Spectroscopy of doubly heavy baryons at LHCb...• Mass: many models been applied to determine...

SpectroscopyofdoublyheavybaryonsatLHCb

MurdoTraillonbehalfoftheLHCbcollaboration

UniversityofGlasgow

Ξ""

25th- 29thSeptember

HADRON M.Traill(Glasgow) 2/21

• LHCbdetectorandperformance• Introductionandphysicsmotivation• RecentresultsinhadronphysicsatLHCb

Outline

Ø Discoveryofdoublycharmedbaryon𝜩𝒄𝒄%%:PRL119,112001(2017)

• Futureplans• Summary

Ξ""

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.112001


LHCbdetectorDesignedforprecisionmeasurementsin

𝑏 and𝑐 flavorphysics

250mradVELO:Excellentvertexreconstruction

Ø IPresolution:20𝝁mØ 𝝉 resolution:45fs

2<𝜂 <5

RICHes:

Magnet:Bendingpower4Tm

JINST3(2008)S08005IJMPA30(2015)1530022

Trackingsystems:Easilyseparatesneighboringstructures(~96%)

EfficientK/𝝅/pseparation(~95%)

• LHCbisuniquelaboratoryforhadronspectroscopystudies

• Excellenttracking,particleidentificationandefficienttriggersystem

Electromagnetic+hadroniccalorimeters

Muonstations

http://iopscience.iop.org/article/10.1088/1748-0221/3/08/S08005/meta

https://arxiv.org/abs/1412.6352


LHCbtriggeranddata• RunI:1.fb-1at7TeV(2011)+2.fb-1at8TeV(2012)• RunII:0.3fb-1(2015)+1.7fb-1(2016)bothat13TeV

• ppcollisionswithluminositylevelingtorunatoptimalinstantaneousluminosity (1.1visiblecrossings)

IJMPA30(2015)1530022

arXiv:1604.05596

RunIITurbostream:• Candidatesreconstructedattriggerlevel

savedforofflineanalysesdirectly

LHCbcanperformfulldetector

alignmentandcalibration

inreal-timeinRunII



Cand

idate

s / (5

MeV

)

0

100

200

300

400

500

600

700

800

900Claimed X(5568) state

Combinatorial

) > 5 GeVs0B(

TpLHCb

Pull

4−2−024

(MeV))±πs0m(B

5550 5600 5650 5700 5750 5800 5850 5900 5950 6000


HadronspectroscopyatLHCb

87±32

arXiv:1608.00435

• LHCbarehugelyactiveinhadronspectroscopystudies

Ø Maincontributorin𝐵"% physics

Ø Helpedestablishtheexistenceoftetraquarkandpentaquarkstates

• Someselectedrecentworkinspectroscopyofbeautyhadrons:

Ø 2015:PrecisemeasurementsofpropertiesofB1(5721)0,+and B2∗(5747)0,+ states

Ø 2015:Observation ofstructureathigherinvariantmassinB+π− and B0π+ spectra

Ø 2016:LHCbdonotseeD∅’sX(5568) tetra-quarkusingmuchlargerandcleaner𝐵01sample

Phys.Rev.Lett.117,152003

JHEP 04 (2015) 024

https://link.springer.com/article/10.1007%2FJHEP04%282015%29024




Physicsmotivation

• DoublyheavybaryonswillopennewsectortostudystrongforceandCPVinbaryonicmatter

Ξ""%%Example:HQETwheretwocharmquarksconsideredasstaticheavydi-quarkreducing ittosimpleQ𝑞4 system

• Heavyhadrons(Q𝑞4,Q𝑄4,QQq,QQQetc)areallofmuchinterestinQCDstudies

• Heavyquarkwavefunctionareapproximatelynon-relativistic

• AllowgreattestinggroundsforphenomenologicalmodelsandlatticeQCDtechniques

PredictionofhadronspectrumfromperturbativeQCDcalculationsnotpossibledueto largecouplingstrength

