Aiola, S., Amhis, Y., Billoir, P., Jashal, B. K., Henry, L., Oyanguren, A., et al. (2021). Hybrid seeding: A standalone track reconstruction algorithm for scintillating fibre tracker at LHCb. Comput. Phys. Commun., 260, 107713–5pp.
Abstract: We describe the Hybrid seeding, a stand-alone pattern recognition algorithm aiming at finding charged particle trajectories for the LHCb upgrade. A significant improvement to the charged particle reconstruction efficiency is accomplished by exploiting the knowledge of the LHCb magnetic field and the position of energy deposits in the scintillating fibre tracker detector. Moreover, we achieve a low fake rate and a small contribution to the overall timing budget of the LHCb real-time data processing.
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Borsato, M. et al, Zurita, J., Henry, L., Jashal, B. K., & Oyanguren, A. (2022). Unleashing the full power of LHCb to probe stealth new physics. Rep. Prog. Phys., 85(2), 024201–45pp.
Abstract: In this paper, we describe the potential of the LHCb experiment to detect stealth physics. This refers to dynamics beyond the standard model that would elude searches that focus on energetic objects or precision measurements of known processes. Stealth signatures include long-lived particles and light resonances that are produced very rarely or together with overwhelming backgrounds. We will discuss why LHCb is equipped to discover this kind of physics at the Large Hadron Collider and provide examples of well-motivated theoretical models that can be probed with great detail at the experiment.
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Calefice, L., Hennequin, A., Henry, L., Jashal, B. K., Mendoza, D., Oyanguren, A., et al. (2022). Effect of the high-level trigger for detecting long-lived particles at LHCb. Front. Big Data, 5, 1008737–13pp.
Abstract: Long-lived particles (LLPs) show up in many extensions of the Standard Model, but they are challenging to search for with current detectors, due to their very displaced vertices. This study evaluated the ability of the trigger algorithms used in the Large Hadron Collider beauty (LHCb) experiment to detect long-lived particles and attempted to adapt them to enhance the sensitivity of this experiment to undiscovered long-lived particles. A model with a Higgs portal to a dark sector is tested, and the sensitivity reach is discussed. In the LHCb tracking system, the farthest tracking station from the collision point is the scintillating fiber tracker, the SciFi detector. One of the challenges in the track reconstruction is to deal with the large amount of and combinatorics of hits in the LHCb detector. A dedicated algorithm has been developed to cope with the large data output. When fully implemented, this algorithm would greatly increase the available statistics for any long-lived particle search in the forward region and would additionally improve the sensitivity of analyses dealing with Standard Model particles of large lifetime, such as KS0 or Lambda (0) hadrons.
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Garcia Martin, L. M., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Roy, S., Sain, R., et al. (2019). Radiative b-baryon decays to measure the photon and b-baryon polarization. Eur. Phys. J. C, 79(7), 634–10pp.
Abstract: The radiative decays of b-baryons facilitate the direct measurement of photon helicity in b -> s gamma transitions thus serving as an important test of physics beyond the Standard Model. In this paper we analyze the complete angular distribution of ground state b-baryon radiative decays to multibody final states assuming an initially polarized b-baryon sample. Our sensitivity study suggests that the photon polarization asymmetry can be extracted to a good accuracy along with a simultaneous measurement of the initial b-baryon polarization. With higher yields of b-baryons, achievable in subsequent runs of the Large Hadron Collider (LHC), we find that the photon polarization measurement can play a pivotal role in constraining different new physics scenarios.
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Gorkavenko, V., Jashal, B. K., Kholoimov, V., Kyselov, Y., Mendoza, D., Ovchynnikov, M., et al. (2024). LHCb potential to discover long-lived new physics particles with lifetimes above 100 ps. Eur. Phys. J. C, 84(6), 608–15pp.
Abstract: For years, it has been believed that the main LHC detectors can play only a limited role of a lifetime frontier experiment exploring the parameter space of long-lived particles (LLPs)-hypothetical particles with tiny couplings to the Standard Model. This paper demonstrates that the LHCb experiment may become a powerful lifetime frontier experiment if it uses the new Downstream algorithm reconstructing tracks that do not allow hits in the LHCb vertex tracker. In particular, for many LLP scenarios, LHCb may be as sensitive as the proposed experiments beyond the main LHC detectors for various LLP models, including heavy neutral leptons, dark scalars, dark photons, and axion-like particles.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Angular analysis of the decay Bs0 → φ e+ e-. J. High Energy Phys., 07(7), 69–29pp.
