W/Z+jet results from the Tevatron Dmitry Bandurin Florida State University On behalf of D0 and CDF Collaborations Moriond QCD 2012, March 15, La Thuile, Italy
Precision QCD tests Photon, W, Z etc. p parton distribution Underlying event Hard process p parton distribution ISR FSR hadronization Jet Colorless probe of parton dynamics in V+jets final state Constraining the structure of the proton (gluon, s-, c- and b- quark PDFs) Constraining ISR/FSR and fragmentation models Search for new interactions => Precision understanding of QCD using V+jet events is an essential part of the Tevatron program 2
More on Motivations WH production W+bb Single top production W+dijet, M jj bump CDF W+jets? PRL106 (2011) 171801 Background to top-quark, Higgs, SUSY and other NP productions Provide detailed measurements of pt and angular distributions of vector boson and jets test of fixed order perturbative QCD, LO ME+PS predictions in EvGen testing and tuning of phenomenological models 3
More on Motivations WH production W+bb Single top production W+dijet, M jj bump? W+jets PRL107, 011804 (2011) Background to top-quark, Higgs, SUSY and other NP productions Provide detailed measurements of pt and angular distributions of vector boson and jets test of fixed order perturbative QCD, LO ME+PS predictions in EvGen testing and tuning of phenomenological models 4
Tevatron collider 5
Tevatron collider luminosity D0 and CDF recorded about 10 fb 1 Efficiency of data taking >90% Current results correspond to 1 1 8 fb luminosity of Apr, 2002 Sep, 2011 Sep 30 is the last day of data taking 6
Z/W+jets production Use leptonic Z/W decays as most precise probe of QCD - high Q2 (~MZ or MW) - very small backgrounds, right down to very small p T! Concentrate on high pt final states - regime of perturbative QCD (and NP) Theory predictions: pqcd (+ corrections for underlying event & hadronization): - LO Z(W) + 1-6 partons - NLO Z(W) + 1, 2 (MCFM) - NLO W+3[4] (Rocket+MCFM, Blackhat+SHERPA) Event generators: - LO 2 1, 2 + parton shower - PYTHIA, HERWIG q q g Z - LO 2 1-6 + (vetoed) parton shower - ALPGEN ( MLM ME-PS matching), - SHERPA (CKKW ME-PS matching) These generators are the main Tevatron and LHC tools - but, leading order large uncertainties - must be tuned to data! 7
Z+jets production: pt, data/nlo Z +jet Jets D0 G. Hesketh 8 Measurement of 1st, 2nd and 3rd jet pt in Z events: - Z ee, midpoint cone R=0.5, jet p T > 20 GeV, jet y < 2.5. - Normalized to inclusive Z production (cancel some uncertainties) Leading jet in Z + jet + X The differential cross section, normalised to inclusive Z production NLO: MCFM - CTEQ6.6M PDF - R2 = F2 = ptz2 + MZ2 Data / NLO LO / NLO + scale uncertainties NLO scale uncertainties 8
Z+jets production: pt, data/nlo +jet Jets Z+jetsZproduction. Jet pt Measurement of 1st, 2nd and 3rd jet pt in Z events: - Z ee, jet pt > 20 GeV, jet y < 2.5. - Normalized to inclusive Z production x-section (cancel some uncertainties) 1st jet in Z + jet + X PLB 678, 45 (2009) 2nd jet in Z + 2jet + X D0 G. Hesketh 9 1.0 fb-1 3rd jet in Z + 3jet + X 9
Z+jets production; jet pt, data/mc Z + Jets D0 G. Hesketh 10 Comparison to Pythia, Herwig, Alpgen and Sherpa Treating the scale choice as a tuneable parameter: Best description from Alpgen with lower scale (default: F2 = ptz2 + MZ2). 1st jet in Z + jet + X 2nd jet in Z + 2jet + X 3rd jet in Z + 3jet + X
W+jets production Dominant background to the single top, ttbar, SM Higgs, many BSM searches D0 4.2 fb-1 - The measurement tests W+n-jet (n=1-4) production cross section vs n-th jet pt Normalized to (W) - Comparison to LO&NLO by Blackhat+Sherpa and Rocket+MCFM Theor. scale uncertainty Phys.Lett. B705 200 (2011) 11
