Λc +→pπ-π+，Λc +→pK-K +和Λc +→pπ-K +的分支分数的测量

, and Λ

with respect to the Cabibbo-favoured Λ

are measured using proton-proton collision data collected with the LHCb experiment at a

7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb

:

)

)

average value for B(Λ

), the corresponding branching fractions are

) = (4.72 ± 0.05 ± 0.11 ± 0.25) ×10

) = (1.08 ± 0.02 ± 0.02 ± 0.06) ×10

) = (1.04 ± 0.09 ± 0.03 ± 0.05) ×10

ing (experiments), Spectroscopy

yield determination 7

yield determination 8

Nonleptonic decays of charmed baryons are a useful environment in which to study the

interplay of the weak and strong interactions. Measurements of their branching fractions

are of great importance in understanding the internal dynamics of the decays. The last few

years have seen advances in the study of Λ

decays, where hh

decay suffered from model dependence, relying on assumptions concern-

cay have been made by the Belle [1] and BESIII [2] collaborations. The precision of a

number of Λ

while the first measurement of a doubly Cabibbo-suppressed (DCS) charmed-baryon decay,

The LHCb detector [10] is a single-arm forward spectrometer covering the pseudorapidity

range 2 < η < 5, designed for the study of particles containing b or c quarks. The detector

includes a high-precision tracking system consisting of a silicon-strip vertex detector sur-

rounding the pp interaction region, a large-area silicon-strip detector located upstream of

a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip

detectors and straw drift tubes placed downstream of the magnet. The tracking system

provides a measurement of momentum, p, of charged particles with a relative uncertainty

that varies from 0.5% at low momentum to 1.0% at 200 GeV/c. The minimum distance of

a track to a primary vertex, the impact parameter (IP), is measured with a resolution of

(15 + 29/p

tified by a calorimeter system consisting of scintillating-pad and preshower detectors, an

electromagnetic calorimeter and a hadronic calorimeter. Muons are identified by a system

composed of alternating layers of iron and multiwire proportional chambers.

stage, based on information from the calorimeter and muon systems, followed by a software

stage which is divided into two parts. The first employs a partial reconstruction of the

candidates from the hardware trigger and a cut-based selection, while the second utilises a

full event reconstruction and further, often more complex, selection criteria on candidates.

Selection requirements can be made on whether a trigger decision was satisfied by any

given object in the event (including non-signal objects). In the offline selection, trigger

decay kinematics of the Λ

generated according to a phase-space distribution. The

The different production mechanisms in the SL and prompt processes necessitate two dis-

tinct selections, which are verified to result in statistically independent samples of Λ

candidates. The selections are developed using a fraction of the Λ

responding to 10% of the integrated luminosity, chosen randomly. This sample is then

discarded from measurements of the ratios of branching fractions, with an appropriate

scaling factor applied to the final results.

product kinematics is reduced. This results in the ratios of trigger acceptance efficiencies

between the Λ

modes being uniform at these stages of the trigger. The muon can-

didate is required to have a p

the hardware trigger and the first stage of the software trigger. The latter uses additional

dates, requiring a high p

muon that is significantly displaced from the PV. This muon

must then form a displaced secondary vertex with between one and three other tracks.

This vertex must have at least one track with p

with respect to

tracks must have χ

event, and have a good fit quality. Three such tracks must then form a high-quality vertex

with a flight-distance-significance greater than 100 (defined as the measured flight distance

from any PV divided by its uncertainty). The p

of the three-particle combination must

also be greater than 1.8 GeV/c.

a common vertex with a fit χ