First V+jets results with CMS. Vitaliano Ciulli (Univ. & INFN Firenze) V+jets workshop, 8-10 Sep 2010, Durham

Transcription

1 First V+jets results with CMS Vitaliano Ciulli (Univ. & INFN Firenze) V+jets workshop, 8- Sep 20, Durham

2 Outline Jet and missing energy reconstruction W and Z selections and cross-section measurement First results on W+jets Systematic uncertainty from Jet Energy Corrections First look at. pb P. Lenzi in the next talk will discuss the prospects for measurements of W/Z + jets with full 20/20 LHC data 2

3 CMS detector Acceptance: - Tracker: η < Electromagnetic Calorimeter: η < 3 - Forward Calorimeter: η < 5.2 3

4 Four different jet types: Jet reconstruction Standard jet reconstruction: anti-kt algorithm with ΔR = 0.5 Calo Jets: based on calorimetric towers only Jet Plus Tracks (JPT): Calo jets complemented with track informations Particle Flow (PF): jet clustering start from a list of identified particles ; more similar to generator level jets Track jets: use only tracks Jet Energy Correction Factor CMS Simulation CaloJets PFJets JPTJets anti-k T R=0.5 Absolute Correction Using different inputs allows for systematic cross-checks Corrected Jet p T (GeV) Results based on PF jets: smaller jet energy corrections in the tracker acceptance, η < 2.5 4

5 Missing transverse energy 6 Missing transverse energy also reconstructed using Particle Flow objects which provide the highest resolution (a) caloe/ T distribution ) (GeV) x,y "(Calibrated E Number of Events / 2 GeV type2 caloe T (Data) type2 caloe T (MC) tce T (Data) tce T (MC) pfe T (Data) pfe T (MC) CMS Preliminary 20 s=7 TeV Data Simulation CMS preliminary 20 Calo!E T [GeV] (b) calo E T distribution Calibrated pf!e T (GeV) ated E/ resolution versus calibrated pf E for the type- Number of Events / GeV Good agreement between MC Data and data 5 in minimum bias 4 events CMS Preliminary 20 s=7 TeV Simulation Number of Events / GeV CMS Preliminary 20 s=7 TeV Data Simulation Tc E T [GeV] Pf E T [GeV] (c) tce/ T distribution 5 (d) pfe/ T distribution

6 W µν events - Event triggered with pt > 9 GeV - Muon pt >20 GeV, η < 2. - Isolation (ΣpT (tk)+ ΣET (had+em))/pt< 5% - MET reconstructed using PF technique - Drell Yan rejection (veto on events with a second muon of pt> GeV) number of events / 5 GeV CMS preliminary 20 data W " µ! EWK QCD # fraction of events / 5 GeV [%] CMS preliminary 20 data-driven template QCD MC, isolated M T! QCD MC, not isolated [GeV] M T [GeV] - Main source of BG: QCD (b hadron decays) - W Signal yield extracted through a Binned Likelihood fit to the MT distribution (Signal + QCD & EWK BGs) - W Signal and EWK MT shapes modeled from MC - QCD MT shape extracted from data (isolation inversion) 6

7 W eν events - Events triggered with ET > 5 GeV - Electron ET > 20 GeV - η <.4442 (Barrel),.566 < η < 2.5 (Endcap) - Isolation (independent cuts on track, em, had) - Drell Yan rejection (veto on events with a second electron of ET>20 GeV) number of events / 5 GeV CMS preliminary 20 # L Data W " e! EWK QCD dt = 98 nb fraction of events / 2.5 GeV [%] CMS preliminary 20-2! inverted-cut sample data-driven template E T [GeV] [GeV] - QCD BG dominated by fake electrons - Unbinned Likelihood fit to the MET distribution - W Signal and Electroweak MET shape modeled from Monte Carlo - QCD background is parameterized and fixed using an inverted isolation cut sample E T 7

