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 Luminosity measurements at D0 and CDF Jet and direct photon production W/Z + jets production W/Z properties Di-Boson production Outline Inclusive jets Dijet mass Inclusive direct photon Direct photon + jet W + jets Z + jets W + c-jets Z rapidity Z p T Z/  * forward-backward asymmetry W mass ZZ production observed More details of these and several other QCD and electroweak results are available on the public web pages of the experiments:

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

Flat means accelerator shutdowns Run IIa Run IIb

5 The CDF and D0 Detectors 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. CDF D0 Luminosity monitors here

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

8  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) σ eff = σ inelastic (f nd *A nd + f sd *A sd + f dd * A dd ) σ inel is the total inelastic cross-section f nd is the non-diffractive fraction and A nd is the acceptance, etc. Counting zeros technique 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 nd = non-diffractive sd = single diffractive dd = double diffractive Acceptances for different topologies from Monte Carlo Material modeling important

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

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

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

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 E T Split/merge after stable proto-jets found Jet Energy Scale: 2-3% at CDF 1-2% at D0 (after 7 years of hard work using MC tuned to data,  +jet & dijet event balance) Energy Resolution: unsmearing procedure using  /ET measured from dijet data. Midpoint cone algorithm (R=0.7) Main Systematics to Jet Measurements Compare data and theory at the “particle level”

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

14 Inclusive Jet Production 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 D0 Run II (L=0.7 fb-1) Six y bins Five y bins

15 Inclusive Jet Production Data favor lower edge of CTEQ 6.5 PDF band at high jet p T Shape well described by MRST2004 DØ Data (and Uncertainty Correlations) available for PDF Fits D0 results – submitted to PRL arXiv:/ [hep-ex]arXiv:/ [hep-ex] Probe of gluon PDF contribution at large jet p T, 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 Limits set for excited quark, massive gluon and Z’/W’ scenarios (see: resonance 1b/) NLO QCD predictions describe data

18 Photon Production Direct photons come unaltered from the hard sub-process Allows us to understand hard scattering dynamics ElectroMagnetic Shower Detection Shower Maximum Detector (CDF) Preshower EM Calorimeter EM shower with very little energy in hadronic calorimeter Geometric isolation No associated track R( , Jet) > 0.7 (cone jets, R = 0.7) Photon Identification Background Estimation Origins: Neutral mesons:  0,  + Instrumental: EM jets Shower shape quantities in NN to estimate purity.

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

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21 Inclusive Photon+jet Production Also fragmentation: Dominant production at low p T  (<120 GeV) is through Compton scattering: qg q+   +jet+X Event selection |   |< 1.0 (isolated) p T > 30 GeV |  jet | < 0.8 (central), 1.5 < |  jet | < 2.5 (forward) p T jet > 15 GeV 4 regions:  g.  jet >0,<0, central and forward jets MET< 12.5 GeV p T (cosmics, W e ) Probe PDF's in the range 0.007<x<0.8 and p T  =900 < Q 2 < 1.6x10 5 GeV [hep-ex] [hep-ex], Submitted to PLB

22 Inclusive Photon + jets Production Similar p T 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 p T  range) Data & Theory agree qualitatively A quantitative difference is observed in the central/forward ratios Need improved and consistent theoretical description for  +jet

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29 W + c-jet Production s (90%) or d (10%) c c W-W- 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(l )  isolated lepton p T >20 GeV, MET>20 GeV |  jet | 20 GeV Muon-in-jet with opposite charge to W is a c- jet candidate Systematic errors largely cancel in the ratio Background WZ, ZZ rarely produce charge correlated jets tt, tb, W+bc and W+b suppresed (small x-sec) 3.5  significance for W+c-jet Agreement with LO and s PDF evolved from larger Q [hep-ex] [hep-ex] Submitted to PLB – D0 Phys. Rev. Lett. 100, (2008) - CDF

