Jet and jet substructure physics at ALICE · Leticia Cunqueiro, Oak Ridge National Laboratory for...
Transcript of Jet and jet substructure physics at ALICE · Leticia Cunqueiro, Oak Ridge National Laboratory for...
JetandjetsubstructurephysicsatALICE
LeticiaCunqueiro,OakRidgeNationalLaboratoryfortheALICECollaboration
CERNseminar,24th September2019
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Jetsinprotonprotonandheavy-ioncollisions
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JetandjetsubstructureplayamajorroleintheLHCphysicsprogramme
Usejetsaswell-callibrated probesofthehotanddensemediumcreatedinheavy-ioncollisions
ThemodificationofthejetyieldsandandselectedhardsubstructurecanconstraindynamicalpropertiesofthehotanddenseQCDmedium.
Maingoalistostudythehigh-temperaturephaseofQCD toinvestigatehowmacroscopicpropertiesofthismatterarisefromQCDinteractions.
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Quantifyingthemedium-inducedmodificationsofjets
• Inclusive/semi-inclusiveobservableslikejetpT spectraandratiosfordifferentresolutionR
• Quantificationofjetshapesbyfunctionsthatdependon4-momentaofconstituents(angularity,pTD,jetmass)…
• Usetheclusteringhistory:
theideaistounwindtheclusteringhistory(decluster thejet)toaccessthesubjet branchesorprongsateachdeclustering step
Thesethreetypeofmeasurementsaredynamicallyconnected!
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plotfromG.Salam,QM18
UnwindtheCambridge-Aachenclustering(orotherconvenientalgorithm)
Ateachstep,registerthekT,∆R coordinates
Followthehardestbranchateachstep
d2P = 2↵s(k?)CR
⇡ dln(z✓)dln( 1✓ )
Invacuum,flat2DdensityexceptforvariationofthecouplingwithscalekTGeneralobservable,otherscanbederivedfromit
kT
𝛥R
Invacuum:theLundplane
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Mapofsplittings inmedium
K.Tywoniuk etal,Noveltoolsandobservablesforjetphysicsinheavyioncollisons,https://arxiv.org/pdf/1808.03689.pdf
Multiplescalesinmedium:
MediumlengthL andtemperatureT
Splittings canbeproduced/decohered inside/outsidethemediumInterplaybetweenL,formationtimetf.anddecoherence timetd
Coherenceangle𝜽c=1/ 𝑞$𝐿3�
structureatanglessmallerthan𝜽cisnotresolvedbythemediumwhere𝒒)=<kT2>/𝜆 (GeV2/fm),thetransportcoefficientofthemediumand𝜆,thedensityofscatteringcentres.
Medium-inducedradiationfollowsdifferent“rules”thanvacuumradiation:Thedensityofsplittings inheavyioncollisionsisnotexpectedtobeconstantintheLundplane
resolved unresolved
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TheLundplaneand(groomed)observables
MostofthejetfeaturesandsubstructurealgorithmscanbederivedfromtheLundplane.
Forinstance:
Fixedformationtimeisadiagonallinewithpostive slopeintheplanetf~2zE/kT2
Constantmomentumfractionzcanbedrawnasalinewithnegativeslope
ThenumberofentriesintheLundplaneisthenumberofdeclustering steps,n.