8 Z µµ and Z ee Z decays selected with same pt cut on the leptons and looser isolation and identification criteria number of events/ 2 GeV CMS preliminary 20 data Z!µ µ " L dt = 98 nb number of events / 2 GeV CMS preliminary 20 data Z! ee " L dt = 98 nb number of events / 2 GeV -2 CMS pre M(µ µ - ) [GeV] M(ee) [GeV] candidates selected the invariant mass range 60 < m µµ < 20 GeV 6 candidates selected in the invariant mass range 60 < mee < 20 GeV Figure : Distribution of M ee for the selected Z e + e candid posed are simulated estimates of signal and background compo CMS preliminary 20 # isolation cones based on lepton-kinematic templates in W % µ$ events [%] The largest uncertainty for the cross section measurement come isolation cones based 2 on lepton-kinematic templates ment, currently estimated to be % []. This uncertainty sho in Z $ µµ events 8 quote it separately from the other systematic uncertainties. ta /" MC CMS preliminary 20 Systematic uncertainties 4 #

9 Cross-section results CMS preliminary ICHEP20 CMS preliminary ICHEP20 $ NNLO, MSTW08 68% CL prediction.44 ± 0.52 nb $ NNLO, MSTW08 68% CL prediction, 6020 GeV 0.97 ± 0.04 nb W " µ! 9.4 ± W " e! 9.34 ± 0.33 stat 0.36 stat W " l! (combined) 9.22 ± 0.24 stat ± 0.58 syst ±.00 lumi nb ± 0.70 syst ±.03 lumi nb ± 0.47 syst ±.0 lumi nb #( pp " W+X " l!+x ) [nb] Z/"*! µµ 0.88 ± 0. stat Z/"*! ee 0.88 ± Z/"*! ll 0.88 ± 0.2 stat 0.08 stat ± 0.04 syst ± 0. lumi nb ± 0.08 syst ± 0. lumi nb (combined) ± 0.04 syst ± 0. lumi nb #( pp! Z/"*+X! ll+x ) [nb] CMS preliminary ICHEP20 % NNLO, MSTW08 68% CL prediction.74 ± 0.04 W! µ$, Z/"*! µµ.38 ±.34 stat ± 0.78 syst W! e$, Z/"*! ee.57 ±.54 stat ±.20 syst W! l$, Z/"*! ll.46 ± 0.99 stat ± 0.65 syst (combined) RW/Z = #( pp! W+X! l$+x )/#( pp! Z/"*+X! ll+x ) Results are on the lower side, but consistent with SM within the uncertainty on luminosity Ratio W/Z is also consistent with the SM expectations CMS preliminary ICHEP20 $ NNLO, MSTW08 68% CL prediction 4.29 ± 0.23 nb 9 W ± " µ -! 0.5 stat ± 0.2 syst ± 0.37 lumi nb

10 Cross-section results BR (pb) "! 4 CMS preliminary 20 CDF Run II D0 Run I UA2 UA W $ l# + + W $ l # - - W $ l # 3 pp + - Z $ l l pp 2 Theory: FEWZ and MSTW08 NNLO PDFs CMS points do not include luminosity uncertainties. Collider energy (TeV)

11 Jets in events with W candidates W selection as for the inclusive analysis Jets reconstructed using Particle Flow objects in η < 2.5 Jets must be separated from the lepton by ΔR > 0.5 avoids counting the lepton as a jet no effects on jet counting as leptons are required to be isolated Signal and EWK background are normalized to NLO cross-section calculated with MCFM number of events / 5 GeV Leading jet ET distribution in W events 3 2 CMS preliminary 20 data W " e!, µ! (MadGraph) $ L EWK QCD + #+jet s leading jet E T = 7 TeV dt = 98 nb [GeV]

12 Jet rates Yields shown for events with n jets inclusive rates Two ET thresholds considered: ET>5 GeV ET>30 GeV (shown here) W signal extracted with a fit to the MT distribution in each sample statistical errors only are shown tt background sizeable for n 3 N( W +! n-jets ) N( W +! n-jets ) N( W +! (n)-jets ) CMS preliminary 20 MadGraph PYTHIA (D6T) normalization: MCFM NLO statistical errors only " W $ e#,µ# jet E T >30 GeV inclusive jet multiplicity, n 2