30 Z rapidity (y Z ) is dependant on x 1,2 A measurement of d  /dy constrains PDFs x1x1 x2x2 New 2.1 fb -1 CDF measurement (~170,000 Z  ee events with |  e | < 2.8 ) Z rapidity

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

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

33 Z p T < 30 GeV region agrees well with ResBos (NLO QCD + CSS resummation with BNLY non-perturbative form factor). The Z p T distribution is predicted to broaden at small-x (large |y Z |) - important for the LHC! Broadening modeled with an additional “small-x” form factor from DIS HERA data. Data with |y Z | > 2 prefers ResBos without “small-x” form factor (NOTE: non-perturbative parameters have not been retuned with additional form factor!).  2 /dof= 11/11  2 /dof = 32/11 New 0.98 fb -1 DØ measurement (~64,000 Z  ee events with |  e | < 3.2 ) Z p T

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

35 e+e+ e-e- pp ** pp ** FORWARD (  F ) : BACKWARD (  B ) : e-e- e+e+ Z and Z/  * couplings to fermions have vector : d  /dcos  * ~ 1 + cos 2  * and axial-vector : d  /dcos  * ~ cos  * components. A FB = (  F -  B ) / (  F +  B ) A FB depends on M Z/  * A FB sensitive to sin 2  w eff cos  * : in Collins-Soper frame (W rest frame) Z/  * Forward-Backward Asymmetry

36 Measurement consistent with the SM prediction (note: large M Z/  * region sensitive to a new Z’ boson). sin 2  w eff extracted from fit to A FB : –  (DØ 1.1 fb -1 ) –  (current world average) New 1.1 fb -1 DØ measurement (~36,000 Z  ee events with |  e |<2.5 ) arXiv:hep-ph/ Z/  * Forward-Backward Asymmetry

37 Motivation for W mass measurements With improved precision also sensitive to possible exotic radiative corrections Radiative corrections (  r) dominated by top quark and Higgs loop, allowing a constraint on the Higgs mass ∆m W  m t 2 ∆m W  ln(m H /m Z ) The current m H constraint is limited by the uncertainty on m W To achieve a similar constraints on m H : ∆m W ≈ ∆m t Current ∆m t = 1.4 GeV corresponds to ∆m W = 8 MeV W mass

38 W mass analysis scheme Transverse plane W  e Scheme: find M W for which the simulated m T corresponds best to the data Since only p T is known via missing E T, calculate W “transverse mass”, m T

39 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 1515 W mass template fits are created for m T, transverse lepton momentum/energy, and E T m W = 80GeV m W = 81 GeV For template fits we need: A fast simulator of W/Z production/decays With calibrated detector simulation PDFs, boson p T, EWK corrections Contribution of backgrounds added to the templates m T template + + W mass analysis scheme Long, detailed analysis: Physical Review D paper is 48 pages long!

40 Fits for the W mass - m T Background contributions: Simulate using MC: W EWK backgrounds (Z,  decays) W mass W   W  e

41 The result and constraints predicted Higgs mass: GeV M H < % CL m W = ± 34 MeV (stat) ± 34 MeV (sys) = ± 48 MeV (stat + sys) Most precise single measuement ! Influence on world average: Central value:  MeV Uncertainty: -15% (29 to 25 MeV) With m t =(170.9 ± 1.8) GeV, Electron and muon channels combined result with 200 pb -1 W mass

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

43 Di-boson Production 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 Today ZZ branching fractions 4 charged leptons very clean (*) ll x 6 BR, but backgrounds difficult (*) CDF and D0 have 2008 results in both Leading order ZZ diagram * * Overwhelmed by QCD multijets e + e -,  +  -, or

CDF ZZ  4  candidate

45 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  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 E T > 35 GeV to eliminate inclusive Z   background

46 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 Q 2 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!

47 Backup Slides

48 Leading Order : PDF constraints from W/Z data: 1)Z rapidity 2)W charge asymmetry 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