D. Sillou

Search for Heavy Stable Charged Particles in pp collisions at sqrt(s)=7 TeV

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at

First measurement of hadronic event shapes in pp collisions at √s=7 TeV

sqrt {s} = 7;{text{TeV}}

Photon multiplicity in the hard radiation of 150 GeV electrons in an aligned germanium crystal

is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 pb−1. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398GeV/c2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Observation of channeling and blocking effect in pair creation in a Ge crystal

Hadronic event shapes have been measured in proton-proton collisions at √ s = 7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 pb−1. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production. Submitted to Physics Letters B ∗See Appendix A for the list of collaboration members ar X iv :1 10 2. 00 68 v1 [ he pex ] 1 F eb 2 01 1

Search for light neutral objects photoproduced in a crystal strong field and decaying into e+e− pairs

Abstract Mean values m of photon multiplicity in the radiation of 150 GeV electrons directed at and near the 〈110〉 axis of a 0.185 mm thick Ge crystal cooled to 100 K have been deduced from the measurements of pair conversion probabilities. Depending on the distribution of multiplicity assumed, values of m ranging from 3.8 to 4.3 are obtained for the previously reported anomalous radiation peak.

Experimental Study of Pair Creation and Radiation in Ge Crystals at Ultrarelativistic Energies (30–200 GeV)

Abstract Angular and energy distributions of electrons and positrons created by 83–133 GeV photons in an aligned crystal (strong field pair creation) have been measured. The experiment exhibits the “blocking” effect for the positron and the difference of energy loss between channeled electron and quasi-channeled positron. The data are well reproduced by a Monte Carlo simulation.

Measurement of the total energy radiated by 150-GeV electrons in a Ge crystal.

Abstract We describe a search for a light neutral object X0 possibly produced by ≈ 100 GeV photons interacting with the QED strong field encountered along the axis of a cooled Ge crystal. We look at the e+e− decay mode, in short (10−18−10−12 s) as well as long (10−13−10−8 s) lifetime detection conditions. For a mass of 1.8 ±0.2MeV/c2 (“Darmstadton” mass) we find no evidence for X0 production. The upper limit for the ratio between e+e− decay rate and pair creation is given as a function of the X0 lifetime. It reaches ≈ 5 × 10−4 and ≈ 2 × 10−5 in the short and long lifetime mode, respectively, including the crystal absorption contribution. However, for the long-lifetime mode and 108 incident photons, 9 events are compatible with neutral objects having masses ranging from 2.1 to 3.5 MeV c 2 . A Monte Carlo simulation of the background gives only 1 event in the same energy range.

Observation of Enhanced Pair Creation for 50-110-GeV Photons in an Aligned Ge Crystal

In recent years a great deal of theoretical work has been devoted to the description of the interaction of ultrarelativistic electrons and positrons and high energy photons moving along the major directions of crystals.1–9 It was predicted that quantum electrodynamic (QED) effects must be taken into account. In particular, the perfect alignment of photons with a crystal axis was predicted to increase the pair production rate above the Bethe-Heitler (BH) value.