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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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arXiv2012

Pair Production of MSSM Higgs Bosons in the Non-decoupling Region at the LHC

We consider the Higgs boson signals from pair production at the LHC within the framework of the MSSM in the non-decoupling (low-m_A) region. In light of the recent observation of a SM-like Higgs boson, we argue that the exploration for Higgs pair production at the LHC is a crucial next step to probe the MSSM Higgs sector. We emphasize that the production of H^\pm A^0 and H^{+}H^{-} depends only on the electroweak gauge couplings while all the leading Higgs production channels via gluon fusion, vector-boson fusion, and Higgsstrahlung depend on additional free Higgs sector parameters. In the non-decoupling region, the five MSSM Higgs bosons are all relatively light and pair production signals may be accessible. We find that at the 8 TeV LHC, a 5σsignal for H^\pm A^0, H^\pm h^0 -> τ^{\pm}νb\bar b and H^{+}H^{-} -> τ^{+}ντ^{-}νare achievable with an integrated luminosity of 7 (11) fb^{-1} and 24 (48) fb^{-1}, respectively for m_A=95 (130) GeV. At the 14 TeV LHC, a 5σsignal for these two channels would require as little as 4 (7) fb^{-1} and 10 (19) fb^{-1}, respectively.

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arXiv2012

Gauge-boson production with multiple jets near threshold

Signatures of new physics beyond the Standard Model are often characterized by large missing transverse energy ($\not E_T$) produced in association with multiple jets. The dominant Standard Model background to such processes comes from gauge-boson production in association with jets. A standard search strategy involves looking for an excess in the $m_{eff}$ distribution, where $m_{eff}= \not E_T +\sum_{J} p^T_J$ and $p^T_J$ denotes the transverse momentum of the $J$-th jet. The region of large $m_{eff}$ is dominated by jet production near threshold, giving rise to large Sudakov logarithms that can change the magnitude and shape of the $m_{eff}$ distribution. We present an effective theory framework for the resummation of such threshold logarithms. We perform an analysis for exclusive jet production using the N-jettiness global event shape, which allows theoretical control to also be maintained over large logarithms induced by vetoing additional jets. As a first step, we give explicit numerical results with next-to-leading-log (NLL) resummation for $pp \to γ+ 2$ jets in the large $m_{eff}$ region.

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arXiv2012

Testing the Technicolor Interpretation of the CDF Dijet Excess at the 8-TeV LHC

Under the assumption that the dijet excess seen by the CDF Collaboration near 150 Gev in Wjj production is due to the lightest technipion of the low-scale technicolor process $ρ_T \rightarrow W π_T$, we study its observability in LHC detectors for 8 TeV collisions and 20 inverse femtobarns of integrated luminosity. We describe interesting new kinematic tests that can provide independent confirmation of this LSTC hypothesis. We show that cuts similar to those employed by CDF, and recently by ATLAS, cannot confirm the dijet signal. We propose cuts tailored to the LSTC hypothesis and its backgrounds at the LHC that may reveal $ρ_T \rightarrow \ellνjj$. Observation of the isospin-related channel $ρ^{\pm}_T \rightarrow Z π^{\pm}_T \rightarrow \ell^+\ell^- jj$ and of $ρ^{\pm}_T \rightarrow WZ$ in the $\ell^+\ell^-\ell^{pm}ν_\ell$ and $\ell^+\ell^- jj$ modes will be important confirmations of the LSTC interpretation of the CDF signal. The $Zπ_T$ channel is experimentally cleaner than $Wπ_T$ and its rate is known from $Wπ_T$ by phase space. It can be discovered or excluded with the collider data expected by the end of 2012. The $WZ \rightarrow 3\ellν$ channel is cleanest of all and its rate is determined from $Wπ_T$ and the LSTC parameter $\sinχ$. This channel and $WZ \to \ell^+\ell^- jj$ are discussed as a function of $\sinχ$.

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arXiv2012

Doubly resonant WW plus jet signatures at the LHC

We present search prospects and phenomenology of doubly resonant signals that come from the decay of a neutral weak-singlet color-octet vector state ω_8 into a lighter weak-triplet color-octet scalar π_8, which can arise in several theories beyond the Standard Model. Taking m_{ω_8}-m_{π_8}>m_W, we demonstrate an analysis of the signals pp \to ω_8 \to π^\pm_8 W^\mp (π^0_8 Z) \to g W^\pm W^\mp (g Z Z). The present 8 TeV LHC run is found to have the potential to exclude or discover the signal for a range of masses and parameters. The preferred search channel has a boosted W-tagged jet forming a resonance with a second hard jet, in association with a lepton and missing energy.

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arXiv2012

Pion transitions from χ_{cJ} to η_c

The charmonium transitions from the $χ_{cJ}$ states to $η_c$ with emission of one or two pions are considered. It is shown that the only processes of such type arising in the leading order in the QCD multipole expansion are the decays $χ_{c1} \to η_c π^+ π^-$ and $χ_{c0} \to η_c π^0$. The absolute rate of the latter decay, in spite of being isotopically suppressed, is by about an order of magnitude larger than that of the former, so that the branching fractions for the two processes are approximately equal, and are expected to be significantly below the recent upper bound reported by BESIII. The rates of both decays are also related to that of another similar transition $h_c \to J/ψπ^0$.

