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b lifetimes

Explore theoretical frameworks, detector elements, and meson lifetime calculations in heavy flavour physics at the 8th International Symposium. Highlights crucial detector components and measurements for B+ and B0 mesons.

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b lifetimes

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  1. b lifetimes SimoneDonati INFN & University of Pisa 8th International Symposium on Heavy Flavour Physics University of Southampton 25 - 29 July 1999

  2. Outline • Introduction • - Theoretical Framework • - Crucial detector elements • B+, B0 lifetime and t(B+ )/t(B0 ) • - Dl and D0l samples • - B vertex charge • - Exclusive reconstruction • B0s lifetime • - DS l correlation • - DS h samples • - Exclusive reconstruction • Lb lifetime • - Lc lepton combination • Summary and Conclusions

  3. Theoretical Framework q, l Baseline SpectatorModel: the light quark acts as a spectator  All b - hadrons have the same lifetime. G = (GF2 mb5/192p3) · | Vcb | 2 · F • q, n W b c • Vcb B D q q But, for charm hadrons: t (D-) ~ 2.5 t (D0) ~ 2.5 t (Ds-) ~ 5.0 t (Lc-) p+ q, l b c w b D- W B0 W B+ c b B+ D0 q,n p+ u d u u u W exchange B+ annihilation D0 b c w p+ Expected lifetime difference ~ 5 - 10 % between B0 and B+(t (B+)  t (B0) ) due to nonspectatoreffects. u u Destructive interference between external / internal W emission

  4. Theoretical Framework • Effects scale as 1/m2q • - Important effects for c hadrons: t (D+) / t (D0) = 2.55  0.04 • - Up to 10 % differences expected for b hadrons (from HQE) • t(Lb)  t (B0d) t (B0s)  t (B+) • Theoretical predictions still unstable • Measurements with a precision of few % needed

  5. B+, B0 meson lifetimes and t(B+) / t(B0) • Dl and D0l samples: CDF, ALEPH, DELPHI, OPAL • B vertex charge: DELPHI, L3, OPAL, SLD • Exclusive reconstruction: ALEPH (BDp), CDF (BJ/y K) • Inclusive reconstruction of Dl combinations(B0 only): • DELPHI, ALEPH, L3

  6. Crucial for B physics • SiliconMicrostripDetector • s d = ( 13 + 40 / pt ) mm • 2D vertex error ~ 60 mm • CentralTrackingChamber • B field = 1.4 T, Radius = 1.4 m • (dpt/pt)2 = (0.0066)2+(0.0009 pt)2 • J/yKs0massresolution ~10MeV/c2 • Lepton (e / m) Detection: fundamental for B - triggers • - Inclusive lepton trigger • b  lncX or b  cX, c lnY(  pt ( B ) ~ 20 GeV/c ) • - Dilepton ( em , mm ) trigger • b  J/y X, y  m+ m- (  pt ( B ) ~ 10 GeV/c ) • b  m- X , b  e+ Y

  7. CDF Experimental Technique (A) lep n All lifetime results are based on the DecayLength measurement Lxy B lep-D direction    (VB - VP) ·pt (D-lep) VP VB D Lxy =  |pt (D-lep)| • Fully reconstructed decays • ct (B) = Lxy m(B) / pt(B)proper D.L. • Partially reconstructed decays • l = Lxy m(B)/pt(D-lep)pseudo-properD.L. • Correction factor pt(D-lep) /pt(B) from • MC, introduced statistically in the fit. pt(D-S-l+) / pt(B0S)

  8. CDF Experimental Technique (B) # events signal sample # events bck. sample Lifetime and background shape are determined from a simultaneous fit of Signal and Background samples. Signal Signal prob. distr. nS nB L =  [ f sig F isig +(1- f sig)  F ibck ]   F jbck j i Bck. prob. distr. Signal fraction under the “D mass” peak Convolution F isig = [Decay exponential  Gaussian resolution ] [ pt(Dl) / pt(B) Smearing ] Background F ibck= Gaussianresolution + [Positive exp. + Negative exp.]  Gaussian resolution Only for part. rec. decays Zero -lifetime bck HF contribution