Abstract: An angular analysis of the decay Bs0 -> phi e+e- is presented, using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8 and 13 TeV. The combined dataset corresponds to an integrated luminosity of 9 fb-1. Observables are determined by fitting time-integrated projections of the angular distribution in three bins of dielectron mass squared, q2, corresponding to [0.1, 1.1], [1.1, 6.0] and [15.0, 19.0] GeV2/c4. The results are compatible with predictions based on the Standard Model of particle physics.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Observation of the decay B0s → K0p(p)over-bar and measurement of the B0(s) → K0p(p)over-bar branching fractions. J. High Energy Phys., 07(7), 121–25pp.
Abstract: A study of the charmless baryonic decays B-(s)(0) -> K(0)p (p) over bar is presented, where B-(s)(0) denotes either a B-0 or a B-s(0) meson. The analysis is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The decay B-s(0) -> K(0)p (p) over bar is observed for the first time, with a measured branching fraction of (9.14 +/- 1.69 +/- 0.90 +/- 0.33 +/- 0.20) x 10(-7) and a significance of 5.6 sigma. The uncertainties respectively account for statistical and systematic contributions, the precision of the branching fraction of the normalisation channel B-0 -> K-0 pi(+)pi(-) and the fragmentation fraction ratio f(s)/f(d). The branching fraction determined for B-0 -> K(0)p (p) over bar is (2.82 +/- 0.08 +/- 0.12 +/- 0.10) x 10(-6), which is the most precise measurement to date.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Amplitude analysis of B+ → ψ(2S)K+ π+ π- decays. J. High Energy Phys., 01(1), 054–69pp.
Abstract: The first full amplitude analysis of B+ -> psi(2S)K+pi(+)pi(-) decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 fb(-1) recorded with the LHCb detector. The rich K+pi(+)pi(-) spectrum is studied and the branching fractions of the resonant substructure associated with the prominent K-1(1270)(+) contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity J(P) = 1(+) in the psi(2S)pi(+) system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the psi(2S)pi(+)pi(-) invariant-mass structure, dominated by X-0 -> psi(2S)rho(770)(0) decays, broadly resembles the J/psi phi spectrum observed in B+ -> J/psi phi K+ decays. Exotic psi(2S)K+pi(-) resonances are observed for the first time.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Observation of muonic Dalitz decays of chib mesons and precise spectroscopy of hidden-beauty states. J. High Energy Phys., 10(10), 122–28pp.
Abstract: The decays of the chi(b1)(1P), chi(b2)(1P), chi(b1)(2P) and chi(b2)(2P) mesons into the Upsilon(1S)mu(+)mu(-) final state are observed with a high significance using proton-proton collision data collected with the LHCb detector and corresponding to an integrated luminosity of 9 fb(-1). The newly observed decays together with the Upsilon(2S) -> Upsilon(1S)pi(+)pi(-) and Upsilon(3S) -> Upsilon(2S)pi(+)pi(-) decay modes are used for precision measurements of the mass and mass splittings for the hidden-beauty states.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Probing the nature of the χc1(3872) state using radiative decays. J. High Energy Phys., 11(11), 121–31pp.
Abstract: The radiative decays chi(c1)(3872) -> (2S) gamma and chi(c1)(3872) -> J/gamma are used to probe the nature of the chi(c1)(3872) state using proton-proton collision data collected with the LHCb detector, corresponding to an integrated luminosity of 9 fb(-1). Using the B+ -> chi(c1)(3872)K+ decay, the chi(c1)(3872) -> psi(2S) gamma process is observed for the first time and the ratio of its partial width to that of the chi(c1)(3872) -> J/psi gamma decay is measured to be Gamma(chi c1(3872))->psi(2S)gamma/Gamma(chi c1(3872)) -> J/psi gamma = 1.67 +/- 0.21 +/- 0.12 +/- 0.04, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainties on the branching fractions of the psi(2S) and J/psi mesons. The measured ratio makes the interpretation of the chi(c1)(3872) state as a pure D-0(D) over bar (*0) + (D) over bar D-0(*0) molecule questionable and strongly indicates a sizeable compact charmonium or tetraquark component within the chi(c1)(3872) state.
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