CMS and a Light Higgs with tt J. R. Incandela University of California Santa Barbara J. R. Incandela University of California Santa Barbara

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 2 Htt Group: The goal was to perform a realistic study of the feasibility of detecting SM Higgs in this channel

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 3 CMS Htt study Recently completed study for the CMS Physics TDR vol. 2 This is a publicly available note: (49 pages). UCSB (JI) Led the group through the completion of this effort and note.

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 4 Overview Analysis involved 4 subgroups Standard top channels: Dilepton, All-hadronic, and e/m + jets Largely independent over past two years Goal: As realistic as possible Include backgrounds with higher order processes (Alpgen) Include multiple interactions (aka pile-up) Fully simulate the detectors Develop and use realistic algorithms: Electron and muon identification Jet and missing Et reconstruction b and c jet tagging, and light quark/gluon mis-tagging A huge amount of work!!

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 5 Light H in conjunction with tt Production Modes Decay Mode

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 6 ISR H→bb MPI t→W - b W + b←t E T > 3 GeV

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 7 Backgrounds Main backgrounds are ttjj, ttbb, ttZ ttjj dominates numerically even though a mis-tagged light quark or gluon jet is required The ttjj xsec is nearly 3 orders of magnitude higher than signal Should one get beyond ttjj, one must still confront ttbb, and ttZ with Z  bb, which are irreducible

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 8 Generators and Cross sections What’s new: Used a more sophisticated generation scheme for the ttNj background PYTHIA alone under-estimates the hard radiation CompHEP overestimates Alpgen+MLM matching is “just right” 

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 9 ALPGEN v.2 & MLM

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 10 Triggering After full CMS detector simulation and digitization, trigger simulations were run. Typically a bit lower efficiency than we ultimately expect More complex and efficient triggers will likely be available.. Trigger offline

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 11 Leptons Likelihoods Developed explicitly for Htt Categorized in Monte Carlo (MC) SIGNAL Matched to lepton form W use an  cone of radius 0.1 (0.01) for electrons (muons) BACKGROUND All others: leptons from b or c hadron decays, fakes

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 12 Muon Reconstruction Muon likelihood: 4 “obvious” variables: Muon p T Track Isolation Calorimeter Isolation 2-D Impact Parameter significance S IP PTPT Calo Iso Track Iso

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 13 Muon Reconstruction 90% for signal and 1.0% for background calculated from the semi-leptonic Htt sample cut is –Log(L)<1.4

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 14 Electron Reconstruction Electron Likelihood: 5 variables: p T E/p Had/EM  p T tracks inside  R=0.3 cone and outside veto cone (  R=0.015)  R between electron candidate and closest track outside veto cone R ≡ √( ∆η 2 + ∆φ 2 )

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 15 Electron Reconstruction 84% for signal 1.5% for background cut is –Log(L) < 1.3

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 16 JETS Iterative Cone Algorithm R=0.5 (0.4 for All-had) ET > 20 (25 All-had) |η| < 2.5 (2.7 All-had) Use MC calibrated jets Remove electrons that match within R < 0.4 R ≡ √( ∆η 2 + ∆φ 2 ) Signal (ttH, M H = 115 GeV) Raw (IC 0.5) MonteCarlo calibrated γ-jet calibrated Jets

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 17 Jet definition: All Hadronic Case Different Cone Sizes Tested Signal and 3 most dangerous Bkg used for testing (ttbb, tt2j, qcd170) 8 most energetic jets in |  | 25GeV Jet-Parton pairing  2 for masses of 2 W and 2 top within 3 sigma Jets paired to b-parton have to be b-tagged Cone  R=0.4 chosen

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 18 E T (ecal + hcal) − ∑ [E T (calib)−E T (raw)] − ∑ p T (μ) Missing E T Calorimeter tower measurements Jet corrections Muon momenta In semi-leptonic Htt channel / Missing Momentum

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 19 bTagging Combined Secondary Vertex Algorithm Mistagging rate as a function of b-jet efficiency for signal (left) and ttjj (center) are shown for various types of jets Gluon jets include splitting to bb or cc in center plot... Tag Rates for b-, c- and uds-jets vs discriminator cut for ttjj sample (right) c uds c g c b

