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M. Poli LenerXI Spring School - "Bruno Touschek"
1
Luminosity measurements with Luminosity measurements with
dimuon and single muon reconstruction of Zdimuon and single muon reconstruction of Z00 and W decays and W decays
OUTLINE: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
M. Poli LenerM. Poli Lener
Details of this work are published in CERN-THESIS-2006-013
M. Poli Lener 2
LHCb spectrometerLHCb spectrometer
1 MHz
CalorimetersMuon system
Pile-up system
Level-0:Level-0: ppTT of of
, e, h, , e, h, Rough pT ~ 20%
40 MHz
2kHz output
HLT:Final state
reconstructionFull detectorinformation
40 kHz
Level-1:Impact parameter
Vertex LocatorTrigger TrackerLevel 0 objects
380 mrad
15 mrad
M. Poli Lener 3
Luminosity measurements at Luminosity measurements at LHCbLHCb
Relative Luminosity:
Correct for systematic effects
Reconstruction and trigger efficiencies
Control the stability of the hardware
Stability of colliding beam conditions
Motivations:
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
Two approaches have been investigated to perform luminosity measurements at LHCb by measuring:
1. vertices of beam-gas interaction through the VELO detector (*)
2. event rates of physical channels with a well known and sizeable cross section
(*) L. Ferro-Luzzi, CERN-PH-EP/2005-023
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Theoretical uncertaintyTheoretical 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
W B.R.(W) 10 x zB.R.(Z+-) W.L.van Neerven et al., Nucl. Phys. B382 (2000) 11
x B
.R. (n
b)
x B
.R.
(nb
)
x B
.R.
(nb
)
W.J. Stirling et al., Eur. Phys. J. C18 (2000) 117
MRST 99, 00 PDF sets
NNLO QCD
5%
5%
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The diagrams for the boson V (Z0 and W) production are:
Pythia settingsPythia settings
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
annihilation
V
QCD radiationV VQED radiation
V
Compton scattering
(LO) (NLO) (NLO) (NLO)
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ZZ00 ++-- decay process decay process((dimuon luminometerdimuon luminometer))
25 kevents of Z0
Single muon coming from WSingle muon coming from W and and ZZ00 decay (decay (single-muon luminometersingle-muon luminometer))
50 kevents of W± ± 5 kevents of Z0 (with a not reconstructed)
Monte Carlo Monte Carlo SamplesSamples
Sz = Lint x 2 tot x (Z x B.R.) 2
where:
2 tot = (genx recx selx trig) 2
(Z x B.R.) 2
2 nb
S1 = Lint x 1tot x ( x BR) 1
where:
1tot = (genx recx selx trig) 1
( x BR) 1tot = (Z x BR) +(W x BR) 22
nb
The annual signal yield will be, assuming Lint =2 fb-1
(1 y =107s & <L > = 2x 1032 cm-2 s-1) :
The performances of these two physical processes can be compared
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Performance of the dimuon luminometerPerformance of the dimuon luminometer
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Acceptance: 4Acceptance: 4 vs 400 mrad vs 400 mrad
ZZ00++-- Number of events
Acceptance (%)
Generated in 4
3780
Found in 400 mrad
1087 28.8 28.8 ± 0.7± 0.7
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
For the next, I will assume the W and Z decays have
the same geometrical acceptance efficiency
Future
work
M. Poli Lener 9
Dimuon selection algorithmDimuon selection algorithm
The signal is represented by a couple of muons (lnL> -8) with:
opposite charge
low significance (IP/IP) < 5
high pT > 10 GeV/c
The strategy of the selection algorithm is a compromise between
a high efficiency on the signalsignal and a large rejection of the backgroundbackground sources
(*) N. Kidonanakis et al., hep-ph/0410367
All the production cross section have been evaluated at NNLO (*)
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 +- & ttW+ W- ) are not yet generated: Z0 +- decay could be rejected requiring an IP cut due to c(tau) ~ 100 m, while the ttW+ W- contribution to the signal is at most ~4‰ considering their cross section x B.R.
