Measurement of the top quark production cross section and search for the SM Higgs boson in dilepton final states with the CMS detector at the LHC pp collider at √s = 7 TeV

Memoria de tesis presentada por Patricia Lobelle Pardo para optar al grado de Doctor en el Departamento de Física Moderna de la Universidad de Cantabria.El Modelo Eständard(SM) describe el comportamiento de todas las partículas subatómicas conocidas, explicando con éxito todos los datos de colisiones de altas energías. Sin embargo, todavía quedan cuestiones por resolver en este modelo, como la naturaleza del mecanismo responsable de la ruptura de la simetría electrodébil y el orígen de la masa. El mecanismo de Higgs proporciona una de las soluciones más simples al problema, requiere la existencia de una nueva partícula escalar, el bosón de Higgs, que todavía no se ha detectado. Todas las propiedades de esta partícula se pueden predecir dentro del Modelo Estándard excepto su masa, que es un parámetro libre de la teor´ıa. Después del descubrimiento del quark top en 1995, el bosón de Higgs es la única pieza que falta en este modelo. La búsqueda del bosón de Higgs se ha llevado a cabo en diferentes experimentos,y, hasta el momento, se han puesto límites a su masa. Las búsquedas en el colisionador e+ e− LEP proporcionaron un límite inferior a la masa de 114.4 GeV /c2 a un nivel de confianza del 95%. Actualmente, los experimentos CDF y D0 en el colisionador pp¯ Tevatron siguen realizando búsquedas de Higgs y han alcanzado suficiente sensibilidad para excluir un bosón de Higgs del SM con una masa comprendida entre aproximadamente 158 and 175 GeV /c2 a un nivel de confianza del 95% C.L. Otras medidas indirectas, como las derivadas de medidas electrodébiles de precisión ponen un límite superior en 185 GeV /c2 al 95% C.L. Por tanto, todos los límites experimentales y teóricos obtenidos hasta el momento favorecen un bosón de Higgs ligero. Todas estas medidas contribuyen, además, a orientar las búsquedas en el LHC. El LHC es un colisionador pp, diseñado para producir colisiones a una energía en centro de masas de √s = 14 TeV, siete veces superior a la del Tevatron, lo que permitir´a estudiar un rango amplio de procesos, tanto dentro del Modelo Estándar como evidencias de física más allá de este Modelo. Por tanto, si el mecanismo de Higgs es válido los experimentos del LHC tienen el potencial para encontrar el bosón de Higgs, permitiendo concluir la búsqueda llevada a cabo durante muchos años en diferentes colisionadores. El trabajo presentado en esta tesis doctoral se centra en la medida de la sección eficaz de producción de pares de quarks top-antitop y en la búsqueda del bosón de Higgs del SM en el modo de desintegración WW, ambos procesos en el estado final dileptónico, con los datos recogidos durante el año 2010 en colisiones pp a √s = 7 TeV, lo que corresponde a una luminosidad integrada de 36 pb−1. Todo esto ha sido posible gracias a las excelentes prestaciones y funcionamiento del detector CMS durante el año 2010.Peer Reviewe

Fine synchronization of the CMS muon drift-tube local trigger using cosmic rays

33 páginas, 12 figuras.-- Open Access.-- CMS Collaboration: et al.The CMS experiment uses self-triggering arrays of drift tubes in the barrel muon trigger to perform the identification of the correct bunch crossing. The identification is unique only if the trigger chain is correctly synchronized. In this paper, the synchronization performed during an extended cosmic ray run is described and the results are reported. The random arrival time of cosmic ray muons allowed several synchronization aspects to be studied and a simple method for the fine synchronization of the Drift Tube Local Trigger at LHC to be developed.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Performance of CMS muon reconstruction in cosmic-ray events

48 páginas, 23 figuras, 3 tablas.-- Open Access.-- CMS Collaboration: et al.The performance of muon reconstruction in CMS is evaluated using a large data sample of cosmic-ray muons recorded in 2008. Efficiencies of various high-level trigger, identification, and reconstruction algorithms have been measured for a broad range of muon momenta, and were found to be in good agreement with expectations from Monte Carlo simulation. The relative momentum resolution for muons crossing the barrel part of the detector is better than 1% at 10 GeV/c and is about 8% at 500 GeV/c, the latter being only a factor of two worse than expected with ideal alignment conditions. Muon charge misassignment ranges from less than 0.01% at 10 GeV/c to about 1% at 500 GeV/c.Acknowledge support from:FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTDS (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Commissioning and performance of the CMS silicon strip tracker with cosmic ray muons