W+jets production D0 Dominant background to the single top, ttbar, SM Higgs, many BSM searches - The measurement tests W+n-jet (n=1-4) production cross section vs n-th jet pt - Comparison to LO&NLO by Blackhat+Sherpa and Rocket+MCFM (different scales) W+1jet W+2jets W+3jets W+4jets - In agreement with QCD NLO in jet pt and #jets - Experimental uncertainties are lower than theoretical (scale) in many cases => tuning the theory - First W+4jets result (only LO prediction has been available for the Tevatron) W+n-jet differential x-section in ~40(!)variables is in a review 12
Z+jets production Two central muons or electrons with y < 1.0, pt > 25 GeV Jets are found by MidPoint Cone algo with R=0.7, jet pt>30 GeV and y <2.1 ΔR(lepton,jet) > 0.7 Z+n-jet data vs Blackhat+Sherpa (LO&NLO), Alpgen+Pythia Comparison to theory using jet pt, y, jet multiplicity, M jj, ΔRjj, Δφjj, MZjj and ptjj CDF Preliminary 8.2 fb-1 Inclusive jet pt Z+ 1 jet Z+ 3 jets => Agreement with NLO predictions for inclusive Z+n-jet (n=1,2,3) productions within theor. scale uncertainties (about 25%, 0 variation by a factor 2) 13
Z+2-jet production Inv.Mass(jet1,jet2) CDF (jet1,jet2) Good agreement with NLO QCD (MCFM) in Mass(j1,j2) and (j1,j2) (Theor. scale uncertainties grow towards smaller angles and masses) 14
D0 (Z+b) / (Z+jet) - Important background to the SM Higgs search in the ZH channel. - Probe of b-quark PDF, important for gb Hb & single-top studies - Measurement of ratio (Z+b) / (Z+j) benefits from cancellation of many systematics => precise comparison with theory Pretag sample NN output PRD83, 031105 (2011) Measurement: 0.0193 0.0022 (stat) 0.0015 (syst) [~8% syst] Most precise measurement of 'Z+b' fraction to date! Consistent with NLO theory: 0.0192 +/- 0.0022 (MCFM, renorm. and factor. scales are at Mz) Differential measurement in b-jet pt, (Z,jet) angles in progress 15
(Z+b) CDF At least on central muon or electron with η < 1.0, pt > 20 GeV Jets: MidPoint Cone algo with R=0.7, jet pt>20 GeV and y <1.5 ΔR(lepton,jet) > 0.7 Measured as ratios (Z+b)/ (Z), (Z+b)/ (Z+jet) Comparison to NLO MCFM Preliminary 7.9 fb-1 Data: MCFM: b-jet fraction vs jet pt vary within 50-65% Both ratios in agreement with NLO QCD within ~20-25% scale uncertainties The measured ratios have same or less uncertainty than NLO QCD predictions. 16
(Z+b)/ (Z) differential b-jet pt CDF b-jet rapitity Z+b differential cross sections are in agreement with NLO MCFM Scale uncertainties (default vs Q2=pT2) are about 25% 17
(W+c)/ (W+jet) Sensitive to s-quark PDF: 90% 's', 10% 'd' signal: OS>>SS backgrounds: OS~SS (subtracted in the diff. 'OS-SS') Data (W e, D0 ℒ = 1/fb Phys.Lett.B666:23-30 (2008) Measurement cuts: lepton pt > 20 GeV missing ET > 20 GeV D0 midpoint jet Rcone=0.5, ptjet > 20 GeV, ηjet < 2.5 channels combined): 0.074 ± 0.019 (stat) ± +0.012-0.014 (sys) Alpgen+Pythia: 0.044 0.003 (CTEQ6.5 PDF uncertainty) 18
W+c production CDF Preliminary 4.3 fb-1 Jet pt>15 GeV, y <2.0 Lepton pt>20 GeV Missing ET>25 GeV Soft lepton tagging (W e, channels) using OS-SS technique W (W+c)*Br(W e/ + ): W e Good agreement data/ NLO theory 3.3 Data, e& combined: 13.3 2.9 pb QCD NLO: 11.3 2.2 pb (LO: 7.5 1.5 pb) Agreement with previously published: PRL100,091803 (2008) 19
CDF (W+b) L= 1.9 fb-1 Phys.Rev.Lett.10,131801 (2010) b-fraction=71% σ(w+b-jets) BR(W l v) = 2.74 ± 0.27 (stat) ± 0.42(syst) pb QCD NLO: 1.2 + 0.14 pb Alpgen : 0.78 pb About a factor 2(3) of discrepancy with NLO (Alpgen)! Results from D0 are coming soon (by DIS) 20
