Measurements of the Branching Fractions ${\cal B}(B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}^{'0})$, ${\cal B}(B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2645)^{0})$ and ${\cal B}(B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2790)^{0}) $

Using the data sample of 711 fb$^{-1}$ of $\Upsilon(4S)$ on-resonance data taken by the Belle detector at the KEKB asymmetric-energy electron-positron collider, we present the first measurements of branching fractions of the decays $B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}^{'0}$, $B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2645)^{0}$, and $B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2790)^{0} $. The signal yields for these decays are extracted from the recoil mass spectrum of the system recoiling against $\bar{\Lambda}_{c}^{-}$ baryons in selected $B^-$ candidates. The branching fraction of $B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2790)^{0}$ is measured to be $ (1.1 \pm 0.4 \pm 0.2)\times 10^{-3}$, where the first uncertainty is statistical and the second systematic. The 90\% credibility level upper limits on ${\cal B}(B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}^{'0})$ and ${\cal B}(B^{-} \to \bar{\Lambda}_{c}^{-} \Xi_{c}(2645)^{0})$ are determined to be $6.5\times 10^{-4}$ and $7.9\times 10^{-4}$, respectively.


I. INTRODUCTION
Charm physics is of high interest mainly due to the fact that the charm system provides a unique laboratory to study the subtle interplay of strong and weak interactions.Baryons with one charm quark and two light quarks are called charmed baryons.In the Heavy Quark Symmetry (HQS) approach [1], the two light quarks are regarded as a light diquark.As chiral symmetry and HQS can provide some qualitative insights into their dynamics, the study of charmed baryons plays an important role in improving our understanding of the quark confinement mechanism.The Ξ c charmed baryon states contain one charm quark, one strange quark, and one up or down quark.The ground state Ξ 0 c and Ξ + c baryons, which have spin-parity quantum numbers J P = 1 2 + and no internal orbital angular momentum, are the only members of the group that decay weakly.A growing number of excited Ξ c states have been observed in different experiments [2].However, much is still unknown about them.Many theoretical approaches have been used to study the excitation spectrum of Ξ c baryons and their decays.These models include quark models, heavy quark 1/m Q and 1/N c expansions, coupled channel model, and QCD sum rules [3][4][5][6][7].Through these QCD-inspired relativistic theories, the mass spectrum of excited Ξ c can be predicted.Recently, the masses and intrinsic widths of isodoublets of the excited Ξ c states Ξ ′ c , Ξ c (2645), Ξ c (2790), Ξ c (2815), and Ξ c (2980) were measured more precisely by Belle by analyzing their exclusive decays [8].
The decay B − → Λ− c Ξ 0 c proceeds via b → ccs transition and has a relatively large branching fraction of the order of 10 −3 [2,9].Therefore, a B-meson factory provides an experimental research platform to investigate the Ξ 0 c excitation spectrum exclusively through B − → Λ− c + anything decays.This makes it possible to search for missing excited Ξ 0 c states.In addition, the measurement of their production rates is a good test for the theoretical calculation of b → ccs transition processes.
In this paper, we measure the branching fractions of B − → Λ− c Ξ * 0 c decays based on data collected by the Belle detector at the KEKB asymmetric-energy electronpositron collider.Here and throughout this paper, Ξ * 0 c represents Ξ ′ 0 c , Ξ c (2645) 0 , and Ξ c (2790) 0 unless otherwise stated.We use a full hadron-reconstruction algorithm [10] to tag a B + signal, denoted B + tag , and then reconstruct a Λ− c using its pK + π − and pK 0 S (K 0 S → π + π − ) decay modes [11] from the remaining tracks.We search for peaks in the invariant mass spectrum of the system recoiling against the Λ− c baryons in the selected B − → Λ− c Ξ * 0 c candidates, to extract Ξ * 0 c signal yields, from which we calculate the branching fractions of B − → Λ− c Ξ * 0 c .

II. THE DATA SAMPLE AND THE BELLE DETECTOR
This analysis utilizes a data sample of 711 fb −1 collected at the Υ(4S) on-resonance corresponding to (772 ± 11) × 10 6 B B pairs.All the data were collected with the Belle detector [12] operating at the KEKB asymmetric-energy e + e − collider [13].The Belle detector is described in detail in Ref. [12].It is a large solid-angle magnetic spectrometer consisting of a silicon vertex detector, a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), a barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter comprised of CsI(TI) crystals located inside a superconducting solenoid coil that provides a 1.5 T magnetic field.An iron flux return placed outside the coil is instrumented to detect K 0 L mesons and to identify muons.
To optimize the signal selection criteria and to determine the signal reconstruction efficiency, Monte Carlo (MC) signal events are generated using EvtGen [14], while Ξ * 0 c inclusive decays are simulated using PYTHIA [15].These events are processed by a detector simulation based on GEANT3 [16].Inclusive MC samples of Υ(4S) → B B (B = B + or B 0 ) and e + e − → q q (q = u, d, s, c) events at √ s = 10.58GeV corresponding to more than 3 times the integrated luminosity of the data are used to check the backgrounds.

