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At least 919 records · Page 51Linked to original sources
arXiv2012

Constraints on UED from W' searches

We obtain contraints on three Universal Extra Dimensional models utilizing limits from the CMS Collaboration on W' production and decay into a single-top-quark final state. We find a weak constraint on the Minimal Universal Extra Dimensions model due to small Kaluza-Klein number violating terms. In contrast, the W' search puts a strong limit on the size of the Dirac mass term of the quarks in Split Universal Extra Dimension models. In Non-minimal Universal Extra Dimension models the W' search constrains the splitting between the boundary localized kinetic terms of the gauge bosons and the quarks. Each of these bounds can be translated into constraints on the mass splitting between the Kaluza-Klein excitations of the SU(2) charged quarks and the Klauza-Klein excitations of the W boson.

hep-ph↗
arXiv2012

The Production and Discovery of True Muonium in Fixed-Target Experiments

Upcoming fixed-target experiments designed to search for new sub-GeV forces will also have sensitivity to the never before observed True Muonium atom, a bound state of a muon and anti-muon. We describe the production and decay characteristics of True Muonium relevant to these experiments. Importantly, we find that secondary production mechanisms dominate over primary production for the long-lived 2S and 2P states, leading to total yields an order of magnitude larger than naive estimates previously suggested. We present yield estimates for True Muonium as a function of energy fraction and decay length, useful for guiding future experimental studies. Discovery and measurement prospects appear very favorable.

hep-ph↗
arXiv2012

Implications of Br(μ-> e γ) and Δa_mu on Muonic Lepton Flavor Violating Processes

We study the implications of the experimental results on the μ-> eγdecay rate and the muon anomalous magnetic moment, on muonic lepton flavor violating processes, such as μ-> 3 e and μN -> e N. We use a model independent approach in this analysis, where these processes are considered to be loop induced by exchanging spin 1/2 and spin 0 particles. We explore two complementary cases, which has no or has an internal (built-in) cancellation mechanism in amplitudes. Our main results are as following. (a) Bounds from rates are used to constrain parameters, such as coupling constants and masses. These constraints can be easily updated by simple scalings, if the experimental situations change. (b) The muon g-2 data favors non-chiral interactions. (c) In μ-> 3 e and μN -> e N processes, Z-penguin diagrams may play some role, while box diagrams contributions are usually highly constrained. (d) In the first case (without any built-in cancellation mechanism), using the recent μ-> eγbound, we find that μ-> 3e and μN -> e N rates are bounded below the present experimental limits by two to three orders of magnitudes in general. Furthermore, by comparing Δa_μand Br(μ->eγ) data, the couplings of μand e are found to be highly hierarchical. Additional suppression mechanism should be called for. (e) In the second case (with a built-in cancellation mechanism), mixing angles can provide additional suppression factors to satisfy the Δa_μand Br(μ-> eγ) bounds. While the μ-> 3 e rate remains suppressed, the bounds on μN -> e N rates, implicated from the latest μ-> eγbound, can be relaxed significantly and can be just below the present experimental limits.

hep-ph↗
arXiv2012

Precision Thrust Cumulant Moments at N^3LL

We consider cumulant moments (cumulants) of the thrust distribution using predictions of the full spectrum for thrust including O(alpha_s^3) fixed order results, resummation of singular N^3LL logarithmic contributions, and a class of leading power corrections in a renormalon-free scheme. From a global fit to the first thrust moment we extract the strong coupling and the leading power correction matrix element Omega_1. We obtain alpha_s(m_Z) = 0.1141 \pm (0.0004)_exp \pm (0.0014)_hadr \pm (0.0007)_pert, where the 1-sigma uncertainties are experimental, from hadronization (related to Omega_1) and perturbative, respectively, and Omega_1 = 0.372 \pm (0.044)_exp \pm (0.039)_pert GeV. The n-th thrust cumulants for n > 1 are completely insensitive to Omega_1, and therefore a good instrument for extracting information on higher order power corrections, Omega'_n/Q^n, from moment data. We find (\tilde Omega'_2)^(1/2) = 0.74 \pm (0.11)_exp \pm (0.09)_pert GeV.

