christopher neu on behalf of the cdf and d collaborations
DESCRIPTION
W/Z + Jets and W/Z + Heavy Flavor Jets at the Tevatron. Christopher Neu on behalf of the CDF and D Collaborations XLIIIrd Rencontres de Moriond QCD and High Energy Interactions 12 March 2008 La Thuile - Aosta Valley, Italy. Outline:. Importance of W/Z + jets - PowerPoint PPT PresentationTRANSCRIPT
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 Page 22
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’
q’
q
q(’)
q(‘)
q
Christopher NeuChristopher Neu Page Page 33
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
Christopher NeuChristopher Neu Page Page 44
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
W+jets signalFake W bkgdReal W bkgd
W+jets signalFake W bkgdReal W bkgd
S/B ~ 10/1
S/B ~ 1.2/1
Christopher NeuChristopher Neu Page Page 55
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.
WW + Inclusive Jets + Inclusive Jets
MLM : ALPGEN (LO) +
Herwig (shower) +
MLM matchingSMPR : MadGraph (LO)
+ Pythia (shower)
+ CKKW matching
MCFM : MCFM (NLO)
Christopher NeuChristopher Neu Page Page 66
Total cross section for jet multiplicity, Total cross section for jet multiplicity, nn: :
25;jet nTn EneW
PRD 77, 011108(R)
WW + Inclusive Jets + Inclusive Jets
MLM : ALPGEN (LO) +
Herwig (shower) +
MLM matchingSMPR : MadGraph (LO)
+ 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.
Christopher NeuChristopher Neu Page Page 77
WW + Inclusive Jets + Inclusive Jets
• 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) +
MLM matchingSMPR : MadGraph (LO)
+ 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.
Christopher NeuChristopher Neu Page Page 88
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)
Christopher NeuChristopher Neu Page Page 99
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)
Christopher NeuChristopher Neu Page Page 1010
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
Christopher NeuChristopher Neu Page Page 1111
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
Christopher NeuChristopher Neu Page Page 1212
W/Z H production
top pair production s-channel single top
W/Z W/Z
ℓ / ,ℓ
/ , ℓ
Christopher NeuChristopher Neu Page Page 1313
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
Christopher NeuChristopher Neu Page Page 1414
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 )
Christopher NeuChristopher Neu Page Page 1515
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.
Christopher NeuChristopher Neu Page Page 1616
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
Christopher NeuChristopher Neu Page Page 1717
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.
Christopher NeuChristopher Neu Page Page 1818
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.
Christopher NeuChristopher Neu Page Page 1919
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
Christopher NeuChristopher Neu Page Page 2020
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.
Christopher NeuChristopher Neu Page Page 2121
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
Christopher NeuChristopher Neu Page Page 2222
Backup SlidesBackup Slides
Christopher NeuChristopher Neu Page Page 2323
WW + Inclusive + Inclusive JetsJets
MLM : ALPGEN (LO) +
Herwig (shower) +
MLM matchingSMPR : MadGraph (LO)
+ Pythia (shower)
+ CKKW matching
MCFM : MCFM (NLO)
Christopher NeuChristopher Neu Page Page 2424
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
Christopher NeuChristopher Neu Page Page 2525
WW + + b-b-JetsJets