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HEP05
International Europhysics Conference on High Energy
Physics
EPS in Lisbon, Portugal. 21-27 July, 2005
Beauty Production at HERA
Beate Naroska (Univ. Hamburg)
Outline
Jets + Muons (H1, ZEUS)
D*muon (H1,ZEUS)
Di-muon (ZEUS)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Heavy 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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Theoretical Description
NLO calculations in massive schemes:
FMNR photoproduction (hadronic resolved component small)
HVQDIS DIS
(no resolved component)
(Frixione, Mangano, Nason, Ridolfi)
(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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Muon + Jet Events
H1, ZEUS final: hep-ex/0502010; hep-ex/0405069;hep-ex/0312057
Select events with
jets ET>6,7 GeV
muon pT>2.5 GeV
possibly scattered electron
use PTrel and/or impact parameter δ
to enrich and determine b fraction
b fraction extracted by fit to
PTrel (ZEUS)
δ, PTrel (H1)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Results DIS Muon + Jet Events
pT (µ)
excess H1 and ZEUS
η µ excess mainly
in forward direction
µ
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Double Tag : Motivation and goals
multi-tagged bb event
no lifetime info used at present
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)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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 separate
b events from charm and
light quark background
like-sign
unlike-sign
and
separation in azimuth ΔΦ or
ΔR (D*µ )
or use inv. mass Mµµ
++/- -
+B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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 :
σcvis(ep → e D* μ X)=250±57±40 pb
(NLO: 286+159-59)
σbvis(ep → e D* μ X)=206±53±35 pb
(NLO: 52+14-9)
Charm: good agreement
Beauty: 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.
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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D*μ – (N)LO FMNR comparisons
Normalized Cross Sections!
• Expected deviations from LO due to higher order effects – flatter pT
distribution and broader ΔΦ peak.
• Good agreement with NLO calculation
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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D*μ – 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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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Data sample L = 121 pb -1
HERA I data, 96-00
ZEUS di-m Events
Aim: Total Cross Section
Selection of muons
with pT>1.5 (0.75) GeV
Total calorimetric
ET (θ>10o) >8 GeV
(+implicit pT , η cuts;
cleaning cuts)
beauty
Remove J/ψ, ψ’, etc:
Non isolation of muons
less than 250 MeV around
muons (2 GeV in
charmonium regions)
good MC description
B. Naroska Un. Hamburg
BH + J/y + y'
charm
LF background
LOW MASS
Beauty at HERA
HIGH MASS
HEP05 Lisbon 21/07/2005
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ZEUS:Signal 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 D*µ sample
Example of breakdown into contributions and agreement with MC:
non-isolated
unlike-sign
µ pairs
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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ZEUS µµ Events: Results
More restrictive cuts on muons (pT>1.5 GeV, -2.2<η<2.5)
For NLO comparison:
two µ’s from different b’s
Mµµ >3.25 GeV
(PhP +DIS)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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H1+ZEUS : Beauty from D*µ and Di-µ Events: NLO
D*µ H1 (vis.)
D*µ ZEUS PhP (rap.b<1, y range)
D*µ ZEUS DIS (rap.b<1, y range)
µµ ZEUS PhP +DIS tot.
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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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: 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
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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ZEUS : Beauty from Di-µ Events
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005
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ZEUS: Muon pT and h distributions
non-isolated
unlike-sign
µ pairs
Purity ~40-50%
ΔΦ
Signal extraction:
charm contribution estimated by D*mu
sample
fake muon backgrnd removed by taking
difference between like-sign and unlike
sign samples
(light flavour cancels)
B. Naroska Un. Hamburg
Beauty at HERA
HEP05 Lisbon 21/07/2005