# Presentation: 688021

## 
  Tom Ferbel
         Department of Energy and University of Rochester

       On Behalf of the D∅ Collaboration
                     Abstracts 195, 196, 201, & 199
                International Europhysics Conference HEP2005                                                   
                       EPS (July 21st-27th 2005) in Lisboa, Portugal

-   Tom Ferbel
-          Department of Energy and University of Rochester
-        On Behalf of the D**∅** Collaboration
-                      Abstracts 195, 196, 201, & 199
**                **International Europhysics Conference** **HEP2005
-                        EPS (July 21st-27th 2005) in Lisboa, Portugal

- Lifetimes of b Hadrons

## Hadrons containing a b quark, such as Bd, Bs,Bc mesons and  Λb baryons, when produced at high transverse momenta (pT) have relatively large boosts, which helps greatly in measuring their lifetimes. 
With Heavy-Quark Effective Field Theory predicting a clear hierarchy of hadronic lifetimes in the decays of b quarks, it      is important to measure with precision the lifetimes of these hadrons.
Absolute lifetimes are of major interest, but ratios are even more valuable to compare with theory, as many sources of systematic uncertainty cancel when any two lifetimes are measured in one experiment (or calculated at NLO to some given order of corrections in Mb-1).

- With Heavy-Quark Effective Field Theory predicting a clear hierarchy of hadronic lifetimes in the decays of b quarks, it      is important to measure with precision the lifetimes of these hadrons.
- Absolute lifetimes are of major interest, but ratios are even more valuable to compare with theory, as many sources of systematic uncertainty cancel when any two lifetimes are measured in one experiment (or calculated at NLO to some given order of corrections in Mb-1).

- Introduction

## Abstract 196, new (and best) Bs0 lifetime based on  400 events/pb μ+υDs–X  data (with Ds–→–→K+K––).
Abstract 195, ratio of B+/B0 lifetimes based on just published [PRL 94, 182001 (2005)] reconstructed semileptonic decays in μ+υD0X  and  μ+υD*–X states. (With D*–→D0–→K+––).
Abstract 201, measurement of lifetimes of Λb0, Bs0 and  Bd0 in exclusive modes Λb0→ J/ψ(μ+μ–) Λ0 (π p–) and Bs0→J/ψ(μ+μ–) –), and Bd0→J/ψ(μ+μ–) K*0(K+π–) and Bd0→J/ψ(μ+μ–) Ks0(π+π–). First measurement of Λb in a fully reconstructed channel. [Λb; Bs0: PRL 94, 102001; ibid, 042001 (2005)] 
Abstract 199, lifetime and mass of Bc+→J/ψ(μ+μ–)μ+υ      for reconstructed μ+μ–μ+ systems. Mass from fully reconstructed J/ψ(μ+μ–)π+  decay is still in the works.

**Abstract 195**, ratio of B+/B0 lifetimes based on just published [PRL **94**, 182001 (2005)] reconstructed semileptonic decays in μ+υD0X  and  μ+υD*–X states. (With D*–→D0–→K+––).
**Abstract 201**,** **measurement of lifetimes of Λb0, Bs0 and  Bd0 in exclusive modes Λb0→ J/ψ(μ+μ–) Λ0 (π p–) and Bs0→J/ψ(μ+μ–) –), and Bd0→J/ψ(μ+μ–) K*0(K+π–) and Bd0→J/ψ(μ+μ–) Ks0(π+π–). First measurement of Λb in a fully reconstructed channel. [Λb; Bs0: PRL **94**, 102001; ***ibid***, 042001 (2005)]
**Abstract 199, **lifetime and mass of** **Bc+→J/ψ(μ+μ–)μ+υ      for reconstructed μ+μ–μ+ systems. Mass from fully reconstructed J/ψ(μ+μ–)π+  decay is still in the works.

- Provides for your pleasure:

## Tracking is done via silicon microstrips and                     

- Tracking is done via silicon microstrips and
-   scintillating fibers in ~2T field
- Muon system has drift tubes and scintillation
-   trigger counters, with good coverage to |η|=2

## Measuring Lifetimes

- Reconstruct primary and decay vertexes of B-hadron candidates
- Calculate the Proper Decay Length in transverse plane from signed transverse decay length Lxy

-   For semileptonic decays, use decay length “” for observed part of hadron, and a factored-in distribution to correct for total momentum.

