1 / 48

Recent QCD and Electroweak Results from the Tevatron at Fermilab

Recent QCD and Electroweak Results from the Tevatron at Fermilab. Prof. Gregory Snow / University of Nebraska /D0 On behalf of the CDF and D0 Collaborations July 3, 2008. Outline. Luminosity measurements at D0 and CDF Jet and direct photon production W/Z + jets production

khan
Download Presentation

Recent QCD and Electroweak Results from the Tevatron at Fermilab

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Recent QCD and Electroweak Results from the Tevatron at Fermilab Prof. Gregory Snow / University of Nebraska /D0 On behalf of the CDF and D0 Collaborations July 3, 2008

  2. Outline • Luminosity measurements at D0 and CDF • Jet and direct photon production • W/Z + jets production • W/Z properties • Di-Boson production • Inclusive jets • Dijet mass • Inclusive direct photon • Direct photon + jet • W + jets • Z + jets • W + c-jets • Z rapidity • Z pT • Z/* forward-backward asymmetry • W mass • ZZ production observed More details of these and several other 2007-2008 QCD and electroweak results are available on the public web pages of the experiments: http://www-cdf.fnal.gov http://www-d0.fnal.gov

  3. Fermilab Tevatron Run II pp at 1.96 TeV D0 CDF Tevatron • Run II started in March 2001 • Peak Luminosity: 2.85 x 1032 cm-2s-1 • Delivered: 4.4 fb-1 (3.8 recorded) • Run I: 140 pb-1 (1992 – 1996) • D0 now records 30 pb-1 per week Main Injector and Recycler 36x36 bunches 396 ns bunch crossing 6 fb-1 expected by April 2009 8 fb-1 by end of FY2010 (D0 recorded > 90% of delivered luminosity in 2008)

  4. Run IIb Run IIa Flat means accelerator shutdowns

  5. The CDF and D0 Detectors CDF D0 • Common features • High field magnetic trackers with silicon vertexing • Electromagnetic and hadronic calorimeters • Muon systems • Competitive Advantages • CDF has better momentum resolution in the central region and displaced track triggers at Level 1 • D0 has better calorimeter segmentation, silicon disks, and a far forward muon system. Luminosity monitors here

  6. Luminosity Detector • Two arrays of forward scintillator. 24 wedges per side each read out with mesh PMTs • Inelastic collisions identified using coincidence of in-time hits in two arrays

  7. Luminosity Detector Two replacements of scintillator to date in Run II due to radiation damage

  8. Counting zeros technique Probability of measuring no inelastic event in a beam crossing Correction term for multiple interactions when separate single-sided hits mimic an inelastic interaction σeff = σinelastic(fnd*And + fsd*Asd + fdd* Add) • σ inel is the total inelastic cross-section • fnd is the non-diffractive fraction and And is the acceptance, etc. nd = non-diffractive sd = single diffractive dd = double diffractive • Acceptances for different topologies from Monte Carlo • Material modeling important inelastic(1.96 TeV) = 60.7 ± 2.4 mb, average of different experiments used both by CDF and D0 S. Klimenko, J. Konigsberg, T.M. Liss, FERMILAB-FN-0741 (2003)

  9. Determining the non-diffractive fractionfrom data fnd yielding minimum 2 matches data well Compare data and Monte Carlo multiplicity distributions (i.e. calculate 2) for different values of fnd in MC at a given luminosity D0 determines luminosity with 6.1% uncertainty, with approx. equal contributions from uncertainties on inelastic and [acceptances, fnd, fsd, fdd, and time-dependent] ingredients of eff

  10. CDF Luminosity Detectors CDF uses similar technique with similar uncertainty

  11. Photon, W, Z etc. parton distribution p Underlying event Hard scattering FSR ISR parton distribution p fragmentation Jet Jet Production in pQCD Jets of particles originate from hard collisions between quark and gluons Quark and gluon density is described by PDFs. Proton remnants form the Underlying Event (U.E.) We compare data to pQCD calculations to NLO ( )

