SEARCH · Searcharxiv

Results for “hep-ex”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources

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

Neutrino mass hierarchy determination with IceCube-PINGU

We discuss the neutrino mass hierarchy determination with atmospheric neutrinos in PINGU (Precision IceCube Next Generation Upgrade), based on a simulation with the GLoBES software including the full three flavor framework and parameter degeneracy, and we compare it to long-baseline experiment options. We demonstrate that the atmospheric mass hierarchy sensitivity depends on the achievable experiment properties and we identify the main targets for optimization, whereas the impact of a large number of tested systematical errors turns out to be small. Depending on the values of theta_23, delta, and the true hierarchy, a 90% CL to 3sigma discovery after three years of operation seems conceivable. We also emphasize the synergy with existing beam and reactor experiments, driven by NOvA, such as the complementary coverage of the parameter space. Finally, we point out that a low intensity neutrino beam with a relatively short decay pipe could be used to determine the mass hierarchy with a sensitivity comparable to the LBNE experiment irrespective of the directional resolution of the detector.

hep-ph↗

arXiv2013

Explanation of the Muon g-2 Anomaly with Vectorlike Leptons and its Implications for Higgs Decays

The deviation of the measured value of the muon anomalous magnetic moment from the standard model prediction can be completely explained by mixing of the muon with extra vectorlike leptons, L and E, near the electroweak scale. This mixing simultaneously contributes to the muon mass. We show that the correlation between contributions to the muon mass and muon g-2 is controlled by the mass of the neutrino originating from the doublet L. Positive correlation, simultaneously explaining both measured values, requires this mass below 200 GeV. The decay rate of the Higgs boson to muon pairs is modified and, in the region of the parameter space that can explain the muon anomalous magnetic moment within one standard deviation, it ranges from 0.5 to 24 times the standard model prediction. In the same scenario, $h \to γγ$ can be enhanced or lowered by ~50% from the standard model prediction. The explanation of the muon g-2 anomaly and predictions for $h \to γγ$ are not correlated since these are controlled by independent parameters. This scenario can be embedded in a model with three complete vectorlike families featuring gauge coupling unification, sufficiently stable proton, and the Higgs quartic coupling remaining positive all the way to the grand unification scale.

hep-ph↗

arXiv2013

Radiative Decays of Cosmic Background Neutrinos in Extensions of MSSM with a Vector Like Lepton Generation

An analysis of radiative decays of the neutrinos $ν_j\to ν_l γ$ is discussed in MSSM extensions with a vector like lepton generation. Specifically we compute neutrino decays arising from the exchange of charginos and charged sleptons where the photon is emitted by the charged particle in the loop. It is shown that while the lifetime of the neutrino decay in the Standard Model is $\sim 10^{43}$ yrs for a neutrino mass of 50 meV, the current lower limit from experiment from the analysis of the Cosmic Infrared Background is $\sim 10^{12}$ yrs and thus beyond the reach of experiment in the foreseeable future. However, in the extensions with a vector like lepton generation the lifetime for the decays can be as low as $\sim 10^{12}- 10^{14}$ yrs and thus within reach of future improved experiments. The effect of CP phases on the neutrino lifetime is also analyzed. It is shown that while both the magnetic and the electric transition dipole moments contribute to the neutrino lifetime, often the electric dipole moment dominates even for moderate size CP phases.

hep-ph↗

arXiv2013

Low-Mass Dark-Matter Hint from CDMS II, Higgs Boson at the LHC, and Darkon Models

The CDMS II experiment has observed three events which may have arisen from weakly interacting massive particle (WIMP) dark matter (DM) with mass of order 9 GeV colliding with nuclei. Although the implied WIMP parameter region seems to be excluded by limits from the XENON experiments, it is interesting that most of this tension can go away if the WIMP-nucleon interaction violates isospin. This motivates us to explore some of the implications for models in which a real gauge-singlet scalar particle, the darkon, serves as the WIMP, taking into account the recent discovery of a Higgs boson at the LHC and Planck determination of the DM relic density. In the simplest scenario, involving only the standard model plus a darkon, the Higgs boson is largely invisible due to its decay into a pair of darkons having the WIMP mass suggested by CDMS II and hence cannot be identified with the one found at the LHC. We find, on the other hand, that a two-Higgs-doublet model supplemented with a darkon has ample parameter space to accommodate well both the new potential DM hint from CDMS II and the Higgs data from the LHC, whether or not the darkon-nucleon interaction conserves isospin.

