Browsing by Author "Varela, J."
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- Beam test evaluation of electromagnetic calorimeter modules made from proton-damaged PbWO$_4$ crystalsPublication . Adams, T. et al. (283 authors); Beirao Da Cruz.E. Silva, C.; Tinoco Mendes, A.D.; Musella, P.; Parracho, P.; Rasteiro Da Silva, J.; Varela, J.The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO(4) crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO(4) crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 10(13) and 1.3× 10(14) cm(−)(2). These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb(−)(1) and 3000 fb(−)(1) respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.
- LHC Forward PhysicsPublication . LHC Forward Physics Working Group collaboration (184 authors); Gallinaro, M.; Hollar, J.; Varela, J.The goal of this report is to give a comprehensive overview of the rich field of forward physics, with a special attention to the topics that can be studied at the LHC. The report starts presenting a selection of the Monte Carlo simulation tools currently available, chapter 2, then enters the rich phenomenology of QCD at low, chapter 3, and high, chapter 4, momentum transfer, while the unique scattering conditions of central exclusive production are analyzed in chapter 5. The last two experimental topics, Cosmic Ray and Heavy Ion physics are presented in the chapter 6 and 7 respectively. Chapter 8 is dedicated to the BFKL dynamics, multiparton interactions, and saturation. The report ends with an overview of the forward detectors at LHC. Each chapter is correlated with a comprehensive bibliography, attempting to provide to the interested reader with a wide opportunity for further studies.
- Search for vectorlike light-flavor quark partners in proton-proton collisions at $\sqrt s$ =8 TeVPublication . CMS collaboration (2223 authors); Nayak, A.; Bargassa, P.; Beirão Da Cruz E Silva, C.; Calpas, B.; Di Francesco, A.; Faccioli, P.; Gallinaro, M.; Hollar, J.; Leonardo, N.; Lloret Iglesias, L.; Seixas, J.; Toldaiev, O.; Vadruccio, D.; Varela, J.; Vischia, P.; David, A.; Veckalns, V.; Musella, P.; Pela, J.; Delgado, A.A search is presented for heavy vectorlike quarks (VLQs) that couple only to light quarks in proton-proton collisions at s=8 TeV at the LHC. The data were collected by the CMS experiment during 2012 and correspond to an integrated luminosity of 19.7 fb−1. Both single and pair production of VLQs are considered. The single-production search is performed for down-type VLQs (electric charge of magnitude 1/3), while the pair-production search is sensitive to up-type (charge of magnitude 2/3) and down-type VLQs. Final states with at least one muon or one electron are considered. No significant excess over standard model expectations is observed, and lower limits on the mass of VLQs are derived. The lower limits range from 400 to 1800 GeV, depending on the single-production cross section and the VLQ branching fractions B to W, Z, and Higgs bosons. When considering pair production alone, VLQs with masses below 845 GeV are excluded for B(W)=1.0, and below 685 GeV for B(W)=0.5, B(Z)=B(H)=0.25. The results are more stringent than those previously obtained for single and pair production of VLQs coupled to light quarks.