  12. Jet Measurements at the Tevatron • CDF/D0 Run II jet results presented here use the • Additional midpoint seeds between pairs of close jets improve IR safety • 4-vector sum scheme instead of sum ET • Split/merge after stable proto-jets found Midpoint cone algorithm (R=0.7) Main Systematics to Jet Measurements • Jet Energy Scale:2-3% at CDF • 1-2% at D0 • (after 7 years of hard work using MC tuned • to data, g+jet & dijet event balance) • Energy Resolution:unsmearing procedure using s/ET measured from dijet data. Compare data and theory at the “particle level”

  13. Jet Events at the Tevatron LHC Three jet event at D0 1st leading Jet (pT ~624 GeV) (at HERA) DØ CDF 3rd leading jet 2nd leading Jet (pT ~594 GeV) Complementary to HERA and fixed target experiments Mjj=1.22 TeV

  14. Inclusive Jet Production D0 Run II (L=0.7 fb-1) Five y bins Six y bins 1% error in JES 5—10% (10—25%) central (forward) x-section • Up to 10 times more data than in Run I • Comparisons to NLO pQCD + non-perturbative • corrections from Pythia • Mikko Voutilainen Ph.D. thesis defense (D0) • Tuesday in Helsinki

  15. Inclusive Jet Production Data favor lower edge of CTEQ 6.5 PDF band at high jet pT Shape well described by MRST2004 D0 results – submitted to PRL arXiv:/0802.2400 [hep-ex] DØ Data (and Uncertainty Correlations) available for PDF Fits • Probe of gluon PDF contribution at large jet pT , i.e. high x • Experimental uncertainties now  theory uncertainties

  16. Inclusive Jet Production Detailed Comparisons: Data and Theory Compatible within Uncertainties - Data favor lower edge of CTEQ 6.1 PDF family The DØ and CDF data are compatible within uncertainties PDFs uncertainties reduced in CTEQ6.5 - Note that the CTEQ6.1 PDF band (CDF) is twice as wide as the CTEQ6.5 PDF band (DØ)

  17. Exclusive Jet Production: Dijet Mass Central dijet production: implications for new physics NLO QCD predictions describe data Limits set for excited quark, massive gluon and Z’/W’ scenarios (see: http://www-cdf.fnal.gov/physics/exotic/r2a/20080214.mjj resonance 1b/)

  18. Photon Production Direct photons come unaltered from the hard sub-process Allows us to understand hard scattering dynamics Photon Identification • EM shower with very little energy in • hadronic calorimeter • Geometric isolation • No associated track • R(g, Jet) > 0.7 (cone jets, R = 0.7) ElectroMagnetic Shower Detection EM Calorimeter Background Estimation • Origins: Neutral mesons: p0, h • + Instrumental: EM jets • Shower shape quantities in NN • to estimate purity. Shower Maximum Detector (CDF) Preshower

  19. Isolated Photon+X Cross Section Previous measurement (326 pb-1): D0 Collab., Phys. Lett. B 639, 151 (2006) • Signal fraction is extracted from • data fit to signal and background • MC isolation-shape templates • Data-Theory agree to within ~20% • within errors • Results consistent with NLO theory • pT dependence similar to former • observations (UA2, CDF) Measurements based on higher stats, ~3 fb-1 with ~300 GeV reach, coming soon

  20. Inclusive Photon+jet Production Also fragmentation: Dominant production at low pTg (<120 GeV) is through Compton scattering: qg q+g Probe PDF's in the range 0.007<x<0.8 and pTg=900 < Q2 < 1.6x105 GeV2 • g+jet+X Event selection • |hg|< 1.0 (isolated) • pT > 30 GeV • |hjet| < 0.8 (central), 1.5 < |hjet| < 2.5 (forward) • pTjet> 15 GeV • 4 regions: hg.hjet>0,<0, central and forward jets • MET< 12.5 GeV + 0.36pT (cosmics, W en) 0804.1107 [hep-ex], Submitted to PLB

