Diapositiva 1

1
Luminosity measurements with dimuon and single
muon reconstruction of Z0 and W decays
M. Poli Lener

• OUTLINE
• LHCb apparatus trigger
• Theoretical uncertainty of Z0 and W production
  cross section
• Pythia settings and MC samples
• Performance of the dimuon luminometer (Z0 ???)
• Performance of the single muon luminometer (W?
  ?? Z0 ???)
• Conclusion

Details of this work are published in
CERN-THESIS-2006-013
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LHCb spectrometer
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Luminosity measurements at LHCb
Motivations

• Relative Luminosity
• Correct for systematic effects
• Reconstruction and trigger efficiencies
• Control the stability of the hardware
• Stability of colliding beam conditions

• Absolute luminosity
• Measure (and publish) cross section
• - bb inclusive production
• - prompt charm
• - weak boson production
• - constrain Parton Distribution Functions
  from
• EW processes
• Measure absolute BR of Bs

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Theoretical uncertainty
Two physical channels are investigated to perform
an on-line luminometer at LHCb due to
theoretical accuracy ( 4) and sizeable cross
sections at ?s 14 TeV
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Pythia settings

• The diagrams for the boson V (Z0 and W)
  production are

• PDF CTEQ4L is used
• The initial state radiation are switched off
• Only Z0 neutral current
• ? interference in matrix elements of Z0/? and
  ? are disabled
• A polar angle ? 400 mrad is required to the
  leptons decaying from bosons

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Monte Carlo Samples
Single muon coming from W and Z0 decay
(single-muon luminometer) 50 kevents of W ??
?? 5 kevents of Z0? ?? (with a ? not
reconstructed)
Z0? ??- decay process (dimuon luminometer) 25
kevents of Z0? ??
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Performance of the dimuon luminometer
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Acceptance 4? vs 400 mrad
In order to evaluate the generation efficiency
(?gen) in 0, 400 mrad a small pre-production
of ? 4 kevents of Z0? ??- have been generated in
4?
??1 vs ??2
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Dimuon selection algorithm
The strategy of the selection algorithm is a
compromise between a high efficiency on the
signal and a large rejection of the background
sources

• The signal is represented by a couple of muons
  (?lnL??gt -8) with
• opposite charge
• low significance (IP/?IP) lt 5
• high pT gt 10 GeV/c

Background processes
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These cuts together with the large di-muon
invariant mass are able to totally rejects
15x106 of minimum bias and 8x106 of b inclusive
events. The first two physical channels (Z0?
??- tt?W W- ) are not yet generated Z0? ??-
decay could be rejected requiring an IP cut due
to c?(tau) 100 ?m, while the tt?W W-
contribution to the signal is at most 4
considering their cross section x B.R. ? 8 pb
against 2 nb of the signal
() N. Kidonanakis et al., hep-ph/0410367
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Dimuon luminometer efficiencies results
The total signal efficiency ? 2?? tot (?genx
?recx ?selx ?trig) 2?? can be computed
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Performance of the single muon luminometer
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Single muon selection algorithm
The signal is given by single muon events coming
from W or Z0 (with a ? not reconstructed)
3520
320
The first three physical channels (W????, Z0?
??-, tt?W W- ) are not yet generated W????
and Z0? ??- decays could be rejected requiring
an IP cut due to c?(tau) 100 ?m, while the
tt?W W- contribution to the signal is at most
4 considering their cross section x B.R.
? 70 pb of the BG against 22
nb of the signal The minimum bias events are not
taking into account because 99 events are
rejected with the previous smooth selection
cuts
() N. Kidonanakis et al., hep-ph/0410367
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Single muon selection algorithm
The single muon selection algorithm is applied on
background ( 8x106 bb inclusive) and signal
events

• Selection
• vertex reconstructed with IP/sigma lt 3
• pT cut

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Single muon luminometer efficiencies results
The total signal efficiency ?1?tot (?genx ?recx
?selx ?trig) 1? can be calculated
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Comparison of luminosity measurements
The performances of these two samples can be
compared
S1? Lint x ?1?tot x (? x BR) 1? with ?1?tot
6.1 (? x BR) 1?tot 22.13 nb
Sz??? Lint x ? 2?? tot x (?Z x B.R.)
2?? with ? 2?? tot 14.3 (?Z x B.R.) 2??
? 1.86 nb
The final annual yield (Lint 2 fb-1) is
5.3x105 selected triggered events ? bandwidth
of 53 mHz ? Z0? ??- event every 20 s
2.7x106 selected triggered events ? bandwidth
of 270 mHz ? Z0 or W muon decays every 4 s
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Spares
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L1 Trigger algorithms
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L1 Trigger algorithms results

• The addition of the new L1 specific algorithm,
  called low IP muon
• reaches a L1 efficiency on the Z0? ?? signal up
  to 85 comparable to that obtained with other
  dimuon processes such as the B0s?J/?(µµ) ?
• requires a limited bandwidth in order to not
  upset the L1 streaming. The bandwidth can be
  computed looking at the muons coming from the bb
  inclusive events which pass L0L1 trigger
  (without any selection cuts)
• ? a negligible value of 50 Hz is
  obtained

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HLT Trigger data flow
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Parton Distribution Function

• New PDF sets have been recently updated
  considering the more recent data from H1 and ZEUS
  at HERA and CDF and D0 at Tevatron
• Alekhin()
• CTEQ6()
• MRST2004()
• ZEUS2005

All these PDFs estimate an uncertainty on the Z
and W boson production cross sections of ? 23
() S.I Alekhin, hep-ph/0508248 () J.Pumplin et
al., A.D. Martin et al, hep-ph/0201195 () A.D.
Martin et al, hep-ph/0507015
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Pythia results

I
I
I I I
Subprocess I Number
of points I Sigma I I
I
I
I I----------------------------------------
--------I---------------------------------I
(mb) I I
I
I I I No Type
I
Generated Tried I I
I
I
I I
I
I
I
I I 0 All included subprocesses
I 7047 120254 I 3.010E-05 I I
1 f fbar -gt Z0
I 2088 10232 I 8.917E-06 I
I 15 f fbar -gt g Z0 I
2596 72079 I 1.127E-05 I I
19 f fbar -gt gamma Z0 I
29 743 I 1.260E-07 I I 30 f
g -gt f Z0 I
2334 37200 I 9.787E-06 I I

I I
I

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Parton momentum distributions
From S. de Capua PhThesis http//sdecapua.home.ce
rn.ch/sdecapua/
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UP UPbar distributions vs PDF sets (Q2104 GeV2)
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DOWN DOWNbar distributions vs PDF sets (Q2104
GeV2)
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STRANGE CHARM distributions vs PDF sets (Q2104
GeV2)
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BOTTOM GLUON distributions vs PDF sets (Q2104
GeV2)
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Single muon selection algorithm
The single muon selection algorithm is applied on
background ( 8x106 bb inclusive) and signal
events

• Pre-selection
• particles identified as muons ? ?lnL??gt -2
  (standard ?lnL??gt -8 )
• well reconstructed tracks ? ?2?-track lt 2.5

• Signal
• Background

?lnL?? hypothesis