SND@LHC is a compact and stand-alone experiment designed to perform measurements with neutrinos produced at the LHC in the pseudo-rapidity region of 7.2 < η < 8.4. The experiment is located 480 m downstream of the ATLAS interaction point, in the TI18 tunnel. The detector is composed of a hybrid system based on an 830 kg target made of tungsten plates, interleaved with emulsion and electronic trackers, also acting as an electromagnetic calorimeter, and followed by a hadronic calorimeter and a muon identification system. The detector is able to distinguish interactions of all three neutrino flavours, which allows probing the physics of heavy flavour production at the LHC in the very forward region. This region is of particular interest for future circular colliders and for very high energy astrophysical neutrino experiments. The detector is also able to search for the scattering of Feebly Interacting Particles. In its first phase, the detector is ready to operate throughout LHC Run 3 and collect a total of 250 fb-1.
We report the direct observation of muon neutrino interactions with the SND@LHC detector at the Large Hadron Collider. A dataset of proton-proton collisions at collected by SND@LHC in 2022 is used, corresponding to an integrated luminosity of . The search is based on information from the active electronic components of the SND@LHC detector, which covers the pseudorapidity region of , inaccessible to the other experiments at the collider. Muon neutrino candidates are identified through their charged-current interaction topology, with a track propagating through the entire length of the muon detector. After selection cuts, 8 interaction candidate events remain with an estimated background of 0.086 events, yielding a significance of about 7 standard deviations for the observed signal.
An amplitude analysis of decays together with a measurement of the polarization vector in semiōleptonic beauty hadron decays is presented. A sample of 400 000 candidates is selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the state are also determined. A significant polarization is found. A large sensitivity of the decay to the polarization is seen, making the amplitude model suitable for polarization measurements in other systems.
Measurements of asymmetries in charmless three-body decays of mesons are reported using proton-proton collision data collected by the LHCb detector, corresponding to an integrated luminosity of . The previously observed asymmetry in decays is confirmed, and asymmetries are observed with a significance of more than five standard deviations in the and decays, while the asymmetry of decays is confirmed to be compatible with zero. The distributions of these asymmetries are also studied as a function of the three-body phase space and suggest contributions from rescattering and resonance interference processes. An indication of the presence of the decays in both and decays is observed, as is violation involving these amplitudes.
Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum and in the pseudorapidity range . The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of . Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.