Recent QCD and Electroweak Results from the Tevatron at Fermilab

Prof. Gregory Snow / University of Nebraska /D0On behalf of the CDF and D0 Collaborations

July 3, 2008

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• 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 pT

• Z/* forward-backward asymmetry• W mass

• ZZ production observed

More details of these and several other 2007-2008 QCD andelectroweak results are available on the public web pages of the experiments:http://www-cdf.fnal.govhttp://www-d0.fnal.gov

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Fermilab Tevatron Run II

• 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 6 fb-1 expected by April 2009

8 fb-1 by end of FY2010(D0 recorded > 90% of

delivered luminosity in 2008)

36x36 bunches396 ns bunch crossing

pp at 1.96 TeV

Main Injectorand Recycler

Tevatron

CDF D0

Flat means accelerator shutdowns

Run IIa

Run IIb

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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.

CDFD0

Luminositymonitorshere

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Luminosity DetectorLuminosity 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

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Luminosity DetectorLuminosity Detector

Two replacements of scintillator to date in Run IIdue to radiation damage

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inelastic(1.96 TeV) = 60.7 ± 2.4 mb, average of different experimentsused both by CDF and D0S. Klimenko, J. Konigsberg, T.M. Liss, FERMILAB-FN-0741 (2003)

)2()0(

1

/)2/(/ fLLffL

inelastic

eff

SSSSeff eeeP

dt

dNL

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.

Counting zeros techniqueCounting zeros technique

Probability of measuringno inelastic event in a beam crossing

Correction term for multiple interactionswhen separate single-sided hits mimic an inelasticinteraction

nd = non-diffractivesd = single diffractivedd = double diffractive

• Acceptances for different topologies from Monte Carlo• Material modeling important

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Determining the non-diffractive fractionDetermining the non-diffractive fractionfrom datafrom data

Compare data and Monte Carlo multiplicity distributions (i.e. calculate 2) for different values of fnd in MC at a given luminosity

fnd yielding minimum 2 matches data well

D0 determines luminosity with 6.1% uncertainty, with approx. equal contributions fromuncertainties on inelastic and [acceptances, fnd, fsd, fdd, andtime-dependent] ingredients of eff

CDF Luminosity DetectorsCDF Luminosity Detectors

CDF uses similar technique with similar uncertainty

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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

3s

Jets of particles originate from hard collisions between quark and gluons

fragmentation

partondistributio

n

partondistributio

n

Jet

Underlyingevent

Photon, W, Z etc.

Hard scattering

ISR FSR

p

p

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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

• 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”

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Jet Events at the Tevatron

Three jet event at D0

1st leading Jet (pT ~624 GeV)

2nd leading Jet (pT ~594 GeV)

3rd leading jet

Mjj=1.22 TeV

DØCDF

(at HERA)

LHCGeV)980(EGeV)980(E

pTeV1.96sp

Complementary to HERA and fixed target experiments

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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 binsFive y bins

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Inclusive Jet ProductionData favor lower edge of CTEQ 6.5 PDF band at high jet pT

Shape well described by MRST2004

DØ Data (and Uncertainty Correlations) available for PDF Fits

D0 results – submitted to PRL arXiv:/0802.2400 [hep-ex]

• Probe of gluon PDF contribution at large jet pT , i.e. high x• Experimental uncertainties now theory uncertainties

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Inclusive Jet ProductionDetailed 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)

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Exclusive Jet Production: Dijet MassCentral dijet production: implications for new physics

Limits set for excited quark, massivegluon and Z’/W’ scenarios

(see: http://www-cdf.fnal.gov/physics/exotic/r2a/20080214.mjj resonance 1b/)

NLO QCD predictionsdescribe data

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Photon ProductionDirect 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.

