Gabriele Benelli

Measurement of the Υ(1S), Υ(2S), and Υ(3S) Polarizations in pp Collisions at s√=7 TeV

The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in protonproton collisions at √ s = 7 TeV, using a data sample of Υ(nS) → μ+μ− decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λθ, λφ, and λθφ, as well as the frame-invariant quantity λ̃, are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y| < 0.6 and 0.6 < |y| < 1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region. Submitted to Physical Review Letters c

Measuring CMS software performance in the first years of LHC collisions

The CMS software framework (CMSSW) is a modular object-oriented data analysis framework enabling the CMS collaboration to process and analyze the fast growing LHC collision data set. A software performance suite of tools has been developed and integrated in CMSSW itself to keep track of CPU time, memory footprint and event size on disk. These three metrics are key constraints in software development in order to meet the requirements considered in the planning and management of the CMS computing infrastructure. The performance suite allows the measurement and tracking of the performance across the framework, storing the results in a dedicated database. A web application is deployed to publish the results, making them easily accessible to software release managers and allowing for automatic integration in CMSSW release cycle quality assurance. The performance suite is also available to individual developers for dedicated code optimization and the web application allows historic regression and comparisons across releases. The performance suite tools and the performance of the CMSSW framework during the first LHC collisions years are described in this paper.

Performance of the CMS silicon Tracker at LHC

The CMS all-silicon Tracker, comprising 16588 modules covering an area of more than 200m2, needs to be precisely calibrated and aligned in order to correctly interpret and reconstruct the events recorded from the detector, ensuring that the performance fully meets the physics research program of the CMS experiment. The performance has been carefully studied since the start of data taking: the noise of the detector, the data integrity, the S/N ratio, the hit resolution and efficiency have been all investigated with time. In 2010 the Tracker has been successfully aligned using tracks from cosmic rays and pp-collisions, following the time dependent movements of its innermost pixel layers. Ultimate local precision is now achieved by the determination of sensor curvatures, challenging the algorithms to determine about 200000 parameters. Remaining alignment uncertainties are dominated by systematic effects that are controlled by adding further information, such as constraints from resonance decays.