Multiple Parton Interactions Studies at CMS

This paper summarizes the Multiple Parton Interactions studies in CMS, focusing on the already performed low pT QCD measurements up to highest centre of mass energies of 7 TeV and discussing the plans for the direct measurement of the multiple high-pT scatterings. The underlying event in pp interactions is studied measuring the charged multiplicity density and the charged energy density in the transverse region, which is defined considering the azimuthal distance of the reconstructed tracks with respect to the leading track-jet of the event, defined from tracks according to a jet clustering algorithms. In addition, we present the measurement of the underlying event using the jet-area/median approach, demonstrating its sensitivity to different underlying event scenarios. Observations in the central region are complemented by the mea- surement of the energy flow in the forward direction for minimum bias and central di-jet events. We compare our underlying event and forward results with the predictions from different Monte Carlo event generators and tunes, aiming to best parametrize the multiple parton interaction energy de- pendence starting from the Monte Carlo tunes developed to best fit the charged particle spectra measured at central rapidities. Finally we discuss the strategy to directly measure the multiple particle interactions rate focusing on the topologies with two hard scatterings in the same event

Minimum Bias and Underlying Event at CMS

The prospects of measuring minimum bias collisions (MB) and studying the underlying event (UE) at CMS are discussed. Two methods are described. The first is based on the measurement of charged tracks in the transverse region with respect to a charge-particle jet. The second technique relies on the selection of muon-pair events from Drell-Yan process

Measurement of the Underlying Event at LHC with the CMS detector

A study of \textit{Underlying Events} (UE) at \textit{Large Hadron Collider} (LHC) with CMS detector under nominal conditions is discussed. Using charged particle and charged particle jets, it will be possible to discriminate between various QCD models with different multiple parton interaction schemes, which correctly reproduce Tevatron data but give different predictions when extrapolated to the LHC energy. This will permit improving and tuning Monte Carlo models at LHC start-up, and opens prospects for exploring QCD dynamics in proton-proton collisions at 14TeV

The Underlying Event at the LHC

We discuss a study of "minimum-bias'' collisions and the "Underlying Event" at CMS (under nominal conditions) by measuring charged particles and muons. The Underlying Event is studied by examining charged particles in the "transverse" region in charged particle jet production and in the central region of Drell-Yan muon-pair production (after removing the muon-pair)

Fourier and Gegenbauer expansions for a fundamental solution of the Laplacian in the hyperboloid model of hyperbolic geometry

Due to the isotropy $d$-dimensional hyperbolic space, there exist a spherically symmetric fundamental solution for its corresponding Laplace-Beltrami operator. On the $R$-radius hyperboloid model of $d$-dimensional hyperbolic geometry with $R>0$ and $d\ge 2$, we compute azimuthal Fourier expansions for a fundamental solution of Laplace's equation. For $d\ge 2$, we compute a Gegenbauer polynomial expansion in geodesic polar coordinates for a fundamental solution of Laplace's equation on this negative-constant sectional curvature Riemannian manifold. In three-dimensions, an addition theorem for the azimuthal Fourier coefficients of a fundamental solution for Laplace's equation is obtained through comparison with its corresponding Gegenbauer expansion.Comment: arXiv admin note: substantial text overlap with arXiv:1201.440

Assembly of the Inner Tracker Silicon Microstrip Modules

This note describes the organization of the mechanical assembly of the nearly 4000 silicon microstrip modules that were constructed in Italy for the Inner Tracker of the CMS experiment. The customization and the calibration of the robotic system adopted by the CMS Tracker community, starting from a general pilot project realized at CERN, is described. The step-by-step assembly procedure is illustrated in detail. Finally, the results for the mechanical precision of all assembled modules are reported

Study of radiation damage and substrate resistivity effects from beam test of silicon microstrip detectors using LHC readout electronics

We present the beam test results of single-sided silicon microstrip detectors, with different substrate resistivities. The effects of radiation damage are studied for a detector irradiated to a fluence of 2.4 multiplied by 10**1**4 n/cm**2. The detectors are read out with the APV6 chip, which is compatible with the 40 MHz LHC clock. The performance of different detectors and readout modes are studied in terms of signal-to-noise ratio and efficiency

Tracker Operation and Performance at the Magnet Test and Cosmic Challenge

During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented

Study of High Level b-trigger Selection of ttH Fully Hadronic Decays

We present the High Level Trigger selection of the ttH channel decaying into hadronic final states at Low Luminosity. The basic idea is to use a fast b-tag where b jets are identified with a simple algorithm after the Level 1 selection. The main source of background considered is direct QCD multijet production. We summarize the efficiency on signal selection and background rejection and fin ally we give an estimate of the expected event rate

High Level Trigger for the ttH channel in fully hadronic decay at LHC with the CMS detector

One of the most promising channels to discover a "light" Higgs boson (mass of 120-130GeV/c/sup 2/) with the CMS detector at LHC is the ttH channel. In this study we investigate the possibility of selecting this channel from the QCD multijets background. We present a High Level Trigger selection for the ttH decaying in fully hadronic final states. The basic idea is to use a fast b-tagging algorithm after the Level-1 trigger selection based on the number of jets and energy cuts. The main background source considered is direct QCD multijet production with pile up at low luminosity (2*10/sup 33/cm/sup -2/s /sup -1/) scenario