13 Jet multiplicity The use of Particle Flow jets allows to lower the jet ET threshold to ET > 5 GeV No big differences within PS (PYTHIA) and ME+PS (MadGraph) But strong dependence on the MC tune (more in next talk) N( W +! n-jets ) N( W +! n-jets ) N( W +! (n)-jets ) CMS preliminary 20 MadGraph PYTHIA (D6T) PYTHIA (P0) PYTHIA (ProPT0) normalization: MCFM NLO statistical errors only " W $ e#,µ# jet E T >5 GeV inclusive jet multiplicity, n 3

14 Jet energy corrections Systematic uncertainty estimated from MC: 5% + 2% η absolute scale will be obtained from γ+jet events: first look gives indications that this error is quite conservative relative uncertainty can be cross-checked with di-jets events: residual miscalibration is within the error band and can be further corrected The uncertainty on the jet rate in W events is %-40% for -4 jets with ET>5 GeV %-20% for -4 jets with ET>30 GeV The uncertainty is even smaller and rather constant for the n+/n ratio Data / Simulation.4.2 Corrected PFJets 43 < dijet p 68 < dijet p 85 < dijet p cor T cor T cor 20 < dijet p Uncertainty T cor T < 68 GeV < 85 GeV < 20 GeV < 50 GeV CMS Preliminary from the dijet p Data / Simulation.4.2 Corrected PFJets Residual Correction Applied 43 < dijet p 68 < dijet p 85 < dijet p cor T cor T cor 20 < dijet p Uncertainty T cor T < 68 GeV < 85 GeV < 20 GeV < 50 GeV! balance method CMS Preliminary ! d from the dijet p balance metho 4

15 W plots with. pb 5

16 Z plots with. pb 6

17 Summary With few hundreds nb we have shown that our detector is well suited to perform nice physics studies with vector bosons and jets basic kinematic variables and measurements are in good agreement with expectations from Monte Carlo the jet ET spectrum in particular can be studied down to very low momentum The LHC is expected to deliver about 30 pb by the end of 20 More (and better) to come... 7

18 Backup slides

19 Systematics errors for W x-sec Efficiencies and scales studied in Z events and recoil studies Background uncertainties from cut inversion studies and control samples PDF uncertainties evaluated via CTEQ66, MSTW08NLO, NNPDF2.0 sets!"#$%& '()(µν (%) '()(&ν (%)!"#$%&'(")%&*$(+)$,%& -./ 0. 2(,33"('455,),"&)6 -.7 /.0 8*%9:$,%&'455,),"&)6 /.;. <%="&$+=>"&"(36'*):9"./ 7.? <42'*):9"':&@'("*%9+$,%&./.A B:)C3(%+&@'*+D$(:)$,%& -.; 7.7 EFG'+&)"($:,&$6',&':))"#$:&)" 7./ 7./ H$I"('$I"%("$,):9'+&)"($:,&$,"*.A.- 2%$:9'*6*$"=:$,)'"((%( '0.- '?.?!+=,&%*,$6'+&)"($:,&$6././ 9

20 Systematic errors for Z x-sec!"#$%& '()(µµ (%) '()(&& (%)!"#$%&'(")%&*$(+)$,%& -./ 0.- (,22"('344,),"&)5 6.0 '7 8*%9:$,%&'344,),"&)5 ;.6 ;.- <%="&$+=>"&"(25'*):9" 6./ '7?@A'+&)"($:,&$5',&':))"#$:&)" B$C"('$C"%("$,):9'+&)"($:,&$,"* ;.D ;.E %$:9'*5*$"=:$,)'"((%( 'E.F '0.0!+=,&%*,$5'+&)"($:,&$5 ';;.6 ';;.6 20

21 MET vs jet multiplicity Uncorrected Calo MET in jet events for different SumET ranges JME--004 Different jet multiplicity bins (jets w/pt>20 GeV,! <3) => MET distribution primarily controlled by SumET, and not jet multiplicities 2