christopher neu on behalf of the cdf and d collaborations

Christopher Neu

on behalf of the CDF and D Collaborations

XLIIIrd Rencontres de Moriond

QCD and High Energy Interactions12 March 2008

La Thuile - Aosta Valley, Italy

W/Z + Jets and W/Z + Heavy Flavor Jets

at the Tevatron

• Importance of Importance of W/Z W/Z + + jetsjets

• Recent Tevatron Recent Tevatron progressprogress

• Summary and futureSummary and future

Outline:Outline:

Christopher NeuChristopher Neu Page 2

Importance of Importance of W/ZW/Z + Jet Physics + Jet Physics

Result (1/fb) D CDFW+jets -- 0.320Z+jets 0.950 1.700

W+b-jets 0.382 1.900Z+b-jets 0.152 2.000W+c-jets 1.000 1.800Z+c-jets -- --

• Important tests of Quantum Important tests of Quantum Chromodynamics (QCD)Chromodynamics (QCD)

• Recent LO and NLO Recent LO and NLO simulations need simulations need experimental verificationexperimental verification

• Signature shared with top Signature shared with top production, Higgs, other production, Higgs, other searches at Tevatron, LHCsearches at Tevatron, LHC

Why study W/Z +jet production?Why study W/Z +jet production?

V=W or Z

V

V

q

q

q’

qq

q’

q

q(’)

q(‘)

q


The CDF and DThe CDF and D Experiments Experiments

• Charged particle tracking in magnetic fieldCharged particle tracking in magnetic field• Electromagnetic and hadronic calorimetryElectromagnetic and hadronic calorimetry• Muon detectionMuon detection• Luminosity monitoring Luminosity monitoring • Three level event triggerThree level event trigger

Common features:Common features:

22 )()(

)2

ln(tan

angleazimuthal

R


WW + Inclusive Jets + Inclusive Jets

• WW selection: selection: seek seek WW e e – ee: E: ET T > 20 GeV, |> 20 GeV, || < 1.1| < 1.1

: missing energy MET: missing energy MET > 30 GeV> 30 GeV

– MMT T ((WW) > 20 GeV/c) > 20 GeV/c22

• Jet definition: Jet definition: – Corrected ECorrected ETT > 20 GeV, | > 20 GeV, || < 2.0| < 2.0

– Cone algorithm, R= 0.4Cone algorithm, R= 0.4

Fake W bkgd

Real W bkgd

W+jets signal

W+jets signalFake W bkgdReal W bkgd



S/B ~ 10/1

S/B ~ 1.2/1


Total cross section for jet multiplicity, Total cross section for jet multiplicity, nn: :

25;jet nTn EneW

PRD 77, 011108(R)

NLO prediction more NLO prediction more accurate than LO!accurate than LO!

Relative rates within each Relative rates within each prediction consistent with prediction consistent with

data.data.


MLM : ALPGEN (LO) +

Herwig (shower) +

MLM matchingSMPR : MadGraph (LO)

+ Pythia (shower)

+ CKKW matching

MCFM : MCFM (NLO)


Total cross section for jet multiplicity, Total cross section for jet multiplicity, nn: :

25;jet nTn EneW

PRD 77, 011108(R)


MLM : ALPGEN (LO) +

Herwig (shower) +


+ Pythia (shower)

+ CKKW matching

MCFM : MCFM (NLO)

Can examine differential cross sections within each multiplicity bin….

NLO prediction more NLO prediction more accurate than LO!accurate than LO!

Relative rates within each Relative rates within each prediction consistent with prediction consistent with

data.data.



• LO calculation procedure: Generate LO calculation procedure: Generate ppppWW+N partons at tree +N partons at tree level, ignore loop corrections, employ parton showerlevel, ignore loop corrections, employ parton shower

• Ambiguities arise:Ambiguities arise:– Possibility for double counting if NPossibility for double counting if Npartonparton N Njetjet

– SMPR and MLM refer to algorithms for avoiding/removing overlapsSMPR and MLM refer to algorithms for avoiding/removing overlaps

PRD 77, 011108(R)

MLM : ALPGEN (LO) +

Herwig (shower) +


+ Pythia (shower)

+ CKKW matching

MCFM : MCFM (NLO)

W+2 jets

At LO, At LO, MadGraph+Pythia+CKKW MadGraph+Pythia+CKKW

provides better performance.provides better performance.