  21. Inclusive Photon + jets Production • Similar pT dependence as inclusive • photons in UA2, CDF, and D0 • Shapes very similar for all PDFs • Measurements cannot be simultaneously • accommodated by the theory • Most errors cancel in ratios between • regions (3-9% across most pTg range) • Data & Theory agree qualitatively • A quantitative difference is observed • in the central/forward ratios Need improved and consistent theoretical description for g+jet

  22. c s(90%) or d(10%) c W- W + c-jet Production • W+c-jet is background to top pair, single top, Higgs. • It can signal the presence of new physics • Direct sensitivity to s-quark PDF • Data Selection • L = 1 fb-1 • W(ln), isolated lepton pT>20 GeV, MET>20 GeV • |hjet| < 2.5, pTjet>20 GeV • Muon-in-jet with opposite charge to W is a c- jet candidate • Background • WZ, ZZ rarely produce charge correlated jets • tt, tb, W+bc and W+b suppresed (small x-sec) 0802.2400 [hep-ex] Submitted to PLB – D0 Phys. Rev. Lett. 100, 091803 (2008) - CDF • 3.5s significance for W+c-jet • Agreement with LO and s PDF evolved from larger Q2 Systematic errors largely cancel in the ratio

  23. Z rapidity x1 x2 • Z rapidity (yZ) is dependant on x1,2 • A measurement of d/dy constrains PDFs New 2.1 fb-1 CDF measurement (~170,000 Z  ee events with |e| < 2.8 )

  24. Z rapidity Forward and backward rapidities combined statistical errors only The preferred theory comparison

  25. Z pT: QCD constraints • Measuring the Z pT distribution tests QCD predictions for initial state gluon radiation tune and validate calculations and Monte Carlo generators. • High Z pT dominated by single (or double) hard gluon emission (pQCD reliable). • Low Z pT dominated by multiple soft emissions (resummation techniques/parton shower Monte Carlos with non-perturbative models required).

  26. Z pT New 0.98 fb-1 DØ measurement (~64,000 Z  ee events with |e| < 3.2 ) • Z pT < 30 GeV region agrees well with ResBos (NLO QCD + CSS resummation with BNLY non-perturbative form factor). • The Z pT distribution is predicted to broaden at small-x (large |yZ |) - important for the LHC! • Broadening modeled with an additional “small-x” form factor from DIS HERA data. • Data with |yZ| > 2 prefers ResBoswithout “small-x” form factor (NOTE: non-perturbative parameters have not been retuned with additional form factor!). 2/dof = 32/11 2/dof= 11/11

  27. Z pT • In Z pT > 30 GeV region a NNLO k-factor is required. • Even then the theory is too low. • The NNLO shape agrees if normalized at Z pT = 30 GeV.

  28. Z/* Forward-Backward Asymmetry BACKWARD (B) : FORWARD (F) : e- e+ * * p p p p e+ e- cos* : in Collins-Soper frame (W rest frame) Z and Z/* couplings to fermions have vector : d/dcos* ~ 1 + cos2* and axial-vector : d/dcos* ~ cos* components. AFB = (F-B) /(F+B) AFB depends on MZ/* AFB sensitive to sin2weff

  29. Z/* Forward-Backward Asymmetry New 1.1 fb-1 DØ measurement (~36,000 Zee events with |e|<2.5 ) • Measurement consistent with the SM prediction (note: large MZ/* region sensitive to a new Z’ boson). • sin2weff extracted from fit to AFB: • 0.2327  0.0019 (DØ 1.1 fb-1) • 0.23152  0.00014 (current world average) arXiv:hep-ph/0804.3220

  30. W mass Motivation for W mass measurements Radiative corrections (r) dominated by top quark and Higgs loop, allowing a constraint on the Higgs mass ∆mW  mt2 ∆mW  ln(mH/mZ) With improved precision also sensitive to possible exotic radiative corrections The current mH constraint is limited by the uncertainty on mW To achieve a similar constraints on mH : ∆mW ≈ 0.006 ∆mt Current ∆mt = 1.4 GeV corresponds to ∆mW = 8 MeV