presentationbyF.Dreyer
ThedifferentSoftDrop(SD)groomingcutscanbedrawnasexclusionregionsintheplane
zg isthemomentumimbalanceofthefirstsplittingsatisfyingtheSDcutProcedureremovessoftandlargeangleemissionsuntilasufficientlysymmetricsplittingisfound
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SoftDrop/massDrop groominginheavyioncollisions
Inpp:limitcontaminationofQCDbackground(andpileup) inacontrolledwaywhileretainingbulkofperturbativeradiation
InPbPb:select“hard”componentofquenchedjets.Toisolatemediumeffects,easiertocalculate
ALICEJetperformanceandcapabilities
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Track-basedjets
FulljetsCentralbarrelplusEMCal clustersEMCal𝞿 coverage:1080|𝜂|<0.7AcceptedclusterspT,cluster>300MeV
Central-barreltracking|𝜂tracks|<0.9High-precision trackingdowntopT,track=0.15GeVJetsarecorrectedtochargedparticlelevel
ALICE,arXiv:1905.02536
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0 50 100 150 200 250 300 350)c (GeV/
Tp
0
0.2
0.4
0.6
0.8
1
1.2
1.4hd Tpd=X
R s2 d /
hd Tpd=0
.2R s2 d
ALICE preliminary-1 = 4 pbintL = 13 TeV, spp,
TkJets, Anti- > 0.3 GeVclusterE, c > 0.15 GeV/track
Tp
R| < 0.7 - jeth| < 0.7, |clusterh| < 0.7, |trackh|
=0.3R=0.2/R
=0.4R=0.2/R
=0.5R=0.2/R
Correlated uncertaintiesShape uncertainties
POWHEG + PYTHIA8
ALI−PREL−315725
0 50 100 150 200 250 300 350)c (GeV/
Tp
8-10
7-10
6-10
5-10
4-10
3-10
2-10
1-10
1
10
210))c (m
b/(G
eV/
hd Tpds2 d
ALICE preliminary-1 = 4 pbintL = 13 TeV, spp,
TkJets, Anti- > 0.3 GeVclusterE, c > 0.15 GeV/track
Tp
R| < 0.7 - jeth| < 0.7, |clusterh| < 0.7, |trackh|=0.2R
=0.3 x 3R
=0.4 x 10R
=0.5 x 30R
=0.6 x 100R
Correlated uncertainties
Shape uncertainties
ALI−PREL−315682
WidekinematicreachattheLHC,fromfewGeVtotheTeV scale
RatiosofcrosssectionsfordifferentR aresensitivetothejettransverseenergyprofile
CrosssectionsandtheirratiosfordifferentjetresolutionR
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SmallR dominatedbysplash-outhadronization losses(~1/R atLO)Large RdominatedbyUEatlowjetpT
NPcorrectionsvsR
CrosssectionsandtheirratiosfordifferentjetresolutionR
RatiosofcrosssectionsingoodagreementwithPOWHEG andfixedorderNLOcalculations
ALICE,arXiv:1909.09718
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ALI-PREL-310033
The2-pronggroomedmomentumimbalance,zg
Thezg invacuumisdirectlylinkedtotheAltarelli-Parisisplittingfunction
NojetpT dependenceobserved,asexpectedifmeasurementoftheQCDzkernel
Larkoskietal,Phys.Rev.Lett.119(2017)no.13,132003
The2-pronggroomedmomentumimbalance:zg andR dependence
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ThejetR dependenceisexploredinawidekinematicrangeAtlowpT (left)plot,non-perturbativeeffectsobscuretheconnectiontotheQCDsplittingfunction
pT,jet
Thenumberofprongspassingthemass-dropcut
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ALICE,arXiv:1905.02512
PYTHIA-basedsimulationsunderestimatethenumberofprongsnotpassingthemassdropcut
Thehardsplittingapertureangle
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Rg
Thesplittingopeninganglefortwodifferentdeclustering strategies:exclusivekT andCA+mass dropgroomingthatselectdifferentsplittings inthejet
N=2exclusivekT declustering,apertureangle CA+SDgrooming,apertureangle
UncorrelatedbackgroundinHeavy-Ioncollisions
17ALICE,JHEP1203(2012)053
Largeregion-to-regionfluctuationsinthebackgroundinducelargejetmomentumirresolutionLow-pT /largeRcombinatorial:needtosuppresscombinatorialjetsSeveraltechniquesareappliedinALICE:data-drivenh-jetcorrelation,applyingaleadinghadronbiasetc.