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 20 Semi-Leptonic Selection Preselection HLT + Isolated Lepton + 6 or 7 Jets ET > 20GeV 4 bTagged jets D>0.5 (70% bTag efficiency) Veto events with two leptons, or wrong lepton. Jet Pairing Likelihood method: L event =L mass xL bTag xL kinematics Mass refers to likelihoods for the obtained masses for hadronic W and tops Kinematics Takes into account b jets from top quarks slightly more energetic than those from H or jj (rather complicated formula…) L btag  L bsele =D h1 xD h2 xD bTopHad xD bTopLep

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 21 Semi-Leptonic Selection Example of performance for muon selection Chosen working points are: 0.55 and 0.72

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 22 Final results 60 fb -1 Muon Channel A bit less S/ √B cause mass constraint but better S/N Electron Channel No discrepancies at    Just less efficiency in e channel for HLT and isolation.       S √B = 2.35 Muon + electron, no systematics

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 23 di-Lepton Selection Signal H forced to bb One W forced to (e, ,  ); the other free Find large contribution from single lepton events (1 real + 1 fake lepton) Preselection 3 b-jets and D>0.7 Selection 2 leptons (e,  ) passing Likelihood criteria –Log(L mu ) 20 GeV At least 4 jets with E T > 20 GeV No additional tagging requirement Corrected E T miss > 40 GeV

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 24 Full Hadron Selection Same analysis as Jet Algo choice and same   mass for jet pairing 8 most energetic jets in |  |<2.7 Centrality Cuts   mass for 2W and 2tops within 3 sigma from expected values 2 working points Low S/N  Higher Significance E T (7th)>30GeV – E T (8th)>20GeV ordered E T jet 3 out of D h1 D h2 D bTopHad1 D TopHad2 > 0.80 CentH>0.55 High S/N  Lower Significance E T (7th)>30GeV – E T (8th)>20GeV ordered E T jet D h1 D h2 D bTopHad1 D TopHad2 orderd in D; D(3th)>0.85 and D(4th)>0.70 CentH>0.55 – CentAll>0.80

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 25 Full Hadron Selection: Results 60 fb -1 An example: tables of this type are in the note for all channels

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 26 Speculation on Mature Experiments The mature CMS working point is taken to have the following systematic uncertainties: Flat 3% JES 10% Jet Resolution 4% in bc-Jet tagging efficiencies 10% in uds-Jet tagging efficiencies 3% in luminosity

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 27 Single Lepton Table Uncertainties from JES and uds-Tagging efficiencies Most dangerous BKGD are tt1j and tt2j

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 28 Single Leptons 60 fb -1 Significances are drastically reduced once reasonable systematic uncertainties are included Led to re-optimization with a looser selection Still pretty grim Muon Electron

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 29 Di-Lepton Table Again - big uncertainties from JES and uds-tagging Most dangerous BKGDs are ttNj

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 30 Hadron Table Again big uncertainties from JES and uds-Tagging efficiencies but…Surprise! The most dangerous background is QCD (look at JES) and then tt4j, tt3j and tt2j…

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 31 The message! Jet Energy Scale and light quark jet mis-tagging are major systematics Furthermore, when signal and background production systematics are included, it gets worse.

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 32 Cross Section uncertainties

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 33 CMS-CDF comparison Exercise performed with the diLepton channel CMS, CDF tag uncertainties taken to be the same (4% bc and 10% uds) Some indication we’re not too far off the mark.

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 34 Is there any hope? A couple of possible mitigating factors: 1.Backgrounds from Data: 60fb-1 of integrated luminosity will provide plenty of data for which detailed studies can be performed to understand the detector and algorithms 2.The availability of large control samples of top events will enable b tagging of high energy jets to be very well understood. This will probably enable some further suppression of light quark and charm jet tagging relative to b tagging. Similarly, experience with real data will likely improve jet reconstruction and energy measurements. Will they be enough? How much work and how much data will it take?

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 35 Summary Statistical Significance for the 4 sub-channels lower than previous studies but still combine to greater than 2.0 in 60 fb-1. But the systematic uncertainties: JES and uds-tagging are major problems They eliminate all sensitivity! (Combined significance of less than 0.2 for all channels) Real data will give the final answer on the feasibility of this channel, but all indications are that it will be very difficult.

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P.K.’s visit to UCSB, September 14, 2006 J. Incandela 37 Muon Selection: Results 60 fb -1

P.K.’s visit to UCSB, September 14, 2006 J. Incandela 38 Electron Selection: Results 60 fb -1