Searches for diboson production at the Tevatron in final states containing heavy-flavor jets

0.79 MB·English

by  Jean-Francois Grivaz

Searches for diboson production at the Tevatron
in final states containing heavy-flavor jets
Jean-Franc¸oisGrivaza
Laboratoiredel’Acce´le´rateurLine´aire(Orsay,France)
OnbehalfoftheCDFandD0Collaborations.
2
1
0 Abstract. RecentsearchesperformedbytheCDFandD0collaborationsattheTevatronfordibosonproduction
2 in final states containing heavy-flavor jets are reported. The searches for WZ and ZZ can be regarded as the
ultimatebenchmarkforthecorrespondingsearchesforalow-massHiggsbosonintheWHandZHfinalstates.
n
Using the exact same techniques as for those Higgs boson searches, the D0 collaboration measured a cross
a
sectionforWZ/ZZproductionof1.13±0.36timesitsexpectationinthestandardmodel,withadibosonsignal
J
significanceof3.3standarddeviations(2.9expected).
7

]
x 1 Introduction areused,chosenbasedonsomeoptimizationofthesearch
e sensitivity but also on the analyzers’ expertise: Artificial
-
p Dibosonproductioninpp¯(orpp)collisionsathighenergy NeuralNetworks(NN),SupportVectorMachines(SVM),
e is a topic of interest in its own right. Since new physics BoostedDecisionTrees(BDT),RandomForests(RF).The
h could manifestitself differentlyin differentfinal states, it final discriminants are subjected to a statistical analysis
[ isimportantthatcorrespondinganalysesbeperformed.At basedontheLog-LikelihoodRatio(LLR)betweentheback-
1 theTevatron,dibosonproductionhasbeenobservedfirstin ground-onlyandthesignal+backgroundhypotheses,with
v fullyleptonicandlaterinsemileptonicfinalstates[1].With marginalizationoverallnuisanceparameterpriors.
0 thelargeintegratedluminositynowavailable,togetherwith Thiswholesequenceofanalysisprocedures,designed
5 improved analysis techniques, it has become possible to to reach sensitivity to a tiny Higgs boson signal in the
5 studydibosonproductioninfinalstatescontainingheavy- presence of large backgrounds, and therefore apparently
1 flavor(HF)jets.Anadditionalinterestforthistopicisthat quiteinvolved,wouldlargelybenefitintermsofreliability
.
1 such final states are encountered almost identically for a frombeingvalidatedthroughtheobservationofasimilar,
0 low-massHiggsbosonproducedinassociationwithavec- butknownsignal.Thesearchfordibosonproductionwith
2 tor boson. It is this aspect of diboson production at the Z → bbinthefinalstatefulfillstheserequirements.Con-
1 Tevatronthatisthefocusofthispresentation. sider a Higgsbosonwith a mass of 115 GeV. In the final
:
v Thesearchesforalow-massHiggsbosonin pp¯ colli- statesofinterest,theproductioncrosssectionsin pp¯ colli-
Xi sions have already been reviewed at this conference [2]. sionsat1.96TeVare:
Therefore, only a brief summary of the methodology is – 27fbforWH →ℓνbbwithℓ=eorµ,
r
a givenhere.TherelevantproductionmodesareW(→ℓν)H, – 5fbforZH →ℓℓbbwithℓℓ=eeorµµ,
Z(→ ℓℓ)H,and Z(→ νν)H, with ℓ an electronor a muon – 15fbforZH →ννbb,
and H → bb. After a trigger selection based on isolated
