Punzi, G., Baldini, W., Bassi, G., Contu, A., Fantechi, R., He, J. B., et al. (2024). Detector-embedded reconstruction of complex primitives using FPGAs. Nucl. Instrum. Methods Phys. Res. A, 1069, 169782–4pp.
Abstract: The slowdown of Moore's law and the growing requirements of future HEP experiments with ever-increasing data rates pose important computational challenges for data reconstruction and trigger systems, encouraging the exploration of new computing methodologies. In this work we discuss a FPGA-based tracking system, relying on a massively parallel pattern recognition approach, inspired by the processing of visual images by the natural brain (“retina architecture”). This method allows a large efficiency of utilisation of the hardware, low power consumption and very low latencies. Based on this approach, a device has been designed within the LHCb Upgrade-II project, with the goal of performing track reconstruction in the forward acceptance region in real-time during the upcoming Run 4 of the LHC. This innovative device will perform track reconstruction before the event-building, in a short enough time to provide pre-reconstructed tracks (“primitives”) transparently to the processor farm, as if they had been generated directly by the detector. This allows significant savings in higher-level computing resources, enabling handling higher luminosities than otherwise possible. The feasibility of the project is backed up by the results of tests performed on a realistic hardware prototype, that has been opportunistically processing actual LHCb data in parallel with the regular DAQ in the LHC Run 3.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of the Lambda(0)(b) -> Lambda+cK+K-pi(-) decay. Phys. Lett. B, 815, 136172–10pp.
Abstract: The Lambda(0)(b) -> Lambda+cK+K-pi(-) decay is observed for the first time using a data sample of proton-proton collisions at centre-of-mass energies of root s = 7 and 8 TeV collected by the LHCb detector, corresponding to an integrated luminosity of 3fb(-1). The ratio of branching fractions between the Lambda(0)(b) -> Lambda K-+(c)+ K-pi(-) and the Lambda(0)(b) -> Lambda D-+(c)s(-) decays is measured to be B(Lambda(0)(b) -> Lambda+cK+K-pi(-))/B(Lambda(0)(b) -> Lambda D-+(c)s(-)) = (9.26 +/- 0.29 +/- 0.46 +/- 0.26) x 10(-2), where the first uncertainty is statistical, the second systematic and the third is due to the knowledge of the D-s(-) -> K+K-pi(-) branching fraction. No structure on the invariant mass distribution of the Lambda K-+(c)+ system is found, consistent with no open-charm pentaquark signature.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Measurement of the CP-violating phase phi(s) from B-s(0) -> J/psi pi(+)pi(-) decays in 13 TeV pp collisions. Phys. Lett. B, 797, 134789–12pp.
Abstract: Decays of B-s(0) and (B) over bar (0)(s) mesons into J/psi pi(+)pi(-) final states are studied in a data sample corresponding to 1.9 fb(-1) of integrated luminosity collected with the LHCb detector in 13 TeV pp collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the CP-violating phase phi(s) = -0.057 +/- 0.060 +/- 0.011 rad, the decay-width difference between the heavier mass B-s(0) eigenstate and the B-0 meson of -0.050 +/- 0.004 +/- 0.004 ps(-1), and the CP-violating parameter vertical bar lambda vertical bar = 1.01(-0.06)(+0.08) +/- 0.03, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV pp collisions obtaining phi(s) = 0.002 +/- 0.044 +/- 0.012 rad, and vertical bar lambda vertical bar = 0.949 +/- 0.036 +/- 0.019.
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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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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2025). Observation of Exotic J/ψφ Resonant Structure in Diffractive Processes in Proton-Proton Collisions. Phys. Rev. Lett., 134(3), 12pp.
Abstract: The first study of J/psi phi production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb(-1.) The data disfavor a nonresonant J/psi phi production but are consistent with a resonant model including several resonant states observed previously only in B+ -> J/psi phi K+ decays. The chi(c0)(4500) state is observed with a significance over 6 sigma and the chi(c1) (4274) is confirmed with a significance of more than 4 sigma.
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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). First Determination of the Spin-Parity of Ξc(3055) +,0 Baryons. Phys. Rev. Lett., 134(8), 081901–13pp.
