Heavy Flavor Production at the Tevatron

0.13 MB·English

by  Chunhui Chen

Heavy Flavor Production at the Tevatron
Chunhui Chen
(RepresentingtheCDFandDØCollaboration)
DepartmentofPhysicsandAstronomy,UniversityofPennsylvania,Philadelphia,PA19104,U.S.A.
4
0
0 Abstract. UsingasubsetofthecurrentRunIIdata,theCDFandDØhaveperformedseveralmeasurementsonheavyflavor
2 production.Inthispaper,wepresentanewmeasurementofpromptcharmmesonproductionbyCDF.Wealsoreportthelatest
CDFIImeasurementsofinclusiveJ/Y productionandb-productionwithoutrequirementofminimumtransversemomentum
n
on J/Y and b-quark. They are the first measurements of the total inclusive J/Y and b quark cross section in the central
a
rapidity region at a hadron collider. The results of J/Y cross section as a function of rapidity, and b-jet production cross
J
sectionmeasuredbyDØarealsoreviewed.
6
1

1 INTRODUCTION celerator has delivered about 300pb−1 integrated lumi-
v nosities,bothexperimentscollectedmorethan200pb 1
−
1 Measurementsof the productioncross section of heavy physics quality data. In this paper, we will give a brief
2
flavor quarks (c and b quarks) in the pp¯ collisions pro- summaryofthelatestresultsonheavyflavorproduction
0
vide us an opportunity to test the prediction based on fromTevatronRunII.
1
theQuantumChromodynamics(QCD).NoonlyisQCD
0
4 oneofthefourfundamentalforcesofthenature,butalso
0 many searches of new physics beyond Standard Model PROMPTCHARMMESON
/ requireagoodunderstandingoftheQCDbackground.
x PRODUCTIONCROSSSECTION
The Bottom quark production cross section has been
e
- measured by both the CDF and DØ experiments [1,
p In orderto helpunderstandingthe discrepancybetween
2] at the Fermilab Tevatron in pp¯ collision at √s =
e measured RunI Bottom quark cross section measure-
h 1.8TeV, and found to be about three times larger than ment and theoretical calculation, one can repeat previ-
: the next-to-leading order (NLO) QCD calculation [3,
v ousmeasurementwithbettercontrolofexperimentalun-
4]. Since then, several theoretical explanation has been
i certainties. An alternative approach is to examine the
X proposed to solve the disagreement, such as the large
production rate of another heavy quark. Charm meson
r contributionsfrom the NNLO QCD processes, possible productioncrosssectionshavenotbeenmeasuredin pp¯
a contribution from “new physics” [5] etc. Recently, a
collisions and may help to solve this disagreement.For
more accuratedescriptionof b quarkfragmentationhas
CDFIIupgrade,oneofthecrucialimprovementwithre-
reducedthediscrepancytoafactor1.7[6].Nevertheless,
specttotheCDFIistheimplementationofaSiliconVer-
further experimental measurements on the heavy flavor
texTrigger(SVT)[9],whichallowsustotriggerondis-
production are essential to shed light on the remaining
placedtracksdecayedfromlong-livedcharmandbottom
cloudsofthislongstandingissue.
hadrons. With this trigger, large amountof fully recon-
Since the end of RunI (1996), the Tevatron had un-
structedcharmmesonhasbeencollected,openinganew
derdonemajorupgrade.Thecenterofmassenergyinthe
window for heavy flavor production studies at hadron
pp¯ collisionwas increasedfrom√s=1.8TeVto√s=
collider.
