EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-PH-EP-2014-237 LHCb-PAPER-2014-053 January 29, 2015

Measurement of the semileptonic $C\\!P$ asymmetry in $B^{0}$–$\kern
3.73305pt\overline{\kern-3.73305ptB}{}^{0}$ mixing

The LHCb collaboration†††Authors are listed at the end of this Letter.

The semileptonic $C\\!P$ asymmetry in $B^{0}$–$\kern
1.79993pt\overline{\kern-1.79993ptB}{}^{0}$ mixing, $a_{\rm sl}^{d}$, is
measured in proton–proton collision data, corresponding to an integrated
luminosity of 3.0 fb-1, recorded by the LHCb experiment. Semileptonic $B^{0}$
decays are reconstructed in the inclusive final states $D^{-}\mu^{+}$ and
$D^{*-}\mu^{+}$, where the $D^{-}$ meson decays into the $K^{+}\pi^{-}\pi^{-}$
final state, and the $D^{*-}$ meson into the $\kern
1.79993pt\overline{\kern-1.79993ptD}{}^{0}(\rightarrow K^{+}\pi^{-})\pi^{-}$
final state. The asymmetry between the numbers of $D^{(*)-}\mu^{+}$ and
$D^{(*)+}\mu^{-}$ decays is measured as a function of the decay time of the
$B^{0}$ mesons. The $C\\!P$ asymmetry is measured to be $a_{\rm
sl}^{d}=(-0.02\pm 0.19\pm 0.30)\%$, where the first uncertainty is statistical
and the second systematic. This is the most precise measurement of $a_{\rm
sl}^{d}$ to date and is consistent with the prediction from the Standard
Model.

Published in Phys. Rev. Lett.

© CERN on behalf of the LHCb collaboration, license CC-BY-4.0.

The inclusive charge asymmetry measured by the D0 collaboration in events with
same charge dimuons [1] shows one of the largest discrepancies with the
Standard Model and it may be a first hint of physics beyond our current
understanding (e.g., Refs. [2, 3, 4]). This asymmetry is sensitive to $C\\!P$
violation in the mixing of neutral $B$ mesons. The neutral ${B}^{0}$ meson and
its antiparticle ${\kern 1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}$ are
flavour eigenstates, formed from a mixture of two mass eigenstates. The time
evolution of this two-state system results in flavour-changing
${{B}^{0}}\rightarrow{{\kern 1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}}$
and ${{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}}\rightarrow{{B}^{0}}$
transitions. Violation of charge-parity ($C\\!P$) symmetry may occur due to
this process if the probability for a ${B}^{0}$ meson to transform into a
${\kern 1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}$ meson is different from
the reverse process. When a meson produced in the ${B}^{0}$ eigenstate decays
semileptonically to a final state $f$, the charge of the lepton reveals the
meson flavour at the time of decay. In such decays, “wrong-sign” transitions,
like ${{B}^{0}}\rightarrow{\kern 1.79993pt\overline{\kern-1.79993ptf}{}}$, can
only happen due to the transition ${{B}^{0}}\rightarrow{{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}}\rightarrow{\kern
1.79993pt\overline{\kern-1.79993ptf}{}}$. The flavour-specific (semileptonic)
asymmetry is defined in terms of partial decay rates $\Gamma$ as

$\displaystyle a_{\rm sl}^{d}\equiv\frac{\Gamma({{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}}\rightarrow
f)-\Gamma({{B}^{0}}\rightarrow{\kern
1.79993pt\overline{\kern-1.79993ptf}{}})}{\Gamma({{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}}\rightarrow
f)+\Gamma({{B}^{0}}\rightarrow{\kern
1.79993pt\overline{\kern-1.79993ptf}{}})}\approx\frac{{\Delta\Gamma_{{d}}}}{{\Delta
m_{{d}}}}\tan\phi_{d}^{12}\ ,$ (1)

and is expressed in terms of the difference between the masses ($\Delta
m_{{d}}$) and widths ($\Delta\Gamma_{{d}}$) of the mass eigenstates, and the
$C\\!P$-violating phase $\phi_{d}^{12}$ [5]. The Standard Model (SM)
prediction, $a_{\rm sl}^{d}=(-4.1\pm 0.6)\times 10^{-4}$ [6], is small
compared to experimental sensitivities. However, $a_{\rm sl}^{d}$ may be
enhanced by virtual contributions from particles that exist in extensions to
the SM [7].

The current most precise measurements are $a_{\rm sl}^{d}=(0.06\pm
0.17^{+0.38}_{-0.32})\%$ by the BaBar collaboration [8] and $a_{\rm
sl}^{d}=(0.68\pm 0.45\pm 0.14)\%$ by the D0 collaboration [9], where the first
uncertainties are statistical and the second systematic. The D0 dimuon
asymmetry, which is related to a linear combination of the semileptonic
asymmetries in the ${B}^{0}$ and ${B}^{0}_{s}$ systems, disagrees with the
theoretical predictions by 3.6 standard deviations. The LHCb collaboration has
previously measured the semileptonic $C\\!P$ asymmetry in the ${B}^{0}_{s}$
system, $a_{\rm sl}^{s}$ [10], consistent with the SM. Improved experimental
constraints are also required on $a_{\rm sl}^{d}$ to confirm or falsify the D0
anomaly.