  9. CDF: B+ and B0 lifetime from B  D()lnXdecays • D candidates searched for • close to the trigger lepton. • a) D0 K+p-( D0 not from D -) • b) D - D0 p-, D0 K+p- • c) D - D0 p-, D0 K+p- p+ p- • d) D - D0 p-, D0 K+p- p0 • Crosstalk from D resonance • B0  D  -l + X, D  - D0 X • B+  D  0l + X, D 0 D -X • decomposed using MonteCarlo • (main source of systematic error) t(B-) = (1.637  0.058+0.045) ps -0.043 t(B0) = (1.474  0.039+0.052) ps t(B-) / t(B0) = 1.110  0.056+0.033 -0.051 -0.030 l (B-) l (B0)

  10. ALEPH: B+ and B0 lifetime from B  D()lnXdecays (A) • Technique similar to CDF • - D +  D0 p+ sample • D0 K-p+ • D0 K-p+p-p+ • D0 K-p+p0 • D0 K0Sp+p- • -D0 sample (D0 not from D +) • D0 K-p+ • D0 K-p+p0 • D0 K0Sp+p-

  11. ALEPH: B+ and B0 lifetime from B  D()lnXdecays (B) t(B0) = ( 1.524  0.053+0.035 ) ps t(B+) = ( 1.646  0.056+0.036 ) ps t(B+) / t(B0) = 1.080  0.062  0.018 -0.032 -0.034

  12. OPAL: B+ and B0 lifetime from Vertex Charge (A) • Inclusive approach • b events selected requiring displaced • vertices and high momentum leptons • Hemisphere tag • T-tag : Jet-charge, vertex charge and • lepton charge used to tag b flavour • M-tag: used to determine decay length • and perform lifetime fit e+ T-tag : identify bb events ( ~ 10,000 reconstructed vertices) b M-tag vertex charge Qvtx =  wi qi Z0 Probability that the track exits from secondary vertex b e- M-tag : perform lifetime measurement

  13. OPAL: B+ and B0 lifetime from Vertex Charge (B) • Excess decay length method • To reduce the bias from the M-tag • the excess to the minimum decay • length which results in a resolvable • secondary vertex is used. t (B0) = ( 1.523  0.057 0.053 ) ps t (B+) = ( 1.643  0.037  0.035) ps t (B+) / t (B0) = 1.079  0.064  0.041 Excess decay length

  14. SLD: B+ and B0 lifetime from Topological Vertexing • Inclusive 3D vertex reconstruction • performed exploiting the excellent • performance of the vertex detector • Decay length  1 mm • Vertex mass  2 GeV/c2 to eliminate • charm and light flavor background • Vertex charge obtained adding the • charge of the corresponding tracks • Charge purity enhanced using • - Beam polarization • - Opposite hemisphere jet charge Reconstructed Vertex Charge t (B0) = ( 1.585  0.021 0.043 ) ps t (B+) = ( 1.623  0.020  0.034) ps t (B+) / t (B0) = 1.037+0.025  0.024 Decay Length (cm) -0.024

  15. CDF: B+ and B0 lifetime from exclusive B  J/y Kdecays 82436 fully reconstructed B+ - B+  J/y K+ - B+  J/y K+ - B+  y (2S) K+ - B+  y (2S) K+ 43627 fully reconstructed B0 - B0  J/y K0S - B0  J/y K0 - B0  y (2S) K0S - B0  y (2S) K0 M (m+ m- p + p - ) M (m+ m- ) l(B+) peak region l (B 0) peak region t(B+) = (1.680.070.02) ps t(B0) = (1.580.090.02) ps t(B+) / t(B0)=1.060.070.02 l(B+) sideband region l (B 0) sideband region

  16. Summary of B+ meson lifetime

  17. Summary of B0d meson lifetime

  18. Summary of t (B+) / t (B0)

  19. B0S meson lifetime • DS l correlation: ALEPH, DELPHI, OPAL, CDF • DS - hadron decays: ALEPH, DELPHI • J/yfexclusive decay: CDF

  20. DELPHI: BS lifetime from DS l correlation (A) • 3.6 million Z0 hadronic decays • B0S  D-S l+nX • - D-S f p+, K0K-, K0SK-, • f p+p-p+, f p+p0, K0K- • - D-S f e-n, f m-n • - D-S f h-X (partially reconstructed) • background sources • - B  D(* ) D(* )+X (D l -nX) • (reduced by high pt lepton and mass) • - Reflections from B+  K-p+p+ • (if one p is misidentified as K) f l h candidates

