Session H4: High Energy Physics II

Sensitivity to New Physics with the $\gamma_{\mathrm{Delayed}} + $ MET Final State

The Collider Detector at Fermilab (CDF) continues to search for new particles produced in the high energy proton anti-proton collisions produced at the Fermi National Accelerator Laboratory (Fermilab). In this talk we discuss the search for heavy, long-lived neutral particles, hypothesized by the Supersymmetry theory, that can be created and travel for awhile before decaying into a photon, the particle of light. Since these photons will arrive at the surface of the detector later than photons produced directly in the primary interaction, we can use custom instrumentation to search for these ``delayed'' photons with a nanosecond timing resolution. We present the results of this search and its implications on the recently discovered Higgs boson.   

An evaluation of the QCD uncertainties of $Z/\gamma^{\ast} \rightarrow \tau\tau$ background for the $H \rightarrow WW$ measurement

The instantaneous luminosity of the Larger Hadron Collider will increase during Run 2 to about $1 \times 10^{34} cm^{-2}s^{-1}$, and the center-of-mass energy will increase to about 14 TeV. This will increase the number of Higgs bosons for more precise physics study. This will also require more precise theoretical predictions. We evaluate the QCD uncertainties on the $Z/\gamma^{\ast} \rightarrow \tau\tau$ background extrapolated from control region to signal region. This is important for the study of $H \rightarrow WW$. Results are presented for the gluon-gluon-fusion event selections and the vector-boson-fusion event selections, respectively.   

Measurement of the Top Quark Mass in Dilepton Final States using Neutrino Weighting in Run II at D{\O}

A measurement is presented of the mass of the top quark (m$_{\mathrm{t}})$ in inclusive dilepton final states of ttbar events. The expected neutrino rapidity distribution is used to solve an otherwise underconstrained kinematic fit to the ttbar hypothesis. Solutions are given weights according to the degree of agreement between their calculated imbalance in transverse momentum (missing E$_{\mathrm{T}})$ and the events observed values of missing E$_{\mathrm{T}}$. The first two moments of the distribution of weights as a function of m$_{\mathrm{t}}$ are used to extract a measurement of m$_{\mathrm{t}}$. Ensemble tests of pseudo-experiments are performed to calibrate and correct the extracted m$_{\mathrm{t}}$, and to estimate its statistical uncertainty. Events corresponding to an integrated luminosity of 9.7 fb$^{\mathrm{-1}}$ of D{\O} Run II data collected in the e$\mu $, ee and $\mu \mu $ channels are used for this analysis. The calibration is performed using a ttbar cross section expected for mt $=$ 172.5 GeV. A number of optimizations are developed and we expect the improvement to the statistical uncertainty of m$_{\mathrm{t}}$ to be 20{\%}.   

Neutral vector boson production in pp and pA collisions at hadron colliders

I discuss the $Z/\gamma^*$ gauge boson production in $pp$ and $p\bar{p}$ collisions with the focus on non-perturbative contributions to the transverse momentum distribution based on the Collins-Soper-Sterman (CSS) resummation formalism. The dependence of the CSS resumed cross section on resummation scales and other factors is estimated. I also present a study of $Z/\gamma^*$ production in proton-lead and lead-lead collisions, where the small-$x$ shadowing and moderate-$x$ antishadowing effects are shown in transverse momentum and rapidity distributions.   

Probing Compressed Top Squarks at the LHC at 14 TeV

A feasibility study is presented for the search of the lightest top squark ($t$) in a compressed scenario, where its mass is approximately equal to the sum of the masses of the top quark and the lightest neutralino $\tilde\chi^0_1$ and there exists no limit from the current 8-TeV data or from the 14-TeV projections. The study is performed in the final state of two $b$-jets, one lepton, large missing transverse energy, and two energetic jets with a large separation in pseudo-rapidity, in opposite hemispheres, and with large dijet mass. The analysis shows that the LHC could probe compressed top squarks mass $\sim 300$ GeV with an integrated luminosity of $300$ fb$^{-1}$ for two ($t$+$\tilde\chi^0_1$) and three body ($b$+$W$+$\tilde\chi^0_1$) final states arising from the stop decay at $5\sigma$ significance with no systematic uncertainty. After including the systematics, the significance for $m_{st}$ = 200 GeV and $\Delta M=7$ GeV is expected to be 6(3)$\sigma $ for 300 fb$^{-1}$ luminosity with 3(5)\% systematic uncertainty, while the significance becomes 4(2)$\sigma$ for the same top squark mass with $\Delta M = -7$ GeV.   

Monte Carlo Study of Leptonic Asymmetry of $t\bar{t}$ at the Fermilab Tevatron

Since the discovery of the top quark 20 years ago, physicists have been studying the properties of this fascinating particle and how it has been produced in collisions. Recent measurements at Tevatron, a proton anti-proton collider, have shown that more top quarks are produced along the same direction as the proton than expected. In this talk, we discuss the methodology used in the measurement as well as the potential implications of this result.   

Exploring the Doubly Charged Higgs of the Left-Right Symmetric Model using Vector Boson Fusion-like Events at the LHC

In this talk we shall present the study of the pair production of the doubly charged Higgs boson of the left-right symmetric models using multilepton final state in the vector boson fusion (VBF)-like processes. The study is performed in the framework consistent with the model's correction to the standard model $\rho_{EW}$ parameter. VBF topological cuts, number of leptons in the final state and $p_T$ cuts on the leptons are found to be effective in suppressing the background. Significant mass reach can be achieved for exclusion/discovery of the doubly charge Higgs boson for the upcoming LHC run with a luminosity of $\mathcal{O}$(10$^3$) fb$^{-1}$.   

