Quarkonium production at ATLAS

0.11 MB·English

by  Darren D Price

Quarkonium production at ATLAS
DarrenD.Pricea(onbehalfoftheATLAScollaboration)
DepartmentofPhysics,IndianaUniversity,Bloomington,IN47405,USA.
Abstract. TheproductionofquarkoniumisanimportanttestinggroundforQCDcalculations.TheJ/ψandΥ
productioncross-sectionsaremeasuredinproton-protoncollisionsatacentre-of-massenergyof7TeVwiththe
2
ATLASdetectorattheLHC.Differentialcross-sectionsarepresentedasafunctionoftransversemomentumand
1
rapidity.ThefractionofJ/ψproducedinB-hadrondecaysisalsomeasuredandthedifferentialcross-sectionsof
0
2 promptandnon-prompt J/ψproductiondeterminedseparately.Measurementsofthefiducialproductioncross-
sectionoftheΥ(1S)andobservationoftheχc,bJ statesarealsodiscussed.
n
a
J
1 Introduction Production of J/ψ can occur promptly from the hard
4
interaction,ormaybeproducednon-promptlyviadecayof
2
Quarkonia are formed from a quark pair of same flavour aB-hadron.J/ψfromb-decayshavepositivedisplaceddi-

] andshouldrepresentoneofthesimplestsystemsdescribed muonverticesandcanbedistinguishedfrompromptpro-
x
by QCD theory. Heavy quarkonium is a multiscale sys- duction(andnon-J/ψbackgrounds)viathepseudo-proper
e
p- tpeemrt,urabllaotwivienganfdornoring-orpoeurtsutrebsattsivoefQthCeDinatenrdplaayricbhetswpeeecn- ttirmanesvdeisrsceridmeicnaayntleτng=thLoxfyt·hmePJJ/D/ψψGv/eprTJt/eψx,.where Lxy isthe
e trumofradialandorbitalexcitationsallowstudiesofspec- A simultaneous unbinned maximum likelihood fit to
h
[ troscopyanddecaydynamics[1].Inaddition,quarkoniais invariantmassandlifetimeallowsustodistinguishprompt
an ideal probe of cold and hot nuclear matter effects[2]. andnon-promptJ/ψproductionfromcombinatorialback-
1 Many open questionsexist in this area, and it has proven ground(seeFigure1foranexampleofsuchafitprojected
v difficultthusfartouniversallydescribethekinematicsand ontothelifetimedistribution)anddeterminethefractionof
2
production properties of quarkonia. ATLAS plans to in- J/ψproducedviaB-decaysasafunctionofp andrapidity
5 T
vestigatequarkoniumproductionthroughmeasurementsof (resultsforonerapiditysliceareshowninFigure2).
9
production,spin-alignmentandassociatedhadronicactiv-
4
ity of these various states. The first production measure-
.
1 mentstowardthisgoalareoutlinedbelow.
0
2 102
ATLAS
1 s ) ∫ s = 7 TeV DToattaal PDF
iv: p2rIondculucstiioven,cprroosms-psteacntidonnomne-parsoumrepmteJn/ψts 15 p L dt = 2.3 pb-1 BSSaiiggcnnkaagllr NPouroonnmd-P pCrto oCmmoppmto pCnoeonnmetpnotnent
X . 10
0