Z /Z /** + Inclusive Jets + Inclusive Jets• Validity of NLO predictions Validity of NLO predictions

borne out in borne out in Z /Z /**+jets? +jets?

• Z /Z /* * selectionselection: seek : seek Z Z //**ee++ee--

– Two ETwo ETT > 25 GeV electrons > 25 GeV electrons

– 66 < M66 < Meeee < 116 GeV/c < 116 GeV/c22

• Jet definition:Jet definition:– Corrected pCorrected pTT > 30, |y| < 2.1 > 30, |y| < 2.1

– Cone algorithm w/ R=0.7Cone algorithm w/ R=0.7

• Major backgrounds: S/B ~ Major backgrounds: S/B ~ 7/17/1– QCD multijetsQCD multijets– W W + jets+ jets– ttbar, dibosonttbar, diboson– Z+Z+, , ZZ

z

z

pE

pEy ln

2

1

NLO prediction once againNLO prediction once againmore accurate than LO!more accurate than LO!

Can’t see the NLO prediction points -

close overlap with data!

hep-ex/0711.3717 (Submitted to PRL)


Z /Z /** + Inclusive + Inclusive JetsJets

• Differential cross Differential cross section:section:– No LO comparison No LO comparison

herehere

NLO predictionNLO prediction

reliable – as reliable – as ininWW+jets+jets

• Analysis would benefit Analysis would benefit from increased from increased statistics to further statistics to further populate the populate the ZZ++2-2-jets sample jets sample

• NLO for NLO for ZZ++3-jets 3-jets would be valuable as would be valuable as well.well.

hep-ex/0711.3717 (Submitted to PRL)


Z /Z /** + Inclusive + Inclusive JetsJets

• DD Z /Z /*(*(eeee)+jets analysis: 950)+jets analysis: 950/pb/pb• Purpose here: Purpose here: compare Pythia compare Pythia ((ppppWW+1+ internal PS) +1+ internal PS) and Sherpa and Sherpa

((ppppWW+N+ internal PS + CKKW matching) +N+ internal PS + CKKW matching) event generatorsevent generators– Test of different prediction techniquesTest of different prediction techniques– Some confidence in CKKW from CDF Some confidence in CKKW from CDF WW+jets LO studies…true here as well?+jets LO studies…true here as well?

Pythia Sherpa


Z /Z /** + Inclusive Jets + Inclusive Jets

Sherpa + CKKW represents data better than Pythia Sherpa + CKKW represents data better than Pythia - p- pTT of jet 1,2,3 of jet 1,2,3 - Z p- Z pTT, Jet multiplicity, Jet multiplicity- - (jet, jet), (jet, jet)

Not unexpected given Not unexpected given the nature of Pythia’s the nature of Pythia’s

calculation.calculation.

Pythia Sherpa

Summary so far…Summary so far…• W/ZW/Z+1,2 jet +1,2 jet NLO predictionsNLO predictions from MCFM from MCFM look reliablelook reliable• NLO predictions NLO predictions not yet in hand not yet in hand for for W/ZW/Z++3 jet 3 jet • Technique of calculating/generating Technique of calculating/generating ppppWW+N+ parton shower + +N+ parton shower +

matching matching scheme (ala ALPGEN, MadGraph, Sherpa) scheme (ala ALPGEN, MadGraph, Sherpa) superior to superior to Pythia+PS alonePythia+PS alone

• Differences among available tools still need to be understoodDifferences among available tools still need to be understood

• W/ZW/Z + heavy flavor ( + heavy flavor (b,cb,c) jets also) jets also

importantimportant– background to top, Higgs, others background to top, Higgs, others – WW++cc production has unique features production has unique features


W/Z H production

top pair production s-channel single top

W/Z W/Z

ℓ / ,ℓ

/ , ℓ


TaggingTagging:: bb’s and Non-’s and Non-bb’s’s

Primary vertex

Secondary vertex

Primary vertex

Tagging of real b jet:

long lifetime+large boost =

secondary vertex

Spurious tagging of light

flavor jet:

