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arXiv2012

Probing Color Octet Couplings at the Large Hadron Collider

Color-octet resonances arise in many well motivated theories beyond the standard model. As colored objects they are produced copiously at the LHC and can be discovered in early searches for new physics in dijet final states. Once they are discovered it will be important to measure the couplings of the new resonances to determine the underlying theoretical structure. We propose a new channel, associated production of $W,Z$ gauge bosons and color-octet resonances, to help determine the chiral structure of the couplings. We present our analysis for a range of color-octet masses (2.5 to 4.5 TeV), couplings and decay widths for the LHC with center of mass energy of 14 TeV and 10 ${\rm fb}^{-1}$ or 100 ${\rm fb}^{-1}$ of integrated luminosity. We find that the LHC can probe a large region of the parameter space up to very small couplings.

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arXiv2012

Multiphotons and Photon-Jets

We discuss an extension of the Standard Model with a new vector-boson decaying predominantly into a multi-photon final state through intermediate light degrees of freedom. The model has a distinctive phase in which the photons are collimated. As such, they would fail the isolation requirements of standard multi-photon searches, but group naturally into a novel object, the photon-jet. Once defined, the photon-jet object facilitates more inclusive searches for similar phenomena. We present a concrete model, discuss photon-jets more generally, and outline some strategies that may prove useful when searching for such objects.

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arXiv2012

Heavy Neutrinos and Lepton Flavour Violation in Left-Right Symmetric Models at the LHC

We discuss lepton flavour violating processes induced in the production and decay of heavy right-handed neutrinos at the LHC. Such particles appear in left-right symmetrical extensions of the Standard Model as the messengers of neutrino mass generation, and can have masses at the TeV scale. We determine the expected sensitivity on the right-handed neutrino mixing matrix, as well as on the right-handed gauge boson and heavy neutrino masses. By comparing the sensitivity of the LHC with that of searches for low energy LFV processes, we identify favourable areas of the parameter space to explore the complementarity between LFV at low and high energies.

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arXiv2012

How Constrained is the cMSSM?

We study the allowed parameter space of the constrained minimal supersymmetric Standard Model (cMSSM) in the light of direct searches, constraints from $B$-physics (including the recent measurement of the branching ratio for $B_s \to μ^+μ^-$) and the dark matter relic density. For low or moderate values of $\tanβ$, the strongest constraints are those imposed by direct searches, and therefore, large areas of the parameter space are still allowed. In the large $\tan β$ limit, however, the $B$-physics constraints are more restrictive, effectively forcing the squark and gluino masses to lie close to or above a TeV. A light Higgs boson could dramatically change the allowed parameter space, but we need to know its mass precisely for this to be effective. We emphasize that it is still too early to write off the cMSSM, even in the large $\tanβ$ limit. Finally we explore strategies to extend the LHC search for cMSSM signals beyond the present reach of the ATLAS and CMS Collaborations.

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arXiv2012

Bounds on R-parity Violation from Resonant Slepton Production at the LHC

We consider the ATLAS and CMS searches for dijet resonances, as well as the ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass energy. We interpret their exclusions in terms of bounds on the supersymmetric R-parity violating parameter space. For this we focus on resonant slepton production followed by the corresponding decay.

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arXiv2012

A Natural 125 GeV Higgs Boson in the MSSM from Focus Point Supersymmetry with A-Terms

We show that a 125 GeV Higgs boson and percent-level fine-tuning are simultaneously attainable in the MSSM, with no additional fields and supersymmetry breaking generated at the GUT scale. The Higgs mass is raised by large radiative contributions from top squarks with significant left-right mixing, and naturalness is preserved by the focus point mechanism with large $A$-terms, which suppresses large log-enhanced sensitivities to variations in the fundamental parameters. The focus point mechanism is independent of almost all supersymmetry-breaking parameters, but is predictive in the top sector, requiring the GUT-scale relation $m_{H_u}^2 : m_{\bar{U}_3}^2 : m_{Q_3}^2 : A_t^2 = 1 : 1+x - 3y : 1-x : 9y$, where $x$ and $y$ are constants. We derive this condition analytically and then investigate three representative models through detailed numerical analysis. The models generically predict heavy superpartners, but dark matter searches in the case of non-unified gaugino masses are promising, as are searches for top squarks and gluinos with top and bottom-rich cascade decays at the LHC. This framework may be viewed as a simple update to mSUGRA/CMSSM to accommodate both naturalness and current Higgs boson constraints, and provides an ideal framework for presenting new results from LHC searches.