In this analysis, $a_{\rm sl}^{d}$ is measured using semileptonic
${{B}^{0}}\\!\rightarrow{{D}^{-}}{\mu^{+}}{{\nu}_{\mu}}X$ and
${{B}^{0}}\\!\rightarrow{{D}^{*-}}{\mu^{+}}{{\nu}_{\mu}}X$ decays, where $X$
denotes any additional particles due to possible feed-down from $\tau^{+}$
decays into ${\mu^{+}}X$ and higher-resonance $D$ decays into ${D}^{(*)-}X$.
The inclusion of charge-conjugate processes is implied. The signal is
reconstructed from ${D}^{(*)-}$ $\mu^{+}$ pairs, with the charm mesons
reconstructed from ${{D}^{-}}\\!\rightarrow{{K}^{+}}{{\pi}^{-}}{{\pi}^{-}}$
and ${{D}^{*-}}\rightarrow{{\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}}(\rightarrow{{K}^{+}}{{\pi}^{-}}){{\pi}^{-}}$
decays. A measurement of $a_{\rm sl}^{d}$ using the quantities in Eq. (1)
requires determining (tagging) the flavour of the ${B}^{0}$ meson at
production. Since this is inefficient in hadron collisions, $a_{\rm sl}^{d}$
is instead determined from the untagged decay rates. The number of observed
final states as a function of the ${B}^{0}$ decay time is expressed as

$\displaystyle N(t)\propto e^{-{\Gamma_{{d}}}t}\biggl{[}$ $\displaystyle
1+\zeta A_{\rm D}+\zeta\frac{a_{\rm sl}^{d}}{2}-\zeta\left(A_{\rm
P}+\frac{a_{\rm sl}^{d}}{2}\right)\cos{\Delta m_{{d}}}\,t\biggr{]}\ ,$ (2)

where $\Gamma_{{d}}$ is the ${B}^{0}$ decay width, and $\zeta=+1(-1)$ for the
$f$ (${\kern 1.79993pt\overline{\kern-1.79993ptf}{}}$) final state. The
asymmetry due to differences in detection efficiencies, $\varepsilon$, between
$f$ and $\kern 1.79993pt\overline{\kern-1.79993ptf}{}$ final states, $A_{\rm
D}\equiv[\varepsilon(f)-\varepsilon({\kern
1.79993pt\overline{\kern-1.79993ptf}{}})]/[\varepsilon(f)+\varepsilon({\kern
1.79993pt\overline{\kern-1.79993ptf}{}})]$, is determined using control
samples of data, as described later. The asymmetry in the ${\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}$ and ${B}^{0}$ effective
production cross sections, $A_{\rm P}\equiv[\sigma({{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}})-\sigma({{B}^{0}})]/[\sigma({{\kern
1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}})+\sigma({{B}^{0}})]$, and
$a_{\rm sl}^{d}$ are determined simultaneously in a fit to the time-dependent
rate of Eq. (2). Effects from higher-order asymmetry terms and a non-zero
$\Delta\Gamma_{{d}}$, taken from experimental bounds [11], result in biases of
less than $10^{-4}$ on $a_{\rm sl}^{d}$ and are ignored. The amount of direct
$C\\!P$ violation in the Cabibbo-favoured decays
${{D}^{-}}\\!\rightarrow{{K}^{+}}{{\pi}^{-}}{{\pi}^{-}}$ and ${{\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}}\\!\rightarrow{{K}^{+}}{{\pi}^{-}}$
is assumed to be negligible. The observed decay time of the semileptonic
signal candidates is corrected using simulation since the final state is only
partially reconstructed.

The LHCb detector [12] includes a high-precision tracking system with a dipole
magnet, providing a measurement of momentum ($p$) and impact parameter (IP)
for charged particles. The IP, defined as the minimum distance of a track to a
proton–proton ($pp$) interaction vertex, is measured with a precision of about
$20{\,\upmu\rm m}$ for high-momentum tracks. The polarity of the magnetic
field is regularly reversed during data taking. Particle identification (PID)
is provided by ring-imaging Cherenkov detectors, a calorimeter and a muon
system. The trigger [13] consists of a hardware stage, based on information
from the calorimeter and muon systems, followed by a software stage, which
applies a full event reconstruction.

In the simulation, $pp$ collisions are generated [14, *Sjostrand:2007gs,
*LHCb-PROC-2010-056, *Lange:2001uf, *Golonka:2005pn], and the interactions of
the outgoing particles with the detector are modelled [19,
*Agostinelli:2002hh, *LHCb-PROC-2011-006]. The $B$ mesons are required to
decay semileptonically to a muon, a neutrino and a ${D}^{(*)-}$ meson. Feed-
down from higher $D$ resonances and $\tau$ decays is based on branching
fractions, either measured [11] or estimated assuming isospin symmetry.

The data used in this analysis correspond to a luminosity of
3.0$\mbox{\,fb}^{-1}$, of which 1.0 (2.0)$\mbox{\,fb}^{-1}$ was taken in 2011
(2012) at a $pp$ centre-of-mass energy of 7
(8)$\mathrm{\,Te\kern-1.00006ptV}$. The selection of candidates relies on the
signatures of high-momentum tracks and displaced vertices from the ${B}^{0}$,
${D}^{-}$ and ${\kern 1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$ decays.
Candidate events are first required to pass the hardware trigger, which
selects muons with momentum transverse to the beam direction ($p_{\rm T}$)
larger than $1.64~{}(1.76){\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ for the 2011
(2012) data. In a first stage of the software trigger, the muon is required to
have a large IP. In a second stage, the muon and at least one of the
${D}^{(*)-}$ decay products are required to be consistent with the topological
signature of $b$-hadron decays [13].

To suppress background, it is required that the tracks from the ${B}^{0}$
candidates do not point back to any $pp$ interaction vertex. The muon, kaon
and pion candidates are required to be well identified by the PID system.
Tracks from the ${D}^{-}$, ${\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$ and ${B}^{0}$ candidates are
required to form well-defined vertices. For the ${D}^{*-}$ $\mu^{+}$ final
state, the difference between the ${D}^{*-}$ and ${\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$ masses should be between 144
and $147{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. The mass of the
${D}^{(*)-}$ $\mu^{+}$ final state is required to be between $3.0$ and
$5.2{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ to allow for missing particles
in the final state; the upper limit removes background from four-body
$b$-hadron decays. Misreconstructed $D$ candidates made from random
combinations of tracks are suppressed by requiring that the ${D}^{-}$ or
${\kern 1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$ decay time is larger
than $0.1{\rm\,ps}$. The contribution from charm decays directly produced in
the $pp$ interaction (prompt $D$) is reduced to below $0.1\%$ by requiring
${D}^{-}$ and ${\kern 1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$
candidates to have an IP larger than $50{\,\upmu\rm m}$.

