i) the lightest Higgs boson of the model; ii) the next-to-lightest Higgs boson; and iii) a combination of both roughly degenerate in mass. The likelihood function for the Higgs signal uses signal rates in the γγ and ZZ --> 4l channels, while that for the Higgs exclusion limits assumes decay through the γγ, ττ, ZZ and W^+W^- channels. In all cases considered we identify the 68% and 95% credible posterior probability regions in a Bayesian approach. We find that, when the constraints are applied with their respective uncertainties, the first case shows strong CMSSM-like behavior, with the stau coannihilation region featuring highest posterior probability, the best-fit point, a correct mass of the lightest Higgs boson and the lighter stop mass in the ballpark of 1 TeV. The second and the third cases, on the other hand, while allowed are disfavored by the constraints from direct detection of dark matter and from BR(B_s->μ^+μ^-). Without the anomalous magnetic moment of the muon the fit improves considerably, especially for negative effective μ parameter. We discuss how the considered scenarios could be tested furtherly at the LHC and in dark matter searches.

hep-ph↗
arXiv2013

Dark Matter Mass Constrained by the Relic Abundance, Direct Detections, and Colliders

We take into account a generic form of a Dirac fermionic dark matter (DM), which communicates with the Standard Model quarks via a scalar mediator, in a model-independent way. Four special interaction scenarios are investigated, where one is parity conserving and the other three are parity violating. Three of them result in the $v$ suppressed DM-nucleon cross sections, where $v \sim 10^{-3} c$ is the velocity of the DM in the laboratory frame. We constrain the masses of the dark matter and mediator as well as the couplings from the thermal relic abundance, and the recent results of the XENON100 direct detection and collider experiments involving the two channels: (i) monojet plus large missing transverse energy, and (ii) dijet. The current monojet constraint is not stronger than that from the requirement of the correct relic density and the null result by the XENON100 direct detection. We find that the dijet resonance measurements can exclude a large part of the parameter space $(m_χ, m_Y)$, where the couplings for the mediator coupled to the dark matter and to the quarks are small and have roughly the same magnitude. The constraint from indirect detections and diphoton resonance searches is also briefly discussed.

hep-ph↗
arXiv2013

Higgs Production Amidst the LHC Detector

We investigate the spectacular collider signatures of macroscopically displaced, neutral particles that decay to Higgs bosons and missing energy. We show that such long-lived particles arise naturally in a very minimal extension of the Standard Model with only two new fermions with electroweak interactions. The lifetime of the long-lived neutral particles can range from 10^{-2} mm to 10^6 mm. In some regions of the parameter space, the exotic signals would have already been selected by the ATLAS and CMS triggers in their 7 and 8 TeV runs, hence hiding in the existing data. We also discuss the possibility of explaining the mild anomalies observed in the diphoton Higgs channel and the WW production at the LHC.

hep-ph↗
arXiv2013

Post-Sphaleron Baryogenesis and an Upper Limit on the Neutron-Antineutron Oscillation Time

A recently proposed scenario for baryogenesis, called post--sphaleron baryogenesis (PSB) is discussed within a class of quark--lepton unified framework based on the gauge symmetry SU(2)_L x SU(2)_R x SU(4)_c realized in the multi--TeV scale. The baryon asymmetry of the universe in this model is produced below the electroweak phase transition temperature after the sphalerons have decoupled from the Hubble expansion. These models embed naturally the seesaw mechanism for neutrino masses, and predict color-sextet scalar particles in the TeV range which may be accessible to the LHC experiments. A necessary consequence of this scenario is the baryon number violating ΔB=2 process of neutron--antineutron (n-\bar{n}) oscillations. In this paper we show that the constraints of PSB, when combined with the neutrino oscillation data and restrictions from flavor changing neutral currents mediated by the colored scalars imply an upper limit on the n-\bar{n} oscillation time of 5 x 10^{10} sec. regardless of the quark--lepton unification scale. If this scale is relatively low, in the (200-250) TeV range, τ_{n-\bar{n}} is predicted to be less than 10^{10} sec., which is accessible to the next generation of proposed experiments.