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Isolated Photon+X Cross Section Previous measurement (326 pb-1):

D0 Collab., Phys. Lett. B 639, 151 (2006)

• 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

• 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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Inclusive Photon+jet Production

Also fragmentation:

Dominant production at low pT(<120 GeV) is through Compton scattering: qg q+

+jet+X Event selection

• ||< 1.0 (isolated)

• pT > 30 GeV

• |jet| < 0.8 (central), 1.5 < |jet| < 2.5 (forward)

• pTjet> 15 GeV

4 regions: g.jet>0,<0, central and forward jets

• MET< 12.5 GeV + 0.36pT (cosmics, W e)

Probe PDF's in the range 0.007<x<0.8 and pT

=900 < Q2 < 1.6x105 GeV2

0804.1107 [hep-ex], Submitted to PLB

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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 pT

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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W + c-jet Production

s (90%) or

d (10%)

cc

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 pT>20 GeV, MET>20 GeV •|jet| < 2.5, pT

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 Q2

0802.2400 [hep-ex] Submitted to PLB – D0 Phys. Rev. Lett. 100, 091803 (2008) - CDF

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• Z rapidity (yZ) is dependant on x1,2

• A measurement of d/dy constrains PDFs

x1

x2

New 2.1 fb-1 CDF measurement (~170,000 Z ee events with |e| < 2.8 )

Z rapidity

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statistical errors only

Z rapidity

Forward and backward rapidities combined

The preferred theorycomparison

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• 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).

Z pT: QCD constraints

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• 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 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 pT

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• 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.

Z pT

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e+

e-

p p* p p*

FORWARD (F) : BACKWARD (B) :

e-

e+

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 sin2weff

cos* : in Collins-Soper frame (W rest frame)

Z/* Forward-Backward Asymmetry

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• Measurement consistent with the SM prediction (note: large MZ/* region sensitive to a new Z’ boson).

• sin2weff extracted from fit to AFB:

– 0.2327 0.0019 (DØ 1.1 fb-1)– 0.23152 0.00014 (current world average)

New 1.1 fb-1 DØ measurement (~36,000 Zee events with |e|<2.5 )

arXiv:hep-ph/0804.3220

Z/* Forward-Backward Asymmetry

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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

∆mW m

t2 ∆m

W ln(m

H/m

Z)

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

W mass

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W mass analysis scheme

mT 2pTl pT

(1 cosl )

Transverse plane

W e

Scheme: find MW for which the simulated mT corresponds best to the data

Since only pT is known

via missing ET, calculateW “transverse mass”, mT

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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

W mass template fits are created

for mT, transverse lepton

momentum/energy, and ET

mW

= 80GeV

mW

= 81 GeV

For template fits we need:

A fast simulator of W/Z production/decays

With calibrated detector simulation

PDFs, boson pT , EWK corrections

Contribution of backgroundsadded to the templates

mT template

+

+

W mass analysis scheme

Long, detailed analysis: Physical Review D paper is 48 pages long!

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Fits for the W mass - mT

Background contributions:Simulate using MC:

W EWK backgrounds (Z , decays)

W mass

W

W e

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The result and constraints

predicted Higgs mass: 76+33-24 GeV

MH < 144 GeV @ 95% CL

mW

= 80413 ± 34 MeV (stat) ± 34 MeV (sys)

= 80413 ± 48 MeV (stat + sys)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,

Electron and muonchannels combinedresult with 200 pb-1

W mass

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Outlook on W mass

MW ≈ 25MeV

2 fb-1

Can surpass the current world average

with a single measurement: MW

CDF < 25 MeV

Provided:

- detector aging

- averaging over longer data-taking period

- larger spread and higher average luminosity

do not deteriorate data quality

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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 byQCD multijets

e+e-, +-, or

CDF ZZ 4 candidate

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Brief summary of ZZ results

CDF (1.9 fb-1)In the 4 charged lepton channel, CDF observes 3 events with an expectedbackground of events.

Combining this with the ZZ ll channel, CDF observes an excess of eventswith 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.

092.0063.0096.0

7.06.04.1)(

ZZpp

.)(4.0.)(1.11.2)( sysstatZZpp

channel

Important selection cut ET > 35 GeVto eliminate inclusive Z background

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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!

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Backup Slides

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Leading Order :

dpp W / Z ll

[ f iq (x p ) f j

q (x p )i, ju,d ,s,(c,b ) f i

q (x p ) f jq (x p )]d

qq W / Z ll dx pdx p

PDF constraints from W/Z data:1) Z rapidity2) W charge asymmetry

PDF constraints with W/Z eventsParton 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