Overview of LHCb results on beauty and charm spectroscopy

We present a summary of new experimental results from LHCb experiment on the status of the charm spectroscopy using inclusive approaches and Dalitz plot analyses of B and Bs decays. We also summarize latest results on the spectroscopy of heavy baryons.


Introduction
The LHCb experiment [1] is collecting very large samples of cc and bb events. The present results are mostly based on data data collected in 2011 and 2012 during the Run 1 period, corresponding to an integrated luminosity of ≈ 3.0 fb −1 .

Charm meson spectroscopy
Two methods are used for studying or discovering new states in LHCb.
• Inclusive approach: the study of inclusive final states D 0 π + , D + π − and D * + π − in the reactions pp → D J X, and of the final states D 0 K + , D + K 0 S and D * + K 0 S in the reactions pp → D sJ X.
In these reactions, -All resonances can be produced.
-The signal to background ratio can be poor. -A spin-parity analysis of three-body decays can only distinguish between Natural and Unnatural Parity assignments.

Observation of new D J mesons
The LHCb experiment has performed an inclusive study of the Dπ and D * π systems using 1 fb −1 of data [2]. In the study of the D * + π − system, with D * + → D 0 π + , the data are separated in terms of the π + helicity angle θ H . The sample with | cos θ H |> 0.75 is defined as "Enhanced Unnatural Parity Sample", while the sample with | cos θ H |< 0.5 is defined as "Natural Parity Sample". The two mass spectra are shown in Fig. 1. In the Enhanced Unnatural Parity sample, above the D 1 (2420) and D * 2 (2460), three new structures are observed: D J (2550) 0 , D J (2760) 0 and D J (3000) 0 . In the Natural Parity sample, two further structures are observed: D * J (2600) 0 and D * J (2760) 0 . The presence of these two Natural Parity states is confirmed by the analysis of the D + π − and D 0 π + data.

First observation and Dalitz plot analysis of
The D + K − π − mass spectrum [3] is shown in Fig. 2 (Left) and contains ≈2000 events in the B − signal region. A standard Dalitz plot analysis of the B − → D + K − π − system has been performed. The

Inclusive studies
Using samples of 0.36 × 10 6 D + K 0 S and 3.15 × 10 6 D 0 K + inclusive candidates [6], the D * s1 (2710) + and D * sJ (2860) + have been observed with parameters consistent with previous measurements [7]. The inclusive D * + K 0 S mass spectrum with enhanced Natural Parity selection is shown in Fig. 6   inclusive and exclusive analyses. Significances are 7.6σ and 7.1σ respectively. A search has been performed for the new spin-1 resonance D * s1 (2860) + observed in the B s decay. However, the same χ 2 /nd f is obtained in fit that excludes it and its resulting statistical significance is 3.3σ. It is concluded that the data are not sensitive to the presence of the D * s1 (2860) + resonance. Figure 7 (Left) shows the threshold region of the D * + K 0 S mass spectrum with enhanced Natural Parity selection. Signals of D s1 (2536) + and D * s2 (2573) + are observed. D * s2 (2573) + is observed here for the first time and has a significance of 6.9σ. Its mass is found to be consistent with that obtained from the DK measurements. The D * s2 (2573) + angular distribution is shown in Fig. 7 (Right) and is consistent with a J P = 2 + Natural Parity assignment. The relative branching fraction of the decay D * s2 (2573) + → D * + K 0 S is measured as and is in agreement with expectations from quark model calculations which predict a value of 0.058 for this ratio [10].

Search for Ξ + cc states
LHCb experiment has performed an initial search for Ξ + cc → Λ c K − π + [16] using a small data set (0.65 f b −1 ). No signal has been found. A more accurate search will be performed using the very high statistics data samples actually available.

Summary
• Several new D J and D sJ mesons have been observed in both inclusive and exclusive B/B s decays.
• The observation of these states in B/B s decays allows the determination of their quantum numbers.
• New high statistics data will be shortly available and new decay channels are being analyzed. These studies will allow to better understand the charm and strange-charm spectrum.
• Progress have been performed in completing the quark model spectrum for heavy baryons. Several new states have been discovered. Large progress are expected in the new future in understanding the heavy baryons using high statistics and high purity new decay channels.