leptonsand/ormissingtransverseenergy(asexpectedfrom for a total of 46 fb. Replacing H → bb by Z → bb, the
neutrinosin the final state), simple kinematicand lepton- correspondingcrosssectionsare
identificationcriteriaareappliedtoreducetheinitialsam-
– 105fbforWZ →ℓνbbwithℓ=eorµ,
ple to a manageable level without significant signal loss;
– 24fbforZZ →ℓℓbbwithℓℓ=eeorµµ,
thebulkoftheremainingbackgroundoriginatingfrommul-
– 73fbforZZ →ννbb,
tijet (MJ) production is removed either by further kine-
matic criteria, or, more frequently in recent searches, by foratotalof202fb.Thesecrosssectionsfordibosonpro-
makinguseofsomemultivariateanalysistechnique(MVA); ductionareseentobeabout4.5timeslargerthanthecorre-
thesampleisthenenrichedinHFjetsthroughtheapplica- spondingonesfora115GeVmassHiggsboson.Itshould
tionofa“b-tagging”algorithm,andoftendividedintosub- however be kept in mind that the dijet mass resolution
samplesaccordingtothenumberofb-taggedjetsandtothe of the CDF and D0 detectors is not sufficient to separate
level of b purity of those tagged jets; final discriminants the W and Z dijet mass peaks, so that WW → ℓνcs is
are constructed for each of these sub-samples, in which a significant resonant background.Furthermore, the non-
advantage is taken of the kinematic differences between resonant(W/Z)bb and (W/Z)cc backgroundsand their re-
the signal and the remaining backgrounds, most impor- latedsystematicuncertaintiesaresubstantiallylargerthan
tantly (W/Z)bb, which is irreducible. A variety of MVAs for a Higgs boson with a mass 25 GeV above that of the
Z boson.Ontheotherhand,thereisrelativelymoresignal
a e-mail:[email protected] contributionfromZ → ccthanfromH → cc.Altogether,
EPJWebofConferences
CDF Run II Preliminary ( 7.5 fb-1 ) 7 9000 DØ 4.3 fb-1, 0 b-tag Data
Number of events122505000 Tight Leptons, Single Tag Events CnTssZMWWW--oojDittebccspnooFtcjbtsLwppa DJ g((ast-t-cachh)) Events / 0.041 45678000000000000000 WWWWTMUonuWZ//pZZclet++irjLHte.tPFs
ZZ 3000
100 WW
WZ 2000
1000
50
0
0 0.10.20.30.40.50.60.70.80.9 1
020 40 60 80 100 120 140 160 180 200 RF Output
M (jet1, jet2) GeV/c2
inv
3 6000 DØ 4.3 fb-1, 1 b-tag Data
Fig. 1. Dijet mass in the 1-tag channel of the CDF search for 83 WW
0 5000 WZ
W(W/Z)[4]. 0. W/Z+LP
s / 4000 WTo/pZ+HF
the observation of (W/Z)(Z → bb), using the same tech- vent 3000 MUnucletirjte.ts
E
2000
niquesasinthesearchesforalow-massHiggsboson,can
beconsideredastheultimatebenchmarkforthosesearches 1000
attheTevatron.
0
0 0.10.20.30.40.50.60.70.80.9 1
A total of eight conference notes or publications rel-
RF Output
evant to diboson production at the Tevatron with HF jets
in the final state were made available for this conference 7 1400 DØ 4.3 fb-1, 2 b-tag Data
6 WW
bytheCDFandD0collaborations.Theanalysesuseinte- 1 1200
gratedluminositiesrangingfrom4.3to8.4fb−1.Forrefer- s / 0. 1000 WWWZ//ZZ++LHPF
ence,thecrosssectionsusedbytheTevatronHiggsCom- nt 800 Top
e Multijets
binationWorkingGroupforinclusivedibosonproduction v
E 600 Uncert.
are:11.34pbforWW,3.22pbforWZ,and1.20pbforZZ;