r Cross-section measurements presented here make use of (
a /

datacollectedviaasinglemuontrigger,firstwithnothresh- s
t
oldon p thenlaterwithathresholdat4GeVasinstanta- n 1
T e
nousluminosityincreased.Triggerand reconstructionef- v
E
ficiencies are measured in data and validatedwith Monte
Carlo simulations. Weights incorporating acceptance and
10-1
efficiencycorrectionsare appliedto quarkoniacandidates
-4 -2 0 2 4 6 8 10
onanevent-by-eventbasisbeforefitsareusedtoextracta
pseudo−proper time [ps]
cross-section.
The acceptance corrections represent the probability Fig. 1. Pseudo-proper time distribution of J/ψ µ+µ candi-
−
for quarkonium with given kinematics to pass basic se- →
datesinthesignalmassregion,for9.5 < p (J/ψ) < 10.0GeV
T
lectioncuts.Theexactvalueofthisprobabilityinagiven and yJ/ψ < 0.75.Thepointsrepresentmeasureddata,thesolid
phase space is dependent on nature of the as yet unmea- linei|sthe| resultofanunbinnedmaximumlikelihoodfittoalldi-
suredspin alignmentof quarkonium.Fivespin-alignment muonpairsinthe2.5 3.5GeVmassregionprojectedontothe
scenarioshavebeenidentifiedthatinducethelargestenve- pseudo-properlifetime−distribution.
lope of variationon visible cross-sections.Measurements
arerepeatedunderapplicationofdifferentacceptancemaps
reflectingdifferentpolarisationstatesasasystematiceffect Thedataanalysedallowforstudyofthe B-production
onmeasuredproductionobservables. fraction across a pT range of 6 to 70 GeV, to far higher
transversemomentathanhavepreviouslybeenstudied.A
a e-mail:[email protected] strong dependence of the fraction is observed as a func-
EPJWebofConferences
on fraction 00..891 ACCTMDLFSA Ss s ==s17=. 9T76e T VTe,eVV,|,yJ|/y|ψyJ|/J<ψ/ψ1|<|.<200.7.65 y [nb/GeV] 101 NonFSA-pOpTriLoNnAm-LaSLpli tgB |ycn→Jrm/oψ se|J<sn/0ψ-ts .Xe7en5cvtieolnope
cti 0.7 Spin-alignment envelope dT
u p
ψ prodpt J/ 000...456 A∫TLL dAt S~ 2.3 pb-1 non-promptσ/d1100--21
m 0.3 2d10-3
Non-pro 00..21 µµ→ψ+-)10-4 ∫AsLT= Ld 7At =ST e2V.2 pb-1
0 1 10 pJ/ψ [GeV] Br(J/10-5 10 pJ/ψ [GeV]
T T
Fig.2. Productionfractionof non-prompt toinclusive J/ψasa V]
function of J/ψ transverse momentum. Overlaid is a band rep- Ge 10 Prompt cross-section
resentingthemaximalvariationoftheresultundervariousspin- nb/ ATLAS |yJ/ψ|<0.75
aClMignSmreesnutltssc.enarios. Comparison is made to existing CDF and dy [ 1 SCpoilno-uarl iEgnvampeonrta etionnve Mloopdeel
pt/dpT10-1 NNLNOLO C*o Clooulor uSri nSginlegtlet
tion of pT, but slow dependence on rapidity in the range promσ 10-2
(0 < y < 2.4)ofrapiditiesstudied.Goodagreementwith 2d10-3
CDF|d|ata (pp collisions at √s = 1.96 TeV) is observed µ-)
+
within the experimental uncertainties, suggesting the B- µ→ 10-4 ATLAS
s= 7 TeV
fractionhaslimiteddependenceoncentre-of-massenergy ψJ/10-5 ∫L dt = 2.2 pb-1
andinitialcollidingparticles,particularlyatlarge pT. Br(
Applyingcandidate-by-candidateefficiencyandaccep-
0 10 20 30 40 50 60 70
tanceweightstodi-muonpairsin p ybins,extractsig- pJ/ψ [GeV]
T
− T
nal yield from unbinned maximum likelihood fit to J/ψ
peak. Figure 3 shows an example of an inclusive differ-
Fig. 4. Non-prompt (top) and prompt (bottom) J/ψ production
entialcross-sectionextractedforonerapiditybin(fourin cross-sectionsasafunctionof J/ψtransversemomentum,com-
total),asafunctionofJ/ψ pT. pared to theoretical predictions (FONLL, in the case of non-
prompt production; NLO and NNLO* and Colour Evaporation
Modelpredictionsforpromptproduction).Overlaidisabandrep-
resentingthevariationoftheresultundervariousspin-alignment
V]102
e Inclusive cross-section assumptions on the non-prompt and prompt components. The
b/G 10 CATMLSA S ||yyJ/ψ||<<01..725 central value assumes anisotropic polarisation for both prompt
y [n Spin-alignmJe/ψnt envelope andnon-promptproduction.
d 1
T
p
d anciesinshapeandnormalisation,highlightingtheuncer-
σ/10-1 tainties that exist in explaining the nature of prompt J/ψ
2
d
) production.
µ+- 10-2
µ ATLAS
→
s= 7 TeV
ψJ/10-3 ∫L dt = 2.2 pb-1 3 Prompt Υ(1S) fiducialproduction
(
Br cross-sectionmeasurement
7 8 910 20 30 40 50
pJ/ψ [GeV]
T Measurement of the Υ(1S) cross-section has been con-
ducted in a similar manner as with J/ψ, also using sin-
Fig. 3. Inclusive J/ψ production cross-section as a function of
glemuontriggers.Incontrasttothe J/ψresults,thismea-
J/ψtransversemomentuminthe y <0.75rapiditybin.
