A mesurement of the mass of the τ lepton using new methods to study semi-invisible decays


  • Johan Andrés Colorado Caicedo Cinvestav-IPN
  • Eduard De La Cruz Burelo Cinvestav-IPN




τ lepton mass; methods to study invisible particles; lepton colliders


Measuring the mass of particles whose decay products cannot be detected poses a significant challenge due to the complexity of reconstructing these decays and measuring various parameters. However, studying processes involving undetectable particles is crucial as it enables us to delve deeper into familiar decays involving energy loss, such as Standard Model processes involving neutrinos. Additionally, it provides an opportunity to test models associated with physics beyond the Standard Model that can be generated in leptonic colliders. In this study, the mass of the tau lepton was determined by comparing three different methods for decays with semi-invisible final states. Specifically, the measurement focused on the decay τ − → π −ντ (signal). Among the three methods employed, the most accurate result was obtained using the Mmin method, yielding a tau lepton mass value of Mτ = 1777.06 ± 0.44 MeV. The measurement utilized official Monte Carlo data provided by the Belle II collaboration, specifically from the MC13a campaign conducted until 2020, with an integrated luminosity of 100fb−1 .


E. Tiesinga et al., CODATA recommended values of the fundamental physical constants: 2018, Rev. Mod. Phys. 93 (2021) 025010, https://doi.org/10.1103/RevModPhys.93.025010

P. D. Group et al., Progress of Theoretical and Experimental Physics Review of Particle Physics, 2022 (2022), https://doi.org/10.1093/ptep/ptac097

W. J. Marciano and A. Sirlin, Electroweak radiative corrections to τ decay, Phys. Rev. Lett. 61 (1988) 1815, https://doi.org/10.1103/PhysRevLett.61.1815

M. Davier, A. Höcker, and Z. Zhang, The physics of hadronic tau decays, Rev. Mod. Phys. 78 (2006) 1043, https://doi.org/10.1103/RevModPhys.78.1043

M. Ablikim, et al., Precision measurement of the mass of the τ lepton, Phys. Rev. D 90 (2014) 012001, https://doi.org/10.1103/PhysRevD.90.012001

B. Aubert et al., Measurements of the τ mass and the mass difference of the τ+ and τ - at BABAR, Phys. Rev. D 80 (2009) 092005, https://doi.org/10.1103/PhysRevD.80.092005

K. Belous et al., Measurement of the τ Lepton Mass and an Upper Limit on the Mass Difference between τ+ and τ -, Phys. Rev. Lett. 99 (2007) 011801, https://doi.org/10.1103/PhysRevLett.99.011801

H. Albrecht et al., A measurement of the tau mass, Physics Letters B 292 (1992) 221, https://doi.org/10.1016/0370-2693(92)90634-G

Belle II Collaboration, et al., τ lepton mass measurement at Belle II (2020), https://arxiv.org/abs/2008.04665

Q.-F. Xiang, et al., Measuring masses in semi-invisible final states at electron-positron colliders, Phys. Rev. D 95 (2017) 075037, https://doi.org/10.1103/PhysRevD.95.075037

E. De La Cruz-Burelo, A. De Yta-Hernandez, and M. Hernandez-Villanueva, New method for beyond the Standard Model invisible particle searches in tau lepton decays, Phys. Rev. D 102 (2020) 115001, https://doi.org/10.1103/PhysRevD.102.115001

Belle II Collaboration et al., Search for lepton-flavor-violating τ decays to a lepton and an invisible boson at Belle II (2022), https://doi.org/10.48550/arXiv.2212.03634

S. Jadach, B. Ward, and Z. Was, The precision Monte Carlo event generator KK for two-fermion final states in e +e − collisions, Computer Physics Communications 130 (2000) 260, https://doi.org/10.1016/S0010-4655(00)00048-5

