7/9/2005 U. Heintz - PiC 2005 1

heavy flavor production

Ulrich Heintz

Boston University

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disclaimers/acknowledgements• not a comprehensive review but selected

results with concentration on b-production at the Tevatron

• not covered at all– c-production– results from e+e- collisions

• material from talks at Moriond, La Thuile, Beauty 2005

• thanks to D.Bauer, I.Belyaev, I.Bloch, M.D’Onofrio, M.Hildreth, V.Papadimitriou

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why?• check our understanding of QCD

– heavy flavor production at high energies checks perturbative QCD

– extracting fundamental parameters of the standard model at hadron colliders requires deep understanding of QCD

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b production at high energies• HERA (H1/ZEUS) 30/920 GeV

– photoproduction Q2<1 GeV2

• hard scales: mb, pT

– deep inelastic scattering Q2>1 GeV2

• hard scales: mb, pT, Q2

• Tevatron (D0/CDF) √s=1.96 TeV– hard scales: mb, pT

• at least one hard scale pQCD should work

concentrate on Tevatron

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b production at high energies

DO Run I (PRL 84 (2000) 5478) CDF Run I (PRL 85 (2002) 5068)

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DØ

• excellent muon acceptance |η|<2• excellent tracking coverage |η|<3• (impact parameter trigger @L2)

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CDF

• excellent mass resolution• particle id: tof and dE/dx• impact parameter trigger @L2

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Tevatron performance• since June 2003 3-fold

increase in – peak luminosity– integrated luminosity per

week– total integrated luminosity

• instantaneous luminosities above 1032cm-2s-1

• total integrated luminosity just reached 1 fb-1

• analyses shown use 40-300 pb-1

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b production at Tevatron• b production cross section at √s=1.96 TeV 50b

– rate few kHz at current luminosities

• many developments in theory in recent years– full calculations to NLO – resummation of log(pT/mb) terms (fixed order NLO +NLL FONLL)– substantial changes in fragmentation functions– new pdf’s

leading order next to leading order

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b cross section measurements• J/ and b-hadron production cross

sections (CDF)

• Inclusive b-jet cross section (CDF)

• High pT cross section for -tagged jets (DØ)

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b cross section using J/ (CDF)• use exclusive decays of b-hadrons to

measure the b-production cross section– inclusive J/ cross section– fraction of J/ from decay of b-hadrons

– b-hadron cross section for all pT

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b cross section using J/ (CDF)• J/’s can originate from

– direct production– decay of excited cc-states– decay of b-hadrons

• dimuon trigger– ¼ 300k J/ events– mass resolution 15-

20 MeV

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b cross section using J/ (CDF)• inclusive J/ cross section

nb 12406.0, 21

19 syststatJByXJpp

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b cross section using J/ (CDF)• long life time of b-hadrons

– c¼ 450 m

• J/ decay vertex displaced

• plot pseudo proper decay time x=Lxy m/pT in bins of pT of J/

• max likelihood fit for b-fraction

p pB

K

fb = 9.4%

fb = 33.7%

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b cross section using J/ (CDF)• systematic error on b-fraction ¼ 3-13%

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b cross section using J/ (CDF)• total inclusive b-hadron cross section

b 4.06.176.0, 5.2

3.2 syststatyXhpp b

%10.016.1/ XJhB b

%10.088.5/ JB

comparison with Run I B+ cross sectionRun II scaled for B+ fragmentation, |y|<1

Ldt¼ 40 pb-1 PRD 71, 032001 (2005)

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high-pT b-jet cross section (CDF)• reconstruct b-decay vertex using displaced

tracks in jet

• Rjet=0.7, |yjet|<0.7

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high-pT b-jet cross section (CDF)• determine b-fraction of tagged jets

in bins of jet pT using mass of particles that point to secondary vertex

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high-pT b-jet cross section (CDF)• b-jet cross section for 38<pT<400 GeV

L dt = 300 pb-1

source of syst error low pT high pT

luminosity 6% 6%

jet energy scale 15% 40%

jet energy scale 6% 6%

b-tagging efficiency 10% 15%

b-fraction 10% 40%

unfolding 8% 8%

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high pT -tagged jet cross section (DØ)• first step to b-production cross section• jet with in cone Ldt = 300 pb-1