III. COMMON EVENT SELECTION CRITERIA
To select the signal candidates, the following event selection criteria are applied.For well-reconstructed charged tracks, except those from K 0 S → π + π − decays, the impact parameters perpendicular to and along the beam direction with respect to the nominal interaction point (IP) are required to be less than 1 cm and 4 cm, respectively, and the transverse momentum in the laboratory frame is required to be larger than 0.1 GeV/c.For the particle identification (PID) of a wellreconstructed charged track, information from different detector subsystems, including specific ionization in the CDC, time measurement in the TOF, and the response of the ACC, is combined to form a likelihood L i [17] for particle species i, where i = π, K, or p. Tracks with R K = L K /(L K +L π ) < 0.4 are identified as pions with an efficiency of 97%, while 5% of kaons are misidentified as pions; tracks with R K > 0.6 are identified as kaons with an efficiency of 95%, while 4% of pions are misidentified as kaons.A track with R π p = L p /(L p + L π ) > 0.6 and R K p = L p /(L p +L K ) > 0.6 is identified as an (anti)proton with an efficiency of about 97%; fewer than 1% of the pions and kaons are misidentified as (anti)protons.With the exception of those from K 0 S decays, all charged tracks are required to be positively identified by the above procedure.
The K 0 S candidates are first reconstructed from pairs of oppositely charged tracks, which are treated as pions, with a production vertex significantly separated from the average IP, then selected using a multivariate analysis using an artificial neural network [18] based on two sets of input variables [19].
Applying a full reconstruction algorithm of hadronic B-meson decays [10]   To improve the recoil mass resolution, we use M rec Figure 1 shows the ∆E tag distribution in the Ξ * 0 c signal region, i.e., 2.5 GeV/c 2 < M rec after applying all of the above requirements.A double-Gaussian function is used as the signal shape and the background shape is described by a first-order polynomial.Because of the small sample size, the parameters of the double-Gaussian function are fixed to the values obtained by fitting the signal MC distribution.The fit results are shown as curves in Fig. 1.We take |∆E tag | < 0.04 GeV as the signal region.values of the parameters in double-Gaussian functions are fixed to those obtained from the fit to the corresponding signal MC distribution.For Ξ c (2645) 0 and Ξ c (2790) 0 signal shapes, the masses and widths of BW functions are fixed to world average values [2].The fit result is shown in Fig. 3.The difference between the fitted background level and the normalized M tag bc and M Λ− c sidebands is due to the contribution from other multibody B − decay modes with a Λ− c , for example,  The points with error bars represent the data, the solid blue curve is the best fit, the dashed curve is the fitted total background, the cyan shaded histogram is the normalized distribution of the M tag bc and M Λ− c sideband events (see Fig. 2).
Here, the statistical significances are defined as −2 ln(L 0 /L max ), where L 0 and L max are the maximized likelihoods without and with a signal component, respectively [20,21].The Ξ c (2790) 0 signal significance becomes 3.0σ when systematic uncertainties are included (see below).
Then the branching fractions are where being the number of accumulated Υ(4S) events.We use a value of 0.514 for B(Υ(4S) → B + B − ) [2]; , respectively.ε are the detection efficiencies of different Λ− c decay modes which are obtained from fits to the signal MC samples and are listed in Table I.
is the assumed branching fraction for  Table II summarizes the fitted results, branching fractions, and statistical significances for

V. SYSTEMATIC UNCERTAINTIES
There are several sources of systematic uncertainties for the branching fraction measurements as listed in Table III, including the reconstruction-efficiency-related sources, the fit uncertainty, the Λ c decay branching fractions, the B meson tag efficiency, and the total number of B B events.
The reconstruction-efficiency-related uncertainties include those for tracking efficiency (0.35% per track), particle identification efficiency (1.44% per kaon, 0.86% per pion, and range from 2.13% to 3.13% per proton), as well as momentum-weighted K 0 S selection efficiency (1.1%) [23].Here, the systematic uncertainty due to the K 0 S selection depends on the K 0 S momuntum and was determined using a control sample of D * + → D 0 (K 0 S π 0 )π + .For the three branching-fraction measurements, the individual reconstruction-efficiencyrelated uncertainties from two different Λ− c decay channels are added linearly weighted by the product of the detection efficiency and Λ− c partial decay width.Then those uncertainties are summed in quadrature to be the final uncertainties related to the efficiency of the reconstruction, yielding 3.1 to 3.5%, depending on the specific decay mode.
We estimate the systematic uncertainties associated with the fit by changing the order of the background polynomial, by changing the range of the fit, and by enlarging the mass resolution by 10%.The observed deviations are taken as systematic uncertainties.The masses of Ξ c (2790) 0 and Ξ c (2815) 0 are rather close, and no Ξ c (2815) 0 signal peak can be seen.The Ξ c (2815) 0 signal significance is only 0.4σ if it is added in the fit.So, we take the difference of the number of Ξ c (2790) 0 signal events as the systematic uncertainty due to the possible contribution of Ξ c (2815) 0 from B − → Λ− c Ξ c (2815) 0 .Finally, all the above uncertainties are summed in quadrature and the sums are taken as the systematic uncertainties associated with the fit.
Uncertainties for the Λ− c decay branching fractions are due to [2].The final uncertainties on the two Λ− c partial decay widths are summed in quadrature with the detection efficiency as a weighting factor.The uncertainty due to the B meson tagging efficiency is 4.2% [24].The uncertainty on B(Υ(4S) → B + B − ) is 1.2% [2].The systematic uncertainty on N Υ(4S) is 1.37%.The sources of uncertainty summarized in Table III are assumed to be independent and thus are added in quadrature to obtain the total systematic uncertainty.
where M B + tag is the reconstructed and m B is the nominal mass [2] of the B + meson and M miss B + tag Λ− c is the invariant mass recoiling against the Λ− c on the signal side, which is calculated using (P c.m.s − P B + tag − P Λ− c ) 2 with P c.m.s , P B + tag , and P Λ− c being four-momenta of the initial e + e − system, the reconstructed B + tag meson, and the reconstructed Λ− c baryon, respectively.

Figure 2 FIG. 1 :
Figure 2 shows the scatter plot of M Λ− c of the signal side in the Ξ * 0 c signal region versus M tag bc of the B + tag .To check for possible peaking backgrounds, the M tag bc

TABLE I :
The detection efficiencies ε