Breakdownofcomponentsofthejetirresolutionduetobackground:numberofparticlesinthejetarea andflow
Averagepedestalbackground Backgroundfluctuationsvsmultiplicity
𝜹(pT)=pT,raw-𝞀Area– pT,probe
Thesuppressionofjetyieldsinheavyioncollisions
StrongsuppressionofjetyieldsinPb-Pb relativetopp
Nojet Rdependencewithinuncertainties,significantfractionofenergytransportedoutsidethejetcone18
ALICE,arXiv:1909.09718
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Newapproachestosuppresscombinatorialbackground
Backgroundfluctuationssuppressed:-Combinatorialjetsreduced-Smallerunfoldingcorrection-ExtendtolowjetpT andlargeR
Caveat:backgroundsubtractionmightbecomemodeldependent
ALI-PERF-324612
Methodpaper:Haake,Loizides Phys.Rev.C99(2019)no.6,064904
Area-basedisanunbiasedmethod,knowsnothingaboutthejetstructure
pTsub=pTraw -𝜌Area
NewMLapproach:aregressionmodeltosubtractbackground.Inputparameters:area-basedsubtractedjetpT,angularity,numberofconstituents,pT ofthe8leadingjetconstituents
Backgroundfluctuations WidthofthefluctuationsvsjetR
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Newapproachestosuppresscombinatorialbackground
ALI-PREL-324739ALI-PREL-325710
LowerpT reachcomparedtopreviousmeasurements
R =0.6measuredforthefirsttimeinALICEinPb-Pb collisions
TheradialprofilemeasuredviatheratioofcrosssectionswithdifferentR issimilartopp
Nuclearmodificationfactor RatioofcrosssectionsforR=0.2adR=0.6
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Largepedestalbackground,impactonsubstructure
PedestalbackgroundcontaminationsubtractedusingArea-derivatives[1]andConstituentSubtraction[2]methods.Residualdifferencesbetweentheprobeandthesubtractedembeddedprobeareunfolded
[1]Soyez etal,Phys.Rev.Lett.110(2013)no.16,162001 [2]Bertaetal,JHEP1908(2019)175
SubtractionPerformanceangularity Subtractionperformance2-subjettiness
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trueSDn
0 2 4 6 8 10 12
em
bS
Dn
0
2
4
6
8
10
12
3−
10
2−10
1−10
ALICE Preliminary
= 2.76 TeVNN
s0-10% Pb-Pb Embedded PYTHIA
=0.4R Charged Jets, TkAnti-
c < 120 GeV/ch,part
T,jetp80 <
ALI-SIMUL-155669
truegR
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
em
bg
R0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
3−
10
2−10
1−10
ALICE Preliminary
= 2.76 TeVNN
s0-10% Pb-Pb Embedded PYTHIA
=0.4R Charged Jets, TkAnti-
c < 120 GeV/ch,part
T,jetp80 <
ALI-SIMUL-155665
truegz
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
em
bg
z
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
3−
10
2−10
1−10
ALICE Preliminary
= 2.76 TeVNN
s0-10% Pb-Pb Embedded PYTHIA
=0.4R Charged Jets, TkAnti-
c < 120 GeV/ch,part
T,jetp80 <
ALI-SIMUL-155673
Detectorandbackgroundresponseforjetsubstructure
Off-diagonalities aredominatedbycaseswherethesubleadingprongisreplacedbyahighermomentumprongsmearedbythebackgroundorpurelycombinatorial
Moreaggressivegroomingoralternativebackgroundsubtractiontobeexplored,inparticularforRg
TheangularitiesinPbPb collisions
Small-R jetsshowmodificationsinthefragmentation:
Smallerangularity(morecollimated)
LargerpTD (harderfragmentation)
Small-R jetsareinterestingtoconstraintheorymodelsbecausetheyarelesssensitivetocertainmodelingredientslikethewakeorcorrelatedbackground
ALICE,JHEP1810(2018)13923
TheangularitiesinPb-Pb collisions
Themodifiedfragmentationismoresimilartothatofquark-jettemplatesPicturecompatiblewithsoftfragmentstransportedatlargeanglesrelativetothejetaxis
ALICE,JHEP1810(2018)139
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ThegroomedmomentumimbalanceinPb-Pb collisions
ALICE,arXiv:1905.02512 25
Apertureangledependenceofthesplittings
Note:normalized tototalnumber ofjetsinthegivenpT bin
ThegroomedmomentumimbalanceinPb-Pb collisions
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Apperture angledependenceofzg inmediumcomparedtovacuum(smeared)referenceAtlargeanglesΔR>0.2,suppressionofsymmetricsplittingsAtsmallanglesΔR<0.1,enhancementofsplittingsNoobservedenhancementofsplittings passingtheSDcutinmediumrelativetovacuumIncreasednumberofuntaggedjetsinmedium
ALICE,arXiv:1905.02512
27ALICE,arXiv:1905.02512
ThegroomedmomentumimbalanceinPb-Pb collisions
Apperture angledependenceofzg inmediumcomparedtovacuum(smeared)referenceAtlargeanglesΔR>0.2,suppressionofsymmetricsplittingsAtsmallanglesΔR<0.1,enhancementofsplittingsNoobservedenhancementofsplittings passingtheSDcutinmediumrelativetovacuumIncreasednumberofuntaggedjetsinmedium
28ALICE,arXiv:1905.02512
ThegroomedmomentumimbalanceinPb-Pb collisions
Apperture angledependenceofzg inmediumcomparedtovacuum(smeared)referenceAtlargeanglesΔR>0.2,suppressionofsymmetricsplittingsAtsmallanglesΔR<0.1,enhancementofsplittingsNoobservedenhancementofsplittings passingtheSDcutinmediumrelativetovacuumIncreasednumberofuntaggedjetsinmedium
ThenumberofSDprongsinPb-Pb collisions
ThenSD countsthenumberofprongsthatpassthemassdropconditionasthejetisiterativelydeclustered
Smallernumberofprongsinmediumthaninvacuum(alsoinagreementwiththemorequark-likefragmentationshownbytheangularities)
29ALICE,arXiv:1905.02512
Iscolorcoherencedrivingthesuppressionofthe2-prongsplittings?
