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Luminosity measurements with dimuon and single muon reconstruction of Z 0 and W decays

Luminosity measurements with dimuon and single muon reconstruction of Z 0 and W decays. M. Poli Lener. OUTLINE: LHCb apparatus & trigger; Theoretical uncertainty of Z 0 and W production cross section; Pythia settings and MC samples;

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Luminosity measurements with dimuon and single muon reconstruction of Z 0 and W decays

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  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 XI Spring School - "Bruno Touschek"

  2. 40 MHz Level-0: pT of m, e, h, g Rough pT ~ 20% Calorimeters Muon system Pile-up system 380 mrad 1 MHz Vertex Locator Trigger Tracker Level 0 objects Level-1: Impact parameter 15 mrad 40 kHz HLT: Final state reconstruction Full detector information 2kHz output LHCb spectrometer

  3. Two approaches have been investigated to perform luminosity measurements at LHCb by measuring: • vertices of beam-gas interaction through the VELO detector (*) • event rates of physical channels with a well known and sizeable cross section (*) L. Ferro-Luzzi, CERN-PH-EP/2005-023 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

  4. MRST 99, 00 PDF sets NNLO QCD 5%  x B.R. (nb)  x B.R. (nb) 5%  x B.R. (nb) W B.R.(W) 10 xzB.R.(Z+-) W.L.van Neerven et al., Nucl. Phys. B382 (2000) 11 W.J. Stirling et al., Eur. Phys. J. C18 (2000) 117 Theoretical uncertainty Two physical channels are investigated to perform an “on-line” luminometerat LHCb due to theoretical accuracy (~ 4%) and sizeable cross sections at s = 14 TeV

  5. V annihilation Compton scattering V V QCD radiation (LO) (NLO) (NLO) (NLO) V QED radiation Pythia settings • The diagrams for the boson V (Z0 and W) production are: • PDF CTEQ4Lis 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

  6. The annual signal yield will be, assuming Lint =2 fb-1 (1 y =107s & <L > = 2x 1032 cm-2 s-1): Sz = Lintx  2 tot x (Z x B.R.) 2 where:  2 tot= (genx recx selx trig) 2 (Z x B.R.) 2 2 nb S1 = Lintx 1tot x ( x BR) 1 where:  1tot= (genx recx selx trig) 1 ( x BR) 1tot= (Z x BR) +(W x BR)  22 nb The performances of these two physical processes can be compared 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 

  7. Performance of the dimuon luminometer

  8. Acceptance: 4 vs 400 mrad Future work For the next, I will assume the W  and Z  decays have the same geometrical acceptance efficiency 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

  9. All the production cross section have been evaluated at NNLO (*) 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> -8) with: • opposite charge • low significance (IP/IP) < 5 • high pT > 10 GeV/c Background processes 60 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

  10. 380 mrad 16 mrad Asymmetric distribution due to radiation in the final state Dimuon invariant Mass GeV/c2 Dimuon luminometer efficiencies & results The total signal efficiency  2 tot= (genx recx selx trig) 2 can be computed

  11. Performance of the single muon luminometer

  12. Background processes All the production cross section have been evaluated at NNLO(*) 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

  13. Signal • Background • Signal • Background To achieve a systematic uncertainty below 4%, a S/B ratio > 25 is needed 22 nb pT spectra IP/IP 500 b  conservative pT > 30 GeV/c Single muon selection algorithm The single muon selection algorithm is applied on background (~ 8x106 bb inclusive) andsignalevents Selection • vertex reconstructed with IP/sigma < 3 • pT cut

  14. Single muon luminometer efficiencies & results The total signal efficiency 1tot= (genx recx selx trig) 1can be calculated

  15. To perform an “on-line” luminosity measurement with an uncertainly < 4%, 700 events must be collected during data taking ~ 31/2 hours ~ 45 minutes Comparison of luminosity measurements The performances of thesetwo samples can be compared S1 = Lintx 1tot x ( x BR) 1 with: 1tot= 6.1 % ( x BR) 1tot= 22.13 nb Sz = Lintx  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 5.3x105selected & triggered events  bandwidth of 53 mHz  Z0 +- event every ~ 20 s 2.7x106selected & triggered events  bandwidth of 270 mHz  Z0 or W muon decays every ~ 4 s

  16. Spares XI Spring School

  17. A new L1 specific algorithm, based on a IP < 0.15 mm and a pT > 10 GeV, is introduced in the L1Decision package (v4r5) L1 Trigger algorithms XI Spring School

  18. 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 tothat obtained with other dimuon processes such as theB0s→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 Hzis obtained XI Spring School

  19. Used by the dimuon luminometer HLT Trigger data flow XI Spring School

  20. 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  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 XI Spring School

  21. 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 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 ========================================================== XI Spring School

  22. <x1> = 0.1 <x2> = 2.5*10-4 Parton momentum distributions From S. de Capua PhThesis http://sdecapua.home.cern.ch/sdecapua/ XI Spring School

  23. UP & UPbar distributions vs PDF sets (Q2=104 GeV2) XI Spring School

  24. DOWN & DOWNbar distributions vs PDF sets (Q2=104 GeV2) XI Spring School

  25. STRANGE & CHARM distributions vs PDF sets (Q2=104 GeV2) XI Spring School

  26. BOTTOM & GLUON distributions vs PDF sets (Q2=104 GeV2) XI Spring School

  27. Signal • Background 2 track Single muon selection algorithm The single muon selection algorithm is applied on background (~ 8x106 bb inclusive) andsignalevents • Pre-selection • particles identified as muons  lnL> -2 (standard lnL> -8 ) • well reconstructed tracks  2-track < 2.5 • Signal • Background lnL hypothesis XI Spring School

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