hep-ph↗
arXiv2013

Improved QCD sum rule study of $Z_{c}(3900)$ as a $\bar{D}D^{*}$ molecular state

In the framework of QCD sum rules, we present an improved study of our previous work [Phys. Rev. D {\bf80}, 056004 (2009)] particularly on the $\bar{D}D^{*}$ molecular state to investigate that the possibility of the newly observed $Z_{c}(3900)$ as a $S$-wave $\bar{D}D^{*}$ molecular state. To ensure the quality of QCD sum rule analysis, contributions of up to dimension nine are calculated to test the convergence of operator product expansion (OPE). We find that the two-quark condensate $<\bar{q}q>$ is very large and makes the standard OPE convergence (i.e. the perturbative at least larger than each condensate contribution) happen at very large values of Borel parameters. By releasing the rigid OPE convergence criterion, one could find that the OPE convergence is still under control. We arrive at the numerical result $3.86\pm0.27 {GeV}$ for $\bar{D}D^{*}$, which agrees with the mass of $Z_{c}(3900)$ and could support the explanation of $Z_{c}(3900)$ in terms of a $S$-wave $\bar{D}D^{*}$ molecular state.

hep-ph↗
arXiv2013

Search for non-pointing photons in the diphoton and E_T^miss final state in sqrt(s) = 7 TeV proton-proton collisions using the ATLAS detector

A search has been performed for photons originating in the decay of a neutral long-lived particle, exploiting the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction of photons, as well as the calorimeter's excellent time resolution. The search has been made in the diphoton plus missing transverse energy final state, using the full data sample of 4.8/fb of 7 TeV proton-proton collisions collected in 2011 with the ATLAS detector at the LHC. No excess is observed above the background expected from Standard Model processes. The results are used to set exclusion limits in the context of Gauge Mediated Supersymmetry Breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying with a lifetime in excess of 0.25 ns into a photon and a gravitino.

hep-ex↗
arXiv2013

CoGeNT: A Search for Low-Mass Dark Matter using p-type Point Contact Germanium Detectors

CoGeNT employs p-type point-contact (PPC) germanium detectors to search for Weakly Interacting Massive Particles (WIMPs). By virtue of its low energy threshold and ability to reject surface backgrounds, this type of device allows an emphasis on low-mass dark matter candidates (wimp mass of about 10 GeV/c2). We report on the characteristics of the PPC detector presently taking data at the Soudan Underground Laboratory, elaborating on aspects of shielding, data acquisition, instrumental stability, data analysis, and background estimation. A detailed background model is used to investigate the low energy excess of events previously reported, and to assess the possibility of temporal modulations in the low-energy event rate. Extensive simulations of all presently known backgrounds do not provide a viable background explanation for the excess of low-energy events in the CoGeNT data, or the previously observed temporal variation in the event rate. Also reported on for the first time is a determination of the surface (slow pulse rise time) event contamination in the data as a function of energy. We conclude that the CoGeNT detector technology is well suited to search for the annual modulation signature expected from dark matter particle interactions in the region of WIMP mass and coupling favored by the DAMA/LIBRA results

astro-ph.CO↗
arXiv2013

Supersymmetric Heavy Higgs Bosons at the LHC

The search for heavy Higgs bosons is an essential step in the exploration of the Higgs sector and in probing the Supersymmetric parameter space. This paper discusses the constraints on the M(A) and tan beta parameters derived from the bounds on the different decay channels of the neutral H and A bosons accessible at the LHC, in the framework of the phenomenological MSSM. The implications from the present LHC results and the expected sensitivity of the 14 TeV data are discussed in terms of the coverage of the [M(A) - tan beta] plane. New channels becoming important at 13 and 14 TeV for low values of tan beta are characterised in terms of their kinematics and the reconstruction strategies. The effect of QCD systematics, SUSY loop effects and decays into pairs of SUSY particles on these constraints are discussed in details.

