Determination of the branching fractions of B-s(0) -> D-s(-/+) K--/+ and B-0 -> Ds-K+

JHEP05(2015)019

Published for SISSA by Springer

Received: January 12, 2015 Revised: February 13, 2015 Accepted: April 7, 2015 Published: May 5, 2015

Determination of the branching fractions of

B

_s0

→ D

_s∓

K

∓

and B

0

→ D

−_s

K

+

The LHCb collaboration

E-mail: l.bel@cern.ch

Abstract: Measurements are presented of the branching fractions of the decays Bs0 →

D_s∓K∓and B0 → D−_s K+relative to the decays B_s0 → D_s−π+and B0 → D−π+, respectively.

The data used correspond to an integrated luminosity of 3.0 fb−1 of proton-proton collisions.

The ratios of branching fractions are

B(B_s0→ D∓_s K∓) B(B0 s → Ds−π+) = 0.0752 ± 0.0015 ± 0.0019 and B(B0→ D−_s K+) B(B0 _{→ D}−_π+₎ = 0.0129 ± 0.0005 ± 0.0008,

where the uncertainties are statistical and systematic, respectively.

Keywords: Hadron-Hadron Scattering, Branching fraction, B physics, Flavor physics

JHEP05(2015)019

Contents

1 Introduction 1

2 Event selection 3

3 Signal yield determination 4

4 Systematic uncertainties 6

5 Determination of branching fractions 7

The LHCb collaboration 11

1 Introduction

This paper presents the measurements of the branching fractions of the decays B_s0 →

D_s∓K± and B0→ D−_s K+, relative to those of the decays B_s0→ D_s−π+ and B0→ D−π+,

respectively. The B_s0→ D_s∓K± system is of interest as it offers a prime opportunity to

measure CP violation in the interference between mixing and decay [1,2]. The B_s0 meson

can decay into both charge-conjugate decays, providing sensitivity to the CKM angle γ [3].

The decays B_s0→ D_s∓K±and B0_s→ D−_s π+occur predominantly through colour-allowed tree

diagrams (see figure 1). A lower bound on the ratio of the B0_s→ D∓_s K± and B0_s→ D−_s π+

branching fractions was derived, B(B_s0→ D∓_s K±)/B(B_s0→ D−_s π+) ≥ 0.080 ± 0.007 [4],

with minimal external experimental and theoretical input. Using SU(3) flavour symmetry,

and measurements of B0→ D−π+ decays at the B-factories, a prediction for the ratio

of branching fractions was calculated, B(B_s0→ D_s∓K±)/B(B_s0→ D−_s π+) = 0.086+0.009_−0.007 [4],

where the uncertainty includes contributions from non-factorisable effects [5] and from

possible SU(3)-breaking effects of up to 20%.

The CDF and Belle collaborations have pioneered the study of this ratio [6,7], followed

by the LHCb collaboration, which measured a ratio about 1.8 standard deviations below

the theoretical bound [8], using data corresponding to an integrated luminosity of 336 pb−1.

The decay B0→ D_s−K+ proceeds through the colour-suppressed W -exchange diagram

and the branching fraction determination allows the size of the W -exchange amplitude to

be estimated, for example in the B_s0→ D∓_s K± decay, as used e.g. in ref. [4]. The existing

branching fraction measurements by BaBar and Belle, B(B0→ D_s−K+) = (2.9 ± 0.4 (stat) ±

0.2 (syst)) × 10−5 [9] and (1.91 ± 0.24 (stat) ± 0.17 (syst)) × 10−5 [10], respectively, show

a difference of about 1.8 standard deviations, and suggest that an enhancement of the

branching fraction due to rescattering effects is small [11]. Note that throughout this paper,

charge conjugation is implied, and thus that the branching fraction B(B0_(s)) corresponds to

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B0 s b c s D− s W+ K+ u s − + B0 s b u s K− W+ D+ s c s B0 s b c s D− s W+ π+ u d − s B0 (s) b d (s) W+ _s c D− s g u s K+

Figure 1. Feynman diagrams of the processes under study. The upper diagrams represent the two tree topologies in which a B0

s meson decays into the D∓sK± final state, and the lower diagrams show the tree diagram of B0

s→ D−sπ+ and the W -exchange topology of B(s)0 → D − s K+.

The pp-collision data used in this analysis correspond to an integrated luminosity of

3.0 fb−1, of which 1.0 fb−1 was collected by LHCb in 2011 at a centre-of-mass energy of

√

s = 7 TeV, and the remaining 2.0 fb−1 in 2012 at√s = 8 TeV.