Ξ"" spectroscopy arXiv:hep-ph/9807375

Mass[Ge

V]

(Q∈ 𝑐, 𝑏;q ∈ 𝑢, 𝑑, 𝑠)

• Precisemeasurementswithsingleheavyhadrons

• Nowexpectedtobeabletoobservedoublyheavybaryons

https://arxiv.org/abs/hep-ph/9807375


Doublyheavybaryons• QQq(Q∈ 𝑐, 𝑏; q ∈ 𝑢, 𝑑, 𝑠) baryonsarenotexoticsystemsbutfirmlypredictedbySM

• Quarkmodelpredictsstatessuchas:Ω""% (𝑐𝑐𝑠),Ξ""% (𝑐𝑐𝑑),Ξ""%%(𝑐𝑐𝑢),Ξ@"% (b𝑐u),Ξ@"1 (b𝑐d)etc.

• MoredoublycharmedbaryonsproducedatLHCb:𝜎(c�̅�, c�̅�)>>𝜎(b𝑏4, c�̅�)>>𝜎(b𝑏4, b𝑏4)

𝐽E=FG

H𝐽E=I

G

HGroundstates Excitedstates

• LightestdoublycharmedstatesΞ""offeredbestchanceofdiscovery

Ø ExcitationsdecaytogroundstatesviaStrong/EMinteraction

Ø Groundstatesdecayweaklywithacharmquarktransitioningintolighterquarks

SU(4)flavormultiplets,PDGReviewofParticlePhysics,Phys.Rev.D86,010001

LHCbseethousandsof𝐵"%(𝑐𝑏4)mesons- Shouldseedoublyheavybaryons!- Nounambiguousevidencebefore2017

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.86.010001


Massandlifetimesproperties• Mass:manymodelsbeenappliedtodeterminemassesofgroundstatesof(QQq)baryons;QCDsumrules,(non-)relativisticQCDpotentialmodels,bagmodel,quarkmodel…

MasssplittingbetweenΞ""% /Ξ""%%expectedtobeafewMeVduetoapprox.isospinsymmetry

• RecentlatticeQCDcomputations:

Ø m(Ξ""% /Ξ""%%)≈ 3.6GeV

Ø m(Ω""% )≈ 3.7GeV

• Ξ@" lifetimespredictedtobegenerallylongerthanΞ"" with:𝜏(Ξ@"% )>𝜏(Ξ@"1 )

• Ξ@" higherat6.75- 7.1GeVwithm(Ξ@"1 )≈m(Ξ@"% )

• Lifetimes:largevariationindoublycharmedbaryonssimilartosinglycharmed

𝜏(Ξ""%%)>>𝜏(Ξ""% )>𝜏(Ω""% ); 𝜏(Ξ""%%)∈ 200-700fs,𝜏(Ξ""% )∈ 50-250fs, 𝜏(Ω""% )≈ 𝜏(Ξ""% )

Referencesshowninback-upslides

Ξ""%%/%mass

Year


SELEXand𝛯""%• SELEX,fixed-targetFermilabexperiment,

claimedfirstobservationof𝛯""% stateinΞ""% → Λ"%𝐾Q𝜋% decaysin2002(6.3σ)

• Signalhadveryunexpectedproperties:Ø Shortlifetime:𝜏 <33fsat90%C.LsuggestsaStrongdecay

Ø Largeproduction:20%Λ"% camefrom𝛯""% decays

• SELEXfindingsneverreproducedbyothergroups

• Uniqueproductionenvironment:Ø 600GeVbeamofhyperonsonfixedtargetofCu/diamond

Ø Productioncross-sectioncouldbeverydifferentthaninppcolliders

SELEXΛ"%𝐾Q𝜋%and𝐷%𝑝%𝐾Qdistributions superposed

Phys.Lett.B628(2005)18-24

Combinedmass:3518.7± 1.7(stat)MeV/𝑐H

• Followedbyevidenceof𝛯""% intheΞ""% → 𝐷%𝑝%𝐾Qmodein2004(4.8σ)

arXiv:hep-ex/0406033

https://arxiv.org/abs/hep-ex/0406033

http://www.sciencedirect.com/science/article/pii/S0370269305013808


LHCbsearchforΞ""%• In2013,LHCbsearchedforΞ""% → Λ"%𝐾Q𝜋%decayswith0.65fbQF of2011data