46 páginas, 17 figuras, 8 tablas.-- Open Access.-- CMS Collaboration: et al.During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comprehensive test, in the presence of the 3.8 T magnetic field produced by the CMS superconducting solenoid. Cosmic ray muons were detected in the muon chambers and used to trigger the readout of all CMS sub-detectors. About 15 million events with a muon in the tracker were collected. The efficiency of hit and track reconstruction were measured to be higher than 99% and consistent with expectations from Monte Carlo simulation. This article details the commissioning and performance of the Silicon Strip Tracker with cosmic ray muons.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Alignment of the CMS muon system with cosmic-ray and beam-halo muons

43 páginas, 11 figuras, 6 tablas.-- Open Access.-- CMS Collaboration: et al.The CMS muon system has been aligned using cosmic-ray muons collected in 2008 and beam-halo muons from the 2008 LHC circulating beam tests. After alignment, the resolution of the most sensitive coordinate is 80 microns for the relative positions of superlayers in the same barrel chamber and 270 microns for the relative positions of endcap chambers in the same ring structure. The resolution on the position of the central barrel chambers relative to the tracker is comprised between two extreme estimates, 200 and 700 microns, provided by two complementary studies. With minor modifications, the alignment procedures can be applied using muons from LHC collisions, leading to additional significant improvements.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Alignment of the CMS silicon tracker during commissioning with cosmic rays

42 páginas, 15 figuras, 3 tablas.-- Open Access.-- CMS Collaboration: et al.The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3–4 microns RMS in the barrel and 3–14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Performance of the CMS Level-1 trigger during commissioning with cosmic ray muons and LHC beams

52 páginas, 25 figuras.-- Open Access.-- CMS Collaboration: et al.The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-taking runs in 2008, and to estimate the level of detector noise. This paper describes the trigger components used, the algorithms that were executed, and the trigger synchronisation. Using data from extended cosmic ray runs, the muon, electron/photon, and jet triggers have been validated, and their performance evaluated. Efficiencies were found to be high, resolutions were found to be good, and rates as expected.Acknowledge support from: FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTDS (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Performance of the CMS cathode strip chambers with cosmic rays

41 páginas, 19 figuras, 4 tablas.-- Open Access.-- CMS Collaboration: et al.The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47μm to 243μm. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns.Acknowledge support from: FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTDS (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Commissioning of the CMS High-Level Trigger with cosmic rays

33 páginas, 3 figuras, 1 tabla.-- Open Access.-- CMS Collaboration: et al.The CMS High-Level Trigger (HLT) is responsible for ensuring that data samples with potentially interesting events are recorded with high efficiency and good quality. This paper gives an overview of the HLT and focuses on its commissioning using cosmic rays. The selection of triggers that were deployed is presented and the online grouping of triggered events into streams and primary datasets is discussed. Tools for online and offline data quality monitoring for the HLT are described, and the operational performance of the muon HLT algorithms is reviewed. The average time taken for the HLT selection and its dependence on detector and operating conditions are presented. The HLT performed reliably and helped provide a large dataset. This dataset has proven to be invaluable for understanding the performance of the trigger and the CMS experiment as a whole.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe

Commissioning of the CMS experiment and the cosmic run at four tesla

39 páginas, 6 figuras, 1 tabla.-- Open Access.-- CMS Collaboration: et al.The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four Tesla in late 2008 in order to complete the commissioning of the experiment for extended operation. The operational lessons resulting from this exercise were addressed in the subsequent shutdown to better prepare CMS for LHC beams in 2009. The cosmic data collected have been invaluable to study the performance of the detectors, to commission the alignment and calibration techniques, and to make several cosmic ray measurements. The experimental setup, conditions, and principal achievements from this data-taking exercise are described along with a review of the preceding integration activities.Individuals have received support from the Marie-Curie IEF program (European Union); the Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation.Peer reviewe