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Feb 01, 2016
R&D STUDIES FOR CMS HE AT THE SUPER LHC CONDITIONS &INCLUSIVE SEARCH FOR NEW PHYSICS AT CMS WITH JETS AND MISSING MOMENTUM SIGNATUREElif Asl AlbayrakPh.D. Thesis DefenseOctober 7th, 2011
*OutlineIntroduction to LHC and CMS ExperimentPart I: Detector StudiesR&D STUDIES FOR HE UPGRADE AT CMSPart II: Physics AnalysisINCLUSIVE SEARCH FOR NEW PHYSICS AT CMS WITH JETS AND MISSING MOMENTUM SIGNATURE
LHC and CMS Experiment
*The Large Hadron ColliderThe LHC is the largest proton-proton (pp) collider designed to run with 14 TeV center of mass energy and 1034cm-2s-1 peak luminosity.It also provides heavy ion collisions to study the quark-gluon plasma state of the matter.There are four experiments at LHC A Toroidal LHC ApparatuS (ATLAS) Compact Muon Solenoid (CMS)The Large Hadron Collider Beauty Experiment(LHC-b)A Large Ion Collider Experiment (ALICE) The CMS is one of the general purpose experiments, designed to study the physics of pp collisions at 14 TeV at the LHC.
*The Compact Muon Solenoid (CMS)The CMS is designed to discover Higgs particle and new physics beyond the Standard Model (SM).Total weight : 12500 TOverall diameter : 15.0 mOverall length : 21.5 mMagnetic field : 4 Tesla
*The CMS DetectorThe CMS has four main subsystems dedicated to measure the energy, momentum and position of photons, electrons, muons and all the other products of 14 TeV pp collisions:The magnetIts bending power allows to determine charge/mass ratio of the tracked particles.Length/radius ratio and high magnetic field (3.8 T) provides a good momentum resolution.The muon systemReconstructing muons, measuring their momentum with a high accuracy and using them for trigger information.The trackerMeasure charged particle trajectories with high efficiency and provide precise reconstruction of secondary vertices originating from LHC collisions.The calorimetersConsists of electromagnetic (ECAL) and hadronic components (HCAL).Measure the energy of electrons, photons and jets with a high precision. High accuracy measurement for the missing transverse energy.
*The Hadronic Calorimeter (HCAL)The HCAL is a compact calorimeter and composed ofBarrel (HB)Endcap (HE)Forward (HF)
The barrel and the endcaps are sampling calorimeters.surround the ECAL and the tracker system.cover the pseudorapidity range up to || < 3.0.The forward calorimeter consists of steel absorbers and quartz fibers embedded in it and extends the coverage up to || < 5.0.
R&D STUDIES FOR HE UPGRADE AT CMS
*The Hadronic Endcap (HE) CalorimeterConsists of two large structures at each end of the hadronic barrel detector.Each HE consists of 14 towers with 5 segmentation.covers the pseudorapidity region 1.3 < || < 3.0, which contains about 34% of the particles produced in the final state.in the current design 19 layers of plastic scintillators (3.8 mm) are placed between the 7.8 cm brass absorber plates.
*Radiation ProblemIf LHC discovers the Higgs boson or new physics we will need higher number of events to study rare events such as MSSM Higgs, Higgs coupling to itself. Higher number of events higher luminosity runs LHC upgrade.With LHC luminosity upgrade the accumulated radiation will damage the CMS and the other detectors.Scintillator tiles used in CMS HE will loose their efficiency and stop providing light collection.As a solution to radiation damage problem, we proposed p-terphenyl (pTp) deposited quartz plates to replace the scintillator tiles. Advantage: quartz plates are radiation hard.Disadvantage: light production for quartz plates, photons from Cherenkov process, creates acutely less photons than a scintillation process.To increase the light collection efficiency, R&D studies are performed on the quartz plates.
*Light EnhancementLight collection created with Cherenkov process increases with 1/2.More photon can be collected if we use a wavelength shifter method with UV absorption spectra.For this purpose different wavelength shifters including p-terphenyl(pTp) , 4% gallium dopped zinc oxide (ZnO:Ga), o-terphenyl (oTp), m-terphenyl (mTp) and p-quarterphenyl (pQp) were tested.
*Different wavelength shifter (WLS) materials are deposited on quartz plates and the coated plates are tested for the light collection efficiency. Evaporation and RF techniques are used to deposit the WLS materials on the quartz plates.Coated plates are prepared at University of Iowa and Fermilab Thin Film Laboratory.Selection of Wavelength ShifterFermilab Thin Film Laboratory ZnO:Ga sputtering system and gunsFermilab Thin Film Laboratory WLS evaporation setupPlain quartz plate
*Selection of Wavelength ShifterQuartz plates coated with different thickness of wavelength shifters are tested atFermilab Meson Test Beam Facility (Nov 07 and Feb 08)CERN H2 area (August 2007)Both pTp and ZnO:Ga enhance the light collection by at least a factor of 4.
