M. Poli Lener XI Spring School - "Bruno Touschek" 1 Luminosity measurements with dimuon and single muon reconstruction of Z 0 and W decays OUTLINE: LHCb

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

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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

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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

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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

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• 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

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Single muon luminometer efficiencies & resultsSingle muon luminometer efficiencies & results

The total signal efficiency 1tot = (genx recx selx trig) 1 can be calculated

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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


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


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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)

http://durpdg.dur.ac.uk/var/tmp/pdfplot25314/plotpaw.ps



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DOWN & DOWNbar distributions vs PDF sets

(Q2=104 GeV2)




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STRANGE & CHARM distributions vs PDF sets

(Q2=104 GeV2)




26

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

Documents

M. Poli Lener XI Spring School - "Bruno Touschek" 1 Luminosity measurements with dimuon and single muon reconstruction of Z 0 and W decays OUTLINE: LHCb