Summary Many new, interesting results are coming from the Tevatron in Vector Boson + jet measurements =>Crucial for understanding backgrounds to NP and SM Higgs searches Some discrepancies with theory suggest HO corrections and some theory components may need study: tuning of scale choices, PDFs, heavy quark fragmentation, etc Understanding of W+b jet x-section is extremely important New results on W+n-jets, Z+b and W+b are coming soon. Be tuned by looking at D0: http://www-d0.fnal.gov/run2physics/qcd/d0_public_qcd.html CDF:http://www-cdf.fnal.gov/physics/new/qcd/QCD.html 2121
BACK UP SLIDES 22
Z+jet production: #jets CDF Good agreement with both NLO QCD predictions up to 3 jets Slight disagreement with Alpgen at 2 jets 23
Corrections to particle level In most cases: data are corrected to particle level particle level measurements are compared to NLO theory NLO theory is corrected to particle level using parton shower MC Chad observable (particle level) = observable (parton level) There is aslo correction (Cue) for the underlying events (MPI). Usually we run Pythia with a couple of Tunes, Herwig+Jimmy and correct predictions with MPI to that without. 24
NLO pqcd and MC models pqcd V+jet predictions calculated with MCFM, Rocket+MCFM, Blackhat+Sherpa Many LO MC programs on the market ME+PS: Alpgen, Sherpa, Madgraph, Helac, Madevent,... PS: Pythia, Herwig, Ariadne,... CKKW the separation of ME and PS for different multijet processes is achieved through a kt-measure undesirable jet configurations are rejected through reweighting of the matrix elements with analytical Sudakov form factors and factors due to different scales in αs MLM matching parameters chosen, ME and PS jets matched in each n-parton multiplicity, events vetoed which do not have complete set of matched jets further suppression required to prevent double counting of n and n+1 samples (replaces Sudakov reweighting in CKKW) 25
Z+b production CDF PRD79, 052008 (2009) - L=2 fb-1 Z ee/μμ + b + X jet pt > 20 GeV, jet η < 1.5 Jet track mass in the secondary vertex is used to discriminate between jet flavors Theory: - MCFM : all calculations are at O( s2) - Pythia, Alpgen (Z+b) / (Z) Data: [3.32 0.53(stat) 0.42(syst)] x10 3 MCFM: 2.3 (2.8) x10 3 Pythia: 3.5 x10 Alpgen: 2.1 x10 3 3,Q 2=Mz 2 jet p2t (Z+b) / (Z+jet) Data: 2.08 0.33(stat) 0.34(syst) % MCFM: 1.8% / 2.2% Pythia: 2.2% Alpgen: 1.5% MCFM( = jet pt2), Pythia provide best agreement to data 26
Z+jets production. Z pt PLB 669, 278 (2008) Particle level phase space: theory predictions 65 GeV< Mμμ < 115 GeV, updated since publication MCFM v5.4 PDF: jet jet Rcone=0.5, pt > 20 GeV MSTW2008 yjet < 2.8, yμ < 1.7 ratios relative to μr2 = μf2 = pt,z2 + MZ2 muons include QED radiation Sherpa 1.1.3 PYTHIA v6.420 Pythia Tune P Pythia Tune QW HERWIG v6.510 + JIMMY v4.31 ALPGEN v2.13+pythia v6.420 ALPGEN v2.13+herwig v6.510 Z pt<30 GeV sensitive to underlying event Pythia can be tuned to reproduce data (tune P0) 27
+ Jet + XJet rapidity28 Z+jetsZproduction. G. Hesketh PLB 669, 278 (2008) Take a more detailed look at Z( ) + 1 jet - we also need good description of jet angles: look at leading jet rapidity Jet rapidity in Z + jet + X PYTHIA pt ordered - new Perugia tune - MRST07 LO* PDF PYTHIA Q2 ordered HERWIG ALPGEN + PYTHIA pt ALPGEN + PYTHIA Q2 ALPGEN + HERWIG Again, Pythia with tune P0 works well! 28
Z + Jet (Z, jet) Z+jets production. ϕ(z,jet) First measurement of (Z, jet)! - Z, y <1.7, ptz > 45 GeV - jet pt>20 GeV, jet y < 2.8 G. Hesketh 29 PLB 682, 370 (2010) PYTHIA pt ordered - new Perugia tune - MRST07 LO* PDF PYTHIA Q2 ordered HERWIG ALPGEN + PYTHIA pt ALPGEN + PYTHIA Q2 ALPGEN + HERWIG - Sherpa describes ϕ(z,jet) shape very well - Small values of ϕ are excluded from MCFM due to significant nonperturbative contributions 29
Default MC Improved/tuned MC 30