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arXiv2011

Supersymmetry With Prejudice: Fitting the Wrong Model to LHC Data

We critically examine interpretations of hypothetical supersymmetric LHC signals, fitting to alternative wrong models of supersymmetry breaking. The signals we consider are some of the most constraining on the sparticle spectrum: invariant mass distributions with edges and end-points from the golden cascade decay chain \tilde{q}_L -> q χ_2^0 (-> \tilde{l}^{\pm} l^{\mp} q) -> χ_1^0 l^+ l^- q. We assume a CMSSM point to be the `correct' one, and fit the signals instead to minimal gauge mediated supersymmetry breaking models (mGMSB) with a neutralino quasi-stable lightest supersymmetric particle, minimal anomaly mediation (mAMSB) and large volume string compactification models (LVS). mAMSB and LVS can be unambiguously discriminated against the CMSSM for the parameter point assumed and 1 inverse femtobarn of LHC data at 14 TeV. However, mGMSB would not be discriminated on the basis of the kinematic end-points alone, and would require further, more detailed investigation. The best-fit points of mGMSB and CMSSM look remarkably similar, making experimental discrimination at the LHC appear unlikely by any means.

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arXiv2012

Jets Plus Same-Sign Dileptons Signatures from Fermionic Leptoquarks at the LHC

Within the 3-3-1 model framework, we consider the production and decay of fermionic leptoquarks into a striking experimental signature at the LHC: a narrow resonance at the $b$ jet plus same-sign dileptons channel. The data already accumulated by the LHC collaborations may hide a large number of events associated to the production and decay of such exotic quarks, allowing one to investigate large portions of the parameters space of the model. The observation or not of such events would shed light on the construction of models presenting heavy exotic quarks.

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arXiv2012

Could two NMSSM Higgs bosons be present near 125 GeV?

We examine GUT-scale NMSSM scenarios in which {\it both} $h_1$ and $h_2$ lie in the 123 -- 128 GeV mass range. Very substantially enhanced $γγ$ and other rates are possible. Broadened mass peaks are natural.

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arXiv2012

Study of X(3915) --> J/ψω in two-photon collisions

We study the process $γγ\to J/ψω$ using a data sample of 519.2 $fb^{-1}$ recorded by the BaBar detector at SLAC at the PEP-II asymmetric-energy $e^+ e^-$ collider at center-of-mass energies near the $Υ(nS)$ ($n = 2,3,4$) resonances. We confirm the existence of the charmonium-like resonance X(3915) decaying to $J/ψω$ with a significance of 7.6 standard deviations, including systematic uncertainties, and measure its mass $(3919.4 \pm 2.2 \pm 1.6) MeV/c^2$ and width $(13 \pm 6 \pm 3) MeV$, where the first uncertainty is statistical and the second systematic. A spin-parity analysis supports the assignment $J^P=0^+$ and therefore the identification of the signal as due to the $χ_{c0}(2P)$ resonance. In this hypothesis we determine the product between the two-photon width and the final state branching fraction to be $(52 \pm 10 \pm 3) eV$

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arXiv2013

ATLAS measurements of the properties of jets for boosted particle searches

Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV. The data correspond to an integrated luminosity of 35 pb^-1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-kt algorithm with distance parameters R = 0.6 and 1.0, with transverse momentum pT > 300 GeV and pseudorapidity |eta| < 2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.

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arXiv2012

Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector

We present a measurement of the semileptonic mixing asymmetry for B0 mesons, a^d_{sl}, using two independent decay channels: B0 -> mu+D-X, with D- -> K+pi-pi-; and B0 -> mu+D*-X, with D*- -> antiD0 pi-, antiD0 -> K+pi- (and charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1} of ppbar collisions at sqrt(s) = 1.96 TeV, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length (VPDL) of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal VPDL regions for each channel, yielding a^d_{sl} = [0.68 \pm 0.45 \text{(stat.)} \pm 0.14 \text{(syst.)}]%. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of B factory measurements.