*Selection of Wavelength ShifterThe pTp and ZnO:Ga enhance the light production by a factor of 4.oTp, mTp, and pQp did not perform as well as pTp and ZnO:Ga.Since ZnO:Ga is more difficult to deposit on the quartz plates and does not provide an advantage compared to pTp deposited quartz plates, we decided to focus on pTp.
*Radiation HardnessDifferent methods were used to test the radiation hardness of pTpThe radiation hardness tests with proton (Indiana University Cyclotron Facility and CERN beam lines) and neutron (Argonne).The 90Sr activated light outputs of pTp samples before and after irradiation were compared (University of Mississippi CMS Laboratories). 16% light output lost after 200 kGy of proton irradiation.
After 200 kGy radiation damage level slows down.
After 400 kGy still have more than 80% of the initial light collection
*The Calorimeter CapabilitiesA calorimeter prototype was built with 2 m pTp deposited (one side) quartz plates . The 15cm x 15cm x 5mm quartz plates are used.For hadronic (electromagnetic) configuration 7cm (2cm) absorbers were used between each layer.The prototype was tested for hadronic capabilities with 30, 50, 80, 130, 200, 250, 300, and 350 GeV pion beams.electromagnetic capabilities with 50, 80, 100, 120, 150 and 175 GeV electron beams.
*Hadronic CapabilitiesDetector linearityHadronic Energy ResolutionLongitudinal Shower ProfileDataGeant4 simulationsDataGeant4 simulations1% hadronic response linearityA good agreement betweendata and simulation.Solid line -> simulationPoints -> data1% hadronic response linearity.15% hadronic resolution at 350 GeV pion beam.On a bigger scale it can reach up to current HE resolution. 8% at 300 GeV pion beam.
*Electromagnetic CapabilitiesDetector linearityElectromagnetic Energy ResolutionLongitudinal Shower ProfileDataGeant4 simulationsDataGeant4 simulations3% em response linearityA good agreement betweendata and simulation.Solid line -> simulationPoints -> data3% electromagnetic response linearity.Above 120 GeV both simulation and data converge to 5.6% It can be used as a radiation hard EM calorimeter for future colliders.
*ResultsTest beam results and Geant4 simulations showed that pTp deposited quartz plates are perfect candidates to replace the current HE scintillator tiles.Both quartz and pTp radiation hard and cost efficientpTp deposited material loses only 20% of the initial light collection after 400 kGy proton irradiation.well above higher luminosity conditions (25Mrad = 250 kGy)pTp deposited quartz plates increase the light yield by at least factor of 4.The pTp deposited quartz plate calorimeter is a good option in terms of accomplish the current HE calorimeter performance.
*INCLUSIVE SEARCH FOR NEW PHYSICS AT CMS WITH JETS AND MISSING MOMENTUM SIGNATUREMotivationSupersymmetryAnalysisData Driven Background EstimationsResult and InterpretationConclusion
*MotivationThe Standard Model (SM) can explain our natures working mechanism with a high accuracy but there are still unanswered questions such asWhy some force carriers have mass but others do not?How does the electroweak symmetry breaking mechanism work?Can gauge couplings be unified at a high mass scale?What is the source of dark matter in the universe?Many beyond SM physics theories such as Supersymmetry, extra dimensions, Technicolor, and fourth family try to address these questions.Supersymmetry (SUSY) is favorite explanation for most of the theorist because it can lead to incorporation of gravity to particle physics
*The Supersymmetry (SUSY)SUSY is a symmetry that relates fermions and bosons.Introduces a spectrum of new particles which are the superpartners of SM particles.Superpartners have the same masses (unbroken symmetry) and quantum numbers with SM particles but differ by half spin difference.Sparticles are not observed in nature SUSY must be broken.
*The Minimal Supersymmetric SM (MSSM)Minimal extension of the SM with minimal particle content.Respects the same SU(3)C x SU(2)L x U(1)Y gauge symmetries as does the SM.Assumes that the interaction between particles conserves R-parity.R = (-1)3(B-L)+2S, which is a multiplicative quantum number with spin S, baryon number B, and lepton number LAll the superpartners are created in pairs.The lightest supersymetric particle (LSP) is stable and weakly interacts with particle.LSP is a candidate for the cold dark matter in the universe.
*Experimental SignatureMultijet events with large missing momentum is the most generic experimental signature for R-parity conserving SUSY.Long cascade decays of sparticles multijetsLSP will escape the detector missing momentum
*INCLUSIVE SEARCH FOR NEW PHYSICS AT CMS WITH JETS AND