hep-ph↗

arXiv2013

Exploring the threshold behavior and implications on the nature of Y(4260) and $Z_c(3900)$

By assuming that Y(4260) either is a $D_1\bar{D}$ molecular state, or has sizeable couplings with $D_0 \bar{D}^*$ and $D_1^\prime \bar{D}$, we investigate several decay modes of Y(4260). Under the special kinematic configurations, triangle singularity (TS) may occur in the rescattering amplitude, which will significantly change the threshold behavior. Obvious threshold enhancements or narrow cusp structures appear quite naturally without introducing a genuine resonance. We emphasize that the radiative decay modes may be useful for studying $D^{(*)}\bar{D}$ $S$-wave scattering.

hep-ph↗

arXiv2013

Single (anti-)top quark production in association with a lightest neutralino at LHeC

In this paper we examine thoroughly the single (anti-)top quark production associated with a lightest neutralino at the possible CERN Large Hadron Electron Collider (LHeC). We calculate the full next-to-leading order (NLO) QCD corrections to the process including all the nonresonant diagrams and do not assume the production and decay factorization for the possible resonant top squarks in the R-parity violating minimal supersymmetric standard model with 19 unrelated parameters. We investigate numerically the effects of the relevant supersymmetry (SUSY) parameters on the cross section, and present the transverse momentum distributions of final (anti-)top quark at both the leading-order (LO) and the QCD NLO. We find that the NLO QCD corrections enhance the LO cross sections in most chosen parameter space, and the NLO QCD impacts on the transverse momentum distributions of the final (anti-)top quark might be resolvable in some cases. We conclude that even with recently known experimental constraints the on SUSY parameters, the production rate could still achieve notable value in the admissible parameter space.

hep-ph↗

arXiv2012

Probing Parton Orbital Angular Momentum in Longitudinally Polarized Nucleon

While the total orbital angular momentum (OAM) of a definite quark flavor in a longitudinally-polarized nucleon can be obtained through a sum rule involving twist-two generalized parton distribution (GPDs), its distribution as a function of parton momentum in light-front coordinates is more complicated to define and measure because it involves intrinsically twist-three effects. In this paper, we consider two different parton OAM distributions. The first is manifestly gauge invariant, and its moments are local operators and calculable in lattice QCD. We show that it can potentially be measured through twist-three GPDs. The second is the much-debated canonical OAM distribution natural in free-field theory and light-cone gauge. We show the latter in light-cone gauge can also be related to twist-three GPDs as well as quantum phase-space Wigner distributions, both being measurable in high-energy experiments.

hep-ph↗

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

Electroweak Constraints on the Fourth Generation at Two Loop Order

If the Higgs-like particle at 126 GeV is the standard model Higgs boson, then SM4, the simplest four generation extension of the SM, is inconsistent with the most recent LHC data. However, 4G variations (BSM4) are possible if the new particle is not the SM Higgs boson and/or if other new quanta modify its production and decay rates. Since LHC searches have pushed 4G quarks to high mass and strong coupling where perturbation theory eventually fails, we examine the leading nondecoupling EW (electroweak) corrections at two loop order to estimate the domain of validity for perturbation theory. We find that the two loop hypercharge correction, which has not been included in previous EW fits of 4G models, makes the largest quark sector contribution to the rho parameter, much larger even than the nominally leading one loop term. Because it is large and negative, it has a big effect on the EW fits. It does not invalidate perturbation theory since it only first appears at two loop order and is large because it does not vanish for equal quark doublet masses, unlike the one loop term. We estimate that perturbation theory is useful for $m_Q\simeq 600$ GeV but begins to become marginal for $m_Q\, \gtap\, 900$ GeV. The results apply directly to BSM4 models that retain the SM Higgs sector but must be re-evaluated for non-SM Higgs sectors.

hep-ph↗

arXiv2012

Probing Near-Conformal Technicolor through Weak Boson Scattering

The recently observed boson at 125 GeV could be a light composite scalar from near-conformal technicolor dynamics: a technicolor Higgs. If this is the case, unitarization of longitudinal weak boson scattering amplitudes, which is due to exchanges of the Higgs and spin-one vector technimesons, is expected to occur in a strong regime, with saturation of the unitarity bounds. This implies that $pp \to V V jj$ processes, where $V$ is either a $W$ or a $Z$ boson, are enhanced, relative to the standard model. We show that this allows probing near-conformal technicolor for couplings and masses of the spin-one resonances which are not directly accessible for direct Drell-Yan production.

