Some Aspects of High $E_T$ Jets in p-p Collisions at LHC

The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. It is the only Standard Model particle not yet observed. It plays a key role in explaining the origin of the mass of other elementary particles, in particular the difference between the massless photon and the very heavy W and Z bosons. Low mass Standard Model Higgs decay predominantly into bbbar mode. The relatively high number of signal events at low Higgs masses is nonetheless much smaller compared to the number of background events especially QCD, which makes a search delicate in this channel. One way to reduce an enormous background is to study Weak Boson Fusion produced Higgs boson which is characterized by two high ET back to back jets in opposite rapidity region. The two high ET jets at opposite rapidity can be used to tag the events where Higgs is produced. Since at LHC, the real data will emerge only after year 2007, the simulated data is the need for the physics analysis. In physics simulated data, each event is randomly generated to mimic the real data events. We simulated thousands of events for signal and backgrounds and studied the events in which Higgs (H) of 120 GeV mass is produced and decays through H->bbbar. The simulated data is generated with proton-proton collisions at center-of-mass energy of 14 TeV by Matrix Element event generator called ALPGEN interfaced wit h hadronisation algorithm of PYTHIA using specific interface for CMS experiment called CMKIN. The LHC is designed such that the collisions will occur at four points, all of which will be surrounded by detectors to measure their specific results of collision. One of these detectors, the CMS detector, will be used to study the Higgs physics. The generated events are passed through the detector simulation package simulating the CMS detector. The digitisation, reconstruction and analysis of the events was performed using softwares specific for CMS experiment. The final state in this channel is a set of quark-jets in the forward and backward rapidity region and b-jets in the central region. This channel is not a potential discovery channel where Higgs boson can be searched due to large QCD background. This channels can be used for the determination of yukawa coupling of Higgs with bottom quark. The method and the selection cuts are optimized to reduce the QCD background to lower level. Of course, these methods can be applied at all the experiments of LHC in general. The Panjab University, Chandigarh is a member of the international collaboration which designed and built the CMS detector. The Indian institutions, Panjab University, Chandigarh and TIFR, Mumbai, have taken the complete responsibility in the design and construction of the HCAL sub-system called Outer Hadron Calorimeter. All detector modules which are scintillator trays were fabricated, tested at these centres and shipped to CERN for installation in CMS detector. The author participated in fabrication, assembly and testing of Outer Hadron Calorimeter modules. The present work aims at developing methods and description of the hardware established for fabrication and testing of HO in the CMS detector. The installation of HO in CMS detector is at the verge of completion. The author has also participated in installation of HO in CMS detector at CERN. The performance of the real assembled calorimeters needs to be evaluated. The best possible method to evaluate the performance of the detector is by exposing them to the beam of particles at various energies, collecting and analysing the data for efficiency. The author has participated in CMS HCAL beam test during the year 2003 at CERN, Geneva for data taking shifts and handling of Data Acquisition System. In CMS HCAL testbeams, the calibration of CMS HO towers or individual tiles during was done in the year using muon beam. These calibration constants have been used in studying the response of HO towers to shower particles, especially pions. Also these constants could be used to monitor the behavior of HCAL towers. The study of the CMS HCAL detector resolution using data collected with pion-beams at di®erent energies is also incorporated.