Experience with muons in analysis: W’ search Carmen Diez Pardos CIEMAT Madrid Muon Barrel Workshop Physics sesion 25/02/2011 1

Outline  Introduction  Muons in W´ searches  Analysis concept  Efficiency determination in W´ (and W xsec measurement)  Background determination  Systematics  Results  Outlook 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)2

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)3 1. Introduction: about this talk 1. Introduction: about this talk The W ʹ →μν Search at the LHC Jump in collision energy (from TeVatron to LHC) single most important factor in search for new heavy particles (Relatively) easy analysis High-p T (unprescaled) single muon trigger Reconstruction of M T by combing high-p T muon, MET Practically background-free channel  Study muon efficiencies, effect of muon momentum resolution and scale, at the moment without high pT muons from collisions An analysis that can lead to one of the first LHC discoveries!  Present an example of a physics channel focusing on the aspects related to muons, as efficiency measurements, reconstruction and systematics

24/02/2011 MB Workshop4 Spectacular signature One high-p T muon in event (“straight track”) Plus, “nothing else” Experimental limits from Tevatron in the channel W‘ → ev: m(W‘)>1.1 TeV [CDF, published] CMS limit from electron channel m(W‘)>1.36 TeV 1 Muon with ~550 GeV W ʹ → μν Topology and Limits C. Diez Pardos (CIEMAT) Event with Max M T

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)5 Analysis strategy Identify high-p T (unprescaled) single muon trigger Follow Exotica Muon group recommendation for muon selection (Backup slides) Reconstruction of M T by combing high-p T muon, MET Determine efficiencies: Efficiencies used for our signal MC (the BG is obtained from data) and to crosscheck if we understand our BG from data/MC comparisons Determine BG from pp collisions (fit in MT sideband extrapolating to signal region) and cosmics Comparison between data and MC MT distributions: No excess seen in data  Set a limit Samples : DATA: 36/pb Nov4ReReco, MC BG: Fall10 38X samples

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)6 1. Object reconstruction: MUONS: Extensive studies of high-p T muon reconstructor Global, tracker-only, TPFMS, cocktail, picky, TMR, DYT: Using „cocktail“ as recommended by Exotica Muon group For this analysis tails of the p T distribution matter Using both MC and cosmics/CRAFT (see also Z` →  note) MET reconstruction: For the dominant background MET is driven by muon-p T measurement: hadronic component less relevant for tail of MET (M T ) distribution

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)7  Why are they important? For BG – comparison data/MC to extract systematics, differences could indicate the source of disagreement For the signal: used to extract the limit (or the xsec!)  There are no high-pt muons in collision data, in order not to rely just on MC we use A data driven method: Tag and Probe using Zmumu events ( AN-2010/233 ): not the official TP package, different background subtraction, no analytical description of the Z->mumu shape For trigger efficiencies, also JetMet triggered data (get to higher values of pT)  The agreement at medium pT between data and MC is also seen at high pT with cosmic muon data. 2. Efficiency measurement

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)8 Single muon id. efficiency: T&P method Selection of a Z->mumu sample  Preselection of tracks with kinematics cut pt >25. GeV and |eta| < 2.1 which combined with an opposite charged track give an invariant mass in the range 60. < Mμμ < 120. GeV.  Match track-muon is done with the track reference in the muon object.  Tag muons must fullfill the following selection: (Exotica, VBTF recommendation)  Must be Global and Tracker Muons  Combined isolation < 0.15 in a cone R < 0.3  Quality cuts related to the track: χ2 0, number of valid tracker hits >10, number of matching segments >1, valid muon hits >0  Muon matched to a L3 muon: hltSingleMu9L3Filtered9 (RunA + Run B until ) hltSingleMu15L3Filtered15 (till run )  The other track is considered as a probe to study the efficiency.

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)9 2.1 Trigger Efficiencies Mixture of triggers in the data, with raising p T threshold Always use lowest-threshold un-prescaled single-muon trigger: HLT_Mu9, HLT_Mu11, HLT_Mu15 All trigger threshold lower than the p T >25 GeV requirement Trigger efficiencies determined with tag-and- probe Flat for p T >25 GeV flat trigger efficiency is used throughout the analysis Run 2010B

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT) Trigger Efficiencies Run2010A Run2010B Run2010B Trigger efficiencies in data are determined with a complementary method (1.5% difference): using jet triggered samples with offline muons, can reach higher values of p T In data no muons with p T >240 GeV while muons from potential W‘ signal are O(>=500 GeV) Extrapolation for high p T needed, done with MC → reasonable agreement with the data driven studies for low p T Efficiency from Data ~ 92%

Data: T&P Determined Efficiencies 2.2 Data: T&P Determined Efficiencies Excellent agreement between MC-predicted and data-derived (T&P) efficiencies (largest discrepancy coming from trigger: 4% assigned as systematic uncertainty) ε Mu Muon reconstruction ε SEL Selection ε ISO Isolation ε TRK Reconstruction inner track Efficiencies are only used for our signal MC, the background is obtained from data 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT) Data: T&P Determined Efficiencies 2.2 Data: T&P Determined Efficiencies Tracking Isolation SelectionReconstruction Data MC

Other Efficiencies to High pT 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)13

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)14 (An analysis with signal…) Efficiencies for W cross-section measurement  Same method used for the W->munu cross-section measurement with all 2010 data (already pre-approved)  Advantage of extracting the efficiencies on a sample of muons kinematically very similar Data MC  The selection is slightly different (d0< 0.2 cm iso<0.1)

