Abstract
Abstract A search for exclusive or semi-exclusive γγ production, pp → p(*) + γγ + p(*) (where p* stands for a diffractively-dissociated proton), and the observation of exclusive and semi-exclusive e+e− production, pp → p(*) + e+e− + p(*), in proton-proton collisions at $ \sqrt{s}=7 $ TeV, are presented. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb−1 recorded by the CMS experiment at the LHC at low instantaneous luminosities. Candidate γγ or e+e− events are selected by requiring the presence of two photons or a positron and an electron, each with transverse energy E T > 5.5 GeV and pseudorapidity |η| < 2.5, and no other particles in the region |η| < 5.2. No exclusive or semi-exclusive diphoton candidates are found in the data. An upper limit on the cross section for the reaction pp → p(*) + γγ + p(*), within the above kinematic selections, is set at 1.18 pb at 95% confidence level. Seventeen exclusive or semi-exclusive dielectron candidates are observed, with an estimated background of 0.85 ± 0.28 (stat.) events, in agreement with the QED-based prediction of 16.3 ± 1.3 (syst.) events.
Highlights
The Compact Muon Solenoid (CMS) detectorA detailed description of the CMS detector can be found in ref. [27]. The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a field of 3.8 T
This paper presents a search for exclusive observation of exclusive and semi-exclusive e+e−
The non-exclusive background is estimated by using the distribution of the numbers of additional tracks and additional towers for dielectron events with all selection criteria applied except the exclusivity requirements, after subtracting the contributions from both exclusive and semi-exclusive e+e− production expected from the simulation
Summary
A detailed description of the CMS detector can be found in ref. [27]. The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a field of 3.8 T. Within the field volume are the silicon pixel and strip tracker, the crystal electromagnetic calorimeter (ECAL) and the brass/scintillator hadron calorimeter (HCAL). In addition to the barrel and endcap detectors, CMS has extensive forward calorimetry. The ECAL provides coverage in the pseudorapidity range |η| < 1.479 in the barrel region (EB) and 1.479 < |η| < 3.0 in the two endcap regions (EE). The HCAL provides coverage for |η| < 1.3 in the barrel region (HB) and 1.3 < |η| < 3.0 in the two endcap regions (HE). The CMS experiment selects data by using a two-level trigger system. The first level consists of custom hardware processors and uses information from the calorimeters and muon systems. The high-level trigger processor farm further decreases the event rate before data storage
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