“mistag”

Displacedtracks

Prompttracks

Displacedtracks

Prompttracks

Secondary vertex

L2d > 0

L2d<0

Tag efficiency for b jets

Tag efficiency for u/d/s/g jets

Jet ET (GeV)

Jet ET (GeV)

Fra

cti

on

al

F

racti

on

al

WW + + bb-Jets-Jets

• Goals: Goals: – Measure Measure W+bW+b-jet production -jet production

cross section cross section – Use measurement to improve Use measurement to improve

background estimate for Higgs background estimate for Higgs

searchsearch

• WW and jets selection here similar to and jets selection here similar to

WW + inclusive jets analysis + inclusive jets analysis– key difference: 1 or 2 jets onlykey difference: 1 or 2 jets only

• Here we need to identify jets thatHere we need to identify jets that

are likely are likely bb’s (via ’s (via high purity high purity

taggingtagging) and determine how many ) and determine how many

are really are really bb’s via ’s via vertex mass:vertex mass:- invariant mass of charged particle - invariant mass of charged particle

tracks in secondary vertextracks in secondary vertex


Vertex Mass Shapes

= u/d/s/g

MMB-hadronsB-hadrons > M > MC-hadronsC-hadrons > M > MLF-hadronsLF-hadrons

soso

MMbb vert vert > M > Mcc

vert vert > M > MLFLFvertvert

From simulation

WW + + b-b-JetsJets

• Largest backgrounds: Largest backgrounds: S/B ~ S/B ~ 3/13/1– ttbar (40% of total bkgd)ttbar (40% of total bkgd)– single top (30%)single top (30%)– Fake Fake W W (15%)(15%)– WZ WZ (5%)(5%)– Total contribution: ~Total contribution: ~180 tagged 180 tagged bb

jetsjets

• Result: Result:

xxBR = 2.74 BR = 2.74 0.27 0.27 (stat)(stat) 0.42 0.42 (syst) (syst) pbpb

• Prediction: Prediction:

xxBR = 0.78 pbBR = 0.78 pb (ALPGEN )(ALPGEN )


This cross section is for b jets from W+b-jet production in events with a high pT central lepton, high pT neutrino and 1 or 2 total jets.

~1000 tagged jetsamong which ~700 are

consistent with coming from a b quark

New result!New result!x3.5 mismatchx3.5 mismatch

High purity b-tagging at

work!

NB:

Publication in preparation.


ZZ + + b-b-JetsJets• Similar CDF analysis for Similar CDF analysis for Z+bZ+b-jets: 2/fb-jets: 2/fb

• Utilize Utilize ZZ ee ee and and • Similar jet definition Similar jet definition

– Corrected ECorrected ET T > 20 GeV, |> 20 GeV, || < 1.5| < 1.5

– Cone algorithm with R=0.7Cone algorithm with R=0.7– Secondary vertex tagsSecondary vertex tags

• Differential cross Differential cross sections with sections with comparisons to LO, comparisons to LO, NLO predictionsNLO predictions

• Dividing by Dividing by (Z) puts (Z) puts LO, NLO on equal LO, NLO on equal footingfooting

• Pythia does a good job Pythia does a good job at low jet ETat low jet ET


ZZ + + b-b-JetsJets

• ALPGEN (LO) and MCFM ALPGEN (LO) and MCFM (NLO) undershoot data in (NLO) undershoot data in several bins several bins

• Pythia surprisingly on target Pythia surprisingly on target in some regimes – LO in some regimes – LO predictions are in other predictions are in other analyses low (eg, Z+jets).analyses low (eg, Z+jets).

Publication in preparation.