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arXiv2012

An inclusive search for the Higgs boson in the four-lepton final state at CDF

An inclusive search for the standard model Higgs boson using the four-lepton final state in proton-antiproton collisions produced by the Tevatron at sqrt(s) = 1.96 TeV is conducted. The data are recorded by the CDF II detector and correspond to an integrated luminosity of 9.7 /fb. Three distinct Higgs decay modes, namely ZZ, WW, and tau-tau, are simultaneously probed. Nine potential signal events are selected and found to be consistent with the background expectation. We set a 95% credibility limit on the production cross section times the branching ratio and subsequent decay to the four lepton final state for hypothetical Higgs boson masses between 120 GeV/c^2 and 300 GeV/c^2.

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arXiv2012

Higgs boson coupling sensitivity at the LHC using H->tau tau decays

We investigate the potential for measuring the relative couplings of a low-mass Higgs boson at the Large Hadron Collider using WH, ZH, and ttbarH production, where the Higgs boson decays to tau-lepton pairs. With 100/fb of sqrt(s) = 14 TeV pp collision data we find that these modes can improve sensitivity to coupling-ratio measurements of a Higgs boson with a mass of about 125 GeV/c^2.

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arXiv2012

Non-standard interaction in neutrino oscillations and recent Daya Bay, T2K experiments

We study the possible constraints on non-standard interaction(NSIs) in a model independent way by considering the recent results from T2K and Daya Bay neutrino oscillations experiments. Using perturbation method we present generic formulas (suitable for T2K baseline and for large $θ_{13}$ as evident from Daya Bay) for the probability of oscillation for $ν_μ\rightarrow ν_e$, taking into account NSIs at source ($ε^s$), detector ($ε^d$) and during propagation ($ε^m$) of neutrinos through matter. Two separate cases of perturbation with small (slightly large) NSI ($ε_{αβ}^m \sim 0.03(0.18)$) are discussed in detail. Using various possible presently allowed NSI values we reanalyze numerically the $θ_{13} - δ$ allowed region given by recent T2K experimental data. We obtain model independent constraints on NSIs in the $δ-ε_{αβ}^m$ plane using the $θ_{13}$ value as measured by Daya Bay, where $δ$ is the CP violating phase. Depending on $δ$ values significant constraints on $ε_{eτ}$ and $ε_{ττ}$, in particular, are possible for both hierarchies of neutrino masses. Corresponding to T2K's 66% confidence level result, the constraints on $ε_{ττ}$ is shown to be independent of any $δ$ value.

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arXiv2012

Interaction of cosmic background neutrinos with matter of periodic structure

We study coherent interaction of cosmic background neutrinos(CBNs) with matter of periodic structure. The mixing and small masses of neutrinos discovered in neutrino oscillation experiments indicate that CBNs which have very low energy today should be in mass states and can transform from one mass state to another in interaction with electrons in matter. We show that in a coherent scattering process a periodic matter structure designed to match the scale of the mass square difference of neutrinos can enhance the conversion of CBNs from one mass state to another. Energy of CBNs can be released in this scattering process and momentum transfer from CBNs to electrons in target matter can be obtained.

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arXiv2012

Di-Vector Boson + Jet Production via Gluon Fusion at Hadron Colliders

We study the production of two electro-weak vector bosons in association with a jet via gluon fusion. In particular we consider the production of $γZg$, $ZZg$ and $W^{+}W^{-}g$ at hadron colliders and compute their cross-sections. Such processes have already produced large number of events at the Large Hadron Collider (LHC) by now. These processes can be background to the Higgs boson production and a number of beyond the standard model scenarios. Therefore it is important to know the values of their contribution. The calculation is based on conventional Feynman diagram approach. In particular we find that the process $g g \to Z Z g$ can make a significant contribution to the process $p p \to Z Z + {\rm jet}$.

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arXiv2012

Shift in the LHC Higgs diphoton mass peak from interference with background

The Higgs diphoton amplitude from gluon fusion at the LHC interferes with the continuum background induced by quark loops. I investigate the effect of this interference on the position of the diphoton invariant mass peak used to help determine the Higgs mass. At leading order, the interference shifts the peak towards lower mass by an amount of order 150 MeV or more, with the precise value dependent on the methods used to analyze and fit the data.

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