  21. DELPHI: BS lifetime from DS l correlation (B) • t(B0S) = ( 1.42+0.14(stat)  0.03 (syst)) ps • Sources of systematic error • - Background fraction +0.0090 • - Cascade decays -0.0100 • - Background from B -0.0020 • - XDs discrim. var. +0.008 • - pt discrim. Var. 0.004 • - t(B+) (1.65  0.04 ps) -0.0010 • - t(B0d) (1.56  0.04 ps) -0.0012 • - t resolution 0.008 • - t acceptance 0.010 • - Simulated evts. Statisitcs 0.020 • Total 0.03 • DGBs / GBs  0.46 @95 C.L. -0.13 -0.0130 +0.0110 +0.0020 +0.0010 +0.0130 f l h sample

  22. DELPHI: BS lifetime from DS h decays (A) • 3.5 million Z0 hadronic decays • - B0S D-S p+ or D-S a+1 • - D-S  f p- or K 0 K+ • Larger statistics than DS l, but • lower purity (hadronambiguity) • B vertex found constraining the • DS h from a common vertex • BS Purity increased using • -DS mass andmomentum • - |cos(y)| • - c2 of the DS vertex • - Opposite hemisphere B tag

  23. DELPHI: BS lifetime from DS h decays (B) t(B0S) = ( 1.49+0.16(stat)+0.07(syst)) ps -0.15 -0.08 • Sources of systematic error • - Sample composition +0.013 • - Background fraction +0.046 • - Back. Parameterization +0.017 • - BS purity +0.005 • - t resolution  0.019 • - t(B+) (1.65  0.04 ps)  0.021 • - t(B0d) (1.56  0.04 ps)  0.019 • - Analysis bias corr.  0.040 • Total +0.07 • DGBs / GBs  0.58 @95 C.L. -0.016 -0.050 -0.012 -0.015 -0.08 DS sidebands

  24. CDF: BS lifetime from BS J/yfdecay Use 58  12 BS J/yfevents Simultaneous fit of the mass and proper decay length distribution M (J/y f ) M (m+ m- ) t(B0S) = (1.34+0.23  0.05) ps -0.19 B0S proper decay length

  25. CDF: BS lifetime from BS D-S l+ndecays • D-S candidates are searched for close • to the trigger lepton • - D-S  f p-, f  K+K- 220  21 ev • - D-S  K 0 K-, K 0  K+ p- 12520 ev • - D-S  K0SK-, K0S p+ p- 33  8 ev • - D-S  f m- n, f  K+K- 205  38 ev • Problem: BS signal faked by Bd decays • D-d  K 0 p-and D-d  K0Sp- can • fake D-S signal if p is assumed as K • Solution: simultaneous fit of the K 0 K- • K 0 p- mass distributions to estimate • both components (crosscheck from • D-d and D-S lifetime difference) • t (B0S) = (1.36  0.09  0.05) ps • World’s best measurement from a single experiment • DGBs / GBs  0.83 @95 C.L. Same data after switching K- to p- K0SK- Mass MC MC

  26. Summary of B0S meson lifetime

  27. CDF: Bcdiscovery and lifetime from Bc J/y lXdecays • Bc meson observed through • the decay • Bc J/y l X(l = e or m) • M(Bc)=6.400.390.13 GeV/c2 • t (Bc) = 0.46+0.18 0.03 ps -0.16 e only m only

  28. Lblifetime • Lc lepton combination : ALEPH, DELPHI, OPAL, CDF • L l+l-method: ALEPH, OPAL

  29. ALEPH: Lb lifetime from Lb L+cl-ndecays • 193 Fully reconstructed L+c l- • - L+c  p K-p+ • - L+c  p K0 • - L+c  L p+ p+ p- • - L+c  L p+ • t (Lb) = LM / p • - 3D decay length (s ~ 180 mm) • - p from L+c l-andnenergy • t(Lb) = 1.18+0.13 0.03 ps -0.12

  30. CDF: Lb lifetime from Lb L+cl-ndecays • 197  25 fully reconstructed L+cl- • -L+c  p K-p+ • - Energy loss in the CTC used for statistical • particle identification • - Physicalbackground from B  Lc DsX • Lb LcDsX reduced using kinematics • - Combinatorial background fraction • estimated from wrong sign Lcl pairs • - pt correction for missing n from MC • - Background lifetime shape estimated • from L+c  p K-p+ sidebands • t(Lb) = 1.32  0.15 0.07 ps

  31. Summary of Lb lifetime

  32. Summary of b lifetime

  33. Conclusion • Current status of b hadrons lifetime • measurements (CDF, LEP and SLD) • has been reviewed • World average for t (B+) / t (B0) is • starting to put in evidence a significant • difference from unity • t (Lb) still much lower than prediction • More data and more work needed from • single experiments

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