hep-ph↗
arXiv2012

Single Top Production as a Probe of B-prime Quarks

We show how single top production at the LHC can be used to discover (and characterize the couplings of) B' quarks, which are an essential part of many natural models of new physics beyond the Standard Model. We present the B' effective model and concentrate on resonant production via a colored anomalous magnetic moment. Generally, B's preferentially decay into a single top quark produced in association with a W boson; thus, this production process makes associated single top production essential to B' searches at the LHC. We demonstrate the background processes are manageable and the signal cross section is sufficient to yield a large signal significance even during the 7 TeV LHC run. Specifically, we show that B' masses of 700 GeV or more can be probed. Moreover, if a B' is found, then the chirality of its coupling can be determined. Finally, we present signal cross sections for several different LHC energies.

hep-ph↗
arXiv2012

Remarks on decays of h_b(2P)

We consider hadronic transitions from the $h_b(2P)$ bottomonium resonance to lower states of bottomonium with emission of either $ω$ meson, or two pions, or $η$ meson. For the former two transitions the branching ratios are related to similar transitions from $χ_{b1}(2P)$ and the recently measured by Belle fractions of the radiative decays of $h_b(2P)$. We argue that the fraction of the $h_b(2P)$ total decay rate remaining for the annihilation rate is on the verge of contradiction with the `parton' picture of bottomonium annihilation resulting in similarity between the decays of $h_b(1,2P)$ and $χ_{b1}(1,2P)$. The contradiction gets even stronger, if the transition $h_b(2P) \to Υ(1S) \, η$ has branching fraction of a few percent or more. We argue that, although quite uncertain, the latter fraction may indeed be that significant.

hep-ph↗
arXiv2012

Combining QCD and electroweak corrections to dilepton production in FEWZ

We combine the next-to-next-to-leading order (NNLO) QCD corrections to lepton-pair production through the Drell-Yan mechanism with the next-to-leading order (NLO) electroweak corrections within the framework of the FEWZ simulation code. Control over both sources of higher-order contributions is necessary for measurements where percent-level theoretical predictions are crucial, and in phase-space regions where the NLO electroweak corrections grow large. The inclusion of both corrections in a single simulation code eliminates the need to separately incorporate such effects as final-state radiation and electroweak Sudakov logarithms when comparing many experimental results to theory. We recalculate the NLO electroweak corrections in the complex-mass scheme for both massless and massive final-state leptons, and modify the QCD corrections in the original FEWZ code to maintain consistency with the complex-mass scheme to the lowest order. We present phenomenological results for LHC studies that include both NNLO QCD and NLO electroweak corrections. In addition, we study several interesting kinematics features induced by experimental cuts in the distribution of photon radiation at the LHC.

hep-ph↗
arXiv2012

Enhanced di-Higgs Production through Light Colored Scalars

We demonstrate enhanced di-Higgs production at the LHC in the presence of modifications of the effective couplings of Higgs to gluons from new, light, colored scalars. While our results apply to an arbitrary set of colored scalars, we illustrate the effects with a real color octet scalar -- a simple, experimentally viable model involving a light (~125-300 GeV) colored scalar. Given the recent LHC results, we consider two distinct scenarios: First, if the Higgs is indeed near 125 GeV, we show that the di-Higgs cross section could be up to nearly one thousand times the Standard Model rate for particular octet couplings and masses. This is potentially observable in \emph{single} Higgs production modes, such as $pp \to h h \to γγb\bar{b}$ as well as $pp \to h h \to τ^+τ^- b\bar{b}$ where a small fraction of the $γγ$ or $τ^+τ^-$ events near the putative Higgs invariant mass peak contain also a $b\bar{b}$ resonance consistent with the Higgs mass. Second, if the Higgs is not at 125 GeV (and what the LHC has observed is an impostor), we show that the same parameter region where singly-produced Higgs production can be suppressed below current LHC limits, for a heavier Higgs mass, also simultaneously predicts substantially enhanced di-Higgs production. We point out several characteristic signals of di-Higgs production with a heavier Higgs boson, such as $pp \to hh \to W^+W^-W^+W^-$, which could use same-sign dileptons or trileptons plus missing energy to uncover evidence.