• Examinedmassrange3.3-3.8GeVbutfoundnoevidenceofΞ""% production

• ExperimentsensitivitystronglydependsonΞ""%lifetimehowever

R=U VWWG ×YZ(VWWG →\WG]^_G)U \WG

• Duetolimitedsensitivityatshortlifetimes,thisnon-observationisnotinconsistentwiththeSELEXclaim

R<0.013for𝜏(Ξ""% )=100fs

R<3.3×10Qb for𝜏(Ξ""% )=400fs

JHEP12(2013)090



SwitchtoΞ""%%

• TheoristssuggestBFcouldbeashighas~10%,seearXiv:1703.09086

• 𝜏(Ξ""%%)>>𝜏(Ξ""% ) soΞ""%% travelsfurtherfromPVmakingonlineselectionsbetteratremovingbkg

• Use1.7fbQF 2016RunII dataat 𝑠 =13TeV

• Dedicatedexclusivetriggerensuringhighefficiency

• Fulleventreconstructiondoneattriggerlevel

• 2 fbQF 2012RunI dataalsoanalysedtocrosscheckresults

Analysisstrategy:

• In2016StartedsearchingfordoublychargedstateinΞ""%% → Λ"%𝐾Q𝜋%𝜋% decays

PRL119,112001(2017)




Ξ""%% → Λ"%𝐾Q𝜋%𝜋% selections• 𝛯""%% cross-sectionmuchsmaller(~×10Qd)thaninelasticcross-sectionin𝑝𝑝 soexpectinglargehadronicbackgrounds

• SamplesofΛ"% → 𝑝%𝐾Q𝜋% expectedtobehighandpure†

†LHCbhassomeoflargestcharmdatasetsintheworld𝜎(pp→c�̅�X; 13TeV) LHCb =2369±3 ± 192𝜇b JHEP1603(2016) 159

Cut-basedselectiononΛ"%:Ø Tracks:positiveparticleID,displacedandlarge𝑝iØ Λ"%:goodvertexquality anddisplacedfromprimaryvertex

• Λ"% combinedwithPID-selected𝐾Q𝜋%𝜋% trackstoform𝛯""%% candidates

MultivariateselectorusedtoselectΞ""%%candidatestrainedon:

Ø DecayFitqualityof𝛯""%%candidates

Ø Kinematicsoffinalstates

Ø 𝛯""%% vertexseparationfromPV

Largestbackgroundsourceexpectedtobecombinatoricsfrom𝛯""%% tracks

Selectortrainedonsimulatedsignalandun-physicalwrong-sign(WS)datarepresentedbkgas:

Ξ""%% → Λ"%𝐾Q𝜋%𝜋Q

PRL119,112001(2017)




Λ"%𝐾Q𝜋%𝜋% massspectrum• Asignificantstructureinrightsign(RS)data

• Notpresentinwrongsign(WS)combinations• NotobservedforΛ"% backgroundcandidates• DistributionssimilarexceptthepeakinRS

PRL119,112001(2017)



Massmeasurement

Localsignificance> 12𝜎

Resolution=6.6± 0.8MeV(consistentwithexpecteddetectorresolution)

Signalyield=313± 33

Systematicsofmassmeasurement

PRL119,112001(2017)


Localsignificance> 12𝜎

Resolution=6.6± 0.8MeV(consistentwithexpecteddetectorresolution)

Signalyield=313± 33


Massmeasurement

Systematics

M(𝛯""%%) –M(𝛬"%) =1134.94 ± 0.72(stat)± 0.27(syst)MeV

M(𝛯""%%) = 3621.40 ± 0.72(stat)± 0.27(syst)± 0.14(𝛬"%) MeV

PRL119,112001(2017)