W/ZW/Z + + b-b-Jets: SummaryJets: Summary

CDF Data PythiaALPGEN Herwig NLONLO(corr'd)

(Z+b jet) (pb) 0.9 - - - 0.51 0.53(Z+b jet)/(Z) (%) 0.34 0.35 0.21 0.21 0.21 0.23(Z+b jet)/(Z+jet) (%) 2.11 2.18 1.45 1.24 1.88 1.77(W+b jet) (pb) 2.7 - 0.8 - - -

• More studies for More studies for W+bW+b-jets are forthcoming-jets are forthcoming

• Need to understand NLO predictionsNeed to understand NLO predictions₋ In In Z+bZ+b-jets it is strange that the NLO prediction -jets it is strange that the NLO prediction

undershoots dataundershoots data₋ Borne out in Borne out in W+bW+b-jets?-jets?

Raw NLO predictions

corrected forunderlying event

and hadronization effects.


WW + Single + Single cc Production Production

• W+single W+single c c production uniqueproduction unique– no no WW+single +single bb analogue at Tevatron analogue at Tevatron

• Exploit feature: Exploit feature: charm semileptonic charm semileptonic daughter and daughter and WW have opposite charge have opposite charge

c

c

W-

s (90%) or

d (10%)

μ

Different tagging algorithm:Soft Muon Identification

used to identify charm hadron decays!

• Result:Result:xxBR = 28.5 BR = 28.5 8.2 8.2 (stat)(stat) 4.4 4.4 (syst) (syst) 1.7 1.7 (lum)(lum) pbpb

• Prediction: Prediction: ALPGENALPGEN

xxBR = 22.2 BR = 22.2 1.2 1.2 (PDF)(PDF) 3.8 3.8 (scale) (scale)

pbpb

Good agreement!Good agreement!

hep-ex/0711.2901 - submitted to PRL


WW + Single + Single cc Production Production

• Similar analysis Similar analysis completed at Dcompleted at D: 1/fb: 1/fb

• Measures Measures

which can be compared which can be compared to the LO prediction: to the LO prediction:

0.040 0.040 0.003 0.003 (PDF)(PDF)

017.0071.0)(

)-single(

jetsW

cW

LO prediction reasonably good. Impact of systematic errors Impact of systematic errors

drawn on theory curve.drawn on theory curve.

Statistical uncertainty drawn for Statistical uncertainty drawn for data points .data points .Publication in

preparation.


ConclusionsConclusions

• W/Z + jets physics plays an W/Z + jets physics plays an important roleimportant role in current collider in current collider physics programs physics programs

• Current NLO predictions for W/Z + Current NLO predictions for W/Z + look to be look to be accurateaccurate, higher , higher multiplicities desirablemultiplicities desirable

• W/ZW/Z+b-jets+b-jets studies have indicated studies have indicated deficiencies in both LO and NLO deficiencies in both LO and NLO predictions; predictions; more study and more more study and more data is needed data is needed

• WW+single +single c c studies indicate studies indicate good good agreement agreement with LO predictionswith LO predictions


Backup SlidesBackup Slides


WW + Inclusive + Inclusive JetsJets

MLM : ALPGEN (LO) +

Herwig (shower) +


+ Pythia (shower)

+ CKKW matching

MCFM : MCFM (NLO)


Identifying Identifying bb Jets Jets

• BB hadron lifetime hadron lifetime: ~1.5 ps: ~1.5 ps– Large boost (v ~ 0.95Large boost (v ~ 0.95cc) )

means the means the BB lifetime is long lifetime is long in the lab framein the lab frame

– BB travels macroscopic travels macroscopic distance before decaying distance before decaying which we can detectwhich we can detect

• Exploit the long lifetime - Exploit the long lifetime - – Reconstruct charged particle Reconstruct charged particle

tracks tracks – See if they intersect at a See if they intersect at a

common point common point – Require the common point Require the common point

be significantly displaced be significantly displaced from the primary p-p from the primary p-p collision pointcollision point

Long-lifetime yields secondary decay

vertex“b-tagging”

L2d

Displacedtracks

d0

Primary vertex,aka p/pbar collision point

Prompttracks

Secondary vertex

Meaning Typical Resolution

d0 Track impact parameter 150um 40um

L2d Vertex displacement 2-3mm 100um


WW + + b-b-JetsJets

christopher neu on behalf of the cdf and d collaborations

Documents

mcfm nlo w

gevmt w

z cjets

w bjets0

z jets0

w inclusive jetsw selection

w cjets1

jets sample nlo