1.96TeV. The large luminosity enhancement dramati- Usingjust5.8 0.3pb 1 data,CDFperformsa mea-
−
callyincreasesthediscoveryreachandmovestheexper- ±
surement of prompt charm meson production cross
imental programinto a regime of precision hadron col-
section [10]. The charm mesons are reconstructed in
liderphysics.Atthesametime,bothCDF[7]andD0[8] thefollowingdecaymodes:D0 K p +,D + D0p +
experimentalcollaborationssignificantlyupgradedtheir with D0 K p +, D+ K p→+p +−, D+ ∗fp→+ with
detectorstoenrichthephysicscapabilities,especiallyfor f K+K→, a−nd their c→harg−e conjugates,→as shown in
the heavy flavor physics program. The Tevatron RunII → −
Fig. 1. We separate charm directly produced in pp¯ in-
data taking period started in April 2002, so far the ac-
teraction (prompt charm) from charm decayed from B
2Entries per 2 MeV/c213000000000 D0fi K-p + (a) 2Entries per 0.3 MeV/c284600000000 (b) D*+Dfi 0fiD0Kp +-,p + ss [nb/GeV/c]/dpd [nb/GeV/c]/dpdTT111111000000234234 D0 ss [nb/GeV/c]/dpd [nb/GeV/c]/dpdTT111100002323 D*+
0 1.8 1.85 1.9 00.14 0.15 0.16 55 1100 1155 2200 55 1100 1155 2200
m(K-p +) [GeV/c2] m(K-p +p +)-m(K-p +) [GeV/c2] ppTT [[GGeeVV//cc]] ppTT [[GGeeVV//cc]]
110033
22 MeV/c2000 D+fi K-p +p + (c) 25 MeV/c230000 D+fi f p +Ds+fi f p + (d) [nb/GeV/c]/dp [nb/GeV/c]/dpTT110033 D+ [nb/GeV/c]/dp [nb/GeV/c]/dpTT110022 D+s
s per 1000 s per ssdd110022 ssdd
ntrie ntrie 100 1100
E E
0 1.7 1.8 1.9 2 0 1.8 1.9 2 2.1 55 1100 11pp55TT [[GGeeVV//cc]]2200 55 1100 11pp55TT [[GGeeVV//cc]]2200
m(K-p +p +) [GeV/c2] m(K+K-p +) [GeV/c2]
FIGURE 2. The measured differential cross section mea-
FIGURE 1. Charm signals summed over all pT bins: (a) surements for y 1, shown by the points. The inner bars
invariant mass distribution of D0 K−p + candidates; (b) represent the s|ta|ti≤stical uncertainties; the outer bars are the
mass difference distribution of D∗+→ D0p + candidates; (c) quadratic sums of the statistical and systematic uncertainties.
invariantmassdistributionofD+ K→−p +p + candidates;(d) Thesolidcurves arethetheoretical predictionsfromCacciari
icnavnadriidaanttesm.ass distribution of D+→→ fp + and D+s → fp + abnadndNs.asTohne[1d1a]s,hwedithcuthrveeunshcoewrtaninwtiietshinthdeicDate+dbcyrotshsessehcatdioend
∗
isthetheoreticalpredictionfromKniehl[12];thedottedlines
indicatetheuncertainty.NopredictionisavailableyetforD+
s
mesons(secondarycharm)usingtheimpactparameterof production.
thecharmcandidatewithrespecttotheprimaryinterac-
tion point. Promptcharm meson points to the beamline
and its impact parameter is zero. The secondary charm underestimate B meson production at √s=1.8TeV by
meson candidate does not necessarily point back to the similarfactors[2,6,13].