ConfirmationinRunI• Similarsearchdonewith2 fbQF ofRunIdatarecordedin2012, 𝑠 =8TeV

• DifferenttriggeranddataprocessingconfigurationthaninRunII

• ButagainaclearpeakisseeninΛ"%𝐾Q𝜋%𝜋%massspectrum:

Ø Localsignificance:>7𝜎

Ø Signalyield:113± 21

Ø Resolution:6.6± 1.4MeV

• Δm(RunI,RunII)=0.8± 1.4MeV(consistentbetweensamples)

PRL119,112001(2017)



WeakDecay• Peakingstructureremainssignificantafter

requiringminimumdecaytime,𝑡 >5𝜎 w.r.tPV:

Ø RunIsignificance:>7σØ RunII significance:>12σ

Inconsistentwithastrongdecay

PRL119,112001(2017)



Cross-checks1. VaryingthresholdvalueofMVAselectorhasnoeffectonsignalsignificance2. MVAefficiencyasafunctionofmass:verysmooth,nobiasing3. Multiplecandidatesdonotcreatefakenarrowstructures4. CheckingcombinationsoftracksfromΛ"% andΞ""%%:againnopeakingstructures

5. VaryingparticleIDselections:nopeakingstructureemergesinWScombinationsbutstructureremainsinRSsample

6. TriedcutbasedselectioninsteadofMVA:Ø requiringgoodvertexfitqualityØ Ξ""%% vertexdisplacedØ tracksarenotproducedfromPV

ü Peaksignificancestill>12𝜎

PRL119,112001(2017)



ComparisonwithSELEX

SELEX𝜩𝒄𝒄%

• Largemassdifference:

𝑚(Ξ""%%)nop@−𝑚(Ξ""% )qrnrs =103± 2MeV

Inconsistentwithbeingisospinpartners:E.g.Guo,Hanhart,andMeissner,PLB698251-255;KarlinerandRosner,arXiv:1706.06961

PRL119,112001(2017)

Phys.Lett.B628(2005)18-24



http://www.sciencedirect.com/science/article/pii/S0370269311002474?via%3Dihub



• SearchingforΞ""%% inadditionaldecaymodes:Ξ""%% → Ξ"%𝜋%,Ξ""%%→ 𝐷%𝑝%𝐾Q𝜋%,Ξ""%% → Λ"% 𝜋%

• Ξ""%% lifetimemeasurements(progressingwell)

• Productioncross-section,quantumnumbers(𝐽E)etc

Ξ""%%

Ξ""% Ω""% • SearchingforisospinpartnerΞ""% inlargersample thanpreviousLHCbmeasurement

• Ω𝑐𝑐+ maybeinfuturebutsmaller𝜏 andhighmultiplicitychannels⟹ low𝜀wx"yz0{.

Prospectswithdoublyheavybaryons

• ContinuesearchesforΞ@", Ω@",Ξ@@ states but smallerXS and BF thanΞ"" decaysduetolargerphasespace

Justthebeginning.Alonglistofstudiesahead.

Ξ@" Ξ@@Ω@"

HADRON 21/21

SummaryLHCbveryactiveinhadronspectroscopystudies

Ø ObservedintwoLHCbdatasets

Ø Significantdisplacementconsistentwithaweaklydecayingparticle

Ø ConsistentwithΞ""%%(𝑐𝑐u)Ø Inconsistentwithbeingisospin

partnerofSELEX’sΞ""% state

Thankyou M(𝛯""%%) = 3621.40 ± 0.78 (tot) MeV/𝑐H

• ObservednarrowstructureinΛ"%𝐾Q𝜋%𝜋% massspectrum

Ξ""

Ξ""PRL119,112001(2017)

M.Traill(Glasgow)

• SearchforΞ""% continuesinLHCb data


Back-up



ResonancesinΞ""%% → Λ"%𝐾Q𝜋%𝜋%RS,sideband-subtracted

PRL119,112001(2017)