Simulation of Gas Electron Multiplier Detector for the CMS Experiment at the Large Hadron Collider

The Compact Muon Solenoid (CMS) Collaboration is proposing an upgrade of the muon detector system by installing Gas Electron Multiplier (GEM), a new type of gaseous detector, in the forward region $(1.54 < | \eta | < 2.2)$. It will consist of two layers of GEM chambers, which will be operating after the $2^{nd}$ Long Shutdown of the Large Hadron Collider (LHC). The GEM system is expected to have better performance in tracking efficiency, time resolution, and position resolution for detecting muons even in large multiple interaction environment. This is also expected to maintain trigger rate for muons in the forward region in a LHC high luminosity operation. We report results of extensive development of its simulation package that is used for physics performance studies.   

Search for Supersymmetry in Dilepton Final States with energetic Two-jets in Vector Boson Fusion-like Topology Using the CMS Detector at the LHC

A search of supersymmetry using Vector Boson Fusion tagged jets is presented using $20$ $fb^{-1}$ of data from proton-proton collisions at center of mass energy of $8$ TeV, collected by the CMS detector in 2012. Final states containing at least two leptons are expected in pair production of charginos and neutralinos. The number of observed events is consistent with the Standard Model expectation. Limits on production and chargino mass at $95 \%$ confidence level are set. The results are complementary to other searches through its direction production.   

Track based alignment of the CMS muon detectors

The muon detectors of the CMS experiment provide fast trigger decisions, muon identifications and muon track measurements. The reconstruction performance of high momenta muons requires an accurate alignment of the CMS muon system and therefore this will be important for a range of physics analyses in Run 2 of the LHC. A track-based alignment procedure for the CMS muon chambers is presented. In addition to discussing the details of the alignment algorithm, the limitations of the muon alignment procedure are reported.   

The Geneva Monte Carlo Framework

The Geneva Monte Carlo framework is a next-generation event generator capable of combining higher-order resummation (NNLL) of large Sudakov logarithms with multiple next-to-leading-order (NLO) matrix-element corrections and parton showering (using Pythia 8) to give a complete description at the next higher perturbative accuracy in alpha\textunderscore s at both small and large jet resolution scales. Results for e$+$e- $+$ jets compared to LEP data and for Drell-Yan production are presented.   

Prediction of an extra gauge-boson coupling for scalar bosons

A fundamental statistical picture that was proposed earlier is shown to lead to three predictions for scalar bosons (Higgses or sfermions) that should be testable in the near future at the LHC. The first is a modification of the propagators, and consequently the cross sections or probabilities for virtual processes. The second is an unrenormalized value near zero for the self-coupling coefficient $\lambda $. The third is an extra gauge-boson coupling for scalar bosons, with a doubling of fields and the Lagrangian containing \begin{eqnarray} \Phi _{b}^{\dag }\left( x\right) \left[ D^{\mu }D_{\mu }-\sigma ^{k}B_{k}\right] \Phi _{b}\left( x\right) \; , \; B_{k}=-\frac{1}{2}F_{l m}\epsilon ^{l m}\,_{k} \nonumber \end{eqnarray} where $F_{\mu \nu } $ is the field-strength tensor for the gauge fields to which the scalar boson is coupled. The extra term violates Lorentz invariance because $k=1,2,3 $ (with $\mu=0,1,2,3 $), and $B_{k} $ is just the magnetic-field part of $F_{\mu \nu } $. This extra term for scalar bosons is the only feature of the theory that violates Lorentz invariance far below the Planck scale. There are precedents, when violation of P and CP were found to arise from the left-handed weak-interaction coupling and the 3-generation Yukawa couplings.   

Radon Plateout on Copper to ilLUMINAte Background Levels in the Super Cryogenic Dark Matter Experiment

The Laboratory for Ultra-pure Material, Isotope and Neutron Assessment (LUMINA) at Southern Methodist University houses one of only five existing UltraLo 1800 production model alpha counters made commercially available by XIA LLC. The instrument has an electron drift chamber with a 707 cm$^{2}$ or 1800 cm$^{2}$ counting region which is determined by selecting the inner electrode size. The SMU team operating this device is part of SuperCDMS materials and screening working group, and uses the alpha counter to study the background rates from the decay of radon in materials used to construct the SuperCDMS experiment. We will present results from initial studies on copper samples exposed to thorium sources in our lab in order to understand radon plateout, on copper and compare storage inside of an aluminum and glass container.   

The Seasonal Dependence and Two Year Stability of the 30cmx30cm Gas Electron Multiplier Calorimeter

The Gas Electron Multiplier (GEM) is one of the detector technologies for high energy physics calorimetry. Its low power demand and high energy precision have made it one of the ideal candidates amongst other detectors. Since 2002, the UT Arlington Advance Detector team has been working on developing a prototype GEM detector to be used as the sensitive medium in a calorimeter for the Silicon Detector(SID) in the International Linear Collider project(ILC). Various sizes of prototype GEM detectors were built. Building upon the initial characterization of the 30cmx30cm detector in 2009, the seasonal dependence and long term stability of the detector's performance is studied in this project. The self trigger mode of the KPiX chip used in this system enables the corrections of the electronics gain variation of the chip and the external trigger for cosmic muons allow stability of the actual detector gains. The pedestal noise hits per channel over time is to study the aging of the chip and detector. Data taken over the past 2.5 years are studied. Results show that the prototype GEM is a stable device with a small variation in its gain over many years.