• Rjet=0.5, |yjet|<0.5

• 4660 -tagged jets

• PYTHIA: 55% of all -tagged jets from heavy flavor (b,c)

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high pT -tagged jet cross section (DØ)• unsmear detector resolution

NLO: Z. Nagy, Phys. Rev. D 68, 094002

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what changed?• long-standing “discrepancies” between predicted

and measured cross sections seem resolved• better theory:

– sum terms with log(pT/mb) (FONLL) • e.g. Cacciari, Frixione,Mangano, Nason, Ridolfi, JHEP 0407 (2004) 033

– better understanding of fragmentation functions– better estimate of theory errors (upward!)

• better parton distributions: – add more gluons

• better experimental observables:– not b-quarks but b-hadrons

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quarkonia production• slightly different theoretical context

– non-relativistic QCD (NRQCD) • Lepage et al., PRD 46 4052 (1992)

– production described by short distance cross sections and nonperturbative matrix elements for evolution to quarkonium state.

– color octet modes required on top of color singlet to describe production (demonstrated by CDF in Run I)

• results: – DØ: Υ(1s) production, Υµµ final state– CDF: prompt J/ polarization

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Y(1S) production (DØ)• test boundary between perturbative and non-perturbative QCD

– perturbative color singlet production suppressed by s

– color evaporation (soft gluons carry away color/spin non-perturbative)

– perturbative color octet production can reproduce high pT region

• V.A. Khoze , A.D. Martin, M.G. Ryskin, W.J. Stirling, hep-ph/0410020

– resum logs to address low pT region

• E.L. Berger, J.Qiu, Y.Wang, Phys Rev D 71 034007 (2005)

color singlet process color octet process

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Y(1S) production (DØ)• unlike charmonium,

all bb-states are produced directly

• 50% of Y(1S) from decay of other bb-states

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Y(1S) production (DØ)• fix mass splittings and relative widths in fit

• 5 free parameters: – m(1S), (1S), n(1S), n(2S), n(3S)

|y(Y)|<0.6 0.6<|y(Y)|<1.2 1.2<|y(Y)|<1.8

all three: 4 GeV < pT(Y) < 6 GeV

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Y(1S) production (DØ)• little variation in the shape of

the cross section as a function of rapidity

• reasonable agreement with calculations by Berger et al, hep-ph/0411026

Ldt = 159 pb-1 hep-ex/0502030, PRL 94 232001 (2005)

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prompt J/ polarization (CDF)• large prompt J/ cross section (Run I)

– color octet mechanism Braaten/Fleming PRL 74 3327 (1995)

– transversely polarized J/ at large pT

transverse alignment (symmetric decays)

longitudinal alignment (asymmetric decays)

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HERA• contributing processes:

• g fusion• resolved

– contributes to photoproduction

– suppressed at high Q2

• 1999-2000 • H1

– e§ p (72 pb-1)

• ZEUS– e+ p (50 pb-1)

920 GeV

28 GeV

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HERA• + dijet• photoproduction

– Q2<1 GeV2

• H1:– b-identification

• large mass– pT of relative to jet

• long life time– impact parameter of

– vis(epebbXejjX)=38.4§3.4(stat)§5.4(syst) pb– prediction: 23.8-5.1

+7.4 GeV

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HERA• + jet

• deep inelastic scattering– 2 GeV2 < Q2 < 100 GeV

• vis(epebbXejX)=16.3§2.0(stat)§2.3(syst) pb• prediction: 9.0-1.6

+2.6 GeV

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HERA• see discrepancy at low p and high

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HERA• discrepancy at high also seen in ZEUS data

• ZEUS vis(epebbXejX)=40.9§5.7(stat)-4.4

+6.0(syst) pb– prediction: 20.6-2.2

+3.1 GeV

hep-ex/0405069 hep-ex/0502010

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conclusions• b production at the Tevatron

– finally NLO QCD and data agree• better theory calculation:

– FONLL + fragmentation functions + pdf’s

• well-defined observables

• quarkonium production– Y(1S) production agrees with pQCD + resummation

predictions – J/ is not transversely polarized as expected by color

octet production

• b production at HERA– pQCD predictions are ¼ 2 low– discrepancies at low pT and high

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