hep-ph↗

arXiv2013

Xenophobic Dark Matter

We consider models of xenophobic dark matter, in which isospin-violating dark matter-nucleon interactions significantly degrade the response of xenon direct detection experiments. For models of near-maximal xenophobia, with neutron-to-proton coupling ratio $f_n / f_p \approx -0.64$, and dark matter mass near 8 GeV, the regions of interest for CoGeNT and CDMS-Si and the region of interest identified by Collar and Fields in CDMS-Ge data can be brought into agreement. This model may be tested in future direct, indirect, and collider searches. Interestingly, because the natural isotope abundance of xenon implies that xenophobia has its limits, we find that this xenophobic model may be probed in the near future by xenon experiments. Near-future data from the LHC and Fermi-LAT may also provide interesting alternative probes of xenophobic dark matter.

hep-ph↗

arXiv2013

Electroweak Supersymmetry (EWSUSY) in the NMSSM

To explain all the available experimental results, we have proposed the Electroweak Supersymmetry (EWSUSY) previously, where the squarks and/or gluino are heavy around a few TeVs while the sleptons, sneutrinos, Bino, Winos, and/or Higgsinos are light within one TeV. In the Next to Minimal Supersymmetric Standard Model (NMSSM), we perform the systematic χ^2 analyses on parameter space scan for three EWSUSY scenarios: (I) R-parity conservation and one dark matter candidate; (II) R-parity conservation and multi-component dark matter; (III) R-parity violation. We obtain the minimal χ^2/(degree of freedom) of 10.2/15, 9.6/14, and 9.2/14 respectively for Scenarios I, II, and III. Considering the constraints from the LHC neutralino/chargino and slepton searches, we find that the majority of viable parameter space prefered by the muon anomalous magnetic moment has been excluded except for the parameter space with moderate to large \tanβ(\ge 8). Especially, the most favorable parameter space has relatively large \tanβ, moderate λ, small μ_{eff}, heavy squarks/gluino, and the second lightest CP-even neutral Higgs boson with mass around 125 GeV. In addition, if the left-handed smuon is nearly degenerate with or heavier than Wino, there is no definite bound on Wino mass. Otherwise, the Wino with mass up to \sim 450 GeV has been excluded. Furthermore, we present several benchmark points for Scenarios I and II, and briefly discuss the prospects of the EWSUSY searches at the 14 TeV LHC and ILC.

hep-ph↗

arXiv2013

Searching for New Physics with bbar -> sbar Bs -> V_1 V_2 Penguin Decays

We present the most general (six-helicity) angular analysis of Bs -> V_1 (-> P_1P'_1) V_2 (-> P_2P'_2) (V_i is a vector meson, and P_i, P'_i are pseudoscalars). We focus on final states accessible to both Bs and Bsbar -- these are mainly bbar -> sbar penguin decays. We also derive the most general decay amplitude, and discuss the differences between it and that used by LHCb in its analysis of Bs -> phi phi. In the standard model, all CP violation is predicted to be small, so that the simple measurement of a sizeable CP-violating observable indicates the presence of new physics. A full fit to the data is not necessary. By determining which of the CP-violating observables are nonzero, one can learn about the structure of the underlying NP. Finally, we apply the angular analysis to Bs -> K^{*0} Kbar^{*0}, and show that there are numerous CP-violating observables that remain in the untagged data sample.

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

Latest constraint on non-standard top-gluon couplings at hadron colliders and its future prospect

Constraints on the non-standard top-gluon couplings composed of the chromomagnetic- and chromoelectric-dipole moments of the top quark are updated by combining the latest data of top-pair productions from the Tevatron, 7-TeV LHC, and 8-TeV LHC. We find that adding the recent 8-TeV data to the analysis is effective to get a stronger constraint on the chromoelectric-dipole moment than the one from the Tevatron and 7-TeV LHC alone. We also discuss how those constraints on the non-standard couplings could be further improved when 14-TeV LHC results become available in the near future.

hep-ph↗