Lambda_b Ratio of Branching Fractions

Lambda_b Ratio of Branching Fractions

We summarize here the blessed results for the measurement of the ratio of branching fractions:

BR(&Lambda_b⁰ &rarr &Lambda_c⁺ &mu^-&nu ) /BR(&Lambda_b⁰ &rarr &Lambda_c⁺ &pi^-) = 20.0 ± 3.0(stat.) ± 1.2(syst.) -2.1+0.7(BR) ± 0.5(UBR),
where the first uncertainty is statistical, the second uncertainty is due to CDF internal systematics and third and forth uncertainties are on measured and unmeasured branching ratios, respectively. As a test of the technique, we also measure the ratio of branching fractions:

BR(B⁰ &rarr D^- &mu⁺&nu ) /BR(B⁰ &rarr D^- &pi⁺) = 9.8 ± 1.0(stat.) ± 0.6(syst.) ± 0.8(BR) ± 0.9(UBR)

BR(B⁰ &rarr D^*- &mu⁺&nu ) /BR(B⁰ &rarr D^*- &pi⁺) = 17.7 ± 2.3(stat.) ± 0.6(syst.) ± 0.4(BR) ± 1.1(UBR)
Combining our measurements with external input we further derive the exclusive branching ratios:
BR(&Lambda_b⁰ &rarr &Lambda_c⁺ &pi^-) = (0.41 ± 0.19(syst. + stat.) -0.08+0.06(p_T spectrum)) %
BR(&Lambda_b⁰ &rarr &Lambda_c⁺ &mu^-&nu ) = (8.1 ± 0.19(stat.) -1.6+1.1(syst.) ± 4.3(BR(&Lambda _b &rarr &Lambda_c⁺ &pi^-)) ) %

These results have been blessed at the B-physics meeting on Thursday, April 14 2005.

Analysis Description:

A brief description of the analysis is contained in a PostScript file.

Figures:

Click on the figures below for a larger version. Encapsulated PostScript versions of each figure may be obtained by clicking on the (EPS) in the caption.

Figure 1: Invariant mass of D+ pi-. The D+ is reconstruted from the decay D+ --> K- pi+ pi+. The red curve is the result of a fit to a signal and background model. Backgrounds from B-meson decays are shown in pink(B0 --> D+ rho-/ D*+ pi-) and green (B0-->D+ X).(EPS)

Figure 2: Invariant mass of K- pi+ pi+. The red curve is the result of a fit to a signal and background model. The dashed line indicates backgrounds from D_s decays where the particles from the D_s were reconstructed as K- pi+ pi+. All events in the distribution contain a muon which has an impact parameter, with respect to the beam line, larger than 120 microns. (EPS)

Figure 3: Invariant mass of D*+ pi-. The D*+ is reconstruted from the decay D*+ --> D0 pi+, D0 --> K- pi+. The red curve is the result of a fit to a signal and background model. Backgrounds from B-meson decays are shown in black(B0 --> D*+ K-), pink(B0 --> D*+ rho-) green(B0-->D*+ X).(EPS)

Figure 4: Invariant mass difference (M(D0 pi+) - M(D0)). The red curve is the result of a fit to a signal and background model. All events in the distribution contain a muon which has an impactd parameter, with respect to the beam line, larger than 120 microns. (EPS)

Figure 5: Invariant mass of Lambda_c+ pi-. The red curve is the result of a fit to a signal and background model. Backgrounds from other B-hadron decays are shown in pink(Lambda_b-->Lambda_c+ K-), tan(4-prong B-meson decays), green(multi-body meson decay) and black(multi-body Lambda_b decays). (EPS)

Figure 6: Invariant mass of p K- pi+. The red curve is the result of a fit to a signal and background model. All events in the distribution contain a muon which has an impactd parameter, with respect to the beam line, larger than 120 microns. (EPS)

Figure 7: Transverse momentum (Pt) of the reconstructed B0 from B0-->D+ pi- decays. The squares are data and the triangles are from a Monte Carlo (MC). Good agreement between the data and MC is needed to determine the correct acceptance for the semileptonic decays. (EPS)

Figure 8: Transverse momentum (Pt) of the reconstructed Lambda_b from Lambda_b --> Lambda_c+ pi- decays. The squares are data and the triangles are from a Monte Carlo (MC). Good agreement between the data and MC is needed to determine the correct acceptance for the semileptonic decays. (EPS)

Figure 9: Invariant mass of the D+ mu-. The squares are data and the triangles are from a Monte Carlo (MC) which includes both the semileptonic signal and associated backgrounds. semileptonic decays. (EPS)

Figure 10: Invariant mass of D*+ mu-. The squares are data and the triangles are from a Monte Carlo (MC) which includes both the semileptonic signal and associated backgrounds. (EPS)

Figure 11: Invariant mass of Lambda_c+ mu-. The squares are data and the triangles are from a Monte Carlo (MC) which includes both the semileptonic signal and associated backgrounds. (EPS)

Figure 12: Ratio of branching fractions for B0--> D+ modes for various subsets of the data. The band represents the result from the full data sample. All uncertainties are statistical only. (EPS)

Figure 13: Ratio of branching fractions for B0--> D*+ modes for various subsets of the data. The band represents the result from the full data sample. All uncertainties are statistical only. (EPS)

Figure14: Ratio of branching fractions for Lambda_b--> Lambda_c+ modes for various subsets of the data. The band represents the result from the full data sample. All uncertainties are statistical only. (EPS)

Tables:

Click on the Tables below for a larger version. PostScript versions of each Table may be obtained by clicking on the (PS) in the caption.

Table 0: Background summary for semileptonic B^0 to D*+ decays. Numbers in parantheses are the estimated uncertainties (100\%)for the unmeasured branching fractions.	Table 1: Background summary for semileptonic B^0 to D+ decays. Numbers in parantheses are the estimated uncertainties (100\%)for the unmeasured branching fractions.	Table 2: Background summary for semileptonic Lambda_b decays. Numbers in parantheses are the estimated uncertainties (100\%)for the unmeasured branching fractions.	Table 3: Summary of semileptonic background contributions from fake muons and quark pair production.
Table 4: Summary of statistical and systemtatic uncertainties for B^0 to D^* ratio of branching ratio measurement.	Table 5: Summary of statistical and systemtatic uncertainties for B^0 to D ratio of branching ratio measurement.	Table 6: Summary of statistical and systemtatic uncertainties for Lambda_b ratio of branching ratio measurement.

R. J. Tesarek

Last modified: Mon May 23 15:55:20 CDT 2005