Beauty Production at HERA

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Beauty Production at HERA

• HEP05
• International Europhysics Conference on High
  Energy
• Physics
• EPS in Lisbon, Portugal. 21-27 July, 2005

Beate Naroska (Univ. Hamburg)
Outline

• Jets Muons (H1, ZEUS)
• Dmuon (H1,ZEUS)
• Di-muon (ZEUS)

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Heavy Quark Production at HERA

• At HERA heavy quarks mainly produced via
  
  photon-gluon
  fusion ?g?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 Description
NLO calculations in massive schemes FMNR
photoproduction (hadronic resolved component
small) (Frixione, Mangano, Nason,
Ridolfi) HVQDIS DIS (no
resolved component)
(Harris, Smith) LO-MEPS models used PYTHIA
photoproduction (DGLAP) (excitationhadronic
resolved) (Bengtsson, Sjostrand) CASCADE
photoproduction (CCFM) (no resolved
component) RAPGAP electroproduction (no resolved
component) (H.Jung)
Example HVQDIS
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Muon Jet Events
H1, ZEUS final hep-ex/0502010
hep-ex/0405069hep-ex/0312057
Select events with jets ETgt6,7 GeV muon
pTgt2.5 GeV possibly scattered electron use
PTrel and/or impact parameter d to enrich and
determine b fraction
b fraction extracted by fit to PTrel (ZEUS) d,
PTrel (H1)
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H1 and ZEUS Photoproduction Results (Muon Jet
Events)

• Good agreement H1-ZEUS

• Reasonable agreement with NLO calculations

• ZEUS no excess at low pTmu

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Results DIS Muon Jet Events
pT (µ) excess H1 and ZEUS
? µ excess mainly in forward direction
µ
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Double Tag Motivation and goals
Two tag strategies Dµ (H1 final, ZEUS
prel.) µµ (ZEUS Prel. NEW)
multi-tagged bb event no lifetime info used at
present
New
No Jets phase space of b production reaches to
low pT(b)
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H1 Dµ correlations

Data sample L 89 pb -1 HERA I data, 97-00
Exploit el. charges of D/µ to separate b events
from charm and light quark background
like-sign unlike-sign and separation
in azimuth ?F or ?R (Dµ ) or use inv. mass Mµµ
/- -
and
-
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Dµ correlations
D yield measured from the ?M technique ?M
mKpps MKp Extract N(Dµ) from fit to Gaussian
peak background N(Dµ) 151 22

2D fit simultaneous likelihood fit to ?M 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 (?2 145.5 / 154 d.o.f)
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Fit Result
V. good agreement between 2D fit and individual
1D fits Nc 53 12 Nb 66 17 Use these to
calculate visible cross sections for scvis(ep
? e D µ X)2505740 pb
(NLO 286159-59) sbvis(ep ? e D µ
X)2065335 pb
(NLO 5214-9)
Charm good agreement Beauty data too high
Visible kinematic region pT (D) gt 1.5 GeV
?(D) lt 1.5 p(µ) gt 2 GeV ?(µ)
lt 1.735 0.05 lt y lt 0.75 Q2 lt GeV2.
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Dµ (N)LO FMNR comparisons
Normalized Cross Sections!

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

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Dµ PYTHIA CASCADE MC comparisons

• 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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ZEUS di-m Events
Data sample L 121 pb -1 HERA I data, 96-00
Aim Total Cross Section Selection of muons with
pTgt1.5 (0.75) GeV Total calorimetric ET
(?gt10o) gt8 GeV (implicit pT , ? cuts cleaning
cuts) Remove J/?, ?, etc Non isolation of
muons less than 250 MeV around muons (2 GeV in
charmonium regions)
beauty BH J/y? y' charm LF background
good MC description
LOW MASS
HIGH MASS
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ZEUSSignal Extraction

• Signal extraction
• use non-isolated µ pairs, all inv. masses
• Use 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 Dµ sample

Example of breakdown into contributions and
agreement with MC
non-isolated unlike-sign µ pairs
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ZEUS µµ Events Results
More restrictive cuts on muons (pTgt1.5 GeV,
-2.2lt?lt2.5)
For NLO comparison two µs from different
bs Mµµ gt3.25 GeV (PhP DIS)
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Comparison to NLO Calculations (Muon Jet
Events)
Data in general above NLO pQCD up to 2 s.d. Good
agreement between H1 and ZEUS
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H1ZEUS Beauty from Dµ and Di-µ Events NLO
Dµ H1 (vis.)
Dµ ZEUS PhP (rap.blt1, y range)
Dµ ZEUS DIS (rap.blt1, y range)
µµ ZEUS PhP DIS tot.
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Summary

• 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 Dµ, 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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ZEUS Muon pT and h distributions
non-isolated unlike-sign µ pairs
Purity 40-50
?F
Signal extraction charm contribution estimated
by Dmu sample fake muon backgrnd removed by
taking difference between like-sign and unlike
sign samples (light flavour cancels)