M(Λ"%)vs. M(Ξ""% ) PRL119,112001(2017)



Productioninppcollisions• ManytheoreticalstudiesonproductionofsuchstatesatLHC

• DoublepartonscatteringbelievedtobedominantaccordingtodoubleheavyproductionLHCbmeasurements

• TypicalapproachisfactorizationofthetwoQ𝑄4 pairproduction,computedinpQCD

• Heavydi-quarkformationandhadronizationthentreatednon-perturbatively

gluon-gluonfusion

charm-charmcollisions

arXiv:hep-ph/9710339



MoreonΞ@"baryons

• UnlikeΞ"" decaysunderinvestigation,likelytobenosinglegoldenmodeforΞ@"

• Multiplechannelswillbestudiedinparallelforbestchanceofadiscovery

• Ongoingworkin𝐽/Ψ ,𝐷%and𝐷1modes

Mass[Ge

V]

arXiv:hep-ph/9811212Ξ@" spectroscopy

Ξ@" → 𝐽/Ψ(Λ"% , Ξ"%, Ξ"1)

• Easierfinalstatessignatures(higher𝑝i ,𝐽/Ψmodes)

• LifetimescouldbelongerthanΞ""arXiv:hep-ph/9901224

• SmallerXSandBF expectedhowever

• Productionrateinorderofmagnitude:𝜎(Ξ@")~ (0.1-0.5)×𝜎(𝐵"%)



• FOCUS@Fermilab:PhotonbeamonBefixedtargetØ SearchedforbothΞ""% andΞ""%% statesØ 7exclusiveΞ"" → Λ"%𝑋modesØ 14exclusiveΞ"" → 𝐷1,%𝑌 modesØ Noevidenceofa𝛯"" state

• BaBar@SLAC:𝑒Q𝑒% at 𝑠 =10.58GeVØ SearchedforbothΞ""% andΞ""%% statesØ SearchedforΞ""

%(%) → Λ"%𝐾Q𝜋%(𝜋%)Ø SearchedforΞ""

%(%) → Ξ"1𝜋%(𝜋%)Ø Noevidenceof𝛯"" states

• Belle@KEK:𝑒Q𝑒% at 𝑠 =10.58GeVØ SearchedforΞ""% → Λ"%𝐾Q𝜋%Ø FoundnewΞ"% resonancedecayingtoΛ"%𝐾Q𝜋%Ø Butstillnoevidenceofa𝛯"" state

Belle2006Ξ""% → Λ"%𝐾Q𝜋%

SELEX

SELEXΞ""%% → Λ"%𝐾Q𝜋%𝜋%Babar2003

Phys.Rev.Lett.97(2006)162001

Phys.Rev.D74(2006)011103 Nucl.Phys.Proc.Suppl.115(2003)33-36

M.Traill(Glasgow)HADRON 27/21

SearchesforΞ"" byotherexperiments

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.74.011103


http://inspirehep.net/record/620821?ln=en


SELEXand𝛯""%%• Inunpublishedworkthatwasshownatseveralconferences,theSELEXcollaborationclaimedtoseetwoccustatesinΛ"%𝐾Q𝜋%𝜋%massspectrum

𝛯""%%(3780)

Ø Width>detectorresolution

Ø ContainedΛ"%𝐾Q𝜋%combinationsfrom𝛯""% observation

𝛯""%%(3452)

Unpublished

Ø Alsoclaimedevidencein𝛯"%𝜋%𝜋Q𝜋%

Ø 67± 3MeVbelowtheir𝛯""% mass

hep-ex/0702001 Charm2007

https://www-selex.fnal.gov/


https://www.classe.cornell.edu/charm07/talks/Tuesday/1400_cooper.pdf


References(notexhaustive)


Morereferences(notexhaustive)


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Spectroscopy of doubly heavy baryons at LHCb...• Mass: many models been applied to determine...

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