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arXiv2012

Searching for $t \to c h$ with Multi-Leptons

The results of a multi-lepton search conducted by the CMS collaboration with 5 fb$^{-1}$ of data collected from 7 TeV $pp$ collisions are used to place the first bound on the rare flavor-changing decay of the top quark to a Higgs boson and charm quark. Combining results from a number of exclusive three- and four-lepton search channels yields an estimated upper limit of ${\rm Br}(t \to ch) < 2.7%$ for a Higgs boson mass of 125 GeV. The sensitivity of future dedicated searches for $t \to c h$ could be improved by adding exclusive same sign di-lepton channels, as well as by sub-dividing channels based on $b$-quark tagging and partial kinematic top quark and Higgs boson tagging. This bound may be interpreted more widely within a range of new physics processes that yield final states with a $W$-boson in association with a Higgs boson. For such processes with kinematics that are similar to top--anti-top production and decay, the estimated limit on cross section times branching ratio corresponds to roughly $σ\cdot {\rm Br}(pp \to WhX) < 9$ pb.

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arXiv2012

Realistic Fermion Masses and Nucleon Decay Rates in SUSY SU(5) with Vector-Like Matter

We show that by adding a vector-like 5+5bar pair of matter fields to the spectrum of the minimal renormalizable SUSY SU(5) theory the wrong relations for fermion masses can be corrected, while being predictive and consistent with proton lifetime limits. Threshold correction from the vector-like fields improves unification of gauge couplings compared to the minimal model. It is found that for supersymmetric spectra lighter than 3 TeV, which would be testable at the LHC, at least some of the nucleon decay modes should have partial lifetimes shorter than about 2.10^34 yrs., which is within reach of ongoing and proposed experiments.

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arXiv2012

Probing Supersymmetry using Event Shape variables at 8 TeV LHC

We have revisited the prospects of Supersymmetry(SUSY) searches at the LHC with 7 TeV energy along with the prediction of the discovery potential at 8 TeV energy assuming an integrated luminosity 5 $fb ^{-1}$ and 20 $\invfb$ with mSUGRA/CMSSM as a model framework. We discuss further optimization of our selection strategy which is based on the hadronic event shape variables. Evaluating the standard model backgrounds and signal rates in detail we predict the discovery reach in the $m_0 - m_{1/2}$ plane for 7 TeV with 5$\invfb$ luminosity. We also present the discovery reach for 8 TeV energy with an integrated luminosity 5$\invfb$ and 20 $\invfb$. A comparison is made between our results and the exclusion plots obtained by CMS and ATLAS. Finally, discovery reach in the gluino and squark mass plane at the 7 TeV and 8 TeV energy is also presented.

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arXiv2012

The Higgs Sector and Fine-Tuning in the pMSSM

The recent discovery of a 125 GeV Higgs, as well as the lack of any positive findings in searches for supersymmetry, has renewed interest in both the supersymmetric Higgs sector and fine-tuning. Here, we continue our study of the phenomenological MSSM (pMSSM), discussing the light Higgs and fine-tuning within the context of two sets of previously generated pMSSM models. We find an abundance of models with experimentally-favored Higgs masses and couplings. We investigate the decay modes of the light Higgs in these models, finding strong correlations between many final states. We then examine the degree of fine-tuning, considering contributions from each of the pMSSM parameters at up to next-to-leading-log order. In particular, we examine the fine-tuning implications for our model sets that arise from the discovery of a 125 GeV Higgs. Finally, we investigate a small subset of models with low fine-tuning and a light Higgs near 125 GeV, describing the common features of such models. We generically find a light stop and bottom with complex decay patterns into a set of light electroweak gauginos, which will make their discovery more challenging and may require novel search techniques.

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arXiv2012

Resonance Chiral Lagrangian analysis of $τ^- \to η^{(\prime)} π^- π^0 ν_τ$ decays

The hadronization structure of $τ^- \to ηπ^- π^0 ν_τ$ decays is analyzed using Chiral Perturbation Theory with resonances, considering only the contribution of the lightest meson resonances at leading order in the $1/N_C$ expansion. After imposing the asymptotic behavior of vector spectral functions ruled by QCD, unknown effective couplings are determined by fitting the $τ^- \to ηπ^- π^0 ν_τ$ branching ratio and decay spectrum to recent data. Predictions for the partner decay $τ^- \to η^\prime π^- π^0 ν_τ$ and the low-energy behavior of the cross section $σ(e^+e^-\to ηπ^+π^-)$ are also discussed.

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arXiv2012

Further search for supersymmetry at sqrt(s) = 7 TeV in final states with jets, missing transverse momentum and isolated leptons with the ATLAS detector

This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy sqrt(s) = 7 TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7 inverse fb. Single- and multi-lepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduced to be sensitive to decay cascades of SUSY particles with small mass differences ("compressed SUSY"). Background uncertainties are constrained by fitting to the jet multiplicity distribution in background control regions. Observations are consistent with Standard Model expectations, and limits are set or extended on a number of SUSY models.

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