primary vertex, it has a rather wide impact parameter
distribution. The shape of the impact parameter distri-
bution of secondary charm is obtained from a Monte INCLUSIVEJ/Y PRODUCTIONCROSS
Carlosimulation.Thedetectorimpactparameterresolu- SECTION
tion is modeled from a sample of K0 p +p decays
S → −
that satisfy the same trigger requirement. The prompt The CDFII detector has improved the dimuon trigger
charm fraction is measured as a function of charm me- systemwithalowerthresholdof1.5GeV/c.Thisallows
son pT. Average over all pT bins, (86.6 0.4)%of the ustotriggertheJ/Y m m +eventwithtransversemo-
tDainc0daml(u7en7sco.3enrs±t,a(i3n8.t88i).e1%s±oon1fl.yD1)).+s%aorefDpr∗o+m,(p8tl9y.1p±r±od0u.4c)e%d(osftaDti+s-, maJb/eoYnuttucm3an9ad.7lildptabht−ees1w(dasayttaadt→,iosCwtiDcna−FtlourpenTcco(eJnr/tsatYrinu)tcy=teod0nG2ly9e)9V,8/a0sc0.s±Uhos8iwn0gn0
The measured prompt charm meson integrated cross inFig.4.AnewmeasurementofthetotalinclusiveJ/Y
section are found to be s (D0,pT 5.5GeV/c, y crosssectionin the centralrapidityregion y 0.6has
1)=13.3 0.2 1.5m b,s (D∗+,pT≥ 6.0GeV/c,|y| ≤ beencarriedout.Thisisthefirstmeasurem|en|t≤oftheto-
1) = 5.2 ±0.1 ±0.8m b, s (D+,pT ≥6.0GeV/c,|y|≤ talinclusiveJ/Y crosssectioninthecentralrapidityre-
11))==40..37±5±0.10.±0±50.7m0.b2a2nmdbs,(wDh+se,repTt≥h≥e8fi.r0sGt ueVnc/ecr,t|a|yi|n|≤≤ty gshioonwantianhFaidgr.o5n,caonldlidtheer.iTnhteegdraiftfeedrecnrotisaslsceroctsisosneicstimoneais-
± ±
is statistical and the second systematic. The measured suredtobe:
differential cross sections are compared to two recent
calculations [11, 12], as shown in Fig. 2 and Fig. 3. s (pp¯ J/Y X, y(J/Y 0.6) Br(J/Y mm )
→ | |≤ × →
Theyarehigherthanthetheoreticalpredictionsbyabout
100%atlow p and50%athigh p .However,theyare =240 1(stat)+35(syst)nb,
T T ± 28
compatible within uncertainties. The same models also − (1)
yy22..55 yy22..55
oror oror
TheThe 22 D0 TheThe 22 D*+
Data/Data/11..55 Data/Data/11..55 40000 CDF Run II Preliminary
299,800 ± 800 Events
11 11 Luminosity = 39.7 pb-1
Width = 24 MeV/c2
00..55 00..55
30000
00 00
55 1100 1155 2200 55 1100 1155 2200 2
ppTT [[GGeeVV//cc]] ppTT [[GGeeVV//cc]] V/c
TheoryTheory22..2255 D+ s/5 Me20000
ata/ata/ ent
DD11..55 v
E
11 10000
00..55
00
55 1100 1155 2200
pp [[GGeeVV//cc]] 0
TT 2.70 2.90 3.10 3.30 3.50
M(mm ) GeV/c2
FIGURE3. Ratioofthemeasuredcrosssectionstothethe-
oretical calculationfromCacciariand Nason. Theinner error
FIGURE4. TheinvariantmassdistributionoftriggeredJ/Y
barrepresentsthestatisticaluncertainty,theoutererrorbarthe
quadraticsumofthestatisticalandsystematicuncertainty.The eventsreconstructedinthe39.7pb−1ofCDFIIdata.
hatchedbandrepresentstheuncertaintyfromvaryingtherenor-
malizationandfactorizationscale.
Taking advantage of the large azimuth coverage of its CDF Run II Preliminary
102
muon system, the DØ measured the differential cross )
sectionoftheinclusiveJ/Y asafunctionoftherapidity V/c Data with stat. uncertainties
using4.74pb 1.ThedistributionisshowninFig.6. Ge Systematic uncertainties
−
(
b/
n
) 101
BOTTOM QUARKPRODUCTION
CROSSSECTION →mm
yJ/
(
r
B
TsuhreedRubnyICcDenFtraanldb-DquØarhkapsroadmucintiiomnucmrostsrasnescvteiorsnemmeoa-- 6) . 1
mentumcutontheb-hadronsduetothetriggerrequire- <0.
ments. Since those measurements only explore a small ||(y
T
fraction( 10%)oftheb-hadron p spectrum,itisnot p
clearfrom∼thedatawhethertheexceTssoverthetheoryis /d 10-1
duetoanoveralldiscrepancyofthebb¯productionrate,or sd
0 4 8 12 16
itiscausedbyashiftinthespectrumtowardhigher pT. p (J/y ) GeV/c
An inclusive measurement of bottom quark production T
overalltransversemomentumcancertainlyhelpresolve FIGURE5. ThedifferentialcrosssectionforinclusiveJ/Y
thisambiguity. asafunctionof pT with y 0.6.
