LHCb

Abstract:

The first observation of the doubly charmed baryon ${\mathrm{\Xi }}_{cc}^{+}$ is reported through its decay to the ${\mathrm{\Lambda }}_c^{+}{K}^{-}{\pi }^{+}$ final state, with a statistical significance exceeding seven standard deviations. The observation is made using proton-proton collision data collected in 2024 with the LHCb Run 3 detector at a center-of-mass energy of 13.6 TeV, corresponding to a total integrated luminosity of $6.9{\mathrm{fb}}^{-1}$ . The ${\mathrm{\Xi }}_{cc}^{+}$ mass is measured to be $3619.97\pm 0.83\pm {0.26}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$ , where the first uncertainty is statistical, the second is systematic, and the third is due to the unknown ${\mathrm{\Xi }}_{cc}^{+}$ lifetime, which is assumed to lie in the range 15–160 fs with a baseline value of 45 fs. The difference between the masses of the ${\mathrm{\Xi }}_{cc}^{+}$ and ${\mathrm{\Xi }}_{cc}^{++}$ baryons is determined to be $-1.77\pm 0.84\pm {0.15}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$ . This is the first observation of a new particle made with the LHCb Run 3 detector.

Abstract:

This paper presents a study of the charmless three-body decays Bs0→KS0h+h′−$$ {B}_{(s)}^0\to {K}_{\mathrm{S}}^0{h}^{+}h{\prime}^{-} $$ (where h(′) = π, K), using a sample of pp collision data collected by the LHCb experiment during Runs 1 and 2 of the LHC, corresponding to an integrated luminosity of 9 fb−1. The decay Bs0→KS0K+K−$$ {B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $$ is observed for the first time, and the following ratios of branching fractions are measured:BB0→KS0K+K−BB0→KS0π+π−=0.578±0.007±0.017,BB0→KS0K±K∓BB0→KS0π+π−=0.1363±0.0035±0.051,BBs0→KS0π+π−BB0→KS0π+π−=0.269±0.011±0.015±0.008,BBs0→KS0K+K−BB0→KS0π+π−=0.0303±0.0041±0.0025±0.0009,BBs0→KS0K±π∓BB0→KS0π+π−=1.818±0.021±0.031±0.056,$$ {\displaystyle \begin{array}{l}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.578\pm 0.007\pm 0.017,\\ {}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{K}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.1363\pm 0.0035\pm 0.051,\\ {}\begin{array}{l}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.269\pm 0.011\pm 0.015\pm 0.008,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.0303\pm 0.0041\pm 0.0025\pm 0.0009,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{\pi}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=1.818\pm 0.021\pm 0.031\pm 0.056,\end{array}\end{array}} $$where the uncertainties are statistical, systematic, and due to knowledge of the ratio of hadronisation fractions of the Bs0$$ {B}_s^0 $$ and B0 mesons, respectively.

Abstract:

Owing to their single-photon sensitivity and fast rise time, micro-channel-plate photomultipliers (MCP-PMTs) make good candidates as photon detectors for the Time Of Internally Reflected CHerenkov light detector (TORCH) that is proposed as part of the phase two upgrade of the LHCb experiment. The TORCH detector has a target time resolution per photon of approximately 70 ps, required to achieve an approximately three standard deviation separation of pions and kaons at 10 GeV/c from their time-of-flight over a 10 m flight distance. A new high-granularity 16-by-96 channel MCP-PMT with a directly coupled anode has been developed in conjunction with Photek Ltd. This device is designed to decrease the pixel pitch to 0.55 mm in the fine pixel direction, giving improved spatial resolution and importantly lower per-pixel occupancies. This paper will cover cross-talk characterisation studies, used to determine the spatial resolution of the device. The experimental results are compared with simulation studies. Overall, the results demonstrate minimal effects of cross-talk on the device's output. A study of a TORCH demonstrator, using older 8-by-64 channel MCP-PMTs, has also been carried out in a beam test at CERN. Initial results from the demonstrator show suitable mechanical and optical performances.