| | surement is presented in a fiducial region: pµ > 4 GeV,
T
ηµ < 2.5toremovetheuncertaintyduetospinalignment
| |
Bycombiningtheinformationfromtheinclusivecross- inthecross-sectionmeasurement.
section and B-fraction measurements, one can extract a Unfolded differential cross-sections are compared to
non-prompt (J/ψ from b-decays) and prompt J/ψ cross- NLO pQCD and significant disagreement is noted. This
sectionversus p andrapidity.MeasurementsofJ/ψfrom behaviourisconsistentwithothertheoreticalpredictions[7]
T
b-decaysisfoundtoagreewellwithFixed-OrderNext-to- at NLO when comparedto prompt J/ψ and Υ data at the
Leading-Logtheoreticalpredictions.Comparisonstocolour Tevatron and LHC, highlighting the need for additional
singletNNLO*pQCDpredictionsandthephenomenolog- higherordercontributionstoaccountfortheobservedpro-
ical Colour Evaporation Model show significant discrep- duction.
2011HadronColliderPhysicssymposium(HCP-2011)
maticsthroughthismethod,butisbalancedbyalowprob-
V] Data 2010 ability for a conversion to occur and successfully be re-
e ATLAS constructed.Measurementvia calorimetrictechniques(as
b/G 102 NRQCD, Pythia8 showninFigure6)benefitfromincreasedsignalefficiency
p atacostofreducedresolution.Recently,similartechniques
µ+-) [ (CdiSreMct oNnlLy)O (hvaivaeΥbe(nenS)us+edγbdyeAcTayLsA)SintobroetchocnasltoruricmttehteryχbaJn(dmtPra)csktaitnegs
µ 10 modes and has led to the discovery[9] of a new set of
→
states,theχ (3P).
) bJ
S
1
(
ϒ 1
(
BR |yϒ(1S)|<1.2 eVeV ATLAS Preliminary
×σ2 dy /dpdT10-10 |ηsµ=|7< T25e.V5,,∫ pLµTd>t=411 .01G3 epVb-1 15 20 25 30 Entries / 10 MEntries / 10 M343400000000 χχDFBcciaat12 ctRake g2sr0ou1ult0nd ∫2pst. (9L χ=0 cd J7<t) ≈T>M e 31(V9µ0 + pGµb-e)-1 V<, 3|y.2(χ5c JG)|e <V 2.4
pϒ(1S) [GeV] 220000 N(χc)= 2960 ± 120
T
α=0.962 ± 0.062
δ=2.7 ± 1.9 MeV
V] Data 2010 110000
e ATLAS
b/G 102 NRQCD, Pythia8 00
p 220000 440000 660000 880000 11000000
µ-) [ (CdiSreMct oNnlLy)O 4400 32..4555 << MM((µµ++µµ--)) << 42..08 GOeRV
+
µ 10
→ 2200
)
S
1 00 220000 440000 660000 880000 11000000
ϒ( 1 MM((µµµµγγ))--MM((µµµµ)) [[MMeeVV]]
(
BR 1.2<|yϒ(1S)|<2.4 Fig.6.Theresultsofasimultaneousfittothesignalregion(top)
× dy |ηµ|<2.5, pµT>4 GeV aonfdχbc1acakngdroχucn2dm(eJ/soψnssidreebcaonndst)rurecgteiodn((vbioattcoamlo)r,ismheotwryinmgesaigsnuarels-
dpT10-1 s=7 TeV,∫ Ldt=1.13 pb-1 tmioennto)fththreouingvhatrhiaenirtrmadaisastidvieffdereecnacyesbtoetJw/eψe+nγth,eviµeµwγeadnadsµaµfusnycs--
σ/
2 0 5 10 15 20 25 30 tems.
d
pϒ(1S) [GeV]
T
Fig. 5. Differential prompt Υ(1S) µ+µ production cross-
→ − References
sectionfor yΥ(1S) < 1.2(top)and1.2 < yΥ(1S) < 2.4(bottom)
as function|of pΥ|(1S) for pµ > 4 GeV, η|µ < 2|.5. Comparison
ismadetocolourT-singletNLTOdirectpro|duc|tionpredictions,and 1. N. Brambilla et al.[QuarkoniumWorkingGroupCol-
the shaded area shows the change in the theoretical prediction laboration], hep-ph/0412158; N. Brambilla et al., Eur.
when varying the renormalisation and factorisation scales by a Phys.J.C71(2011)1534[arXiv:1010.5827[hep-ph]].
factor of two. A comparison is also made to a model based on 2. The ATLAS Collaboration, Phys. Lett. B 697 (2011)
NRQCDnativetoPythia8,foraparticularchoiceofparameters. 294[arXiv:1012.5419[hep-ex]].
3. The ATLAS Collaboration, Nucl. Phys. B 850 (2011)
387[arXiv:1104.3038[hep-ex]].
4 Reconstructionof χcJ mesons through 4. D.Acostaetal.[CDFCollaboration],Phys.Rev.D71
radiative decays (2005)032001[hep-ex/0412071].
5. V.Khachatryanetal.[CMSCollaboration],Eur.Phys.
The χ and χ mesons in radiative decays to a J/ψ and J.C71(2011)1575[arXiv:1011.4193[hep-ex]].
c1 c2
a photon have been observed via calorimetry. Measuring 6. TheATLASCollaboration,Phys.Lett.B705,9(2011)
theproductioncross-sectionsoftheχ arecrucialforpre- [arXiv:1106.5325[hep-ex]].
cJ
ciseunderstandingof J/ψproductionandactsasatestof 7. J. P. Lansberg, Eur. Phys. J. C 61 (2009) 693
pQCDinitsownright. [arXiv:0811.4005[hep-ph]].
PhotonsatATLAScanalsobeidentifiedandmeasured 8. The ATLAS Collaboration, ATLAS-CONF-2011-136
throughreconstructionofthetracksfromelectron-position (https://cdsweb.cern.ch/record/1383839).
9. TheATLASCollaboration,arXiv:1112.5154[hep-ex].
pairsassociatedwithaphotonconversionoccurringinthe
InnerDetector.ThetrackingcapabilitiesofATLASallow
for much more precise measurement of the photon kine-