Detection asymmetries caused by left-right asymmetries in the reconstruction
efficiency change sign when the polarity of the LHCb magnet is inverted. Other
asymmetries, such as those induced by differing nuclear cross sections for
${K}^{+}$ and ${K}^{-}$ mesons, do not depend on the magnet polarity. The
detection asymmetry of the ${{K}^{+}}{{\pi}^{-}}{{\pi}^{-}}{\mu^{+}}$ final
state is factorized into a ${{\pi}^{-}}{\mu^{+}}$ component, where the pion is
the hard one (i.e., from the ${\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}$ decay or the higher-$p_{\rm T}$
pion in the ${D}^{-}$ decay), and a ${{K}^{+}}{{\pi}^{-}}$ component, where
the pion is the soft one.

For the ${{\pi}^{-}}{\mu^{+}}$ component, any asymmetry arising from the
different tracking efficiencies is suppressed by weighting the signal
candidates such that the muon and hard pion have the same $p_{\rm T}$ and
pseudorapidity ($\eta$) distributions. This reduces the effective sample size
by about 40%, but makes the pion and muon appear almost symmetric to the
tracking system. The asymmetry from the pion PID requirements is measured
using a sample of unbiased ${{D}^{*-}}\rightarrow{{\kern
1.99997pt\overline{\kern-1.99997ptD}{}}{}^{0}}(\rightarrow{{K}^{+}}{{\pi}^{-}}){{\pi}^{-}}$
decays, weighted to match the $p_{\rm T}$ and $\eta$ distributions of the hard
pions in the signal decays. The asymmetry from the muon PID and trigger
requirements is measured using a low-background sample of
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\rightarrow{\mu^{+}}{\mu^{-}}$
decays with both muons reconstructed in the tracking system and with at least
one muon without trigger and muon identification requirements. The
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ candidates are weighted such
that the muons have the same $p_{\rm T}$ and $\eta$ distributions as those in
the signal decays.

For the ${{K}^{+}}{{\pi}^{-}}$ component, the detection asymmetry is
determined using prompt ${D}^{-}$ decays into
${{K}^{+}}{{\pi}^{-}}{{\pi}^{-}}$ and
${{K}^{0}}(\rightarrow{{\pi}^{+}}{{\pi}^{-}}){{\pi}^{-}}$ final states [22].
This method assumes no direct $C\\!P$ violation in these two decay modes. The
candidates in the calibration samples have the same PID requirements as those
in the signal samples. The calibration samples are weighted such that the
kinematic distributions of the particles agree with those of the kaon and soft
pion in the signal samples. A small correction is applied to account for the
${K}^{0}$ detection and $C\\!P$ asymmetry [22]. The average
${{K}^{+}}{{\pi}^{-}}$ detection asymmetry is dominated by the difference in
the nuclear interaction cross sections of ${K}^{+}$ and ${K}^{-}$ mesons of
approximately $1\%$.

The values of $a_{\rm sl}^{d}$ and $A_{\rm P}$ are determined from a two-
dimensional maximum likelihood fit to the binned distributions of ${B}^{0}$
decay time and charm meson mass, simultaneously for both $f$ and $\kern
1.79993pt\overline{\kern-1.79993ptf}{}$ final states. The fit model consists
of components for signal, background from ${B}^{+}$ decays to the same final
state, and combinatorial background in the $D$ mass distributions. The
${B}^{+}$ background comes from semileptonic ${B}^{+}$ decays into
${D}^{(*)-}$ $\mu^{+}$ ${\nu}_{\mu}$ and at least one other charged particle.
As this background is difficult to distinguish from ${B}^{0}$ signal decays,
fractions of this fit component are obtained from simulation and fixed in the
fit to $(12.7\pm 2.2)\%$ for the ${D}^{-}$ $\mu^{+}$ sample and $(8.8\pm
2.2)\%$ for the ${D}^{*-}$ $\mu^{+}$ sample. The uncertainties are dominated
by the knowledge of the branching fractions.

The mass distributions for ${D}^{-}$ and ${D}^{0}$ candidates are shown in
Fig. 1. To describe the mass distributions, the signal and ${B}^{+}$
background are modelled by a sum of two Gaussian functions with a power-law
tail, and the combinatorial background by an exponential function.

Figure 1: Mass distributions after weighting of (top) ${D}^{-}$ candidates in
the ${D}^{-}$ $\mu^{+}$ sample and of (bottom) ${D}^{*-}$ candidates in the
${D}^{*-}$ $\mu^{+}$ sample, with fit results overlaid.

To describe the time distributions, the signal is modelled by the decay rates
of Eq. (2). The ${B}^{0}$ decay time is estimated from the ${B}^{0}$ flight
distance $L$, the ${D}^{(*)-}$ $\mu^{+}$ momentum $p$ and the known ${B}^{0}$
mass $m_{B}$ [11] as $t=\left\langle k\right\rangle m_{B}L/p$, where
$\left\langle k\right\rangle$ represents a statistical correction accounting
for the momentum of the missing particles in the final state. The value of
$\left\langle k\right\rangle$ is determined from simulation as the average
ratio between the reconstructed and true momenta of the ${B}^{0}$ meson,
$k\equiv p_{\rm rec}/p_{\rm true}$. The value of $\left\langle k\right\rangle$
depends on the ${D}^{(*)-}$ $\mu^{+}$ mass and is empirically parameterised by
a second-order polynomial. This parameterisation is used to correct the
${B}^{0}$ decay time. After this mass correction, the
$k/\kern-2.5pt\left\langle k\right\rangle$ distribution has an RMS of 0.14.
The decay time distribution in the fit is described as a convolution of the
decay rates with the $k/\kern-2.5pt\left\langle k\right\rangle$ distribution.

The efficiency as a function of the estimated decay time varies due to the IP
requirements and track reconstruction effects. This is accounted for by
multiplying the convoluted decay rates with an empirical acceptance function
of the form $(1-e^{-(t-t_{0})/\alpha})(1-\beta t)$, where $t_{0}$ and $\alpha$
describe the effect of the IP requirements, and $\beta$ describes the track
reconstruction effect. Since $\beta$ is fully correlated with the ${B}^{0}$
lifetime, the latter is fixed to the known value [11], while $\beta$ is
allowed to vary in the fit.