Abstract: The Xi(0(-))(b) -> Xi(c)(3055)(+(0))(-> D+(0)Lambda)pi(-) decay chains are observed, and the spin-parity of Xi(c)(3055)(+(0)) baryons is determined for the first time. The measurement is performed using protonproton collision data at a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1), recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the Xi(c)(3055)(+(0)) baryons is determined to be 3/2(+) with a significance of more than 6.5 sigma (3.5 sigma) compared to all other tested hypotheses. The up-down asymmetries of the Xi(0(-))(b) -> Xi(c)(3055)(+(0))pi(-) transitions are measured to be -0.92 +/- 0.10 +/- 0.05 (-0.92 +/- 0.16 +/- 0.22), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the Xi(c)(3055)(+(0)) baryons correspond to the first D-wave lambda-mode excitation of the Xi(c) flavor triplet.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2025). Measurement of the Branching Fraction Ratios R(D+) and R(D*+) Using Muonic τ Decays. Phys. Rev. Lett., 134(6), 061801–13pp.
Abstract: The branching fraction ratios of (B) over bar (0) -> D+tau(-)(v) over bar (tau) and (B) over bar (0) -> D*(+)tau(-)(v) over bar (tau) decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0 fb(-1) collected by the LHCb experiment in proton-proton collisions at root s = 13 TeV. The reconstructed final states are formed by combining D+ mesons with tau(-) -> mu(-) (v) over bar (mu)(v) over bar (tau) candidates, where the D+ is reconstructed via the D+ -> K- pi(+) pi(+) decay. The results are R(D+) = 0.249 +/- 0.043 +/- 0.047, R(D*(+)) = 0.402 +/- 0.081 +/- 0.085, where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of -0.39 and are compatible with the standard model.
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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). Observation of the Open-Charm Tetraquark Candidate Tcs0* (2870)0 in the B- → D- D0KS0 Decay. Phys. Rev. Lett., 134(10), 101901–13pp.
Abstract: An amplitude analysis of B- -> D- (DKS0)-K-0 decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 9 fb(-1), collected with the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV. A resonant structure of spin-parity 0(+) is observed in the (DKS0)-K-0 invariant-mass spectrum with a significance of 5.3s. The mass and width of the state, modeled with a Breit-Wigner line shape, are determined to be 2883 +/- 11 +/- 8 MeV/c(2) and 87(-47)(+22) +/- 17 MeV, respectively, where the first uncertainties are statistical and the second systematic. These properties and the quark content are consistent with those of the open-charm tetraquark candidate T-cs0(*)(2870)(0) observed previously in the D+K- final state of the B- -> D-D+K- decay. This result confirms the existence of the T-cs0(*)(2870)(0) state in a new decay mode. The T-c10(*) (2900)(0) state, reported in the B- -> D-D+K- decay, is also searched for in the (DKS0)-K-0 invariant-mass spectrum of the B- -> D- (DKS0)-K-0 decay, without finding evidence for it.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Observation of New Charmonium or Charmoniumlike States in B+ → D*±D∓K+ Decays. Phys. Rev. Lett., 133(13), 131902–14pp.
Abstract: A study of resonant structures in B+ -> D*(DK+)-D-+/--K--/+ and B+ -> D*(DK+)-D-+/--K--/+ decays is performed, using proton-proton collision data at center-of-mass energies of root s = 7, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to D*D-+/-(+) and D*D-+/-(-) states linked by C parity. This procedure allows the C parities of resonances in the D*D-+/-(-/+) mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into D*D-+/-(-/+): eta(c)(3945), h(c)(4000), chi(c1)(4010), and h(c)(4300), with quantum numbers J(PC) equal to 0(-+), 1(+-), 1(+-), and 1(+-), respectively. At least three of these states have not been observed previously. In addition, the existence of the T-(c) over bar(s) over bar0*(2870)(0) and T-(c) over bar(s) over bar1*(2900)(0) resonances in the D-K+ mass spectrum, already observed in the B+ -> D+D-K+ decay, is confirmed in a different production channel.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for Time-Dependent CP Violation in D0 → π+ π- π0 Decays. Phys. Rev. Lett., 133(10), 101803–12pp.
Abstract: A measurement of time-dependent CP violation in D-0 -> pi(+) pi(-) pi(0) decays using a pp collision data sample collected by the LHCb experiment in 2012 and from 2015 to 2018, corresponding to an integrated luminosity of 7.7 fb(-1), is presented. The initial flavor of each D-0 candidate is determined from the charge of the pion produced in the D*(2010)(+) -> D-0 pi(+) decay. The decay D-0 -> K- pi(+) pi(0) is used as a control channel to validate the measurement procedure. The gradient of the time-dependent CP asymmetry Delta Y in D-0 -> pi(+) pi(-) pi(0) decays is measured to be Delta Y = (-1.3 +/- 6.3 +/- 2.4) x 10(-4), where the first uncertainty is statistical and the second is systematic, which is compatible with CP conservation.
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