Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 188.882 LHC PhysicsExperimental Methods and MeasurementsJet Energy Scale[Lecture 23, May 04, 2009]C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 2Organization Project 3●there are missing hand-ins please send them in :-) Final Conference●program is final●it is very important you get started very soon●there will be technical details next lectureFinal Conference Project LHC Physics: “Experimental Methods and Measurements” Plenary Session (12:00–13:30, May 19, 5th floor 26-528 Room)●Welcome and LHC Overview (C.Paus)●Search for Standard Model Higgs Boson: Overview (?)●Search for Higgs in H→ZZ* (M.Chan)●Search for Higgs in H→WW* (H.Gray)C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 4Lecture Outline Jet Energy Scale calibration●CMS calorimeters●outline of the problem●γ+Jet sample calibrationC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 5Calorimetry Definition (from Wikipedia)●“.. the science of measuring the heat of chemical reactions or physical changes. Calorimetry involves the use of a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat.”●calorimetry in particle physics does not:●measure heat directly, but nevertheless determines the energy●does not measure heat of chemical reactions of physical changes, but it measures the energy of particles●calorimeters in particle physics are split into electromagnetic and hadronicIce-calorimeter from Antoine Lavoisier's 1787 Elements of Chemistry.C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 6Calorimetry in CMS Overview●ECAL: Lead Tungstate (PbWO4), silicon pre-shower●HCAL: brass and steel with scintillatorsC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 7Calorimetry Usage Largest amount of particles●hadrons and photons●neutral hadrons and photons are only measured in the calorimeter●ECAL – electromagnetic calorimeter are usually very precise (shower is simpler, detector easier to instrument)●HCAL – hadronic calorimeter make a huge differences for jets and the missing energy (they drive the resolution)●quarks and gluons (partons) manifest themselves as jets●jets are mostly measured in the calorimeters●essential in many searches and “bread and butter” measurements●calibration of calorimetry is far from trivialC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 8Determination of Jet EnergiesEnergy measurement●electromagnetic: straight forward and precise●hadronic more complex●single pion is easy●but particles come in jets●overlapping energy depositions●tracks are measured ....●have to find optimal way to combine all information●various variables influence energy determ.●depends on spec. sampleJet Energy Scale determinationC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 9The Jet Energy Scale (JES) Three main parts of Jet Energy Scale●Offset: not from hard process (noise, pile-up, underlying event)●Response: calorimeter response function (Rj(E), Rj(η,φ))●Showering: energy leakage (into/out of) jet cone Remarks●largest effect is usually the response function●once η,φ dependence is corrected, overall (absolute) response can be calibrated●test beam calibrations crucial for overall understanding●absolute calibration in data with γ+Jetstealing from: http://www-clued0.fnal.gov/~cammin/CMS-042607.pdfC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 10γ+Jet Events Event properties●single photon and single jet in event (gluon/quark jets)●photon energy very well known (ECAL)●transverse energy has to be conserved●careful though, there details like are higher orders etc.●do not know much about energy in z directionC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 11γ+Jet Events Transverse energy balance Technically more inclusive●response + shower in one step●corrects to parton level●better for jet cross section etc.●depends on the jet algorithm Alternatively●remove jet forming and add all measured energy●corrects to particle level (better for top or Higgs mass)C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 12γ+Jet Events Transverse energy balance●already conceptually because Higher order diagrams are present●initial state radiation reduces parton momentum●long tail in pT(parton)●measure peak position in bins of pTγsources: CMS NOTE-2006/042, CMS IN-2003/036C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 13γ+Jet Events Methods brings intrinsic biases●selection of events●initial state radiation●background: di-jet events with γ like jet (pT dependent)●different quark-gluon composition of signal and background●imbalance caused by zero suppression (algorithm in calorimeter readout)C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 14γ+Jet Events Sensitivity to selection cuts (blue-true, red-measured)●isolation of photons●opening angle jet-photon: Δφ●veto a 2nd jetC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 15γ+Jet Eventsfrom backgroundtotalphoton isolationpT γ instead of partonbg gluon dominatedDifferences betweenq and gluon jetsC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 16γ+Jet EventsC.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 17Conclusion Jet Energy Scale calibration ●use γ+Jet sample●balance in transverse momentum●correct only to first order (ISR causes bias)●corrections are sample dependent●correction in sample similar to signal desirable●top sample will become very important (W inside top decay)C.Paus, LHC Physics: Analysis Setup and Jet Energy Scale 18Next Lecture Details of Higgs Analyses●Search for Higgs in H→(qq)ZZ*●Search for Higgs in H→(qq)WW* ●Search for Higgs in