theywereobtainedwithmcfm[3]atnext-to-leadingorder. 400
200
0
0 0.10.20.30.40.50.60.70.80.9 1
2 Towards the benchmark RF Output
Fig.2.Finaldiscriminantinthe0-,1-,and2-tagchannelsofthe
2.1 W(W/Z)inℓν+HF D0searchforW(W/Z)[5].
TheCDFcollaborationperformedasearchfor(W → ℓν)
(W/Z)production,wherethe(W/Z)decaystoHFjets[4]. chosento define0-,1-,and2-tagsamples, wherethetwo
Thisanalysisusesanintegratedluminosityof7.5fb−1.The jetswithlargest pT (leadingjets)areconsideredforbtag-
basic selection criteria are: a lepton (e or µ) with p > ging. But the actual values of the tightest operatingpoint
T
20 GeV, missing E (MET) > 20 GeV, and exactly two passedbyeachjetareusedamongthe15inputsofthefinal
T
jets with p > 20 GeV and |η| < 2. The bulk of the MJ discriminant,arandomforest.TheRFoutputsinthethree
T
backgroundisrejectedbyanSVM,andtheremainingMJ b-tagchannelsareshowninFig.2,fromwhichaW(W/Z)
andW+jetsnormalizationsareobtainedfromatemplatefit productioncrosssection of1.2±0.2timesitsSM expec-
to the METdistribution.Alleast onejetis requiredto be tationisobtained,holdingtheWW/WZproductionratioto
b-tagged by a secondary vertex algorithm. The final dis- its SM value. The signal significance is 8.0 s.d. (6.0 ex-
criminants used are the dijet mass in the 1-tag and 2-tag pected).Morerelevantforthepurposeofthispresentation
channels,ofwhichanexampleisshowninFig.1.Asignal istheresultobtainediftheWWproductioncrosssectionis
crosssection of 1.1+03 times its standardmodel(SM) ex- constrainedtoitsSMvaluewithinitsuncertaintyof7%:a
−04
pectationisobtained,holdingtheWW/WZ productionra- crosssectionof1.3±0.6timesitsSMexpectationforWZ
tiotoitsSMvalue.Thesignificanceofthedibosonsignal production,andasignificanceof2.2s.d.(1.2expected)for
is3.0standarddeviations(s.d.)fromthebackground-only theWZsignal.
hypothesis(3.0expected).Inthisanalysis,however,most
ofthesensitivityisactuallycomingfromWW production
inthe1-tagchannel,withW →cs. 2.2 Z(W/Z)inℓℓ+HF
TheD0collaborationperformedasearchforthissame
final state [5], using an integrated luminosity of 4.3 fb−1. The CDF collaborationperformeda search for (Z → ℓℓ)
The basic selection criteria are: an electron (muon) with (W/Z) production,wherethe(W/Z)decaystoHFjets[6].
p > 20(15) GeV , MET > 20 GeV, and at least two Thisanalysisusesanintegratedluminosityof6.6fb−1.The
T
jets with p > 20 GeV and |η| < 2.5. To reject most of basic selection criteria are: an ee or µµ lepton pair with
T
the MJ background,a so-called “triangle cut” is applied: p (ℓ)>20GeV,76<m <106GeV,andatleasttwojets
T ℓℓ
m > 40GeV−0.5MET,wherem isthetransversemass with p >20GeVand|η|<2.Theoriginalityofthisanal-
T T T
oftheleptonandthemissingE .Twelveoperatingpoints ysis is that it uses, after b-tagging to separate heavy and
T
aredefinedfortheD0b-taggingalgorithm,corresponding lightflavorjets,anewquark-gluondiscriminanttosplitthe
to an increasing b purity. The loosest operating point is light-flavorsampleintoaquark-richandagluon-richsam-
HadronColliderPhysicssymposium(HCP-2011)
ple.Thefinaldiscriminantisthedijetmassineachofthe
three sub-samples so defined. The analysis howeverdoes
not have (yet) enough sensitivity for the observationof a
diboson signal, and only a 95% C.L. upper limit of 1.3
timestheSMexpectationforZ(W/Z)productionhasbeen
set(2.3expected).
2.3 (W/Z)Z inMET+HF
TheCDFcollaborationperformeda searchfor(W → ℓν/
Z → νν)Z production,wheretheZ decaysto HFjets[7].
Thisanalysisusesanintegratedluminosityof5.2fb−1.The
basicselectioncriteriaare:MET>50GeV,supplemented
witharequirementonthemissingE significance,atmost
T
onelepton(eorµ),andatleasttwojetswith p >20GeV
T
and|η| < 2.ThebulkoftheMJbackgroundisrejectedby
therequirementthattheazimuthalanglebetweenthemiss-
ing E and any jet be larger than 0.4 radians. The shape
T
of the remaining MJ background is taken from events in
whichtheazimuthalanglebetweenthemissingE andthe
T
missing p , the formercalculatedfromcalorimeterinfor-
T
mationandthelatterfromchargedparticletracks,islarger
thanoneradian.Theremainingsampleisdividedintotwo
sub-samples, one with zero or one b-tagged jet, and the
otherwithtwob-taggedjets. Thefinaldiscriminantisthe
dijet mass in each of those two sub-samples, as shown
in Fig. 3. The results are obtained with the WW produc-
tion cross section fixed to its SM value, within its uncer-
tainty,andwiththeWZ/ZZratiofixedtoitsSMvalue.The
normalizationofthe(W/Z)+jetsbackgroundisallowedto
floatindependentlyinthetwosub-samples.Asignalcross
section of 1.1+07 times its standard model expectation is
−06
obtained.Thesignificanceofthedibosonsignalis1.9s.d.
(1.7 expected). Because this analysis accepts events with
Fig.3.Dijetmassinthe(0+1)-and2-tagchannelsof theCDF
zerooronelepton,bothWZandZZproductioncontribute
searchfor(W/Z)Z[7].
tothesensitivity.
assess the signal significance, next translated into Gaus-
3 The ultimate benchmark sianstandarddeviations.Theconsistencyoftheresultwith
thestandardmodelwasdeterminedinasimilarway,using
ThefollowingmutuallyexclusiveanalysesbytheD0col- signal+backgroundpseudo-experiments.Unlessotherwise
laborationare exactcopies of the correspondingsearches specified,theratiooftheWZandZZproductioncrosssec-
for a low-mass Higgs boson. The only changes are the tionswasheldfixedtoitsSMvalue.
MVAtrainings,inwhichthesignalisnowWZ/ZZinstead
ofWH/ZH,whileWW remainsabackground.
In each of the analyses, fits of the nuisance parame-
3.1 WZ inℓν+HF
ters were performed to the final discriminant outputs in
all sub-channels, with systematic uncertainties correlated
across signal and backgrounds as appropriate. The main TheD0collaborationperformedthissearchinadatasam-
sourcesofuncertaintyare:theratioofheavytolightflavor plecorrespondingtoanintegratedluminosityof7.5fb−1[8].
production in (W/Z)+jets; the various object reconstruc- An isolated lepton (e or µ), missing E , and two or three
T
tion and identification efficiencies; the jet energy calibra- jetsarerequired.TheMJbackgroundisrejectedbya“tri-
tion and resolution; the b-tagging efficiency and the rate angle cut” in the muon channel and using a BDT in the
of wrongly tagged light-flavor jets. Three kinds of fits to electron channel. The sample is split into a 1-tag and a
the data were performed: in one of them, the signal rate 2-tag sub-sample, based on the loosest b-tagging operat-
was also fitted, and the diboson production cross section ingpointasintheD0analysisreportedinSec.2.1.Asin
was thereforemeasured;in the other ones, the signalrate thatsameanalysis,theremainingb-tagginginformationis
was set either to zero (background-onlyhypothesis)or to usedin thefinaldiscriminant,aBDT with14inputs.The
itsSMvalue(signal+backgroundhypothesis),fromwhich BDT outputin the2-tagchannelisshowninFig.4 (top).
the observedLLR was deduced.These fits were repeated Asignalcrosssectionof1.6±0.8timesitsstandardmodel
on pseudo-experiments, and the fraction of background- expectationisobtained,withasignificanceof2.2s.d.(1.4
onlypseudo-experimentsyieldingacrosssectionvalueat expected).TheobservedLLRiscomparedtoexpecteddis-
least as large as the one observed (p-value) was used to tributionsinthebackground-onlyandsignal+background
EPJWebofConferences
nts Double Tag DØ Preliminary, 7.5 fb -1
ve 6600 Data
E VZ
5500 WW
Z+LF
Z+bb
4400 Z+cc
Top
Multijet
3300 VZ x 5
2200
1100
00
00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11
VZ RF Output
PEs / Bin111122246802000000DØ Preliminary, 7.5 fb -1 BSOBB-+--bOOOBsnnne LlllryyyvL eRLLLdLLL RRRL L±±R21σσ mber of Pseudo Experiments112205050000 Dp -Ø v a P l ur ee l: i00m..40in17a oerybx,ps Lee=rcvt7ee.5dd fb-1 BBBSO+---bOOOBsnnne LlllryyyLv eRLLLdLLL RRRL L±±R21σσ
100 Nu
80
50
60
40
20 -015 -10 -5 0 5 10 15
LLR
0
-15 -10 -5 0 5 10 15
LLR Fig.5.IntheD0searchforZZ[9]:finaldiscriminantinthe2-tag
Fig.4.IntheD0searchforWZ[8]:finaldiscriminantinthe2-tag channel (top); observed LLR value and expected LLRdistribu-
channel (top); observed LLRvalue and expected LLR distribu- tionsinthebackground-onlyandsignal+backgroundhypotheses
tionsinthebackground-onlyandsignal+backgroundhypotheses (bottom).
(bottom).
VZ Analysis sample (two b-tags)
hisydpoomthiensaetseidnbFyigW.4Z(pbroottdoumct)i.oTnh.esensitivityofthissearch nts / 0.12344505000 DS+0B P Freitliminary Run II 8.4 fb-1 DVToZapta
e V+h.f./WW
Ev300 V+l.f.
250 Multijet
3.2 ZZ inℓℓ+HF 200
150
100
TheD0collaborationperformedthissearchinadatasam-
50
plecorrespondingtoanintegratedluminosityof7.5fb−1[9]. 0-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
An electron or muon pair in a Z-mass window , and two Final Discriminant
or three jets are required.The sample is split into a 1-tag VZ→ννbb Analysis
aiabonbn-ngtsdeaegtoanhgfce2eetd-lhoto,aeofogsjnmeesetiusbstbsi-ig-itsnashaggttimlgyrEhepTaqtllneuyi:dnirbioetn-hmntetaehegslnegiotgeo2.nds-Tat,eoallw,gyta;iastkihkaneminntahopedmelevo1,aath-tntitwetcaargofigjesetjaetiomstpsfpaptaselhrseree--, Puesdo Experiments / 0.12345678000000000000 Dpp--0vv aaPllruueeeli m00..i00n71a65r yoo,rr 8 12.4..42 f ssb-ii1gg eoxbps BSOBB-+--bOOOBsnnne LlllryyyvL eRLLLdLLL RRRL L±±R21σσ
formed,whichimprovessignificantlythedijetmassreso-
200
lution.ThefinaldiscriminantisanRFwith19inputs,the
100
output of which is shown for the 2-tag channel in Fig. 5 0 -15 -10 -5 0 5 10 15
(top).Asignalcrosssectionof0.1±0.6timesitsstandard LLR
modelexpectationisobtained.Thesignificanceisonly0.1
Fig. 6. In the D0 search for (Z/W)Z [10]: final discriminant in
s.d.(1.5expected),notinconsistentwiththesignal+back-
the2-tagchannel(top);observedLLRvalueandexpectedLLR
groundhypothesis.TheobservedLLRiscomparedtoex-
distributionsinthebackground-onlyandsignal+backgroundhy-
pected distributions in the background-only and signal+
potheses(bottom).
backgroundhypothesesinFig.5(bottom).Thesensitivity
ofthissearchisdominatedbyZZproduction.
sub-sample,basedontheloosestb-taggingoperatingpoint
3.3 (Z/W)Z inMET+HF asintheD0analysisreportedinSec.2.1.Asinthatsame
analysis, the remaining b-tagging information is used in
TheD0collaborationperformedthissearchinadatasam- thefinaldiscriminant,aBDTwith32(!)inputs.TheBDT
plecorrespondingtoanintegratedluminosityof8.4fb−1[10]. outputinthe2-tagchannelisshowninFig.6(top).Asig-
The selection requires a large MET with a large signifi- nalcrosssectionof1.5±0.5timesitsstandardmodelex-
cance,andtwojetsnotback-to-backintheplanetransverse pectation is obtained, with a significance of 2.8 s.d. (1.9
tothebeamdirection;itrejectseventswithanelectronor expected).TheobservedLLRiscomparedtoexpecteddis-
amuonsatisfyingthecriteriaoftheWZsearchreportedin tributionsinthebackground-onlyandsignal+background
Sec. 3.1. The bulk of the MJ backgroundis next rejected hypothesesinFig.6(bottom).Thesensitivityofthissearch
using a BDT. The sample is split into a 1-tagand a 2-tag is shared by (Z → νν)Z and by (W → ℓν)Z production,
HadronColliderPhysicssymposium(HCP-2011)
ents 340000 DØ Preliminary, 7.5-8.4 fb-1 ments 106 DØ Preliminary, 7.5-8.4 fb-1
Ev 200 eri 105
-1100000 Pseudo Exp 110043 O b Ssiegrnviefdic pa-nVcea:l u3e.:2 08. 0s.0d0.52
-200 Data - Bkgd # 102 Observed Cross Section
-300 Bkgd Uncert.
-400 VZ 10
-500
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0 2 4 6 8 10 12 14
MVA ordered by s/b Fitted Cross Section (pb)
Fig.7.InthecombinationofD0searchesforWZ/ZZ[11],final ents3500 DØ Preliminary, 7.5-8.4 fb-1
discriminant re-cast into common bins of signal-to-background m
ratio. The fitted background has been subtracted, with the blue peri3000 Signal+Bkgd Pseudo-Experiments
linesindicatingthefittedbackgrounduncertainty.Thefittedsig- o Ex2500 Mean: 4.52 pb, RMS: 1.52 pb
nalisshownasaredhistogram. ud2000
# Pse1500 Observed Cross Section
1000
wheretheleptonfromtheW decayfallsoutsideoftheac-
500
ceptanceorfailstheidentificationcriteria.
0
0 2 4 6 8 10 12 14
Fitted Cross Section (pb)
3.4 Combination Fig.8.InthecombinationofD0searchesforWZ/ZZ[11],com-
parison of the measured signal cross section with expectations
TheD0searchesforWZ/ZZ reportedintheprevioussub- frompseudo-experiments inthebackground-only (top)andsig-
sections were combined using the exact same techniques nal+background(bottom)hypotheses.
asforthecombinationofthesearchesfortheHiggsboson.
Sincethebinningofthefinaldiscriminantoutputsarenot
identical in the various sub-channels, these outputs were 0.022500 DØ Preliminary, 7.5-8.4 fb-1 BB--OOnnllyy LLLLRR ±1σ
rTeh-cearsetsiunlttoofcotmhemfiotnfrboimnswofhiscihgntahle-tosi-gbnaaclkgcrroosusndsercattiioon. ments / 2000 BSO+-bOBsen LrlvyLe LRd LLRL R±2σ
is measured is shown in Fig. 7. The result is 1.13±0.36 peri1500
x
times the SM cross section. This result can be compared E
o
with the expectation from pseudo-experiments drawn in ud1000
e
the background-only and signal+background hypotheses Ps
500
inFig.8.Fromtheformer,asignalsignificanceof3.3s.d.
is deduced (2.9 expected), while the latter shows consis- 0
-40 -30 -20 -10 0 10 20 30 40
tency with the signal+background hypothesis within 0.3 LLR
s.d. The observedLLR is compared to expected distribu-
Fig. 9. In the combination of D0 searches for WZ/ZZ [11],
tionsinthetwohypothesesinFig.9.Theresultsofthefit
observed LLR and expected LLR distributions in the sig-
ofthedibosonproductioncrosssectiontothecombinedfi- nal+backgroundandbackground-onlyhypotheses.
naldiscriminantcan also be used to plotother quantities,
suchasthedijetmass,asshowninFig.10.
AfitwasalsoperformedinwhichtheWZandZZcross
– bb:60%
sectionswereleftuncorrelated.Theresultsare,relativeto
– cc:22%
theSMcrosssections,1.8±0.5forWZ and0.4±1.1for
– cs:8%
ZZ.TheseresultsarecorrelatedasshowninFig.11,where
– other:9%
itcanbeseenthattheSMexpectationlieswithinthe68%
C.L. contour of the data. The deviation from the SM is It should however be kept in mind that these values
as expected, given the results of the individual channels correspondto a definitionofthe1-tagand2-tagchannels
reportedintheprevioussubsections. according to the loosest of the twelve b-tagging operat-
ing points used at D0, and that the remaining b-tagging
informationisusedasinputtothefinaldiscriminant.The
3.5 Afrequentlyaskedquestion
weightofthebbcomponentisthereforesubstantiallylarger
thantheabovenumberswouldsuggest.
The question was raised at this conference of the flavor
composition of the final diboson samples. The answer is
givenherefortheD0searchintheMET+HFfinalstate[10].
Inthe1-tagchannel: 4 Summary
– bb:16%
– cc:19%
A numberof analyseshave recently addressedthe search
– cs:23%
for diboson production at the Tevatron with heavy-flavor
– other:41%
(HF)jetsinthefinalstate.Themainresultsarethefollow-
Inthe2-tagchannel: ing.
EPJWebofConferences
eV) 89000000 DØ Preliminary, 7.5-8.4 fb-1 – iTnhethCeDℓFν+cHolFlabchoarantnioenl wobitsherave3d.0WsWta/nWdaZrdprdoedvuiacttiioonn
0 G 7000 DWaZta (s.d.)significance[4].
s / (1 56000000 ZBZkgd – In that same channel, the D0 collaboration reached a
ent 4000 significanceof2.2s.d.forWZ productionalone[5].
v – The CDF collaborationobtained a significance of 1.9
E 3000
s.d.forWZ/ZZproductioninthemissingE (MET)+HF
2000 T
1000 channel,withzerooroneleptonaccepted[7].
0
0 50 100 150 200 250 300 350 400 The D0 collaboration recycled their searches for a low-
Dijet Mass [GeV]
mass Higgsboson in data samplescorrespondingto inte-
V) 600 DØ Preliminary, 7.5-8.4 fb-1, 1 b-tag gratedluminositiesof7.5to8.4fb−1,usingWZandZZ as
Ge 500 Data - Bkgd asignalinsteadofWH andZH.
0 400 Bkgd Uncert.
s / (2 300 WZZZ – FcaonrcteheofW2.Z2ss.idg.nwalaisnotbhteaiℓnνe+dH[8F].final state, a signifi-
nt 200
Eve 100 – FortheZZ signalintheℓℓ+HFfinalstate,thesignifi-
canceisonly0.1s.d.[9].
0
– FortheWZ/ZZ signalintheMET+HFfinalstatewith
-100
noidentifiedleptons,asignificanceof2.8s.d.wasob-
0 50 100 150 200 250 300 350 400 tained[10].
Dijet Mass [GeV]
Those three searches were combined to reach a signifi-
V) 200 DØ Preliminary, 7.5-8.4 fb-1, 2 b-tag cance of 3.3 s.d. (2.9 expected), thereby establishing ev-
e
G 150 Data - Bkgd idence for diboson production in final states containing
0 Bkgd Uncert.
s / (2 100 WZZZ hmeeaavsyu-rfleadvtoorbjeets1.[1131]±. T0h.3e6ptrimodeuscittisonstcarnodsasrdsemctoiodnelwexas-
nt 50
e pectation.
v
E 0 Theseanalyseshaveprovidedadirectvalidationofthe
-50 proceduresandtechniquesusedinthesearchesforalow-
massHiggsbosonattheTeavtron.
-100
0 50 100 150 200 250 300 350 400
Dijet Mass [GeV]
V) 700 DØ Preliminary, 7.5-8.4 fb-1 References
Ge 600 Data - Bkgd
nts / (20 345000000 BWZZkZgd Uncert. 123... AFJ...MSRf.ooCrbzasaom,ntp,hbteheselelsaepnrpodrcoRec.eedKeid.niEgnslgl.iss.,Phys.Rev.D60,(1999)
ve 200
E 100 113006.
0 4. TheCDFCollaboration,CDFNote10598.
-100 5. The D0 Collaboration, submitted to Phys. Rev. Lett.,
-200 arXiv:1112.0536[hep-ex].
0 50 100 150 200 250 300 350 400
Dijet Mass [GeV] 6. TheCDFCollaboration,CDFNote10601.
7. The CDF Collaboration, to appear in Phys. Rev. D,
Fig.10.InthecombinationofD0searchesforWZ/ZZ[11],post-
arXiv:1108.2060[hep-ex].
fitdijetmassdistributioninthe1-and2-tagchannelscombined
8. TheD0Collaboration,D0Note6220-CONF.
(top),and,afterfittedbackgroundsubtraction,inthe1-tagchan-
9. TheD0Collaboration,D0Note6256-CONF.
nel,2-tagchannel,and1-and2-tagchannelscombined,fromrow
10. TheD0Collaboration,D0Note6223-CONF.
2to4.Thebluelinesindicatethefittedbackgrounduncertainties.
11. TheD0Collaboration,D0Note6260-CONF.
pb)4.5 DØ Preliminary Standard Model
ction (3.45 L = 7.5-8.4 fb -1 M68e%as Curoenmtoeunrt
Cross Se2.53 95% Contour
Z 2
Z
1.5
1
0.5
0
0 2 4 6 8 10 12
WZ Cross Section (pb)
Fig.11.InthecombinationofD0searchesforWZ/ZZ[11],fit-
ted WZ and ZZ production cross sections compared to the SM
expectation.