| |≤
Notice that large fraction of b-hadron H decays to
b
J/Y finalstates,whereH denotesbothhadronandanti-
b
hadron. CDF performed an analysis to extract the in- the prompt J/Y ’s, which are directly produced or de-
clusive b-hadron cross section from the measured in- cayed from higher charmonium states, their vertex are
clusive J/Y production cross section. Due to the long at the proton-antiprotoninteractionpoint. As the result,
livelifetimeoftheb-hadrons,thevertexoftheJ/Y de- we can statistically separate these two components by
cayedfromab-hadron(secondaryJ/Y )isusuallyhun- examining the projected J/Y decay distance along its
dreds microns away from the primary vertex, while for
JJ//yy CCrroossss SSeeccttiioonn ppeerr uunniitt ooff rraappiiddiittyy
b102 c)
oss Section, n D zppeTT((rJJo//yy R))>>u58nGG2ee VVP//ccRELIMINARY nb/(GeV/ 101 CDF RuDanta wIiIth Pstartiseticlaiml uncinertaainrtiyes
Cr ) Systematic uncertainties
10 (Includes correlated uncertainties)
→mm
y(J/ 1
r
B
) .
X
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6J/y R1.a8pidity2 →yJ/
b 10-1
H
FIGURE6. ThedifferentialcrosssectionforJ/Y asafunc- (
r
B
tionof y.
| | ) .
b
H
(
T
p
d 10-2
/ 0 5 10 15 20 25
CDF Run II Preliminary sd p (H ) GeV/c
T b
101
)
eV/c DSyastate wmitaht ics tuantiscteicrtaali nutniecsertainties oFfIGpTU(RHEb)8w.ithb-|yh|a≤dro0n.6d.ifferentialcrosssectionasafunction
G
(Includes correlated uncertainties)
(
b/
n
) 1 Luckily, the b-hadron decayed at rest can still trans-
fer a few ( 1.7) GeV/c transverse momentum to its
→mm J/Y daught∼er because of the large b-hadronmass. The
yJ/ knowledgeofthesecondaryJ/Y productionwithtrans-
(
r verse momenta less than 2.0GeV/c allows us to probe
B
) . 10-1 the b-hadrons with low transverse momenta down to
zero. Therefore using the measured b-hadron differen-
yp(J/T From b twiaelacrreoasbslseetcotieoxntrwacitthth1e.b2-5h≤adrpoTn(dJi/fYfe)re≤nti1a7l.c0roGsesVse/cc-,
d
/ tionasafunctionofp (H )downtop (H )=0GeV/c.
T b T b
sd
10-2 Todoso,weperformaconvolutionthatisbasedonthe
0 4 8 12 16
p (J/y ) GeV/c Monte Carlo template of the b-hadron transverse mo-
T mentum distribution. The unfolding procedure is then
FIGURE7. b-hadrondifferentialcrosssectionasafunction repeated using the measured b-hadronproductionspec-
of pT(J/Y ). trum as the input spectrum for the next iteration, until
the c 2 comparison between the input and output spec-
trumcalculatedaftereachiterationbecomesstable.The
transverse momentum. The measured b-fraction is then measuredb-hadroncrosssectionasafunctionofpT(Hb)
applied to the previouslymeasuredinclusive J/Y cross is plotted in Fig. 8. The total b-hadron cross section is
sectiontoobtainthedifferentialproductioncrosssection foundtobe
ofH J/Y X asafunctionof p (J/Y ).However,the
b→ T s (pp¯ H X, y(H ) 0.6) Br(H J/Y X)
above algorithmto extractb-fraction does not work for → b | b |≤ × b→
J/Y candidatewithlowtransversemomentum,because
Br(J/Y mm )=24.5 0.5(stat)+4.7(syst)nb,
ab-hadronwithlowpT doesnottravelfarawayfromthe × → ± 3.9
− (2)
primaryvertexinthetransverseplane.Thereforeamini-
mump (J/Y ) 1.25GeV/crequirementisimposedfor Thetotalsingleb-quarkcrosssectionisobtainedbydi-
T
≥ videdthismeasurementbytwo,thebranchingfractions,
theb-hadroncrosssectionmeasurementasafunctionof
p (J/Y )inorderto havea reliabledeterminationofb- andtherapiditycorrectionfactorsobtainedfromMC.We
T
fraction.Themeasureddifferentialcrosssectionresultis
showninFig.7.
