First observation and measurement of the relative Branching Fractions of charm resonant decay modes in the Λb0 --> Λc+ π- π+ π- decay

Primary authors: P. Azzurri, P. Barria. M. A. Ciocci, S. Donati. E. Vataga

Analysis blessed by the B Group on October 29, 2009. Analysis details can be found in: Public note

Introduction

This page documents the first observation of the Λb0 --> Λc+ π- π+ π- decay mode and the first observation and first measurement of the relative Branching Fractions of the charm resonant decay modes

Λb0 -->Λ(2595)c+ π- --> Λc+ π- π+ π-

Λb0 -->Λ(2625)c+ π- -->Λc+ π- π+ π-

Λb0 -->Σ(2455)c++ π- π- -->Λc+ π- π+ π-

Λb0 -->Σ(2455)c0 π+ π- -->Λc+ π- π+ π-

This analysis was motivated by the recent observation of the similar resonant structure in the semileptonic decay mode Λb0 --> Λc+ π- π+ l- ν ([1]).

The measurements of the Branching Fractions can be compared to the theoretical predictions to test the heavy quark effective theory (HQET, [2]).

Analysis overview

The analysis uses 2.4 fb-1 of data collected by the CDF trigger on impact parameters (two-track-trigger). The Λc+ is reconstructed in the p K- π+ decay mode and three tracks, assumed to be pions, are added to reconstruct the Λb0 --> Λc+ π- π+ π- decay mode. The offline selection is optimized by maximising the figure of merit S/(S+B)^1/2 where S is the signal yield and B is the background [ Optimised Selection ]. A clean signal is observed in the mass difference m(Λc+ π- π+ π-) - m(Λc+).

The Λb0 -->Λ(2595)c+ π- and Λb0 -->Λ(2625)c+ π- candidates are identified by searching for resonant signals in the mass difference m(Λc+ π- π+) - m(Λc+) distribution, reconstructed in a +-3 sigma mass window on the Λb0 signal.

The Λb0 -->Σ(2455)c++ π- π- candidates are identified by searching for a resonant signal in the mass difference m(Λc+ π+) - m(Λc+) distribution, reconstructed in a +-3 sigma mass window on the Λb0 signal.

The Λb0 -->Σ(2455)c0 π+ π- candidates are identified by searching for a resonant signal in the mass difference m(Λc+ π-) - m(Λc+) distribution, reconstructed in a +-3 sigma mass window on the Λb0 signal.

The relative Branching Fractions of the resonant decay modes are measured using the yields of each decay mode estimated by fitting the data and the relative efficiencis estimated with Monte Carlo [ Estimated Yields ].

Final results.

  • BR( Λb0 -->Λ(2595)c+ π- --> Λc+ π- π+ π-) /BR( Λb0 --> Λc+ π- π+ π-(all))= (2.5 +- 0.6(stat.) +- 0.5(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Λ(2625)c+ π- --> Λc+ π- π+ π-) /BR( Λb0 --> Λc+ π- π+ π-(all))= (6.2 +- 1.0(stat.) +1.0 -0.9(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Σ(2455)c++ π- π- --> Λc+ π- π+ π-) /BR( Λb0 --> Λc+ π- π+ π-(all))= (5.2 +- 1.1(stat.) +- 0.8(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Σ(2455)c0 π+ π- --> Λc+ π- π+ π-) /BR( Λb0 --> Λc+ π- π+ π-(all))= (8.9 +- 2.1(stat.) +1.2 -1.0(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Λc+ ρ0 π- + Λc+ π- π+ π-(other) --> Λc+ π- π+ π-) /BR( Λb0 --> Λc+ π- π+ π-(all))= (77.3 +- 3.1(stat.) +3.0 -3.3(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Λ(2595)c+ π- --> Λc+ π- π+ π-) /BR( Λb0 --> Λ(2625)c+ π- --> Λc+ π- π+ π-)= (40.3 +- 9.8(stat.) +2.3 -1.8(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Σ(2455)c++ π-π- --> Λc+ π- π+ π-) /BR( Λb0 --> Σ(2455)c0 π+ π- --> Λc+ π- π+ π-)= (58.1 +- 16.9(stat.) +6.3 -9.1(syst.)) x 10-2 [ Systematics ].
  • BR( Λb0 -->Λ(2625)c+ π- --> Λc+ π- π+ π-) /BR( Λb0 --> Σ(2455)c++ π- π- --> Λc+ π- π+ π-)= (1.20 +- 0.26(stat.) +0.05 -0.09(syst.)) [ Systematics ].
  • List of Figures.

    References.

    1. T. Aaltonen et al, The CDF Collaboration, "First measurement of the ratio of Branching Fractions BR(Λb0 --> Λc+ μ- ν)/ BR(Λb0 --> Λc+ π-)", Phys. Rev. D79, 032001 (2009).
    2. A. V. Manohar and M. B. Wise, Cambr. Monogr. Part. Phys. Nucl. Phys. Cosmol. 10, 1 (2000); S. Godfrey and N. Isgur, Phys. Rev. D32, 189 (1985);
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