The LHCb detector [12] is a single-arm forward spectrometer covering the pseudorapidity

range 2 < η < 5, designed for the study of particles containing b or c quarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector sur-rounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream of the magnet. The polarity of the magnet is reversed periodically throughout data-taking. The tracking system provides a measurement of momentum, p, with a relative uncertainty that varies from 0.4% at low momentum to 0.6% at 100 GeV/c. The minimum distance of a track to a primary vertex,

the impact parameter, is measured with a resolution of (15 + 29/pT) µm, where pT is the

component of p transverse to the beam, in GeV/c. Different types of charged hadrons are distinguished using information from two ring-imaging detectors.

The trigger 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. The software trigger requires a two-, three- or four-track secondary vertex with a significant displacement from the primary pp interaction vertices (PVs). At least one charged particle

must have a transverse momentum pT> 1.7 GeV/c and be inconsistent with originating from

the PV. A multivariate algorithm [13] is used for the identification of secondary vertices

consistent with the decay of a b hadron.

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Selection efficiency (%) Kinematic PID Total

B0→ D−π+ 1.89 ± 0.01 74.29 ± 0.07 1.40 ± 0.01

B0_s→ D−_s π+ 1.92 ± 0.02 67.10 ± 0.09 1.29 ± 0.01

B0_s→ D∓_s K± 2.08 ± 0.01 55.52 ± 0.17 1.15 ± 0.01

B0→ D−_s K+ 1.70 ± 0.03 58.11 ± 0.82 0.99 ± 0.02

Table 1. Kinematic and PID selection efficiencies for each signal decay, as determined from simulated events and data, respectively. “PID” refers to the selection efficiencies of the PID requirements only, while “Kinematic” refers to the remaining event selection. The kinematic efficiencies represent weighted averages determined from events simulated at √s = 7 TeV (34%) and √s = 8 TeV (66%). The binomial uncertainties result from the size of the simulated samples.

LHCb configuration [16]. Decays of hadronic particles are described by EvtGen [17]. The

interaction of the generated particles with the detector and its response are implemented

using the Geant4 toolkit [18,19] as described in ref. [20].

2 Event selection

Candidate B0_(s)mesons are reconstructed by combining a D_(s)± candidate decaying into three

light hadrons, D−→ K+_π−_π− _{or D}−

s → K+K−π−, with an additional pion or kaon (the

“bachelor” particle). Each of the four final-state light hadrons is required to have a good track quality, high momentum and transverse momentum, and a large impact parameter

with respect to the primary vertex. The contribution from charmless B_(s)0 decays, such as

B_s0→ K+K−π+π−, is suppressed by requiring the D_(s)± candidate to have a significant flight

distance from the reconstructed B_(s)0 decay vertex, and by requiring its mass to fall within a

small mass window of+22₋₂₄MeV/c2 around the D±_(s) mass [21]. To reduce the combinatorial

background, a multivariate algorithm is applied. This boosted decision tree (BDT) [22, 23]

is identical to that used in the analysis of the CP asymmetry in B0_s→ D∓_s K± decays [3],

and was trained with B_s0→ D_s−π+ candidates from data, using a weighted data sample

based on the sPlot technique [24] as signal and candidates with an invariant mass greater

than 5445 MeV/c2 as background. The variables with the highest discriminating power

are found to be the difference between the χ2 from the vertex fit of the associated PV

reconstructed with and without the considered b-hadron candidate, the pT of the final-state

particles, and the angle between the b-hadron momentum vector and the vector connecting its production and decay vertices.

Misidentification of particles leads to peaking backgrounds in the signal region, for

example B_s0→ D−_s π+ events reconstructed as B0_s→ D_s∓K± candidates. Pions and kaons

in these decays are required to satisfy particle identification (PID) requirements, and approximately 60% of the signal is retained while over 99% of the background is rejected. The

efficiencies of these requirements are determined by studying kinematically selected D∗+→

D0(→ K−π+)π+ and Λ → pπ− decays obtained from data, which provide high-purity PID.

In the B0→ D−π+ selection, loose PID requirements are applied since the branching

JHEP05(2015)019

from misidentification. In the B0_s → D−_s π+ and B_s0→ D∓_s K± selections, a stricter PID

requirement is applied to the D+_s decay products, to distinguish D+_s and D+ mesons.