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)15 W cross-section measurement  The ratio is roughly flat in pT, the correction is applied in eta bins  Good agreement between data and MC  The correction factor is incorporated to the cross-section measurement, as a correction to Aw*eff factors

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)16 Uncertainty on the number of background events due to statistical uncertainty of the sideband fit itself Signal Background Source of systematic uncertainty Value Luminosity11 % Muon p T resolution 0.14 TeV -1 Muon momentum scale0.4 % MET resolution10 % Trigger and other efficiency4 % (Back to W’) 4. Systematic uncertainties Focus on systematics related to muon

Systematic in MT due to momentum scale and resolution Method: 'Distort' the muon momentum by certain amount, recreate MET with the new momentum and recalculate MT. Assign the relative difference between # of events with 'standard' MT and 'distorted MT”> 600 GeV as a systematic Muon distorted like:  Momentum scale pt'=pt+a0*pt^2  Momentum resolution 1/pt' = 1/pt + C*Gaussian(0,1) 24/02/2011 MB Workshop17C. Diez Pardos (CIEMAT) Updated studies with all data, effects also depend on eta, phi

Systematic in M T due to momentum scale and resolution Realistic values for the resolution and momentum scale from data (results available at the time of doing the analysis, most conservative values taken, it doesn´t affect significatively the analysis)  MuscleFit (CMS AN-2010/059), SIDRA ( CMS AN-2010/059 ) studies for Z->mumu – intermediate pT (a0 = /40GeV, C = 0.14/TeV)  Cosmic studies: alignment, end point analysis (pt' = pt + ( / )*pt, C = /TeV) ( CMS PAS TRK , For W cross-section this systematics (with the latest results from muon momentum resolution and scale) is estimated to be <0.1% Results Cosmics are the only way to have information about high-pT (TeV) muons 24/02/2011 MB Workshop18C. Diez Pardos (CIEMAT) Updated studies with all data: esId=0&materialId=slides&confId=127861

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)19 Search strategy & limit setting: good agreement data-MC, no excess seen → set an exclusion limit Apply search window for high M T region and compare #expected - #observed events Use a sliding search window to optimize the limit as done for electron channel Search window Combined exclusion m(W‘)<1.58 TeV Present Tevatron limits m(W‘)<1TeV [D0 publ.], 1.1TeV [CDF, to be pulished] Final results: Final results: M T Distribution & Limit setting

Outlook Search for W´   performed with 36/pb  No excess seen in data  set exclusion on W´-mass with SM-like couplings of m(W‘)<1.39 TeV, combined with electron exclusion: m(W‘)<1.58 TeV Trigger, reconstruction and selection efficiencies studied in data (up to pT~200 GeV) with tag-and-probe and extrapolated to higher pT  Cosmics are still our only high pt muons... Used cosmic data to cross-check the muon momentum resolution, scale from Z->mumu studies Next year challenge: start dealing with real high pT muons from collisions 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)20

Back up 2124/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)22 Samples: Data and MC Im thinking about removing the tables or at least some columns,and summarise it in a couple of lines DATA: 36/pb Nov4ReReco MC BG: Fall10 38X samples MC Signal

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)23 Sideband Get total pp background from M T data spectrum Choose a region with low signal contamination (~1%) Fit sideband, extrapolate to high M T tail to predict # of (pp) background events in signal region Method proven to work in MC Background in MC is sum of all SM contributions (but mainly: W→μν) Cosmics not described by this method Extrapolation region Method (Back to W’) 3. Background determination

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)24 Goal: determine potential cosmics contamination, not described by sideband fit Cosmic contamination more relevant for tail of M T distribution Cosmic contamination for d0 < 0.02 cm pp cosmics 3.1 Cosmic Background

Table for d0 Optimization 2524/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)

Backup: Search Window for C&C 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)26 Cut-and-count method

24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)27 1. Select a muon: Trigger selection: HLT_Mu9, HLT_Mu11, HLT_Mu15 2. Muon identification and quality cuts: Follow Exotica Muon group recommondation ◦ Tracker & global muon ◦ ≥ 11 silicon tracker hits ◦ ≥ 1 pixel hit ◦ χ² /N dof < 10 ◦ Transverse impact parameter d0 < 0.02 cm (order of magnitude tighter than VBTF recommondation) ◦ At least 2 matched muon segments 3. Acceptance η < Exactly 1 global muon with p T > 25 GeV 5. Relative combined isolation in a cone ( Δ R < 0.3) < Dedicated kinematic selection ◦ 0.4 < pT / MET < 1.5 ◦ Δ ( φ μ,υ ) > 2.5 Selection

More on T&P method 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)28

More on T&P method 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)29

More on T&P method 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)30

Outlook Search for W´   performed with 36/pb  No excess seen in data  set exclusion on W´-mass with SM-like couplings of m(W‘) 1.58 TeV Trigger, reconstruction and selection efficiencies studied in data (up to pT~200 GeV) with tag-and-probe and extrapolated to higher pT  Cosmics are still our only high pt muons... Main background Standard Model W  , others contribute <10% in region high MT. Data-driven method for background: using sideband-fit to determine total background in signal region  Check the effect of muon reco, etc Next year: start dealing with real high pT muons  CHALLENGE, NEED FOR COSMICS??? 24/02/2011 MB WorkshopC. Diez Pardos (CIEMAT)31