S. Jadach, B. Ward, and Z. Wa¸s, Coherent exclusive exponentiation for precision Monte Carlo calculations, Phys. Rev. D 63 (2001) 113009, https://doi.org/10.1103/PhysRevD.63.113009

S. Jadach, J. H. Kühn, and Z. Wa¸s, TAUOLA - a library of Monte Carlo programs to simulate decays of polarized τ leptons, Computer Physics Communications 64 (1991) 275, https://doi.org/10.1016/0010-4655(91)90038-M

E. Barberio, B. van Eijk, and Z. Wa¸s, Photos-a universal Monte Carlo for QED radiative corrections in decays, Computer Physics Communications 66 (1991) 115, https://doi.org/10.1016/0010-4655(91)90012-A

T. Sjöstrand et al., An introduction to PYTHIA 8.2, Computer Physics Communications 191 (2015) 159, https://doi.org/10.1016/j.cpc.2015.01.024

C. Carloni Calame et al., Large-angle Bhabha scattering and luminosity at flavour factories, Nuclear Physics B 584 (2000) 459, https://doi.org/10.1016/S0550-3213(00)00356-4

C. Carloni Calame et al., The BABAYAGA event generator, Nuclear Physics B - Proceedings Supplements 131 (2004) 48, https://doi.org/10.1016/j.nuclphysbps.2004.02.008

C. M. Carloni Calame, An improved parton shower algorithm in QED, Physics Letters B 520 (2001) 16, https://doi.org/10.1016/S0370-2693(01)01108-X

G. Balossini, et al., Matching perturbative and parton shower corrections to Bhabha process at flavour factories, Nuclear Physics B 758 (2006) 227, https://doi.org/10.1016/j.nuclphysb.2006.09.022

F. Berends, P. Daverveldt, and R. Kleiss, Radiative corrections to the process e +e − → e +e +µ +µ −, Nuclear Physics B 253 (1985) 421, https://doi.org/10.1016/0550-3213(85)90540-1

F. Berends, P. Daverveldt, and R. Kleiss, Complete lowestorder calculations for four-lepton final states in electronpositron collisions, Nuclear Physics B 253 (1985) 441, https://doi.org/10.1016/0550-3213(85)90541-3

F. Berends, P. Daverveldt, and R. Kleiss, Monte Carlo simulation of two-photon processes: II: Complete lowest order calculations for four-lepton production processes in electron-positron collisions, Computer Physics Communications 40 (1986) 285, https://doi.org/10.1016/0010-4655(86)90115-3

S. Uehara, TREPS: A Monte-Carlo Event Generator for Twophoton Processes at e +e − Colliders using an Equivalent Photon Approximation (2013), https://arxiv.org/abs/1310.0157

T. Kuhr et al., The Belle II Core Software, Computing and Software for Big Science 3 (2018) 1, https://doi.org/10.1007/s41781-018-0017-9

S. Agostinelli et al., Geant4-a simulation toolkit, Nucl. Instrum. Meth. A Detectors and Associated Equipment 506 (2003) 250, https://doi.org/10.1016/S0168-9002(03)01368-8

R. Brun and F. Rademakers, ROOT: An object oriented data analysis framework, Nucl. Instrum. Meth. A 389 (1997) 81, https://doi.org/10.1016/S0168-9002(97)00048-X

A. Hocker et al., TMVA - Toolkit for Multivariate Data Analysis (2007) https://doi.org/10.48550/arXiv.physics/0703039

W. Verkerke and D. Kirkby, The RooFit toolkit for data modeling (2003), https://arxiv.org/abs/physics/0306116




How to Cite

Colorado Caicedo JA, De La Cruz Burelo E. A mesurement of the mass of the τ lepton using new methods to study semi-invisible decays. Supl. Rev. Mex. Fis. [Internet]. 2023 Sep. 18 [cited 2023 Dec. 10];4(2):021107 1-8. Available from: https://rmf.smf.mx/ojs/index.php/rmf-s/article/view/7082