For these decays, a further selection requirement is applied to reduce the background

from Λ0_b→ Λ+_cπ− decays, where one of the D_s+ daughters is a misidentified proton. This

requirement removes any candidate which fulfils two criteria: that there is a large probability

for one of the D_s+ daughters to be a misidentified proton, and that when the D+_s decay

is reconstructed under the Λ+_c hypothesis, its invariant mass falls within 21 MeV/c2 of

the nominal Λ+_c mass [21]. This procedure almost fully eliminates this background. The

efficiency of the selection is obtained from simulation and is summarised in table 1.

3 Signal yield determination

An unbinned maximum likelihood fit to the candidate invariant mass distribution is

per-formed for each of the three final states, D−π+, D_s−π+, and D∓_sK±. The signal shapes are

parametrised by a double-sided Crystal Ball shape [25]. This function consists of a central

Gaussian part, whose mean and width are free parameters, and power-law tails on both lower and upper sides, to account for energy loss due to final-state radiation and detector resolution effects. The functional form for the combinatorial background, an exponential

function with an offset, is obtained from same-charge D±_s π± combinations in data. All

parameters of the combinatorial background are left free in the fit to data.

The physical backgrounds can be split into two categories: misidentified backgrounds, predominantly where one of the final state pions (kaons) is mistaken for a kaon (pion); and partially reconstructed backgrounds, where a neutral pion or a photon is not included in the

candidate reconstruction, causing the reconstructed B_(s)0 mass to shift to lower values. Some

backgrounds fall into both categories. The number of background components considered varies per final state; the list of background components for each final state can be found

in the legend of figures 2 and 3. The invariant mass shapes of these backgrounds are

obtained from simulation at √s = 8 TeV, with the event selection applied. The yield of

each background is a parameter in the fit, with most background components

Gaussian-constrained around the expected yield normalised to the B0→ D−π+ yield obtained from

data. The constraints are assigned an uncertainty of 10%, which reflects the uncertainties from production fractions, branching fractions, and reconstruction efficiencies. The resulting background yields from the fit deviate typically around one standard deviation from the

expected values. The results of the fits for the three final states are shown in figures2and3,

and in table2. The three fits are independent, and no parameters are shared among them.

Various consistency checks are performed for each of the fits. The fitted yield of

B_s0→ D−_s π+ events reconstructed in the D∓_s K± final state, which is allowed to vary in the

fit, is consistent with the expected yield based on the relative branching fraction, particle misidentification probability and reconstruction efficiency. For each of the fits, consistency is also found between the fitted yield for both magnet polarities separately and the fraction of data corresponding to that polarity. This demonstrates that the relative yields are stable as a function of time and magnet polarity.

JHEP05(2015)019

] 2 c ) [MeV/ + π − D ( m 5000 5200 5400 5600 5800 ) 2 c MeV/ 1 ( Candidates / 0 2000 4000 6000 8000 10000 + π − D → 0 B + π − s D → 0 s B + K − D → 0 B + π − * D → 0 B + ρ − D → 0 B − π + c Λ → b Λ Combinatorial

LHCb

(a) ] 2 c ) [MeV/ + π − s D ( m 5200 5400 5600 5800 ) 2 _c MeV/ 5 ( Candidates / 0 2000 4000 6000 8000 + π − s D → 0 s B + π − s D → 0 B + π − D → 0 B + ρ − s D → 0 s B + π − * s D → 0 s B Combinatorial

LHCb

(b)

Figure 2. Results of the fits to the invariant mass distributions of the final states (a) D−π+ and (b) D−_sπ+_. Yield B0→ D−π+ 458 940 ± 959 B_s0→ D_s−π+ 75 566 ± 342 B_s0→ D_s∓K± 5 101 ± 100 B0→ D_s−K+ 2 452 ± 98

JHEP05(2015)019

]

2

c

) [MeV/

+

K

s −

D

(

m

5200 5400 5600 5800

)

2

c

MeV/

5

(

Candidates /

0 200 400 600 ± K s ± D → s 0 B + K s − D → 0 B + K − D → 0 B + π s − D → s 0 B (*)+ K s − (*) D → s 0 B p s − (*) D → b Λ ) + ρ , + π ( s − (*) D → s 0 B Combinatorial

LHCb

Figure 3. Result of the fit to the invariant mass distribution of the final state D∓_sK±.