hep-ph↗
arXiv2013

High Energy WW Scattering at the LHC with the Matrix Element Method

Perhaps the most important question in particle physics today is whether the boson with mass near 125 GeV discovered at the Large Hadron Collider (LHC) is the Higgs Boson of the Standard Model. Since a particularly important property of the Standard Model Higgs is its role in unitarizing longitudinal WW scattering, we study the ability of the LHC to probe this process in the case of same-sign W pair production. We find that the use of the Matrix Element Method increases the significance with which the Higgs sector can be probed in this channel. In particular, it allows one to distinguish between a light and heavy SM Higgs in this channel alone with a high degree of significance, as well as to set important limits in the parameter space of the Two Higgs Doublet Model and the Strongly-Interacting Light Higgs Model with less than 200/fb at the 14-TeV LHC, thus providing crucial information about the putative Higgs boson's role in electroweak symmetry breaking.

hep-ph↗
arXiv2013

The weak radiative pion vertex in τ^- ->π^-ν_τl^+ l^- decays

We carry out a detailed study of the branching fractions and lepton pair invariant-mass spectrum of τ^- ->π^- ν_τl^+l^- decays (l=e,μ). In addition to the model-independent (QED) contributions, we include the structure-dependent (SD) terms, which encode information on the hadronization of QCD currents. The form factors describing the SD contributions are evaluated by supplementing Chiral Perturbation Theory with the inclusion of the lightest multiplet of spin-one resonances as active degrees of freedom. The Lagrangian couplings have been determined demanding the known QCD short-distance behaviour to the relevant Green functions and associated form factors in the limit where the number of colours goes to infinity. As a result, we predict BR(τ^- ->π^-ν_τe^+e^-)= (1.7^{+1.1}_{-0.3})x10^{-5} and BR(τ^- -> π^-ν_τμ^+μ^-) = [0.03,1.0]x10^{-5}. According to this, the first decay could be measured in the near future, which is not granted for the second one.

hep-ph↗
arXiv2011

Two-flavor QCD correction to lepton magnetic moments at leading-order in the electromagnetic coupling

We present a reliable nonperturbative calculation of the QCD correction, at leading order in the electromagnetic coupling, to the anomalous magnetic moment of the electron, muon, and tau leptons using two-flavor lattice QCD. We use multiple lattice spacings, multiple volumes, and a broad range of quark masses to control the continuum, infinite-volume, and chiral limits. We examine the impact of the commonly ignored disconnected diagrams and introduce a modification to the previously used method that results in a well-controlled lattice calculation. We obtain 1.513(43) 10^(-12), 5.72(16) 10^(-8), and 2.650(54) 10^(-6) for the leading-order two-flavor QCD correction to the anomalous magnetic moment of the electron, muon, and tau, respectively, each accurate to better than 3%.

hep-lat↗
arXiv2011

Associated WH production at hadron colliders: a fully exclusive QCD calculation at NNLO

We consider QCD radiative corrections to Standard Model Higgs boson production in association with a W boson in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. Our calculation includes finite-width effects, the leptonic decay of the W boson with its spin correlations, and the decay of the Higgs boson into a bbbar pair. We present selected numerical results at the Tevatron and the LHC.

hep-ph↗
arXiv2011

New Constraints on Neutrino Velocities

The OPERA collaboration has claimed that muon neutrinos with mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that such superluminal neutrinos would lose energy rapidly via the bremsstrahlung of electron-positron pairs ($ν\rightarrow ν+e^-+e^+$). For the claimed superluminal neutrino velocity and at the stated mean neutrino energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. Thus we refute the superluminal interpretation of the OPERA result. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.

hep-ph↗