DØ Run 2 Preliminary precise measurements on the heavy flavor production
V) will be available in the near future. At the same time,
Ge
sd (nb/jetdET10-1 DPyatthaia, CTEQ4M, dR<0.3 spneliosvmreer,asolutohcthehrearsasatphneeaclbtysb¯secosofrhrhaeevlaaevtiyaolnsfloaanvbdoerecnc¯prccooadrrrrueiceltaditoioonuntmdteuocreihnxag--
theproduction.Inthenextafewyears,acombinationof
10-2 betterexperimentaldataandimprovedtheoryshouldad-
vanceourknowledgesoftheheavyquarksproduction.
10-3
20 30 40 50 60 70 80 90 100 ACKNOWLEDGMENTS
EjTet (GeV)
FIGURE 9. Measured RunII b-jet cross sectioncompared We thanktheCDFandDØcollaborationfortheirhelps
totheoreticalprediction. whilepreparingthispaper.Wealsothanktheconference
organizersforawonderfulmeeting.
find:
s (pp¯ b¯X, y(b) 0.6)
REFERENCES
→ | |≤
(3)
=18.0 0.4(stat) 3.8(syst)m b,
± ± 1. Abbott,B.,etal.,Phys.Lett.,B487,264–272(2000).
and 2. Acosta,D.,etal.,Phys.Rev.,D65,052005(2002).
s (pp¯ b¯X, y(b) 1) 3. Nason, P.,Dawson, S.,andEllis,R.K.,Nucl.Phys.,
→ | |≤ (4) B327,49–92(1989).
=29.4 0.6(stat) 6.2(syst)m b. 4. Albajar,C.,etal.,Phys.Lett.,B186,237(1987).
± ± 5. Berger, E.L.,et al.,Phys. Rev. Lett.,86, 4231–4234
(2001).
B-JET PRODUCTIONCROSSSECTION 6. Cacciari,M.,andNason,P.,Phys.Rev.Lett.,89,122003
(2002).
7. Blair,R.,etal.(1996),FERMILAB-PUB-96-390-E.
Using 3.4pb−1 of data, a b-jet productioncross section 8. Abachi,S.(1996),FERMILAB-PUB-96-357-E.
analysishasbeenperformedbyDØ.Thecandidateevent 9. Ashmanskas, W.,et al.,Nucl. Instrum. Meth., A447,
isselectedbyassociatingamuontrackwithajet,which 218–222(2000).
isdefinedwithR=pD h 2+D f 2conealgorithm.Notice 10. Acosta,D.,etal.,Phys.Rev.Lett.,91,241804(2003).
11. Cacciari,M.,andNason,P.,JHEP,09,006(2003).
thefactthatthemuondecayedfrombquarkhasahigher
12. Kniehl.,B.(Privatecommunication),Theircalculation
transversemomentumwithrespecttothenetmomentum
employsthemethoddescribedinB.A.Kniehl,G.Kramer,
vector of combined muon and jet, the corresponding B.Potter,Nucl.Phys.B597,337-369(2001).
distribution is then used to fit the b-jet fraction. The 13. Binnewies,J.,Kniehl,B.A.,andKramer,G.,Phys.Rev.,
signal template is modeled from a b m Monte Carlo D58,034016(1998).
simulation, and the background tem→plate is extracted 14. Abbott,B.,etal.,Phys.Rev.Lett.,85,5068–5073(2000).
from1.5millionQCDevents.Aftercorrectingthemuon
andjetreconstructionefficiency,andthe calorimeterjet
energyresolution,theb-jetcrosssectionisobtained.The
preliminary result is shown in Fig. 9 compared to the
theoretical prediction. This measurement is consistent
withthepreviousRunImeasurement[14].
CONCLUSION
Theunderstandingoftheheavyflavorproductioniscur-
rently one of the most important challenges faced by
QCD. In this paper, we present the most recent mea-
surementsfrom CDF and DØ experiments.Given large
amount of data that have already been collected, rapid
improvement of Tevatron performance, and further un-
derstanding of the detector, we expect that much more