https://doi.org/10.1140/epjc/s10052-013-2655-8
Regular Article - Experimental Physics
Observation of 
–
mixing and measurement of mixing frequencies using semileptonic B decays
1
CERN, 1211, Geneva 23, Switzerland
2
Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
3
Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
4
Center for High Energy Physics, Tsinghua University, Beijing, China
5
LAPP, Université de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France
6
Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France
7
CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
8
LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France
9
LPNHE, Université Pierre et Marie Curie, Université Paris Diderot, CNRS/IN2P3, Paris, France
10
Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
11
Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
12
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
13
School of Physics, University College Dublin, Dublin, Ireland
14
Sezione INFN di Bari, Bari, Italy
15
Sezione INFN di Bologna, Bologna, Italy
16
Sezione INFN di Cagliari, Cagliari, Italy
17
Sezione INFN di Ferrara, Ferrara, Italy
18
Sezione INFN di Firenze, Firenze, Italy
19
Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy
20
Sezione INFN di Genova, Genova, Italy
21
Sezione INFN di Milano Bicocca, Milano, Italy
22
Sezione INFN di Padova, Padova, Italy
23
Sezione INFN di Pisa, Pisa, Italy
24
Sezione INFN di Roma Tor Vergata, Roma, Italy
25
Sezione INFN di Roma La Sapienza, Roma, Italy
26
Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland
27
Faculty of Physics and Applied Computer Science, AGH - University of Science and Technology, Kraków, Poland
28
National Center for Nuclear Research (NCBJ), Warsaw, Poland
29
Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania
30
Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
31
Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
32
Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia
33
Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia
34
Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia
35
Institute for High Energy Physics (IHEP), Protvino, Russia
36
Universitat de Barcelona, Barcelona, Spain
37
Universidad de Santiago de Compostela, Santiago de Compostela, Spain
38
European Organization for Nuclear Research (CERN), Geneva, Switzerland
39
Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
40
Physik-Institut, Universität Zürich, Zürich, Switzerland
41
Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands
42
Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands
43
NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
44
Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine
45
University of Birmingham, Birmingham, United Kingdom
46
H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom
47
Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
48
Department of Physics, University of Warwick, Coventry, United Kingdom
49
STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
50
School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
51
School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom
52
Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
53
Imperial College London, London, United Kingdom
54
School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
55
Department of Physics, University of Oxford, Oxford, United Kingdom
56
Massachusetts Institute of Technology, Cambridge, MA, United States
57
University of Cincinnati, Cincinnati, OH, United States
58
University of Maryland, College Park, MD, United States
59
Syracuse University, Syracuse, NY, United States
60
Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil
61
Institut für Physik, Universität Rostock, Rostock, Germany
62
Celal Bayar University, Manisa, Turkey
* e-mail: Rob.Lambert@cern.ch
Received:
7
August
2013
Revised:
21
October
2013
Published online:
4
December
2013
The and B
0 mixing frequencies, Δm
s
and Δm
d
, are measured using a data sample corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in pp collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8×106 candidate events are selected of the type 
(+ anything), where about half are from peaking and combinatorial backgrounds. To determine the B decay times, a correction is required for the momentum carried by missing particles, which is performed using a simulation-based statistical method. Associated production of muons or mesons allows us to tag the initial-state flavour and so to resolve oscillations due to mixing. We obtain 
The hypothesis of no oscillations is rejected by the equivalent of 5.8 standard deviations for and 13.0 standard deviations for B
0. This is the first observation of mixing to be made using only semileptonic decays.
© Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica, 2013
