Beauty Production at HERA

B. Naroska Un. Hamburg Beauty at HERA HEP05 Lisbon 21/07/2005

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Beauty Production at HERA Beauty Production at HERA

HEP05HEP05International Europhysics Conference on International Europhysics Conference on High EnergyHigh Energy

PhysicsPhysicsEPS in Lisbon, Portugal. 21-27 July, 2005EPS in Lisbon, Portugal. 21-27 July, 2005

Beate Naroska (Univ. Hamburg)

Outline

Jets + Muons (H1, ZEUS)D*muon (H1,ZEUS)Di-muon (ZEUS)


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Heavy Quark Production at HERAHeavy Quark Production at HERA• At HERA heavy quarks mainly produced via

photon-gluon fusion: γg→bb, cc

in photoproduction c & b are produced rarely w.r.t. u, d, s ; also c ≈ 200 * b. Cross sections directly sensitive to gluon density in

the proton Contributions from hadronic component of the

photon expected: which and how much?

TESTS OF QCD AND PROTON/PHOTON STRUCTURE


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Theoretical DescriptionTheoretical DescriptionNLO calculations in massive schemes:FMNR photoproduction (hadronic resolved component small) (Frixione, Mangano, Nason, Ridolfi) HVQDIS DIS (no resolved component) (Harris, Smith)

LO-ME+PS models used:PYTHIA photoproduction (DGLAP) (excitation+hadronic resolved) (Bengtsson, Sjostrand)

CASCADE photoproduction (CCFM) (no resolved component)

RAPGAP electroproduction (no resolved component) (H.Jung)

Example: HVQDIS


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Muon + Jet EventsMuon + Jet Events

Select events with jets ET>6,7 GeV muon pT>2.5 GeV possibly scattered electronuse PT

rel and/or impact parameter δto enrich and determine b fraction

H1, ZEUS final: hep-ex/0502010; hep-ex/0405069;hep-ex/0312057

b fraction extracted by fit toPT

rel (ZEUS)δ, PTrel (H1)


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H1 and ZEUS Photoproduction Results (Muon + Jet Events)Muon + Jet Events)

Good agreement H1-ZEUS

ZEUS no excess at low pTmuReasonable agreement with NLO calculations


6Results DIS Muon + Jet EventsResults DIS Muon + Jet Events

pT (µ)excess H1 and ZEUS

η µ excess mainly in forward direction

µ


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multi-tagged bb event

no lifetime info used at present

Double Tag : Motivation Double Tag : Motivation andand goals goals

Two tag strategies: D*µ (H1 final, ZEUS prel.)µµ (ZEUS Prel. NEW)New

No Jets: phase space of b production reaches to low pT(b)


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H1: D*μ correlations

Data sample L = 89 pb -1 HERA I data, 97-00

Exploit el. charges of D*/µ to separateb events from charm and light quark background like-sign unlike-signand separation in azimuth ΔΦ or ΔR (D*µ )or use inv. mass Mµµ

and

+-

++/- -


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D*μ correlations

D* yield measured from the ΔM technique : ΔM = mKππs – MKπ

Extract N(D*μ) from fit to Gaussian peak + background : N(D*μ) = 151 ± 22

‘2D fit’ – simultaneous likelihood fit to ΔM in 4 correlation regions to extract c and b contributions

D* peak and background shape from 1D fit

6 free parameters: Nc, Nb and four background regions (χ2 = 145.5 / 154 d.o.f)


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V. good agreement between 2D fit and individual 1D fits

Nc = 53 ± 12Nb = 66 ± 17

Use these to calculate visible cross sections for : σc

vis(ep → e D* μ X)=250±57±40 pb (NLO: 286+159-59)σb

vis(ep → e D* μ X)=206±53±35 pb (NLO: 52+14-9)

Fit Result

Charm: good agreementBeauty: data too high

Visible kinematic region : pT (D*) > 1.5 GeV; |η(D*)| < 1.5; p(μ) > 2 GeV; |η(μ)| < 1.735; 0.05 < y < 0.75; Q2 < GeV2.


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D*D*μμ – (N)LO FMNR comparisons – (N)LO FMNR comparisons

• Expected deviations from LO due to higher order effects – flatter pT distribution and broader ΔΦ peak.• Good agreement with NLO calculation

Normalized Cross Sections!


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D*D*μμ – PYTHIA & CASCADE MC – PYTHIA & CASCADE MC comparisonscomparisons

• Both MCs give a good description of the data• NB: Although different approaches to parton evolution are taken, the differences are smaller than the experimental errors


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beauty

BH + J/+ '

charm

LF background

ZEUS di-ZEUS di- Events Events

Aim: Total Cross SectionSelection of muonswith pT>1.5 (0.75) GeV

Total calorimetric ET (θ>10o) >8 GeV(+implicit pT , η cuts; cleaning cuts)

Remove J/ψ, ψ’, etc:Non isolation of muonsless than 250 MeV around muons (2 GeV in charmonium regions)

good MC description LOW MASS HIGH MASS

Data sample L = 121 pb -1 HERA I data, 96-00


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Signal extraction: use non-isolated µ pairs, all inv. massesUse data for background determination•fake muon background removed by taking difference between like-sign and unlike sign samples (light flavour cancels) •charm contribution estimated with D*µ sample

ZEUS:Signal ExtractionZEUS:Signal Extraction

Example of breakdown into contributions and agreement with MC:

non-isolatedunlike-signµ pairs


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For NLO comparison:two µ’s from different b’sMµµ >3.25 GeV(PhP +DIS)

ZEUS µµ Events: Results

More restrictive cuts on muons (pT>1.5 GeV, -2.2<η<2.5)


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Comparison to NLO Calculations (Muon + Jet Events)Comparison to NLO Calculations (Muon + Jet Events)

Data in general aboveNLO pQCD up to 2 s.d.

Good agreement between H1 and ZEUS


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D*µ ZEUS PhP (rap.b<1, y range)

D*µ H1 (vis.)

D*µ ZEUS DIS (rap.b<1, y range)

µµ ZEUS PhP +DIS tot.

H1+ZEUS : Beauty from D*µ and Di-µ Events: NLO


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SummarySummary

Beauty results HERA I with jets and muon final

B Cross sections tend to be above NLO pQCD calculations

Shapes of differential distributions deviate from QCD only in few places

(e.g. forward, low pTµ)

Double Tag Analyses started: D*µ, µµ - stat. limited

reach to low pT(b)– total cross section possible

Measured cross sections higher than NLO QCD

Shape of Differential Distributions described: NLO effects visible


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ZEUS : Beauty from Di-µ Events


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Signal extraction: charm contribution estimated by D*mu samplefake muon backgrnd removed by taking difference between like-sign and unlike sign samples(light flavour cancels)

ZEUS: Muon pZEUS: Muon pTT and and distributions distributions

non-isolatedunlike-signµ pairs

ΔΦ

Purity ~40-50%

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Beauty Production at HERA

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