8 pb against 2 nb of the signal
Background processes
60
M. Poli Lener 10
Dimuon luminometer efficiencies & Dimuon luminometer efficiencies & resultsresults
The total signal efficiency 2 tot = (genx recx selx trig) 2 can be computed
380 mrad
16 mrad
Dimuon invariant Mass GeV/c2
Asymmetric distribution due to radiation in the final state
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Performance of the Performance of the single single muon luminometermuon luminometer
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Single muon selection algorithmSingle muon selection algorithm
The signal is given by single muon events coming from
W or Z0 (with a not reconstructed)
The first three physical channels (W, Z0 +-, ttW+ W- ) are not yet generated:
W and Z0 +- decays could be rejected requiring an IP cut due to c(tau) ~ 100 m, while the ttW+ 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
All the production cross section have been evaluated at NNLO (*)
Background processes
(*) N. Kidonanakis et al., hep-ph/0410367
320
3520
M. Poli Lener 13
• Signal
• Background
pT spectra
Single muon selection algorithmSingle muon selection algorithm
Selection
vertex reconstructed with IP/sigma < 3
pT cut
IP/IP
• Signal
• Background
To achieve a systematic uncertainty below 4%, a S/B ratio > 25 is needed 22 nb
500 b
conservative pT > 30 GeV/c
The single muon selection algorithm is applied on
background (~ 8x106 bb inclusive) and signal events
M. Poli Lener 14
Single muon luminometer efficiencies & resultsSingle muon luminometer efficiencies & results
The total signal efficiency 1tot = (genx recx selx trig) 1 can be calculated
M. Poli Lener 15
Comparison of luminosity Comparison of luminosity measurementsmeasurements
Sz = Lint x 2 tot x (Z x B.R.) 2
with:
22 tot tot = 14.3% = 14.3%
((Z Z x B.R.) x B.R.) 22
1.86 nb 1.86 nb
S1 = Lint x 1tot x ( x BR) 1
with:
11tottot = 6.1 % = 6.1 %
(( x BR) x BR) 11tottot = 22.13 nb = 22.13 nb
The performances of these two samples can be compared
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
To perform an “on-line” luminosity measurement with an uncertainly < 4%, 700 events must be collected during data
taking~ 31/2 hours ~ 45 minutes
M. Poli LenerXI Spring School
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SparesSpares
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L1 Trigger algorithmsL1 Trigger algorithms
A new L1 specific algorithm, based on a IP < 0.15 mm and a pT
> 10 GeV, is introduced in the L1Decision package (v4r5)
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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 B0
s→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 L0&L1 trigger (without any selection cuts)
a negligible value of ~ 50 Hz is obtained
L1 Trigger algorithms & L1 Trigger algorithms & resultsresults
M. Poli LenerXI Spring School
19Used by the dimuon Used by the dimuon luminometerluminometer
HLT Trigger data flowHLT Trigger data flow
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Parton Distribution Parton Distribution FunctionFunction
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 2÷3
% (*) 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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========================================================== 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 N:o 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 -> Z0 I 2088 10232 I 8.917E-06 I I 15 f + fbar -> g + Z0 I 2596 72079 I 1.127E-05 I I 19 f+ fbar -> gamma + Z0 I 29 743 I 1.260E-07 I I 30 f + g -> f + Z0 I 2334 37200 I 9.787E-06 I I I I I ==========================================================
Pythia resultsPythia results
M. Poli LenerXI Spring School
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<x1> = 0.1
<x2> = 2.5*10-4
From S. de Capua PhThesis http://sdecapua.home.cern.ch/sdecapua/
Parton momentum distributions
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UP & UPbar distributions vs PDF sets
(Q2=104 GeV2)
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DOWN & DOWNbar distributions vs PDF sets
(Q2=104 GeV2)
M. Poli LenerXI Spring School
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STRANGE & CHARM distributions vs PDF sets
(Q2=104 GeV2)
M. Poli LenerXI Spring School
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BOTTOM & GLUON distributions vs PDF sets
(Q2=104 GeV2)
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Single muon selection algorithmSingle muon selection algorithmThe single muon selection algorithm is applied on
background (~ 8x106 bb inclusive) and signal events
Pre-selection
particles identified as muons lnL> -2 (standard lnL> -8 )
well reconstructed tracks 2-track < 2.5
lnL hypothesis
• Signal
• Background
2 track
•Signal
• Background
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