hep-ph↗
arXiv2012

Is the New Resonance Spin 0 or 2? Taking a Step Forward in the Higgs Boson Discovery

The observation of a new boson of mass $\sim 125\gev$ at the CERN LHC may finally have revealed the existence of a Higgs boson. Now we have the opportunity to scrutinize its properties, determining its quantum numbers and couplings to the standard model particles, in order to confirm or not its discovery. We show that by the end of the 8 TeV run, combining the entire data sets of ATLAS and CMS, it will be possible to discriminate between the following discovery alternatives: a scalar $J^P=0^+$ or a tensor $J^P=2^+$ particle with minimal couplings to photons, at a $5σ$ statistical confidence level at least, using only diphotons events. Our results are based on the calculation of a center-edge asymmetry measure of the reconstructed {\it sPlot} scattering polar angle of the diphotons. The results based on asymmetries are shown to be rather robust against systematic uncertainties with comparable discrimination power to a log likelihood ratio statistic.

hep-ph↗
arXiv2012

A charged Z' to conciliate the apparent disagreement between top-antitop Tevatron forward-backward asymmetry and LHC charge asymmetry

We propose a charged, electrically neutral, and flavour changing Z' model to conciliate the apparent disagreement between the important excess found in the top-antitop Tevatron forward-backward asymmetry and the null -compatible with negative- results found in the LHC charge asymmetry. We show that this model contributes positively to the forward-backward asymmetry, whereas naturally a new cancellation is turned on at the LHC, yielding a null, or even negative, charge asymmetry. We found the region in parameter space that is simultaneously allowed by the stringent Tevatron and LHC observables. We show that the model is safe to atomic parity violation constraints and to tj resonance searches, and propose a possible increase in the Z' width to avoid ttj constraints. We evaluate the constraints to the model, as well as distinctive features in the fore-coming experimental results.

hep-ph↗
arXiv2012

Final state interactions in single- and multi-particle inclusive cross sections for hadronic collisions

We study the role of low momentum transfer (soft) interactions between high-transverse momentum heavy particles and beam remnants (spectators) in hadronic collisions. Such final-state interactions are power suppressed for single-particle inclusive cross sections whenever that particle is accompanied by a recoiling high-p_T partner whose momentum is not fixed. An example is the single-top inclusive cross section in top pair production. Final-state soft interactions in multi-particle inclusive cross sections, including transverse momentum distributions, however, produce leading power corrections in the absence of hard recoiling radiation. Nonperturbative corrections due to scattering from spectators are generically suppressed by powers of Λ/p'_T, where Λis a hadronic scale, and p'_T is the largest transverse momentum of radiation recoiling against the particles whose momenta are observed.

hep-ph↗
arXiv2012

A Supersymmetric Explanation of the Excess of Higgs--Like Events at the LHC and at LEP

The LHC collaborations have recently announced evidence for the production of a "Higgs--like" boson with mass near 125 GeV. The properties of the new particle are consistent (within still quite large uncertainties) with those of the Higgs boson predicted in the Standard Model (SM). This discovery comes nearly ten years after a combined analysis of the four LEP experiments showed a mild excess of Higgs--like events with a mass near 98 GeV. I show that both groups of events can be explained simultaneously in the minimal supersymmetric extension of the SM, in terms of the production and decay of the two neutral CP--even Higgs bosons predicted by this model, and explore the phenomenological consequences of this explanation.

