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Overview of the 'final' mW(4q) results

Overview of the 'final' mW(4q) results. …or some publicity for my thesis. Jorgen D’Hondt University of Brussels. Short reminder about the analysis ‘Final’ results of full LEP2 data set Systematic uncertainties : Colour Reconnection LEP WW Workshop (February 2003).

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Overview of the 'final' mW(4q) results

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  1. Overview of the 'final' mW(4q) results …or some publicity for my thesis Jorgen D’Hondt University of Brussels • Short reminder about the analysis • ‘Final’ results of full LEP2 data set • Systematic uncertainties : Colour Reconnection • LEP WW Workshop (February 2003) DELPHI General Meeting, CERN, March 2003

  2. WW events • CC03 W-pair production • Born or tree level • Separation of W-vertices ~0.1 fm • (due to small range of weak force) • Independent W decay ?? lepton BR = 1/3 Cross talk systematics neutrino W Possible WW final state • qq’QQ’ : fully hadronic (BR~45%) • qqlnl : semi leptonic (BR~44%) • lnll’nl’ : fully leptonic (BR~11%) quark BR = 2/3 anti-quark W Up to 40000 WW events selected at LEP2

  3. W mass from 4q channel • MW reconstructed from decay products of W boson • MW resolution : ~10 GeV measured and ~3 GeV after kin.fit • qqQQ • Kinematic fit : • Conservation of (p,E) : 4C • Improves E resolution • Analysis methods : • Reweighting A,L,O • Convolution D • Challenge : • Jet pairing • Hard gluon radiation before 4C fit detail after 4C fit

  4. Invariant W mass spectra TPC-S6 Full data except TPC-S6 Very nice plots for the publication I consider them as final !!

  5. Kinematic fit initial state final state e- object 1 QFT object 2 jetpairing ambiguity clustering ambiguity ISR ambiguity e+ 4C : conservation of (E, p) [Ee-+ Ee+ , pe-+ pe+= 0]initial [Eobj.1+ Eobj.2 , pobj.1+ pobj.2 ]final E and p resolution parametrized from jet-angles (DELPHI) c2i(m1,m2)

  6. W mass from 4q events (example DELPHI) Construction of 2D experimental ideogram pi(mW+,mW-) “ likelihood ratio function “ reflects the reconstructed mass information from the kinematics of the event • All jet pairings weight(r)  (cos qW- , DQ(W-,W+) , 1/kt gluon jet) • 3 clustering algorithms weight(s) = (45% , 36% , 19%) • ISR hypothesis g lost in beam pipe 4C  3C kin.fit if pz/Dpz 1.5 sigma MC parameterizedweight wISR pz/Dpz wISR.(3C) + (1-wISR).(4C) r {1,…3,…,10} pi(mW+,mW-)  exp[-0.5 ci2(mW+,mW-) ] if 5 jet event s {1,2,3} MC mW- t {1,2} + mW+ pi(mW+,mW-) =  wr,s,t . pir,s,t(mW+,mW-) r,s,t

  7. W mass from 4q events (example DELPHI) Construction of event likelihood Li(MW) “convolution of theoretical predicted function and ideogram ” PS Th.pdf(mW+,mW-,MW) = Peff. Signal (mW+,mW-,MW) + (1-Peff) . Background MC event purity from jet topology (qjj,Ej) WW and ZZ Breit-Wigner terms and Phase-Space correction Li(MW)=L(MW)  maximum likelihood MW i{events} ( calibration needed )

  8. Statistical bias on estimators • TPC-S6 period not treated different for mass but for the width the • shift was applied. • The c2/ndf of the fits are acceptable and are propagated into the • systematic uncertainties

  9. Slope of the calibration curves Bias Bias 2.6 test 2.09 Generated W width Generated W width • Slope was linear and compatible with unity for mass estimator. • Reweighting method as been successfully checked !! (W width)

  10. Statistical cross-checks W mass W width symmetric uncertainties asymmetric uncertainties • Complete data set except TPC-S6 period • Good agreement between expectation and data values...

  11. The results • ~4s bug for width was mine… is fixed now !!! • Good agreement between expectation and data values…

  12. Systematic uncertainties (4q) illustration of main systematic uncertainties cross-talk * between W’s LEP beam energy W- PS e- Hadro QFT e+ PS detector W+ Hadro g ISR fragmentation modeling * * processes not known from first principles

  13. List of systematics

  14. MLBZ's Jet reconstruction systematics !! Method has been verified to high precision (~15%)

  15. List of systematics

  16. Electroweak Radiative Corrections Hadronic WW channel within DELPHI ref

  17. List of systematics

  18. Bose-Einstein Correlations The total shift can be downscaled according to the LEP combined measurements. For the moment ~25% fraction of the LUBOEI BE32 model. 40 10 MeV/c2 (W mass)