## Hadronic Modes

- Use dimuon (J/ψ) events, and then
- Search for a long-lived neutral decaying to two oppositely charged tracks, pointing to vertex of J/ψ:
-     Λb0→ J/ψ(μ+μ–) Λ0(pπ–)
-     Bd0→ J/ψ(μ+μ–) Ks0(π+π–)
- Or for two tracks originating at the J/ψ vertex:
-     Bs0→ J/ψ(μ+μ–) –)
-     Bd0→ J/ψ(μ+μ–) K*0(K+π–)
- Search for similar topologies at same time, analyze in similar way, so as to minimize errors on ratios of particle lifetimes

## Semileptonic Modes

- No specific muon selection at trigger level, but offline require  pTμ >2GeV/c, and p >3GeV/c (this depends on analysis).
- Bc+→J/ψ μ+υX uses dimuon decays of J/ψ, and third muon at decay vertex, to fit μ+μ–μ+ to mass and lifetime
- Bd0→μ+υD*–(D0π–)X and Bd+ → μ+υD0(K+π–)X are used for direct measurement of ratio of lifetimes of Bd0 and Bd+
- Bs0→Ds–μ+υX, where Ds–→ +–)π–  is used to extract Bs0 lifetime, with proper decay length “” for observed part of signal smeared with a “K factor” distribution based on Monte Carlo.

## Bs0→ μ+υDs–X  (with Ds–→–→K+K––)

- Mass distribution of Ds– () candidates when significance on “”exceeds 5 s.d. Dark points correspond to correct Ds– charge combinations, and crosses to wrong ones. Smooth curve is fit to right-sign combinations. Peaks are for **D****–** and **D****s**–, respectively

## Bs0→ μ+υDs–X  (with Ds–→–→K+K––)

- Mass distribution of () candidates, whithout significance criterion

## Bs0→ μ+υDs–X  (cont’d)

- Distribution in “” for **B****s****0 ****signal** and superimposed fit (dashed), with combinatorial background represented by dotted curve.

- Both agree with previous world
- averages, and our
- semileptonic result
- for Bs0is currently most precise at:               1.420 ± 0.071 ps

- Results for  Bs

- s0stat)syst)  ps  (Semileptonic mode)
- s0stat(syst) psHadronic mode)

## New Method for (Bd+)/(Bd0)

- Ratio established by:
- Fitting to the number of D*μ candidates (~85% from B0) as a function of visible proper decay length “”.
- Fitting to the number of D0μ candidates (~83% from B+)  as a function of “”.
- Finding the ratio of the numbers as a function of “”.
- If this ratio is independent of “”, the lifetimes are equal.  Any difference manifests itself as a slope in this ratio vs “” .
- This new D**∅** technique can be used in other measurements of ratios

## (Bd+)/(Bd0) from large clean sample of μ+υD0X and μ+υD*–X, with D*–→D0–→K+––

## Λb0 → J/ψ(μ+μ–) Λ0 (π p–) 

## Bc+ →J/ψ(μ+μ–)μ+υ Lifetime(See 95 ± 17 events excess in mass and in lifetime)

## Results for Lisboa

-     (Bs0) = 1.420±0.043 (stat) ±0.057 (syst)  ps
- Best single measurement of flavor-specific Bs0, with dominant systematic uncertainty from estimate of background. Prediction for d0slsoimportant in extraction of ss.
-  (Bd+)(Bd0) = 1.080± 0.016 (stat) ± 0.014 (syst)  ps               Competitive and most precise measurement of ratio at Tevatron, mainly limited by model for parameterization of signal and background in the fit to data. Theory predicts 1.06 ± 0.02.
-         b0stat) syst)  ps
-       b0 )/Bd0) = statps
- First measurement of b0in a fully reconstructed exclusive channel. Theory for ratio is 0.86  0.06
-         (Bcstat) syst)  ps
- ased on first analysis with signal in excess of 5 s.d. Analysis being updated and completed for publication.

## Summary

- D∅ has new and many emerging results in the area     of b-hadronic lifetimes.
- D∅ semileptonic Bs0 lifetime is best measurement available.
- Measurement of hadronic Λb lifetime is best for a fully reconstructed channel.
- Significant contributions to world averages.
- Unfortunately, all D∅ results are consistent with HQET and with world averages. Have to try harder!