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Excited B states at LEP

Excited B states at LEP. Peter Kluit (NIKHEF) DELPHI/LEP. Introduction & history Theory Experimental overview Excited B u,d results Search for B s ** and S b ( * ) Summary. Introduction History. Boom of B physics at LEP around 1994 vertex detectors exclusive reconstruction

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Excited B states at LEP

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  1. Excited B states at LEP Peter Kluit (NIKHEF) DELPHI/LEP • Introduction & history • Theory • Experimental overview • Excited Bu,d results • Search for Bs** and Sb(*) • Summary Peter Kluit

  2. Introduction History • Boom of B physics at LEP • around 1994 • vertex detectors • exclusive reconstruction • Discovery Bs meson at LEP • B baryons • Precision lifetimes • Bd oscillations Event Bs→ y`f→mm KK Peter Kluit

  3. Inclusive B reconstruction • New technique (~1994) • High rapidity particles • Secondary vertex • Energy-momentum constraint • Estimate B four-momentum • Physics result: • precision mass B*→Bg • Production V/(V+P)=0.75 g →e+e- Peter Kluit

  4. Discovery of excited B states OPAL 1995 Reconstruct B**→B p Inclusive B fragmentationp OPAL 1995 1995 Prel. 1997 Prel. 1997 Bs**Sb(*) Peter Kluit

  5. Theory HQET Heavy Q, light quark q sqql →jq; sQqjq→ J Charm system measured: Broad GBroady300 MeV Expect B system Dm doublet ~Dmc mc/mb ~13 MeV Narrow • Similar for Bs**, decay to Bs*p Isospin forbidden • Dominant decay Bs**→ B(*) K, if above threshold Peter Kluit

  6. B production at LEP production fractions adjusted to world average Peter Kluit

  7. Experimental overview Bud** Narrow states Some numbers recomputed using common inputs OPAL 01 Br(B**→B*pX)=0.85±0.26±0.12 Peter Kluit

  8. Experimental issues • Crucial treatment of background • Taken from MC, except ALEPH exclusive analysis • Induces high production rate, shifted mass peaks, instabilities ALEPH exclusive Peter Kluit

  9. New DELPHI B** analyses • Focus on the background • using control sample: High efficiency • Reduction by neural networks: High purity • Full LEP I statistics, reprocessed data, improved analysis techniques, inclusive B reconstruction b and anti b tagging B charge Peter Kluit

  10. Analyses steps • Reconstruct weakly decaying B and combine with p from primary vertex • Samples separated b/b tag qB vertex charge • High Efficiency:soft cuts, signal/wrong sign similar shape • High Purity:tight cuts, neural network Peter Kluit

  11. High efficiency Analysis • Simultanous fit to signal and background B** signal Narrow: B*2 mass and Dm(B*2-B1) free Br(B*2 →B*p/Bp)=1.1±0.3 Broad:extrapol from Charm m(B*1)=m(B1),Dm(B1-B0)=45 MeV G=300(330) MeV DELPHI Enhancement at Q~500 MeV, G~300 MeV (~2 s.d.) Peter Kluit

  12. High purity analysis • Fit background MC times polynome • Signal resolution free parameter Significant deviations MC at low and high Q values • Largest Systematics • Background parametrisation • Energy scale • Cuts NN rapidity • Modeling: • With/without 500-state • Spin/state counting B0 B+ Fits not sensitive to Broad states and to spin/state counting (< 2 s.d.) Peter Kluit

  13. Summary of B** results • Total rate s(B**ud)/s(b) (broad+narrow) DELPHI preliminary m(B*2)=5738 ± 14 MeV andm(B1)=5732 ± 20 MeV Peter Kluit

  14. Comparison of LEP Results • Rate s(B**ud)/s(b) (narrow)~factor 1.5-2 lower • Due to background treatment, inclusive analyses at LEP overestimate the rate • Compatible with ALEPH exclusive analysis • m(B*2)=5739 ± 10 MeV DELPHI:5738 ± 14 MeV • Total rate=0.24±0.07±0.05DELPHI:0.157±0.011±0.029 • Compare to s(D**narrow)/s(c) = 0.17 ±0.05 • FUTURE recommend exclusive analyses extracting the background from data Peter Kluit

  15. DELPHI B**s search • Channel Bs**→B(*)+ K- • Using neural networks for identification of kaon and B vertex charge • Fit signal (Gaussian), free background • Total Significance 3.8s • systematics included • Background shape • Identification K/ NN • Energy scale Peter Kluit

  16. Interpretation & discussion • Most likely Bs2*→B K- • (B*K reduced by factor 10) Where is Bs1→B*K? Dm 13 MeV DELPHI preliminary Bs1 Puzzle: Large Dm? Enhanced Bs1→Bs*p? Results m(Bs2*)=5852 ± 5 MeV OPAL: 5800-5900 MeV Rate s(Bs2*)/s(b)=0.0093±0.0020±0.0013 OPAL: 0.020 ±0.006 Peter Kluit

  17. DELPHI Sb(*) search • Channel Sb± (*)→Lbp± • Using neural networks for identification B baryon • Fit signal, free background Preliminary Upper limit 95% CL s(Sb(*))/s(b) < 0.012 Old prel. DELPHI result not confirmed Peter Kluit

  18. Summary • New DELPHI measurements for B**ud • Total production rate: s(B**ud)/s(b)=0.157±0.011±0.029 • m(B*2)=5738 ± 14 MeV and m(B1)=5732 ± 20 MeV • New results ~factor 1.5-2 lower than previous due to background • Compatible with ALEPH exclusive, and charm production • Search for B**s • Signal at 3.8s with m(Bs2*)=5852 ± 5 MeV; Bs1 Puzzle • Production rate: s(Bs2*)/s(b)=0.0093±0.0020±0.0013 • Search for Sb(*) • Limit production rate:s(Sb(*))/s(b)< 0.012 at 95% CL Preliminary Peter Kluit

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