hep-ph↗
arXiv2012

Spin Determination for Fermiophobic Bosons

We discuss the prospects for production and detection of fermiophobic bosons (exotic bosons decaying only to standard model gauge bosons) at the LHC, and describe simple methods for determining spin. We consider two complementary approaches to spin determination: the search for decays in the diphoton channel, and the comparison of events with no extra spectator jets to those with one extra jet. We show that these approaches can together allow the fermiophobic bosons spin to be determined over a wide range of parameter space. We study both even and odd parity states.

hep-ph↗
arXiv2012

Jet production and the inelastic pp cross section at the LHC

We suggest that, if current measurements of inclusive jet production for central rapidities at the LHC are extended to lower transverse momenta, one could define a visible cross section sensitive to the unitarity bound set by the recent determination of the inelastic proton-proton cross section.

hep-ph↗
arXiv2012

Direct bound on the minimal Universal Extra Dimension model from the $t\bar{t}$ resonance search at the Tevatron

In the minimal Universal Extra Dimension (mUED) model, the second Kaluza-Klein (KK) gluon $g^{(2)}$ has loop-induced vertices with the standard model quarks, mediated by the first KK modes of the quark and the gluon/Higgs boson. With a top quark pair, this vertex is enhanced by the cooperation of the strong coupling of a gluon and the large Yukawa coupling of a top quark, leading to substantial branching ratio of $Br(g^{(2)} \to t \bar{t}) \approx 7%-8%$. As the $g^{(2)}$ coupling with two gluons appears via dimension-6 operator, $q\bar{q}\to g^{(2)}\to t\bar{t}$ is the golden mode for the mUED model. Hence the best channel is the $t\bar{t}$ resonance search in $p\bar{p}$ collisions. The recent Tevatron data at $\sqrt{s}=1.96$ TeV with an integrated luminosity of 8.7 fb$^{-1}$ are shown to give the first direct bound on the $g^{(2)}$ mass above 800 GeV. The implication and future prospect at the LHC are discussed also.

hep-ph↗
arXiv2012

Potential of a Neutrino Detector in the ANDES Underground Laboratory for Geophysics and Astrophysics of Neutrinos

The construction of the Agua Negra tunnels that will link Argentina and Chile under the Andes, the world longest mountain range, opens the possibility to build the first deep underground labo- ratory in the Southern Hemisphere. This laboratory has the acronym ANDES (Agua Negra Deep Experiment Site) and its overburden could be as large as \sim 1.7 km of rock, or 4500 mwe, providing an excellent low background environment to study physics of rare events like the ones induced by neutrinos and/or dark matter. In this paper we investigate the physics potential of a few kiloton size liquid scintillator detector, which could be constructed in the ANDES laboratory as one of its possible scientific programs. In particular, we evaluate the impact of such a detector for the studies of geoneutrinos and galactic supernova neutrinos assuming a fiducial volume of 3 kilotons as a reference size. We emphasize the complementary roles of such a detector to the ones in the Northern Hemisphere neutrino facilities through some advantages due to its geographical location.

hep-ph↗
arXiv2013

High-resolution supernova neutrino spectra represented by a simple fit

To study the capabilities of supernova neutrino detectors, the instantaneous spectra are often represented by a quasi-thermal distribution of the form f(E) = E^alpha e^{-(alpha+1)E/E_{av}} where E_{av} is the average energy and alpha a numerical parameter. Based on a spherically symmetric supernova model with full Boltzmann neutrino transport we have, at a few representative post-bounce times, re-converged the models with vastly increased energy resolution to test the fit quality. For our examples, the spectra are well represented by such a fit in the sense that the counting rates for a broad range of target nuclei, sensitive to different parts of the spectrum, are reproduced very well. Therefore, the mean energy and root-mean-square energy of numerical spectra hold enough information to provide the correct alpha and to forecast the response of multi-channel supernova neutrino detection.

astro-ph.SR↗