Observation of the diphoton decay of the Higgs boson and measurement of its properties

Peer reviewe

Violenza e diritto nell'era nucleare

A search has been performed for long-lived particles that could have come to rest within the CMS detector, using the time intervals between LHC beam crossings. The existence of such particles could be deduced from observation of their decays via energy deposits in the CMS calorimeter appearing at times that are well separated from any proton–proton collisions. Using a data set corresponding to an integrated luminosity of 18.6fb-1 of 8TeV proton–proton collisions, and a search interval corresponding to 281 h of trigger livetime, 10 events are observed, with a background prediction of 13.2+3.6−2.5 events. Limits are presented at 95 % confidence level on gluino and top squark production, for over 13 orders of magnitude in the mean proper lifetime of the stopped particle. Assuming a cloud model of R-hadron interactions, a gluino with mass ≲1000GeV and a top squark with mass ≲525GeV are excluded, for lifetimes between 1 μs and 1000s. These results are the most stringent constraints on stopped particles to date

Party government : a rationalistic conception

Digitised version produced by the EUI Library and made available online in 2020

Search for excited quarks in the gamma plus jet final state in proton-proton collisions at root s=8 TeV

A search for excited quarks decaying into the gamma + jet final state is presented. The analysis is based on data corresponding to an integrated luminosity of 19.7 fb(-1) collected by the CMS experiment in proton-proton collisions at root s = 8 TeV at the LHC. Events with photons and jets with high transverse momenta are selected and the gamma + jet invariant mass distribution is studied to search for a resonance peak. The 95% confidence level upper limits on the product of cross section and branching fraction are evaluated as a function of the excited quark mass. Limits on excited quarks are presented as a function of their mass and coupling strength; masses below 3.5 TeV are excluded at 95% confidence level for unit couplings to their standard model partners

Description and performance of track and primary-vertex reconstruction with the CMS tracker

A description is provided of the software algorithms developed for the CMS tracker both for reconstructing charged-particle trajectories in proton-proton interactions and for using the resulting tracks to estimate the positions of the LHC luminous region and individual primary-interaction vertices. Despite the very hostile environment at the LHC, the performance obtained with these algorithms is found to be excellent. For t (t) over bar events under typical 2011 pileup conditions, the average track-reconstruction efficiency for promptly-produced charged particles with transverse momenta of p(T) > 0.9GeV is 94% for pseudorapidities of vertical bar eta vertical bar < 0.9 and 85% for 0.9 < vertical bar eta vertical bar < 2.5. The inefficiency is caused mainly by hadrons that undergo nuclear interactions in the tracker material. For isolated muons, the corresponding efficiencies are essentially 100%. For isolated muons of p(T) = 100GeV emitted at vertical bar eta vertical bar < 1.4, the resolutions are approximately 2.8% in p(T), and respectively, 10 m m and 30 mu m in the transverse and longitudinal impact parameters. The position resolution achieved for reconstructed primary vertices that correspond to interesting pp collisions is 10-12 mu m in each of the three spatial dimensions. The tracking and vertexing software is fast and flexible, and easily adaptable to other functions, such as fast tracking for the trigger, or dedicated tracking for electrons that takes into account bremsstrahlung

Measurement of the production cross section ratio sigma(chi b2(1P))/sigma(chi b1(1P)) in pp collisions at root s=8TeV

A measurement of the production cross section ratio sigma(chi b2(1P))/sigma(chi b1(1P)) is presented. The chi b1 (1P) and chi b2 (1P) bottomonium states, promptly produced in pp collisions at root s = 8TeV, are detected by the CMS experiment at the CERN LHC through their radiative decays chi b1,2(1P) -> Y(1S) + gamma. The emitted photons are measured through their conversion to e(+) e(-) pairs, whose reconstruction allows the two states to be resolved. The Y(1S) is measured through its decay to two muons. An event sample corresponding to an integrated luminosity of 20.7 fb(-1) is used to measure the cross section ratio in a phase-space region defined by the photon pseudorapidity, vertical bar eta(gamma)vertical bar < 1.0; the Y(1S) rapidity, vertical bar y(Y)vertical bar < 1.5; and the Y(1S) transverse momentum, 7 < p(T)(Y) < 40 GeV. The cross section ratio shows no significant dependence on the.(1S) transverse momentum, with a measured average value of 0.85 +/- 0.07 (stat + syst) +/- 0.08 (BF), where the first uncertainty is the combination of the experimental statistical and systematic uncertainties and the second is from the uncertainty in the ratio of the chi b branching fractions