  31. W mass analysis scheme W  e Transverse plane Since only pT is known via missing ET, calculate W “transverse mass”, mT Scheme: find MW for which the simulated mT corresponds best to the data

  32. W mass analysis scheme mT template W mass template fits are created for mT, transverse lepton momentum/energy, and ET mW = 81 GeV mW = 80GeV For template fits we need: A fast simulator of W/Z production/decays With calibrated detector simulation PDFs, boson pT , EWK corrections + Calibrate l± track momentum with mass measurements of J/ and 1S Calibrate calorimeter energy using track momentum of e from W decays Calibrate recoil simulation with Z decays + Contribution of backgrounds added to the templates Long, detailed analysis: Physical Review D paper is 48 pages long! 15

  33. W mass Fits for the W mass - mT W  e W   Background contributions: Simulate using MC: W EWK backgrounds (Z ,  decays)

  34. W mass The result and constraints mW = 80413 ± 34MeV (stat) ± 34MeV (sys) = 80413 ± 48MeV (stat + sys) Electron and muon channels combined result with200 pb-1 Most precise single measuement ! Influence on world average: Central value: 80392  80398 MeV Uncertainty: -15% (29 to 25 MeV) With mt=(170.9 ± 1.8) GeV, predicted Higgs mass: 76+33-24 GeV MH < 144 GeV @ 95% CL

  35. MW ≈ 25MeV 2 fb-1 Outlook on W mass Can surpass the current world average with a single measurement: MWCDF < 25 MeV • Provided: • detector aging • averaging over longer • data-taking period • larger spread and • higher average luminosity • do not deteriorate data quality

  36. Di-boson Production e+e-, +-, or  Leading order ZZ diagram * * Today • Several recent results on di-boson production • and limits on anomalous trilinear couplings • Mention today only ZZ production • First observation at a hadron collider • (Seen at LEP) • Very small cross section • Theory: (ZZ) = 1.4 – 1.6 pb Overwhelmed by QCD multijets • ZZ branching fractions • 4 charged leptons very clean (*) • ll x 6 BR, but backgrounds difficult (*) • CDF and D0 have 2008 results in both

  37. CDF ZZ  4 candidate

  38. Brief summary of ZZ results • CDF (1.9 fb-1) • In the 4 charged lepton channel, CDF observes 3 events with an expected • background of events. • Combining this with the ZZ  ll channel, CDF observes an excess of events • with a probability of 5.1  10-6 that the excess is all background. • CDF measures (stat. + sys.) pb, consistent with SM theory. • D0 (2.2 fb-1) • D0 recently published a paper on the search • for Z  4 charge leptons, setting a cross section • upper limit based on 1 fb-1 and first Tevatron • limits on anomalous neutral trilinear ZZZ, • ZZ* gauge couplings. • New prelim. result in ZZ  llchannel • yields pb • consistent with SM theory.  channel Important selection cut ET > 35 GeV to eliminate inclusive Z   background

  39. Summary • Using unprecedented statistics for QCD and Electroweak processes, • the Tevatron experiments are providing: • Higher precision results that will help constraint future-generation • parton distribution function determinations • A view of higher x and Q2 processes than have ever been observed • Higher precision results that will help us understand backgrounds • to Higgs and new particle searches at the LHC • A view of low cross-section processes, like ZZ production, and associated • information on anomalous trilinear gauge couplings • And, as usual, stay tuned for new results emerging as we collect more data!

  40. Backup Slides

  41. Leading Order : PDF constraints with W/Z events Parton Distribution Functions (PDFs) describe the momentum distribution of partons in the (anti-)proton. They are obtained from parameterized fits to data (fits performed by CTEQ and MRST groups). Well constrained PDFs are essential for many measurements and searches at hadron colliders. probability of quark i to carry proton momentum fraction x PDF constraints from W/Z data: • Z rapidity • W charge asymmetry

More Related