- Aaij, R
- Adeva, B
- Adinolfi, M
- Adrover, C
- Affolder, A
- Ajaltouni, Z
- Albrecht, J
- Alessio, F
- Alexander, M
- Ali, S
- Alkhazov, G
- Cartelle, PA
- Alves, AA
- Amato, S
- Amerio, S
- Amhis, Y
- Anderlini, L
- Anderson, J
- Andreassen, R
- Andrews, JE
- Andrianala, F
- Appleby, RB
- Gutierrez, OA
- Archilli, F
- Artamonov, A
- Artuso, M
- Aslanides, E
- Auriemma, G
- Baalouch, M
- Bachmann, S
- Back, JJ
- Baesso, C
- Balagura, V
- Baldini, W
- Barlow, RJ
- Barschel, C
- Barsuk, S
- Barter, W
- Bauer, T
- Bay, A
- Beddow, J
- Bedeschi, F
- Bediaga, I
- Belogurov, S
- Belous, K
- Belyaev, I
- Ben-Haim, E
- Bencivenni, G
- Benson, S
- Benton, J
- Berezhnoy, A
- Bernet, R
- Bettler, MO
- Van Beuzekom, M
- Bien, A
- Bifani, S
- Bird, T
- Bizzeti, A
- Bjørnstad, PM
- Blake, T
- Blanc, F
- Blouw, J
- Blusk, S
- Bocci, V
- Bondar, A
- Bondar, N
- Bonivento, W
- Borghi, S
- Borgia, A
- Bowcock, TJV
- Bowen, E
- Bozzi, C
- Brambach, T
- Van Den Brand, J
- Bressieux, J
- Brett, D
- Britsch, M
- Britton, T
- Brook, NH
- Brown, H
- Burducea, I
- Bursche, A
- Busetto, G
- Buytaert, J
- Cadeddu, S
- Callot, O
- Calvi, M
- Gomez, MC
- Camboni, A
- Campana, P
- Perez, DC
- Carbone, A
- Carboni, G
- Cardinale, R
- Cardini, A
- Carranza-Mejia, H
- Carson, L
- Akiba, KC
- Casse, G
- Garcia, LC
- et al.
The B and B mixing frequencies, Δm and Δm , are measured using a data sample corresponding to an integrated luminosity of 1.0 fb collected by the LHCb experiment in pp collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8 × 10 candidate events are selected of the type B → D μ (+ 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 initialstate flavour and so to resolve oscillations due to mixing. We obtain Δm = (17.93 ± 0.22 (stat) ± 0.15 (syst)) ps , Δm = (0.503 ± 0.011 (stat) ± 0.013(syst)) ps . The hypothesis of no oscillations is rejected by the equivalent of 5.8 standard deviations for B and 13.0 standard deviations for B . This is the first observation of B mixing to be made using only semileptonic decays. 0 0 −1 6 0 − + −1 −1 0 0 0 s s d (s) (s) s d s s