The decay-time model for the ${B}^{+}$ background is similar to that of the
signal, except that ${B}^{+}$ mesons do not mix. As the momentum spectra of
the ${B}^{0}$ and ${B}^{+}$ decay products are nearly identical, the detection
asymmetry is the same as that of the signal. The ${B}^{+}$ production
asymmetry is taken as $(-0.6\pm 0.6)\%$ from the observed asymmetry in
${{B}^{+}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{K}^{+}}$
decays [23] after correcting for the kaon detection and measured $C\\!P$
asymmetries [11].

The combinatorial background in the $D$ meson mass is dominated by other
decays of charm hadrons produced in $b$-hadron decays. Hence, the decay-time
model is the same as for the signal, but setting $a_{\rm sl}^{d}$ to zero. The
corresponding values for $A_{\rm P}$ and $A_{\rm D}$ are allowed to vary in
the fit.

In summary, the parameters related to the ${B}^{+}$ background, the detection
asymmetry, $\Delta m_{{d}}$, $\Gamma_{{d}}$, $t_{0}$, and the power-law tail
in the mass distributions are fixed in the fit; all other parameters are
allowed to vary. The fit is done in the decay-time interval $[1,15]{\rm\,ps}$.
The effective ${B}^{0}$ signal yield after weighting is 1.8 million in the
${D}^{-}$ $\mu^{+}$ sample and 0.33 million in the ${D}^{*-}$ $\mu^{+}$
sample.

Separate fits are done for the two magnet polarities, the 2011 and 2012 data-
taking periods, and for the ${D}^{-}$ $\mu^{+}$ and ${D}^{*-}$ $\mu^{+}$
samples. To reduce the bias from any possible, unaccounted detection
asymmetry, the arithmetic average of the measured values for the two magnet
polarities is taken. The resulting $a_{\rm sl}^{d}$ values for the 2011 and
2012 run periods are combined with a weighted average. This gives $a_{\rm
sl}^{d}=(-0.19\pm 0.21)\%$ for the ${D}^{-}$ $\mu^{+}$ sample and $a_{\rm
sl}^{d}=(0.77\pm 0.45)\%$ for the ${D}^{*-}$ $\mu^{+}$ sample, where the
uncertainties are only statistical. The production asymmetries are not
averaged between the run periods as they may depend on the $pp$ centre-of-mass
energy. The decay rates and charge asymmetries as functions of the corrected
decay time are shown in Fig. 2. The weighted averages from the ${D}^{-}$
$\mu^{+}$ and ${D}^{*-}$ $\mu^{+}$ samples are used to determine the final
results. The separate fits give compatible results for $a_{\rm sl}^{d}$ and
$A_{\rm P}$. The largest difference is seen in the 2011 data for opposite
magnet polarities, where $a_{\rm sl}^{d}$ differs by about two standard
deviations. This is present in both decay modes and may arise from a
statistical fluctuation of the detection asymmetry, which is highly correlated
between the two decay samples. This difference is not seen in the larger 2012
data set.

Figure 2: Decay rate and charge asymmetry after weighting versus decay time
for (top) the ${D}^{-}$ $\mu^{+}$ sample and (bottom) the ${D}^{*-}$ $\mu^{+}$
sample. The data from the two run periods and magnet polarities are combined
and the fit results are overlaid. The number of bins in the asymmetry plots is
reduced for clarity. The visible asymmetry in these plots can be fully
attributed to the non-zero detection and production asymmetries (not to
$a_{\rm sl}^{d}$), as explained in the text.

The systematic uncertainties are listed in Table 1. The largest contribution
comes from the detection asymmetry, where the dominant uncertainty is due to
the limited size of the calibration samples. Additional uncertainties are
assigned to account for background in the calibration samples, and the
corresponding weighting procedures. The systematic effect from any residual
tracking asymmetry is estimated using ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\rightarrow{\mu^{+}}{\mu^{-}}$ decays [24]. The uncertainty from a
possible pion nuclear-interaction charge asymmetry is estimated to be
$0.035\%$, using a parameterisation [11] of the measured cross sections of
pions on deuterium [25, *Carroll74, *Carroll76, *Carroll79], and the LHCb
detector simulation.

The second largest contribution to the systematic uncertainty comes from the
knowledge of the ${B}^{+}$ background, and is dominated by the ${B}^{+}$
production asymmetry. Uncertainties arising from the ${B}^{+}$ fraction,
decay-time model, and acceptance are also taken into account. Other $b$-hadron
backgrounds are expected from semileptonic ${\mathchar 28931\relax}^{0}_{b}$
and ${B}^{0}_{s}$ decays and from hadronic $B$ decays. The fraction of
background from ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{D}^{(*)+}{\mu^{-}}{{\overline{\nu}}_{\mu}}X_{n}$
decays, where $X_{n}$ represents any neutral baryonic state, is estimated to
be roughly 2% using the ratio of ${\mathchar 28931\relax}^{0}_{b}$ to
${B}^{0}$ production cross sections [29], simulated efficiencies, and the
branching ratio of ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{D}^{0}}p{{\pi}^{-}}$ relative to that of
${{\mathchar 28931\relax}^{0}_{b}}\rightarrow{{\mathchar
28931\relax}^{+}_{c}}{{\pi}^{-}}$ decays [30]. The ${\mathchar
28931\relax}^{0}_{b}$ production asymmetry is estimated to be $(-0.9\pm
1.5)\%$, determined from the raw asymmetry observed in ${{\mathchar
28931\relax}^{0}_{b}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}p{{K}^{-}}$ [31] and subtracting kaon and proton detection asymmetries.
The uncertainty on the ${\mathchar 28931\relax}^{0}_{b}$ production asymmetry
results in a systematic uncertainty on $a_{\rm sl}^{d}$ of $0.07\%$. The
systematic effect from an estimated $2\%$ contribution from ${B}^{0}_{s}$
decays is small, since the production asymmetry vanishes due to the fast
${B}^{0}_{s}$ oscillations. Hadronic decays ${B}\rightarrow{D}^{(*)-}DX$,
where the $D$ meson decays semileptonically to produce a muon, have a
different $k$-factor distribution compared to the signal. Simulation shows
that these decays correspond to approximately $1\%$ of the data and their
effect is negligible. The systematic effect from the combinatorial background
in the $D$ mass distributions is assessed by varying the mass model in the
fit.

The uncertainty on the shape of the $k$-factor distributions comes from
uncertainties in the semileptonic branching fractions of ${B}^{0}$ mesons to
higher-mass $D$ resonances. Such decays are considered as signal, but have
slightly different $k$-factor distributions. In the ${D}^{-}$ $\mu^{+}$ sample
about half of the ${D}^{-}$ candidates originate from higher-mass $D$
resonances. The uncertainties on these fractions are about 2%. The systematic
effect on $a_{\rm sl}^{d}$ and $A_{\rm P}$ is determined by varying the
fractions by 10% to account for possible unknown intermediate states. The
effect of a dependence of the $k$-factor with ${B}^{0}$ decay time is small,
and the effect on the difference in the $B$ momentum distributions between
data and simulation, evaluated using
${{B}^{+}}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}{{K}^{+}}$
decays, is negligible.

Systematic effects due to imperfect modelling of the decay time are tested by
varying the acceptance function and extending the fit region down to
$0.4{\rm\,ps}$. The effect from varying $\Delta m_{{d}}$ within its
uncertainty [11] is taken into account. Effects associated with variations in
${B}^{0}$ decay-time binning are negligible.

Table 1: Systematic uncertainties (in %) on $a_{\rm sl}^{d}$ and $A_{\rm P}$ for 7 and 8$\mathrm{\,Te\kern-1.00006ptV}$ $pp$ centre-of-mass energies. Entries marked with – are found to be negligible. Source of uncertainty |  $a_{\rm sl}^{d}$ | $A_{\rm P}(7\mathrm{\,Te\kern-1.00006ptV})$ | $A_{\rm P}(8\mathrm{\,Te\kern-1.00006ptV})$
---|---|---|---
Detection asymmetry | 0.26 | 0.20 | 0.14
${B}^{+}$ background | 0.13 | 0.06 | 0.06
${\mathchar 28931\relax}^{0}_{b}$ background | 0.07 | 0.03 | 0.03
${B}^{0}_{s}$ background | 0.03 | 0.01 | 0.01
Combinatorial $D$ background | 0.03 | – | –
$k$-factor distribution | 0.03 | 0.01 | 0.01
Decay-time acceptance | 0.03 | 0.07 | 0.07
Knowledge of $\Delta m_{{d}}$ | 0.02 | 0.01 | 0.01
Quadratic sum | 0.30 | 0.22 | 0.17

The ${\kern 1.79993pt\overline{\kern-1.79993ptB}{}}{}^{0}$–${B}^{0}$
production asymmetries for the two centre-of-mass energies are $A_{\rm
P}(7\mathrm{\,Te\kern-1.00006ptV})=(-0.66\pm 0.26\pm 0.22)\%$ and $A_{\rm
P}(8\mathrm{\,Te\kern-1.00006ptV})=(-0.48\pm 0.15\pm 0.17)\%$, where the first
uncertainty is statistical and the second systematic. These asymmetries refer
to ${B}^{0}$ mesons in the ranges $2<\mbox{$p_{\rm
T}$}<30{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and $2.0<\eta<4.8$, without
correcting for $p_{\rm T}$\- and $\eta$-dependent reconstruction efficiencies.
The production asymmetry at 7$\mathrm{\,Te\kern-1.00006ptV}$ is compatible
with previous results [32] and with the production asymmetry at
8$\mathrm{\,Te\kern-1.00006ptV}$. The determination of the $C\\!P$ asymmetry
in semileptonic ${B}^{0}$ decays is

$\displaystyle a_{\rm sl}^{d}$ $\displaystyle=(-0.02\pm 0.19\pm 0.30)\%\ ,$

which is the most precise measurement to date and compatible with the SM
prediction and earlier measurements [33].

## Acknowledgements

We express our gratitude to our colleagues in the CERN accelerator departments
for the excellent performance of the LHC. We thank the technical and
administrative staff at the LHCb institutes. We acknowledge support from CERN
and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); NSFC
(China); CNRS/IN2P3 (France); BMBF, DFG, HGF and MPG (Germany); SFI (Ireland);
INFN (Italy); FOM and NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA
(Romania); MinES and FANO (Russia); MinECo (Spain); SNSF and SER
(Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (USA). The Tier1
computing centres are supported by IN2P3 (France), KIT and BMBF (Germany),
INFN (Italy), NWO and SURF (The Netherlands), PIC (Spain), GridPP (United
Kingdom). We are indebted to the communities behind the multiple open source
software packages on which we depend. We are also thankful for the computing
resources and the access to software R&D tools provided by Yandex LLC
(Russia). Individual groups or members have received support from EPLANET,
Marie Skłodowska-Curie Actions and ERC (European Union), Conseil général de
Haute-Savoie, Labex ENIGMASS and OCEVU, Région Auvergne (France), RFBR
(Russia), XuntaGal and GENCAT (Spain), Royal Society and Royal Commission for
the Exhibition of 1851 (United Kingdom).

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LHCb collaboration

R. Aaij41, B. Adeva37, M. Adinolfi46, A. Affolder52, Z. Ajaltouni5, S. Akar6,
J. Albrecht9, F. Alessio38, M. Alexander51, S. Ali41, G. Alkhazov30, P.
Alvarez Cartelle37, A.A. Alves Jr25,38, S. Amato2, S. Amerio22, Y. Amhis7, L.
An3, L. Anderlini17,g, J. Anderson40, R. Andreassen57, M. Andreotti16,f, J.E.
Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F. Archilli38, A.
Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, M. Baalouch5, S.
Bachmann11, J.J. Back48, A. Badalov36, C. Baesso60, W. Baldini16, R.J.
Barlow54, C. Barschel38, S. Barsuk7, W. Barter47, V. Batozskaya28, V.
Battista39, A. Bay39, L. Beaucourt4, J. Beddow51, F. Bedeschi23, I. Bediaga1,
S. Belogurov31, K. Belous35, I. Belyaev31, E. Ben-Haim8, G. Bencivenni18, S.
Benson38, J. Benton46, A. Berezhnoy32, R. Bernet40, M.-O. Bettler47, M. van
Beuzekom41, A. Bien11, S. Bifani45, T. Bird54, A. Bizzeti17,i, P.M.
Bjørnstad54, T. Blake48, F. Blanc39, J. Blouw10, S. Blusk59, V. Bocci25, A.
Bondar34, N. Bondar30,38, W. Bonivento15,38, S. Borghi54, A. Borgia59, M.
Borsato7, T.J.V. Bowcock52, E. Bowen40, C. Bozzi16, T. Brambach9, D. Brett54,
M. Britsch10, T. Britton59, J. Brodzicka54, N.H. Brook46, H. Brown52, A.
Bursche40, J. Buytaert38, S. Cadeddu15, R. Calabrese16,f, M. Calvi20,k, M.
Calvo Gomez36,p, P. Campana18, D. Campora Perez38, A. Carbone14,d, G.
Carboni24,l, R. Cardinale19,38,j, A. Cardini15, L. Carson50, K. Carvalho
Akiba2, G. Casse52, L. Cassina20, L. Castillo Garcia38, M. Cattaneo38, Ch.
Cauet9, R. Cenci23, M. Charles8, Ph. Charpentier38, M. Chefdeville4, S.
Chen54, S.-F. Cheung55, N. Chiapolini40, M. Chrzaszcz40,26, X. Cid Vidal38, G.
Ciezarek41, P.E.L. Clarke50, M. Clemencic38, H.V. Cliff47, J. Closier38, V.
Coco38, J. Cogan6, E. Cogneras5, V. Cogoni15, L. Cojocariu29, G. Collazuol22,
P. Collins38, A. Comerma-Montells11, A. Contu15,38, A. Cook46, M. Coombes46,
S. Coquereau8, G. Corti38, M. Corvo16,f, I. Counts56, B. Couturier38, G.A.
Cowan50, D.C. Craik48, M. Cruz Torres60, S. Cunliffe53, R. Currie53, C.
D’Ambrosio38, J. Dalseno46, P. David8, P.N.Y. David41, A. Davis57, K. De
Bruyn41, S. De Capua54, M. De Cian11, J.M. De Miranda1, L. De Paula2, W. De
Silva57, P. De Simone18, C.-T. Dean51, D. Decamp4, M. Deckenhoff9, L. Del
Buono8, N. Déléage4, D. Derkach55, O. Deschamps5, F. Dettori38, A. Di Canto38,
H. Dijkstra38, S. Donleavy52, F. Dordei11, M. Dorigo39, A. Dosil Suárez37, D.
Dossett48, A. Dovbnya43, K. Dreimanis52, G. Dujany54, F. Dupertuis39, P.
Durante38, R. Dzhelyadin35, A. Dziurda26, A. Dzyuba30, S. Easo49,38, U.
Egede53, V. Egorychev31, S. Eidelman34, S. Eisenhardt50, U. Eitschberger9, R.
Ekelhof9, L. Eklund51, I. El Rifai5, Ch. Elsasser40, S. Ely59, S. Esen11,
H.-M. Evans47, T. Evans55, A. Falabella14, C. Färber11, C. Farinelli41, N.
Farley45, S. Farry52, RF Fay52, D. Ferguson50, V. Fernandez Albor37, F.
Ferreira Rodrigues1, M. Ferro-Luzzi38, S. Filippov33, M. Fiore16,f, M.
Fiorini16,f, M. Firlej27, C. Fitzpatrick39, T. Fiutowski27, P. Fol53, M.
Fontana10, F. Fontanelli19,j, R. Forty38, O. Francisco2, M. Frank38, C.
Frei38, M. Frosini17,g, J. Fu21,38, E. Furfaro24,l, A. Gallas Torreira37, D.
Galli14,d, S. Gallorini22,38, S. Gambetta19,j, M. Gandelman2, P. Gandini59, Y.
Gao3, J. García Pardiñas37, J. Garofoli59, J. Garra Tico47, L. Garrido36, D.
Gascon36, C. Gaspar38, R. Gauld55, L. Gavardi9, A. Geraci21,v, E. Gersabeck11,
M. Gersabeck54, T. Gershon48, Ph. Ghez4, A. Gianelle22, S. Gianì39, V.
Gibson47, L. Giubega29, V.V. Gligorov38, C. Göbel60, D. Golubkov31, A.
Golutvin53,31,38, A. Gomes1,a, C. Gotti20, M. Grabalosa Gándara5, R. Graciani
Diaz36, L.A. Granado Cardoso38, E. Graugés36, E. Graverini40, G. Graziani17,
A. Grecu29, E. Greening55, S. Gregson47, P. Griffith45, L. Grillo11, O.
Grünberg63, B. Gui59, E. Gushchin33, Yu. Guz35,38, T. Gys38, C.
Hadjivasiliou59, G. Haefeli39, C. Haen38, S.C. Haines47, S. Hall53, B.
Hamilton58, T. Hampson46, X. Han11, S. Hansmann-Menzemer11, N. Harnew55, S.T.
Harnew46, J. Harrison54, J. He38, T. Head38, V. Heijne41, K. Hennessy52, P.
Henrard5, L. Henry8, J.A. Hernando Morata37, E. van Herwijnen38, M. Heß63, A.
Hicheur2, D. Hill55, M. Hoballah5, C. Hombach54, W. Hulsbergen41, P. Hunt55,
N. Hussain55, D. Hutchcroft52, D. Hynds51, M. Idzik27, P. Ilten56, R.
Jacobsson38, A. Jaeger11, J. Jalocha55, E. Jans41, P. Jaton39, A. Jawahery58,
F. Jing3, M. John55, D. Johnson38, C.R. Jones47, C. Joram38, B. Jost38, N.
Jurik59, S. Kandybei43, W. Kanso6, M. Karacson38, T.M. Karbach38, S.
Karodia51, M. Kelsey59, I.R. Kenyon45, T. Ketel42, B. Khanji20,38, C.
Khurewathanakul39, S. Klaver54, K. Klimaszewski28, O. Kochebina7, M. Kolpin11,
I. Komarov39, R.F. Koopman42, P. Koppenburg41,38, M. Korolev32, A.
Kozlinskiy41, L. Kravchuk33, K. Kreplin11, M. Kreps48, G. Krocker11, P.
Krokovny34, F. Kruse9, W. Kucewicz26,o, M. Kucharczyk20,26,k, V.
Kudryavtsev34, K. Kurek28, T. Kvaratskheliya31, V.N. La Thi39, D. Lacarrere38,
G. Lafferty54, A. Lai15, D. Lambert50, R.W. Lambert42, G. Lanfranchi18, C.
Langenbruch48, B. Langhans38, T. Latham48, C. Lazzeroni45, R. Le Gac6, J. van
Leerdam41, J.-P. Lees4, R. Lefèvre5, A. Leflat32, J. Lefrançois7, S. Leo23, O.
Leroy6, T. Lesiak26, B. Leverington11, Y. Li3, T. Likhomanenko64, M. Liles52,
R. Lindner38, C. Linn38, F. Lionetto40, B. Liu15, S. Lohn38, I. Longstaff51,
J.H. Lopes2, N. Lopez-March39, P. Lowdon40, D. Lucchesi22,r, H. Luo50, A.
Lupato22, E. Luppi16,f, O. Lupton55, F. Machefert7, I.V. Machikhiliyan31, F.
Maciuc29, O. Maev30, S. Malde55, A. Malinin64, G. Manca15,e, G. Mancinelli6,
A. Mapelli38, J. Maratas5, J.F. Marchand4, U. Marconi14, C. Marin Benito36, P.
Marino23,t, R. Märki39, J. Marks11, G. Martellotti25, A. Martín Sánchez7, M.
Martinelli39, D. Martinez Santos42,38, F. Martinez Vidal65, D. Martins
Tostes2, A. Massafferri1, R. Matev38, Z. Mathe38, C. Matteuzzi20, B. Maurin39,
A. Mazurov45, M. McCann53, J. McCarthy45, A. McNab54, R. McNulty12, B.
McSkelly52, B. Meadows57, F. Meier9, M. Meissner11, M. Merk41, D.A. Milanes62,
M.-N. Minard4, N. Moggi14, J. Molina Rodriguez60, S. Monteil5, M. Morandin22,
P. Morawski27, A. Mordà6, M.J. Morello23,t, J. Moron27, A.-B. Morris50, R.
Mountain59, F. Muheim50, K. Müller40, M. Mussini14, B. Muster39, P. Naik46, T.
Nakada39, R. Nandakumar49, I. Nasteva2, M. Needham50, N. Neri21, S. Neubert38,
N. Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C. Nguyen-Mau39,q, M.
Nicol7, V. Niess5, R. Niet9, N. Nikitin32, T. Nikodem11, A. Novoselov35, D.P.
O’Hanlon48, A. Oblakowska-Mucha27,38, V. Obraztsov35, S. Oggero41, S.
Ogilvy51, O. Okhrimenko44, R. Oldeman15,e, C.J.G. Onderwater66, M. Orlandea29,
J.M. Otalora Goicochea2, A. Otto38, P. Owen53, A. Oyanguren65, B.K. Pal59, A.
Palano13,c, F. Palombo21,u, M. Palutan18, J. Panman38, A. Papanestis49,38, M.
Pappagallo51, L.L. Pappalardo16,f, C. Parkes54, C.J. Parkinson9,45, G.
Passaleva17, G.D. Patel52, M. Patel53, C. Patrignani19,j, A. Pearce54, A.
Pellegrino41, M. Pepe Altarelli38, S. Perazzini14,d, P. Perret5, M. Perrin-
Terrin6, L. Pescatore45, E. Pesen67, K. Petridis53, A. Petrolini19,j, E.
Picatoste Olloqui36, B. Pietrzyk4, T. Pilař48, D. Pinci25, A. Pistone19, S.
Playfer50, M. Plo Casasus37, F. Polci8, A. Poluektov48,34, E. Polycarpo2, A.
Popov35, D. Popov10, B. Popovici29, C. Potterat2, E. Price46, J.D. Price52, J.
Prisciandaro39, A. Pritchard52, C. Prouve46, V. Pugatch44, A. Puig Navarro39,
G. Punzi23,s, W. Qian4, B. Rachwal26, J.H. Rademacker46, B.
Rakotomiaramanana39, M. Rama18, M.S. Rangel2, I. Raniuk43, N. Rauschmayr38, G.
Raven42, F. Redi53, S. Reichert54, M.M. Reid48, A.C. dos Reis1, S.
Ricciardi49, S. Richards46, M. Rihl38, K. Rinnert52, V. Rives Molina36, P.
Robbe7, A.B. Rodrigues1, E. Rodrigues54, P. Rodriguez Perez54, S. Roiser38, V.
Romanovsky35, A. Romero Vidal37, M. Rotondo22, J. Rouvinet39, T. Ruf38, H.
Ruiz36, P. Ruiz Valls65, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B.
Saitta15,e, V. Salustino Guimaraes2, C. Sanchez Mayordomo65, B. Sanmartin
Sedes37, R. Santacesaria25, C. Santamarina Rios37, E. Santovetti24,l, A.
Sarti18,m, C. Satriano25,n, A. Satta24, D.M. Saunders46, D. Savrina31,32, M.
Schiller42, H. Schindler38, M. Schlupp9, M. Schmelling10, B. Schmidt38, O.
Schneider39, A. Schopper38, M. Schubiger39, M.-H. Schune7, R. Schwemmer38, B.
Sciascia18, A. Sciubba25, A. Semennikov31, I. Sepp53, N. Serra40, J. Serrano6,
L. Sestini22, P. Seyfert11, M. Shapkin35, I. Shapoval16,43,f, Y. Shcheglov30,
T. Shears52, L. Shekhtman34, V. Shevchenko64, A. Shires9, R. Silva Coutinho48,
G. Simi22, M. Sirendi47, N. Skidmore46, I. Skillicorn51, T. Skwarnicki59, N.A.
Smith52, E. Smith55,49, E. Smith53, J. Smith47, M. Smith54, H. Snoek41, M.D.
Sokoloff57, F.J.P. Soler51, F. Soomro39, D. Souza46, B. Souza De Paula2, B.
Spaan9, P. Spradlin51, S. Sridharan38, F. Stagni38, M. Stahl11, S. Stahl11, O.
Steinkamp40, O. Stenyakin35, S. Stevenson55, S. Stoica29, S. Stone59, B.
Storaci40, S. Stracka23, M. Straticiuc29, U. Straumann40, R. Stroili22, V.K.
Subbiah38, L. Sun57, W. Sutcliffe53, K. Swientek27, S. Swientek9, V.
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S. Tourneur39, M.T. Tran39, M. Tresch40, A. Trisovic38, A. Tsaregorodtsev6, P.
Tsopelas41, N. Tuning41, M. Ubeda Garcia38, A. Ukleja28, A. Ustyuzhanin64, U.
Uwer11, C. Vacca15, V. Vagnoni14, G. Valenti14, A. Vallier7, R. Vazquez
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Velthuis46, M. Veltri17,h, G. Veneziano39, M. Vesterinen11, B. Viaud7, D.
Vieira2, M. Vieites Diaz37, X. Vilasis-Cardona36,p, A. Vollhardt40, D.
Volyanskyy10, D. Voong46, A. Vorobyev30, V. Vorobyev34, C. Voß63, J.A. de
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J. Wang59, D.R. Ward47, N.K. Watson45, D. Websdale53, M. Whitehead48, J.
Wicht38, D. Wiedner11, G. Wilkinson55,38, M. Wilkinson59, M.P. Williams45, M.
Williams56, H.W. Wilschut66, F.F. Wilson49, J. Wimberley58, J. Wishahi9, W.
Wislicki28, M. Witek26, G. Wormser7, S.A. Wotton47, S. Wright47, K. Wyllie38,
Y. Xie61, Z. Xing59, Z. Xu39, Z. Yang3, X. Yuan3, O. Yushchenko35, M.
Zangoli14, M. Zavertyaev10,b, L. Zhang59, W.C. Zhang12, Y. Zhang3, A.
Zhelezov11, A. Zhokhov31, L. Zhong3.

1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3Center for High Energy Physics, Tsinghua University, Beijing, China
4LAPP, Université de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France
5Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-
Ferrand, France
6CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
7LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France
8LPNHE, Université Pierre et Marie Curie, Université Paris Diderot,
CNRS/IN2P3, Paris, France
9Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
10Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
11Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
12School of Physics, University College Dublin, Dublin, Ireland
13Sezione INFN di Bari, Bari, Italy
14Sezione INFN di Bologna, Bologna, Italy
15Sezione INFN di Cagliari, Cagliari, Italy
16Sezione INFN di Ferrara, Ferrara, Italy
17Sezione INFN di Firenze, Firenze, Italy
18Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy
19Sezione INFN di Genova, Genova, Italy
20Sezione INFN di Milano Bicocca, Milano, Italy
21Sezione INFN di Milano, Milano, Italy
22Sezione INFN di Padova, Padova, Italy
23Sezione INFN di Pisa, Pisa, Italy
24Sezione INFN di Roma Tor Vergata, Roma, Italy
25Sezione INFN di Roma La Sapienza, Roma, Italy
26Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of
Sciences, Kraków, Poland
27AGH - University of Science and Technology, Faculty of Physics and Applied
Computer Science, Kraków, Poland
28National Center for Nuclear Research (NCBJ), Warsaw, Poland
29Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest-Magurele, Romania
30Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
31Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
32Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow,
Russia
33Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN),
Moscow, Russia
34Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State
University, Novosibirsk, Russia
35Institute for High Energy Physics (IHEP), Protvino, Russia
36Universitat de Barcelona, Barcelona, Spain
37Universidad de Santiago de Compostela, Santiago de Compostela, Spain
38European Organization for Nuclear Research (CERN), Geneva, Switzerland
39Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
40Physik-Institut, Universität Zürich, Zürich, Switzerland
41Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands
42Nikhef National Institute for Subatomic Physics and VU University Amsterdam,
Amsterdam, The Netherlands
43NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
44Institute for Nuclear Research of the National Academy of Sciences (KINR),
Kyiv, Ukraine
45University of Birmingham, Birmingham, United Kingdom
46H.H. Wills Physics Laboratory, University of Bristol, Bristol, United
Kingdom
47Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
48Department of Physics, University of Warwick, Coventry, United Kingdom
49STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
50School of Physics and Astronomy, University of Edinburgh, Edinburgh, United
Kingdom
51School of Physics and Astronomy, University of Glasgow, Glasgow, United
Kingdom
52Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
53Imperial College London, London, United Kingdom
54School of Physics and Astronomy, University of Manchester, Manchester,
United Kingdom
55Department of Physics, University of Oxford, Oxford, United Kingdom
56Massachusetts Institute of Technology, Cambridge, MA, United States
57University of Cincinnati, Cincinnati, OH, United States
58University of Maryland, College Park, MD, United States
59Syracuse University, Syracuse, NY, United States
60Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de
Janeiro, Brazil, associated to 2
61Institute of Particle Physics, Central China Normal University, Wuhan,
Hubei, China, associated to 3
62Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia,
associated to 8
63Institut für Physik, Universität Rostock, Rostock, Germany, associated to 11
64National Research Centre Kurchatov Institute, Moscow, Russia, associated to
31
65Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC,
Valencia, Spain, associated to 36
66Van Swinderen Institute, University of Groningen, Groningen, The
Netherlands, associated to 41
67Celal Bayar University, Manisa, Turkey, associated to 38

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS),
Moscow, Russia
cUniversità di Bari, Bari, Italy
dUniversità di Bologna, Bologna, Italy
eUniversità di Cagliari, Cagliari, Italy
fUniversità di Ferrara, Ferrara, Italy
gUniversità di Firenze, Firenze, Italy
hUniversità di Urbino, Urbino, Italy
iUniversità di Modena e Reggio Emilia, Modena, Italy
jUniversità di Genova, Genova, Italy
kUniversità di Milano Bicocca, Milano, Italy
lUniversità di Roma Tor Vergata, Roma, Italy
mUniversità di Roma La Sapienza, Roma, Italy
nUniversità della Basilicata, Potenza, Italy
oAGH - University of Science and Technology, Faculty of Computer Science,
Electronics and Telecommunications, Kraków, Poland
pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
qHanoi University of Science, Hanoi, Viet Nam
rUniversità di Padova, Padova, Italy
sUniversità di Pisa, Pisa, Italy
tScuola Normale Superiore, Pisa, Italy
uUniversità degli Studi di Milano, Milano, Italy
vPolitecnico di Milano, Milano, Italy