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Coherentlimit𝜃 <𝜃Csmall-angleprongsareresolvedasasinglecolorcharge
Incoherentlimit 𝜃 >𝜃Clargeangleprongsareresolvedbythemedium independentlyandthusmorequenched
However:thedatatrendsofthezg aredescribedbytwomodels(JEWELandHYBRID)thatdonothavecolorcoherencebuiltin;thissuggeststhatthedrivingmechanismissomethingsimplerlikeformationtimeorkinematicbiases.
Resolvedsubstructure Unresolvedsubstructure
Casalderrey-Solana,Mehtar-Tani,Salgado,Tywoniuk Phys.Lett.B725(2013)357–360
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Ifitisnotcolorcoherencewhatdictatesthesuppressionofsplittingsatlargeangle,isitdrivenbyformationtimeeffects?
Atlargeangles/energies:
Smallpopulationofunmodifiedvacuumsplittings:earlyvacuumsplittings arequenchedastheytraversethemedium
Orisitakinematiceffect?ByselectinglargeanglesplittingswebiastowardshigherQ2 structuresthataremorequenched?
tf~2zE/kT2 ~1/(z𝜽2)
LilianaApolinario,https://indico.cern.ch/event/577856/contributions/3424218/
Formation timevsdeclustering steps,jetchronography?
5- 4- 3- 2- 1- 0 1 2 3 4 5
)hardest,graphT
log(k
5-4-3-2-1-012345)
hard
est,
decl
uste
ring
Tlo
g(k
1
10
210
310
410 = 5.02 TeVsPythia8 pp > 80 GeV/c jet
Tp
5- 4- 3- 2- 1- 0 1 2 3 4 5
)hardest,graphT
log(k5-4-3-2-1-012345)
hard
est&
&SD
, dec
lust
erin
gT
log(
k
1
10
210
310 = 5.02 TeV + HIC toy backgroundsPythia8 pp
> 80 GeV/c, Constituent Subtraction jetT
p
Correlationbetweentheparton showerandthedeclustering
https://indico.gsi.de/event/8938/
ThesekindoftestsproposedanddiscussedatEmmiworkshop:thespace-timestructureofjetquenching,theoryandexperiment
Canwefindaregionofthephasespaceforwhichthecorrelationbetweenthegraphandthedeclusteredbranchesisrobust?ThehardestemissionfromthegraphseemswellcorrelatedtothehardestbranchafterembeddingintoheavyionbackgroundconstituentsubtractionandSDgrooming.
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Thedeadcone
Probability foraheavyquarkQtoradiateasoftgluon:
Inthelimitofsmallanglesbutstill
Inthecasewhere
Y.Dokshitzer,V.A.Khoze andS.I.Troyan “OnspecificQCDpropertiesofheavyquarkfragmentation”
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where𝚹0 =mQ/E
Battaglia etal,http://cds.cern.ch/record/989441/files/cer-002652356.pdf
Thedeadcone:implicationsandexperimentaldifficulties
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Thedecaysoftheheavyflavour particleshappenatsimilarangularscalesandpollutethedeadcone
Battaglia,Orava,Sami “Astudyofdepletionoffragmentationparticlesatsmallanglesinb-jetswiththeDELPHIdetectoratLEP”Thefirstandonlyattemptofdirectdeadconemeasurementatcolliders
Choiceofareferenceaxis:jetaxis,thrust,thedirectionofthevertex?
Thereareessentially2indirectconsequencesofthedeadcone:
-RestrictionofhardgluonswithsmallkT ,whichisthemostprobablecomponentoftheradiation(P~𝞪S(kT2))->reductionofz,FFpeakedatlargervaluesofz
-Smallerintrajetmultiplicities
kT
zpt,jet
TheLundplaneforheavyflavours
Q
Wefollowtheprongcontainingtheheavyflavorateachdeclustering step
Prongwithheavyflavour almostalwaysthehardest:noambiguitywhencomparingtolightquarks
Ateachstepofthejettree:parentsubjet,Eradiator.
For𝛳 <mQ/Eradiator weexpecttoseeasuppressionofsplittings.
