Decoding the Mechanism for the Origin of Dark Matter in the Early Universe Using LHC Data

It is shown that LHC data can allow one to decode the mechanism by which dark matter is generated in the early universe in supersymmetric theories. We focus on two of the major mechanisms for such generation of dark matter which are known to be the Stau Coannihilation (Stau-Co) where the neutralino is typically Bino like and annihilation on the Hyperbolic Branch (HB) where the neutralino has a significant Higgsino component. An investigation of how one may discriminate between the Stau-Co region and the HB region using LHC data is given for the mSUGRA model. The analysis utilizes several signatures including multi leptons, hadronic jets, b-tagging, and missing transverse momentum. A study of the SUSY signatures reveals several correlated smoking gun signals allowing a clear discrimination between the Stau-Co and the HB regions where dark matter in the early universe can originate.Comment: 7 pages, 5 figs, 2 columns, Accepted for publication in Physical Review

Inclusive SUSY Searches using Missing Energy plus Multijets in pp collisions at s\sqrt{s}=14 TeV with CMS

An inclusive analysis strategy for SUSY searches in pp collisions at sqrt(s)=14 TeV with the CMS detector is discussed. The missing transverse energy plus multijets canonical signature is used. Emphasis is put in methods to normalize the backgrounds using the data and in understanding the experimental systematic uncertainties. A 5 sigma excess can be observed with O(pb^-1) at a particular low mass SUSY point. The 5 sigma discovery reach contours in the mSUGRA parameter space for 1 and 10 fb^-1 are obtained

Using Jet Substructure at the LHC to Search for the Light Higgs Bosons of the CP-Violating MSSM

The CP-violating version of the Minimal Supersymmetric Standard Model (MSSM) is an example of a model where experimental data do not preclude the presence of light Higgs bosons in the range around 10 -- 110 GeV. Such light Higgs bosons, decaying almost wholly to b-bbar pairs, may be copiously produced at the LHC, but would remain inaccessible to conventional Higgs searches because of intractable QCD backgrounds. We demonstrate that a significant number of these light Higgs bosons would be boosted strongly enough for the pair of daughter $b$-jet pairs to appear as a single `fat' jet with substructure. Tagging such jets could extend the discovery potential at the LHC into the hitherto-inaccessible region for light Higgs bosons.Comment: LaTeX, 33 pages, 5 eps figures and 5 tables embedded. minor changes, to appear in Physical Review

Commissioning of the CMS zero degree calorimeter using LHC beam

This paper reports on the commissioning and first running experience of the CMS Zero Degree Calorimeters during December 2009. All channels worked correctly. The ZDCs were timed into the data acquisition system using beam splash events. These data also allowed us to make a first estimate of channel-by-channel variations in gain.Comment: 6 pages, 8 figures, Presented at CALOR2010: 14th International Conference for Calorimetry in High Energy Physic

Where the Sidewalk Ends: Jets and Missing Energy Search Strategies for the 7 TeV LHC

This work explores the potential reach of the 7 TeV LHC to new colored states in the context of simplified models and addresses the issue of which search regions are necessary to cover an extensive set of event topologies and kinematic regimes. This article demonstrates that if searches are designed to focus on specific regions of phase space, then new physics may be missed if it lies in unexpected corners. Simple multiregion search strategies can be designed to cover all of kinematic possibilities. A set of benchmark models are created that cover the qualitatively different signatures and a benchmark multiregion search strategy is presented that covers these models.Comment: 30 pages, 8 Figures, 3 Tables. Version accepted at JHEP. Minor changes. Added figur

Exact Solution of Photon Equation in Stationary G\"{o}del-type and G\"{o}del Space-Times

In this work the photon equation (massless Duffin-Kemmer-Petiau equation) is written expilicitly for general type of stationary G\"{o}del space-times and is solved exactly for G\"{o}del-type and G\"{o}del space-times. Harmonic oscillator behaviour of the solutions is discussed and energy spectrum of photon is obtained.Comment: 9 pages,RevTeX, no figure, revised for publicatio

Bigger, Better, Faster, More at the LHC

Multijet plus missing energy searches provide universal coverage for theories that have new colored particles that decay into a dark matter candidate and jets. These signals appear at the LHC further out on the missing energy tail than two-to-two scattering indicates. The simplicity of the searches at the LHC contrasts sharply with the Tevatron where more elaborate searches are necessary to separate signal from background. The searches presented in this article effectively distinguish signal from background for any theory where the LSP is a daughter or granddaughter of the pair-produced colored parent particle without ever having to consider missing energies less than 400 GeV.Comment: 26 pages, 8 Figures. Minor textual changes, typos fixed and references adde

Decay mechanisms in CdS buffered Cu In,Ga Se2 thin film solar cells after exposure to thermal stress Understanding the role of Na

Due to their tunable bandgap energy, Cu In,Ga Se2 CIGSe thin film solar cells are an attractive option for use as bottom devices in tandem configurations. In monolithic tandem devices, the thermal stability of the bottom device is paramount for reliable application. Ideally, it will permit the processing of a top device at the required optimum process temperature. Here, we investigate the degradation behavior of chemical bath deposited CBD CdS buffered CIGSe thin film solar cells with and without Na incorporation under thermal stress in ambient air and vacuum with the aim to gain a more detailed understanding of their degradation mechanisms. For the devices studied, we observe severe degradation after annealing at 300 C independent of the atmosphere. The electrical and compositional properties of the samples before and after a defined application of thermal stress are studied. In good agreement with literature reports, we find pronounced Cd diffusion into the CIGS absorber layer. In addition, for Na containing samples, the observed degradation can be mainly explained by the formation of Na induced acceptor states in the TCO front contact and a back contact barrier formation due to the out diffusion of Na. Supported by numerical device simulation using SCAPS 1D, various possible degradation models are discussed and correlated with our finding

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu