Abstract
The differential branching fraction of the rare decay Λ 0 b → Λμ+μ− is measured as a function of q2, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment. Evidence of signal is observed in the q2 region below the square of the J/ψ mass. Integrating over 15 < q2 < 20 GeV2/c4 the differential branching fraction is measured as
where the uncertainties are statistical, systematic and due to the normalisation mode, Λ 0 b → J/ψΛ, respectively. In the q2 intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon (A ℓFB ) and hadron (A hFB ) systems are measured for the first time. In the range 15 < q2 < 20 GeV2/c4 they are found to be
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Change history
26 September 2018
The angular distribution of the dimuon system of the decays.
References
T. Mannel and S. Recksiegel, Flavor changing neutral current decays of heavy baryons: The Case Λb → Λγ, J. Phys. G 24 (1998) 979 [hep-ph/9701399] [INSPIRE].
G. Hiller, M. Knecht, F. Legger and T. Schietinger, Photon polarization from helicity suppression in radiative decays of polarized Λb to spin-3/2 baryons, Phys. Lett. B 649 (2007) 152 [hep-ph/0702191] [INSPIRE].
P. Böer, T. Feldmann and D. van Dyk, Angular Analysis of the Decay Λb → Λ(→ Nπ)ℓ + ℓ −, JHEP 01 (2015) 155 [arXiv:1410.2115] [INSPIRE].
M.J. Aslam, Y.-M. Wang and C.-D. Lu, Exclusive semileptonic decays of Λb → −Λℓ + ℓ − in supersymmetric theories, Phys. Rev. D 78 (2008) 114032 [arXiv:0808.2113] [INSPIRE].
Y.-M. Wang, Y. Li and C.-D. Lu, Rare Decays of Λb → Λ + γ and Λb → Λ + ℓ + ℓ − in the Light-cone Sum Rules, Eur. Phys. J. C 59 (2009) 861 [arXiv:0804.0648] [INSPIRE].
C.-S. Huang and H.-G. Yan, Exclusive rare decays of heavy baryons to light baryons: Λb → Λγ and Λb → Λℓ + ℓ −, Phys. Rev. D 59 (1999) 114022 [hep-ph/9811303] [INSPIRE].
C.-H. Chen and C.Q. Geng, Rare Λb → Λℓ + ℓ − decays with polarized Λ, Phys. Rev. D 63 (2001) 114024 [hep-ph/0101171] [INSPIRE].
C.-H. Chen and C.Q. Geng, Baryonic rare decays of Λb → Λℓ + ℓ −, Phys. Rev. D 64 (2001) 074001 [hep-ph/0106193] [INSPIRE].
C.-H. Chen and C.Q. Geng, Lepton asymmetries in heavy baryon decays of Λb → Λℓ + ℓ −, Phys. Lett. B 516 (2001) 327 [hep-ph/0101201] [INSPIRE].
F. Zolfagharpour and V. Bashiry, Double Lepton Polarization in Λb → Λℓ + ℓ − Decay in the Standard Model with Fourth Generations Scenario, Nucl. Phys. B 796 (2008) 294 [arXiv:0707.4337] [INSPIRE].
L. Mott and W. Roberts, Rare dileptonic decays of Λb in a quark model, Int. J. Mod. Phys. A 27 (2012) 1250016 [arXiv:1108.6129] [INSPIRE].
T.M. Aliev, K. Azizi and M. Savci, Analysis of the Λb → Λℓ + ℓ − decay in QCD, Phys. Rev. D 81 (2010) 056006 [arXiv:1001.0227] [INSPIRE].
R. Mohanta and A.K. Giri, Fourth generation effect on Λb decays, Phys. Rev. D 82 (2010) 094022 [arXiv:1010.1152] [INSPIRE].
S. Sahoo, C.K. Das and L. Maharana, Effect of both Z and Z ′ -mediated flavor-changing neutral currents on the baryonic rare decay Λb → Λℓ + ℓ −, Int. J. Mod. Phys. A 24 (2009) 6223 [arXiv:1112.4563] [INSPIRE].
W. Detmold, C.-J.D. Lin, S. Meinel and M. Wingate, Λb → Λℓ + ℓ − form factors and differential branching fraction from lattice QCD, Phys. Rev. D 87 (2013) 074502 [arXiv:1212.4827] [INSPIRE].
T. Gutsche, M.A. Ivanov, J.G. Korner, V.E. Lyubovitskij and P. Santorelli, Rare baryon decays Λb → Λℓ + ℓ −(ℓ = e, μ, τ) and Λb → Λγ: differential and total rates, lepton- and hadron-side forward-backward asymmetries, Phys. Rev. D 87 (2013) 074031 [arXiv:1301.3737] [INSPIRE].
S. Meinel, Flavor physics with Λb baryons, PoS(LATTICE 2013)024 [arXiv:1401.2685] [INSPIRE].
CDF collaboration, T. Aaltonen et al., Observation of the Baryonic Flavor-Changing Neutral Current Decay Λb → Λμ + μ −, Phys. Rev. Lett. 107 (2011) 201802 [arXiv:1107.3753] [INSPIRE].
LHCb collaboration, Measurement of the differential branching fraction of the decay Λ 0 b → Λμ + μ −, Phys. Lett. B 725 (2013) 25 [arXiv:1306.2577] [INSPIRE].
M. Beylich, G. Buchalla and T. Feldmann, Theory of B → K (*) ℓ + ℓ − decays at high q 2 : OPE and quark-hadron duality, Eur. Phys. J. C 71 (2011) 1635 [arXiv:1101.5118] [INSPIRE].