ForlowEradiator ,whichmeanspenetratingthejettodeeplevels,thephasespaceforthedeadconeobservationgrows. 36
Eradiator,1Eradiator,2
Eradiator,3
𝛳1
𝛳2
𝛳3
TheLundplaneforheavyflavoursLundplaneredrawnintermsofthesplittingangleandtheparent(radiator)energy
Relativedifference toinclusivejets:blueregions indicatesuppressionofradiationofftheheavy-flavourprong
Forgivenradiatorenergy, suppressioneffectsappearatsmalleranglesforD-jetsthanB-jets,asexpected
Akeyaspectistoselecthardsplittingsbycuttingln(kT)>0, tosuppresshadronization effects
Cunqueiro,Ploskon,Phys.Rev.D99(2019)no.7,074027 37
D-jets,parton-level B-jets,parton-level
D-jets,hadron-level B-jets,hadron-level
Relativ
edifferen
cestoinclusivejets
Thedistributionofsplittingangles
Pythiasimulationspredictsuppressioneffectsof theorderof20%(100%)forD-jet(B-jets)relativetoinclusivejetsatanglesof0.1radianstypicallyresolvablewithatrackingdevice.
NoconstrainonthejetpT ,itissufficient todecluster thejetdeepenough toreachsubjet energyscalessenstivie tomassscaleCunqueiro,Ploskon,Phys.Rev.D99(2019)no.7,074027 38
Relativediffference ofD-jetsandinclusivejets Relativediffference ofB-jetsandinclusivejets
HeavyFlavour jetswithfullkinematicreconstructionoftheheavyflavour hadron
D0invariantmassdistributionfortheKpi channel FullyreconstructedD0-jetspectrum
D0 mesonDecaychannelD0->K-𝞹+,BR=3.89%TPCdE/dx+TOFPIDforK/𝞹 discriminationTopological selections(secondaryvertex)pT,D>3GeV/c ALICE,JHEP1908(2019)133 39
Upcomingnewresultsat13TeV!
Isitpossibletomeasurethedeadconedirectlyat13TeV usingD0-jets?staytunedforQMinonemonth:https://indico.cern.ch/event/792436/
Otherfundamentalpropertiesofheavyflavour jetswithinreach:
HeavyFlavour jetswithfullkinematicreconstructionoftheheavyflavour hadron
ALICE,JHEP1908(2019)133
P.IltenetalPhys.Rev.D96(2017)
Measurethegroomed splittingmomentum imbalancezg,whentheleadingprong isheavy-flavourTagged.->Q->Qg
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D0-jetfragmentationfunction
Summary
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• Strongsuppressionofjetyieldsandlargeoutofconeradiationinheavyioncollisionsrelativetopp
• Small-RjetshapesindicateaharderandmorecollimatedfragmentationofthejetcoreinHIC
• Substructuremeasurementsusingclusteringhistoryverypromissing:
Accessregionsoftheintra-jetphasespacethataretheoretically/experimentallymorerobust
Suppressionofsymmetricsplittings atlargeapertureanglesinHICrelativetopp.earlysplittings thatarefullyembeddeden mediumandthusmorequenched?
Accesssplittingtimeviathebranchkinematics?
• NewbackgroundsubtractiontechniquesallowtoexpandtheexploredphasespacetolowjetpT andlargeR,nex:extensiontojetsubstructure
• Interestingprospectsforheavyflavour jetsandsubstructure,fundamentalpropertieslikedeadcone
StaytunedforQM19inNovember!
ALI-SIMUL-320949
HeavyFlavour jets
OntheimportanceoftheReconstructionofthedecays
43PlotsfromKatharinaGarner, showing theeffectofturningonthedecaysatthelevelofsubstructureofb-jets
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ThesplittingmapinPbPb
Noveltoolsandobservables forjetphysicsinheavy-ioncollisionsAndrewsetal,https://arxiv.org/pdf/1808.03689.pdf
Powerfulvisualtoolsforsearchesofmedium-inducedsignal
10 20 30 40 50 60 70 80 90 100
/GeV
)c
) (m
b hd
ch T,je
tp
/(ds2 d
5-10
4-10
3-10
2-10
1-10 ALICE Preliminary
= 5.02 TeVNNsPb -p
= 0.4R, Tkcharged b-jets, anti-
)c (GeV/chT,jetp
10 20 30 40 50 60 70 80 90 100
Ratio
to d
ata
0.5
1
1.5
2
2.5Datasystematic uncertaintyPOWHEG HVQPOWHEG systematic uncertainty
ALI−PREL−323633
HeavyFlavour jets,workinprogressFullyreconstructedb-jetspectrum
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