Prospects for the first Measurement of the ttbar Cross Section in the Muon plus Jets Channel at sqrt(s)=10 TeV with the CMS Detector 2009 A feasibility study is presented of the first measurement of the $t\bar{t}$ pair production cross section in the muon-plus-jets channel at a center-of-mass energy of 10 TeV, using the CMS detector at the LHC. Events are selected which contain one highly energetic muon and at least four jets. Several techniques are used to identify the three jets originating from the hadronic top decay. The \ttbar cross section is extracted by means of template fits to discriminating distributions. The amount of QCD background is determined in a data-driven way using two complementary approaches. Statistical and systematical uncertainties are evaluated using ensemble tests. With $20\rm\ pb^{-1}$ of data, the \ttbar pair production cross section in the muon plus jets channel is expected to be measurable with 12-18\% statistical and 20-25\% systematic error, where the latter is dominated by the jet energy scale uncertainty. CMS-PHYSICS-ANALYSIS-SUMMARIES

Expectations for observation of top quark pair production in the dilepton final state with the early CMS data at sqrt s = 10 TeV Expectations for the observation of top-quark pair production in proton-proton collisions at the \lhcE{10} with two leptons (electron or muon) in the final state are presented. The emphasis is put on an analysis strategy for the early phase of CMS operation with data corresponding to an integrated luminosity of $10 \pbinv$. The Standard Model signal and background sources are surveyed for a selection based on the requirement of two leptons (electron or muon) in the final state, at least two hadronic jets and missing transverse energy. A clear signal stands out, and the signal cross section can be measured with a statistical uncertainty of about $15\%$ and a systematic uncertainty close to $10\%$ excluding the uncertainty on the integrated luminosity, which is expected to be $10\%$. A complementary approach is also presented for the early phase of operation which relies on jets reconstructed in the tracker and does not make use of the missing transverse energy observable. A good signal sensitivity can be obtained with such a selection which relies minimally on the calorimeter measurements. Having established simple and robust analysis strategies for the early phase, the possibility to further gain in sensitivity by exploiting the $b$-quark content of the events is studied for an integrated luminosity of $100\pbinv$. CMS-PHYSICS-ANALYSIS-SUMMARIES

List of Participants 2011 COUNCIL

Charmless charged two-body $B$ decays at LHCb with 2011 data 2011 Using an integrated luminosity of 320 $\mathrm{pb}^{-1}$ collected by LHCb in the first part of the 2011 run, we reconstruct a large sample of the charmless charged two-body decay modes of $B$ hadrons, providing measurements of the direct $CP$ asymmetries $A_{CP}(B^0 \rightarrow K\pi)=-0.088 \pm 0.011\mathrm{(stat)} \pm 0.008\mathrm{(syst)}$ and $A_{CP}(B^0_s \rightarrow \pi K)=0.27 \pm 0.08\mathrm{(stat)} \pm 0.02\mathrm{(syst)}$. The former constitutes the best measurement in the world as well as the first observation of $CP$ violation at LHCb, while the latter is the first evidence of $CP$ violation in the $B^0_s \rightarrow \pi K$ decay. Furthermore, we measure the branching fractions $\mathcal{BR}(B^0 \rightarrow K^+K^-)=(0.13 ^{+0.06}_{-0.05} \mathrm{(stat)} \pm 0.07\mathrm{(syst)})\times10^{-6}$ and $\mathcal{BR}(B^0_s \rightarrow \pi^+\pi^-)=(0.98 ^{+0.23}_{-0.19} \mathrm{(stat)} \pm 0.11\mathrm{(syst)})\times10^{-6}$. In particular, the absence of a $B^0_s \rightarrow \pi^+\pi^- $ signal is rejected with a statistical significance of 5.3$\sigma$. INTNOTELHCBCONFPUBL

Strong Coupling Problem with Time-Varying Sound Speed Joyce Austin Khoury Justin 2011 For a single scalar field with unit sound speed, there are exactly three distinct cosmological solutions which produce a scale invariant spectrum of curvature perturbations in a dynamical attractor background, assuming vacuum initial conditions: slow-roll inflation; a slowly contracting adiabatic ekpyrotic phase, described by a rapidly-varying equation of state; and an adiabatic ekpyrotic phase on a slowly expanding background. Of these three, only inflation remains weakly coupled over a wide range of modes, while the other scenarios can produce at most 12 e-folds of scale invariant and gaussian modes. In this paper, we investigate how allowing the speed of sound of fluctuations to evolve in time affects this classification. While in the presence of a variable sound speed there are many more scenarios which are scale invariant at the level of the two-point function, they generically suffer from strong coupling problems similar to those in the canonical case. There is, however, an exceptional case with superluminal sound speed, which suppresses non-gaussianities and somewhat alleviates strong coupling issues. We show that even these scenarios are constrained and only able to produce at most 28 e-folds of scale invariant and gaussian perturbations. This condition results from the combined requirements of matching the observed amplitude of curvature perturbations, demanding that the Hubble parameter remain sub-Planckian, and keeping non-gaussianities under control. We therefore conclude that inflation remains the unique cosmological scenario, assuming a single degree of freedom on an attractor background, capable of producing arbitrarily many scale invariant modes while remaining weakly coupled. Alternative mechanisms must inevitably be unstable or rely on multiple degrees of freedom. PREPRINT

On Truncation of irreducible representations of Chevalley groups Mahnkopf Joachim 2011 We prove part of a higher rank analogue of the Mazur-Gouvea Conjecture. More precisely, let $\tilde{\bf G}$ be a connected, reductive ${\Bbb Q}$-split group and let $\Gamma$ be an arithmetic subgroup of $\tilde{\bf G}$. We show that the dimension of the slope $\alpha$ subspace of the cohomology of $\Gamma$ with values in an irreducible $\tilde{\bf G}$-module $L$ is bounded independently of $L$. The proof is elementary making only use of general principles of the representation theory of algebraic groups; it is based on consideration of certain truncations of irreducible representations of Chevalley groups. PREPRINT