Increasing the uniformity of characteristics of a plastic scintillator by reducing its internal stresses

This paper presents the results of the study of internal stresses effect on the light collection uniformity in a plastic scintillator (PS) and setting conditions for obtaining long plastic scintillators with a low level of internal stresses. Plastic scintillators based on polystyrene were used as test samples, produced in an air polymerizer from styrene monomer by radical thermoinitiated polymerization in an aluminum ampoule. To reduce internal stresses in the polystyrene polymer base of the PS, scintillator samples were annealed at a temperature of 100 °С. After a 12 hours exposure, the samples were gradually cooled at a rate of 2.5 °C/h. To reduce the surface tension due to the adhesion of the PS to the walls of the polymerization mold, the inner coating of the polymerization mold with polytetrafluoroethylene was used. The values of internal stresses in the PS material before and after additional annealing of the samples, as well as in the case of using the anti-adhesive coating, were determined. The control of internal stresses was carried out using a PKS-250M circular polariscope. To calculate the internal stresses, the difference of main stresses in the flat plates of the plastic scintillator was calculated. The dimensions of scintillator plates for evaluation of internal stresses are 10×50×300 mm. To measure the uniformity of the relative light output distribution along the long plastic scintillator, samples with dimensions of ø50x1000 mm were used. The obtained data showed that additional annealing of plastic scintillator blanks and the use of anti-adhesive coating for the polymerization mold reduce the level of internal stresses in the plastic scintillator from 1.8÷2.9 MPa to 0.55÷1.0 MPa. The nonuniformity of the relative light output distribution along the long plastic scintillator with dimensions of ø50x1000mm was reduced to ΔС ≤3 %

Search for leptophobic Z ' bosons decaying into four-lepton final states in proton-proton collisions at root s=8 TeV

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Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV

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Search for high-mass diphoton resonances in proton-proton collisions at 13 TeV and combination with 8 TeV search

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Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos, and b quarks

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Measurements of differential production cross sections for a Z boson in association with jets in pp collisions at root s=8 TeV

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Search for neutral resonances decaying into a Z boson and a pair of b jets or τ leptons

A search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged τ leptons or a bb‾ pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 fb −1 . No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models

Phenomenological MSSM interpretation of CMS searches in pp collisions at √s=7 and 8 TeV

Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at root s = 7 and 8 TeV and have integrated luminosities of 5.0 fb(-1) and 19.5 fb(-1), respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed

Performance of reconstruction and identification of τ leptons decaying to hadrons and vτ in pp collisions at √s=13 TeV

The algorithm developed by the CMS Collaboration to reconstruct and identify τ leptons produced in proton-proton collisions at √s=7 and 8 TeV, via their decays to hadrons and a neutrino, has been significantly improved. The changes include a revised reconstruction of π⁰ candidates, and improvements in multivariate discriminants to separate τ leptons from jets and electrons. The algorithm is extended to reconstruct τ leptons in highly Lorentz-boosted pair production, and in the high-level trigger. The performance of the algorithm is studied using proton-proton collisions recorded during 2016 at √s=13 TeV, corresponding to an integrated luminosity of 35.9 fb¯¹. The performance is evaluated in terms of the efficiency for a genuine τ lepton to pass the identification criteria and of the probabilities for jets, electrons, and muons to be misidentified as τ leptons. The results are found to be very close to those expected from Monte Carlo simulation