M. Beneke and T. Feldmann, Symmetry breaking corrections to heavy to light B meson form-factors at large recoil, Nucl. Phys. B 592 (2001) 3 [hep-ph/0008255] [INSPIRE].
LHCb collaboration, The LHCb Detector at the LHC, 2008 JINST 3 S08005 [INSPIRE].
LHCb collaboration, LHCb Detector Performance, Int. J. Mod. Phys. A 30 (2015) 1530022 [arXiv:1412.6352] [INSPIRE].
R. Aaij et al., Performance of the LHCb Vertex Locator, 2014 JINST 9 P09007 [arXiv:1405.7808] [INSPIRE].
LHCb Outer Tracker Group collaboration, R. Arink et al., Performance of the LHCb Outer Tracker, 2014 JINST 9 P01002 [arXiv:1311.3893] [INSPIRE].
LHCb RICH Group collaboration, M. Adinolfi et al., Performance of the LHCb RICH detector at the LHC, Eur. Phys. J. C 73 (2013) 2431 [arXiv:1211.6759] [INSPIRE].
A.A. Alves Jr. et al., Performance of the LHCb muon system, 2013 JINST 8 P02022 [arXiv:1211.1346] [INSPIRE].
R. Aaij et al., The LHCb Trigger and its Performance in 2011, 2013 JINST 8 P04022 [arXiv:1211.3055] [INSPIRE].
T. Sjöstrand, S. Mrenna and P.Z. Skands, A Brief Introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852 [arXiv:0710.3820] [INSPIRE].
LHCb collaboration, Handling of the generation of primary events in Gauss, the LHCb simulation framework, IEEE Nucl. Sci. Symp. Conf. Rec. (NSS/MIC) (2010) 1155 [INSPIRE].
D.J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Meth. A 462 (2001) 152 [INSPIRE].
P. Golonka and Z. Was, PHOTOS Monte Carlo: A Precision tool for QED corrections in Z and W decays, Eur. Phys. J. C 45 (2006) 97 [hep-ph/0506026] [INSPIRE].
GEANT4 collaboration, J. Allison et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270 [INSPIRE].
GEANT4 collaboration, S. Agostinelli et al., GEANT4: A Simulation toolkit, Nucl. Instrum. Meth. A 506 (2003) 250 [INSPIRE].
LHCb collaboration, The LHCb simulation application, Gauss: Design, evolution and experience, J. Phys. Conf. Ser. 331 (2011) 032023 [INSPIRE].
A.J. Buras and M. Münz, Effective Hamiltonian for B → X s e + e − beyond leading logarithms in the NDR and HV schemes, Phys. Rev. D 52 (1995) 186 [hep-ph/9501281] [INSPIRE].
A.J. Buras, M. Misiak, M. Münz and S. Pokorski, Theoretical uncertainties and phenomenological aspects of B → X s γ decay, Nucl. Phys. B 424 (1994) 374 [hep-ph/9311345] [INSPIRE].
LHCb collaboration, Measurements of the Λ 0 b → J/ψΛ decay amplitudes and the Λ 0 b polarisation in pp collisions at \( \sqrt{s}=7 \) TeV, Phys. Lett. B 724 (2013) 27 [arXiv:1302.5578] [INSPIRE].
Particle Data Group collaboration, K.A. Olive et al., Review of particle physics, Chin. Phys. C 38 (2014) 090001 [INSPIRE].
W.D. Hulsbergen, Decay chain fitting with a Kalman filter, Nucl. Instrum. Meth. A 552 (2005) 566 [physics/0503191] [INSPIRE].
M. Feindt and U. Kerzel, The NeuroBayes neural network package, Nucl. Instrum. Meth. A 559 (2006) 190 [INSPIRE].
M. Feindt, A neural Bayesian estimator for conditional probability densities, physics/0402093 [INSPIRE].
G. Punzi, Sensitivity of searches for new signals and its optimization, eConf C 030908 (2003) MODT002 [physics/0308063] [INSPIRE].
T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, Ph.D. Thesis, Institute of Nuclear Physics, Krakow Poland (1986) [INSPIRE] and online pdf version at [DESY-F31-86-02].
T.M. Aliev and M. Savci, Polarization effects in exclusive semileptonic Λb → Λℓ + ℓ − decay, JHEP 05 (2006) 001 [hep-ph/0507324] [INSPIRE].
S. Descotes-Genon, J. Matias and J. Virto, Understanding the B → K * μ + μ − anomaly, Phys. Rev. D 88 (2013) 074002 [arXiv:1307.5683] [INSPIRE].
LHCb collaboration, Differential branching fractions and isospin asymmetries of B → K (*) μ + μ − decays, JHEP 06 (2014) 133 [arXiv:1403.8044] [INSPIRE].
LHCb collaboration, Precision measurement of the ratio of the Λ 0 b to \( {\overline{B}}^0 \) lifetimes, Phys. Lett. B 734 (2014) 122 [arXiv:1402.6242] [INSPIRE].
G.J. Feldman and R.D. Cousins, A Unified approach to the classical statistical analysis of small signals, Phys. Rev. D 57 (1998) 3873 [physics/9711021] [INSPIRE].
B. Sen, M. Walker and M. Woodroofe, On the unified method with nuisance parameters, Statist. Sinica 19 (2009) 301 [INSPIRE].
Open Access
This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.
Author information
Authors and Affiliations
Consortia
Corresponding author
Additional information
ArXiv ePrint: 1503.07138
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.
The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
The LHCb collaboration., Aaij, R., Adeva, B. et al. Differential branching fraction and angular analysis of Λ 0 b → Λμ+μ− decays. J. High Energ. Phys. 2015, 115 (2015). https://doi.org/10.1007/JHEP06(2015)115
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/JHEP06(2015)115