  19. List of systematics largest systematic uncertainty …but !!

  20. Colour Reconnection in WW • W decay vert. ~0.1 fm distance • hadronisation scale ~1 fm large space-time overlap • suppressed in parton shower : • due to group structure of QCD at least 2 gluons must be emitted • W width restrict the energy range of primary gluons from q1Q4 and q2Q3 ~ (as2/MW)GW/Nc2 • CR effect could occur in the confined region ??? as<<1 as1 T.Sjöstrand and V.A.Khoze, Z.Phys. C62 (1994) Models to emulate the CR effect

  21. Simulating the CR effect CR implemented in existing fragmentation models : • PYTHIA : string reconfiguration if they overlap or cross in space-time • SK1(lateral flux tube) : via event string overlap O : pCR = 1-exp(-·O) • ARIADNE : rearrangement of colour dipoles to reduce the string length (mass) • AR2 : only after soft gluon radiation (Eg < GW) • HERWIG : rearrangement of colour dipoles changing the size of the clusters SK1 mW shift • Latest preliminary predictions for the W-mass • PYTHIA (SK1) ~ 50 MeV/c2 • ARIADNE (AR2) ~ 70 MeV /c2 • HERWIG ~ 40 MeV/c2 • Statistical uncertainty (LEP2) ~ 30 MeV /c2 K ~ 0.66 PCR

  22. CR C Colour Reconnection B A • Design observable sensitive to the CR effect : • particle flow (counting particles  R) • R = D C + D A + B Not sensitive to our observable ?? 2.1s 2.6s 49 %

  23. W mass observables Influence on W mass estimator (MeV/c2) for different values of k(SK1) DELPHI preliminary mW is assumed to be unknown but it must be invariant for different estimators mW(std)-mW(cone) from MC as function of k MC prediction Correlation between W mass estimators ~ 83 %  uncertainty on the difference is small

  24. Combination SK1 combination particle flow (LEP) and DmW (DELPHI) no correlation assumed between the two measurement methods (good approximation) Updated DELPHI measurement of DmW for Moriond Conference ~100 MeV/c2

  25. Combination SK1 LEP expected : no correlation assumed between the two measurement methods (good approximation) 68% CL for k [0.78 , 2.18] central value 1.37 70 MeV/c2 106 MeV/c2 144 MeV/c2

  26. Results General case, no calibration, DELPHI only DELPHI all channels (preliminary)

  27. LEP WW Workshop February 2003 • Most important point was the ‘bug’ in the ALEPH Monte Carlo simulation of the energy clusters in their calorimeters • Effect on LEP W mass (not official and not to be made public !!!!!) DELPHI General Meeting, CERN, March 2003

  28. Stability in ALEPH July 2002 mvqq tvqq evqq Apply momentum cut on particles entering the W mass analysis Results relative to standardmomentum cut in the particle selection qqQQ lvqq In qqQQ channel sensitive to Colour Reconnection but this cannot be in the lvqq channel Shifts in GeV

  29. Energy flow reconstruction … all similar to DELPHI, but ... • Summary of their bugs : • forgot to include the magnetic field in their simulation of the calorimeters •  include it !! • remnants of EM showers or satellites of electron not perfect similated (type 6) •  ECAL cleaning, remove the remnants in data and MC !!

  30. Energy flow reconstruction ECAL HCAL Bhabha events at Z peak Bhabha events at Z peak Correct B field no B field

  31. Energy flow reconstruction … all similar to DELPHI, but ... • Summary of their bugs : • forgot to include the magnetic field in their simulation of the calorimeters •  include it !! • remnants of EM showers or satellites of electron not perfect similated (type 6) •  ECAL cleaning, remove the remnants in data and MC !!

  32. Used to cut away anything within 2.5 degrees from track moved cut ECAL barrel region Now increased to 8 degree Correct B field no B field

  33. tvqq tvqq mvqq evqq evqq mvqq Shift between new and old mW value • Including B field • Including ECAL cleaning qqQQ lvqq In the LEP combined W mass ALEPH has a very large width ~46% (due to small systematic errors)

  34. New LEP results LEP combined / all channels mW = 80.446 ± 0.042 80.411 ± 0.043 direction of shift ~10 GeV Not to be made public outside of this room !!!

  35. Same features within DELPHI ??? Mixed Lorentz Boosted Z0’s !!!! Other experiments didn’t investigated this technique. Only qqQQ channel, to be checked in lvqq channel.

  36. Outlook • Hadronic W mass/width analysis ready • All systematic uncertainties estimates • Some of them are surprisingly large (electroweak radiative corrections) and not completely understood • Some can have a more optimal treatment (Colour Reconnection) but should be desided together with other LEP experiments • Measurement of Colour Reconnection is very important • … ALEPH will have new updated results • … indirect Higgs mass will shift by +10 GeV/c2

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