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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. (2020). Observation of a new baryon state in the Lambda(0)(b)pi(+)pi(-) mass spectrum. J. High Energy Phys., 06(6), 136–26pp.
Abstract: A new baryon state is observed in the Lambda(0)(b)pi(+)pi(-) mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies root s = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The mass and natural width of the new state are measured to be m = 6072.3 +/- 2.9 +/- 0.6 +/- 0.2 MeV, Gamma = 72 +/- 11 +/- 2 MeV, where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Lambda(0)(b) baryon mass. The new state is consistent with the first radial excitation of the Lambda(0)(b) baryon, the Lambda(b)(2S)(0) resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Lambda(b)(5912)(0) and Lambda(b)(5920)(0) states are also reported.
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Fu, J., Giorgi, M. A., Henry, L., Marangotto, D., Martinez-Vidal, F., Merli, A., et al. (2019). Novel Method for the Direct Measurement of the tau Lepton Dipole Moments. Phys. Rev. Lett., 123(1), 011801–5pp.
Abstract: A novel method for the direct measurement of the elusive magnetic and electric dipole moments of the tau lepton is presented. The experimental approach relies on the production of tau(+) leptons from D-s(+) -> tau(+)nu(tau) decays, originating in fixed-target collisions at the LHC. A sample of polarized tau(+)leptons is kinematically selected and subsequently channeled in a bent crystal. The magnetic and electric dipole moments of the tau(+) lepton are measured by determining the rotation of the spin-polarization vector induced by the intense electromagnetic field between crystal atomic planes. The experimental technique is discussed along with the expected sensitivities.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2013). Precision measurement of the e(+)e(-) -> K+K-(gamma) cross section with the initial-state radiation method at BABAR. Phys. Rev. D, 88(3), 032013–28pp.
Abstract: A precise measurement of the cross section for the process e(+)e(-) -> K+K-(gamma) from threshold to an energy of 5 GeV is obtained with the initial-state radiation (ISR) method using 232 fb(-1) of data collected with the BABAR detector at e(+)e(-) center-of-mass energies near 10.6 GeV. The measurement uses the effective ISR luminosity determined from the e(+)e(-) -> mu(+)mu(-)(gamma)gamma(ISR) process with the same data set. The corresponding lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is found to be a(mu)(KK,LO) = (22.93 +/- 0.18(stat) +/- 0.22(syst)) x 10(-10). The charged kaon form factor is extracted and compared to previous results. Its magnitude at large energy significantly exceeds the asymptotic QCD prediction, while the measured slope is consistent with the prediction.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2012). Precise measurement of the e(+)e(-) -> pi(+)pi(-)(gamma) cross section with the initial-state radiation method at BABAR. Phys. Rev. D, 86(3), 032013–49pp.
Abstract: A precise measurement of the cross section of the process e(+)e(-) -> pi(+)pi(-) (gamma) from threshold to an energy of 3 GeV is obtained with the initial-state radiation (ISR) method using 232 fb(-1) of data collected with the BABAR detector at e(+)e(-) center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e(+)e(-) -> mu(+)mu(-) (gamma)gamma(ISR), which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e(+)e(-) -> pi(+)pi(-) (gamma) is obtained with a systematic uncertainty of 0.5% in the dominant rho resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured pi pi cross section from threshold to 1.8 GeV is (514.1 +/- 2.2(stat) +/- 3.1(sys)) x 10(-10).
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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. (2020). Precision measurement of the B-c(+) meson mass. J. High Energy Phys., 07(7), 123–21pp.
Abstract: A precision measurement of the B-c(+) meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9.0 fb(-1). The B-c(+) mesons are reconstructed via the decays B-c(+)-> J/psi pi(+), B-c(+)-> J/psi pi(+)pi(-)pi(+), B-c(+)-> J/psi pp<overbar>pi(+), B-c(+)-> J/psi D-s(+), B-c(+)-> J/psi (DK+)-K-0 and B-c(+)-> B-s(0)pi(+). Combining the results of the individual decay channels, the B-c(+) mass is measured to be 6274.47 +/- 0.27 (stat) +/- 0.17 (syst) MeV/c(2). This is the most precise measurement of the B-c(+) mass to date. The difference between the B-c(+) and B-s(0) meson masses is measured to be 907.75 +/- 0.37 (stat) +/- 0.27 (syst) MeV/c(2).
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