4 Systematic uncertainties

Systematic uncertainties arise from the fit model and the candidate selection, and are

summarised in table 3. The systematic uncertainty from the fit model is determined by

applying variations to the fit model and comparing the yield to the nominal result, taking the difference as a systematic uncertainty. These variations include a different combinatorial shape, fixing the signal shape tail parameters to values obtained from simulation, and using background shapes determined from simulation matching the LHCb conditions during 2011

(√s = 7 TeV). In the D−π+ analysis, the fit range is reduced to start at 5100 MeV/c2. In

the D∓_s K± analysis, the as yet unobserved decay Λ0_b→ D_s−p is omitted from the fit.

The uncertainty on the candidate selection is separated into three parts: the uncertainty due to the kinematic selection, that due to the PID requirements on the final state pions and kaons, and that due to the hardware trigger efficiency. The first of these uncertainties is determined from the selection efficiency difference between magnet polarities in simulation, and by estimating the uncertainty on the BDT selection efficiency due to differences between data and simulation. This is calculated by reweighting simulated events to match the data more closely, and calculating the difference in BDT efficiency between those and the unweighted samples. The uncertainty on the PID efficiency and misidentification rate is

estimated by comparing the PID performance measured using a simulated D∗ calibration

sample with that observed in simulated signal events. The systematic uncertainty from the hardware trigger efficiency arises from measured differences between the pion and kaon trigger efficiencies which are not reproduced in the simulation. The uncertainty is scaled with the fraction of events where a pion or a kaon from the reconstructed decay was responsible for triggering.

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Source B 0 s→ D∓s K± B_s0→ D−s π+ B0→ D−_s K+ B0_{→ D}−_π+ Fit model 1.1 3.6 Candidate selection 2.1 2.9 Hardware trigger 1.0 1.2 Charmless background – 1.0 Total 2.5 4.9

Table 3. Systematic uncertainties on the ratios of branching fractions, in %, obtained as described in the text. The total uncertainty is obtained by adding the separate contributions in quadrature.

A further systematic uncertainty is added to account for possible charmless B0 decays

peaking under the B0→ D−_s K+ signal. Some of the uncertainties cancel in the ratios of

branching fractions, leading to lower overall systematic uncertainties than those determined individually for each decay channel. The total systematic uncertainty for each ratio of branching fractions is the quadratic sum of the individual systematic uncertainties.

5 Determination of branching fractions

The ratios of branching fractions are evaluated using the expression B(A) B(B) = εB εA NA NB fB fA B_D± (s) B_D± (s) , (5.1)

where εX, fX and NX are the selection efficiency, the hadronisation fraction, and the

fitted yield of decay X, respectively, and B_D±

(s) is the branching fraction of D

±

(s) decays, as

appropriate. The following values are used as input [21]:

B(B0→ D−π+) = (2.68 ± 0.13) × 10−3,

B(B0_s→ D−_s π+) = (3.04 ± 0.23) × 10−3,

B(D−→ K+π−π−) = (9.13 ± 0.19) × 10−2,

B(D−_s → K+K−π−) = (5.39 ± 0.21) × 10−2.

As a cross-check, a value B(B_s0→ D_s−π+) = (2.95 ± 0.01 (stat)) × 10−3 was obtained from

the measured B_s0→ D_s−π+ and B0→ D−π+ yields using eq. (5.1). This measurement is

compatible with the world-average value, and the central value is unchanged with respect

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The following results are obtained

B(B_s0→ D_s∓K±) B(B0 s→ D−s π+) = 0.0752 ± 0.0015 (stat) ± 0.0019 (syst), B(B_s0→ D_s∓K±) = (2.29 ± 0.05 (stat) ± 0.06 (syst) ± 0.17(B_B0 s)) × 10 −4_, B(B0_{→ D}− s K+) B(B0_{→ D}−_π+₎ = 0.0129 ± 0.0005 (stat) ± 0.0007 (syst) ± 0.0004(BD±_(s)), B(B0→ D_s−K+) = (3.45 ± 0.14 (stat) ± 0.20 (syst) ± 0.20(B_B0_,D± (s) )) × 10−5,

where the uncertainties labelled (B) arise from the uncertainties on the branching fractions used as input.

The branching fractions of B_s0→ D∓_s K± and B0→ D−_s K+ presented here are more

precise than the current world-average values. The result for B(B_s0→ D∓_s K±)/B(B_s0→

D−_s π+) is compatible with theoretical expectations [4] and with the previous result from

LHCb. As expected [5], the branching fraction of the decay B0 → D_s−K+, dominated

by the W -exchange topology, is suppressed compared to the decay B0→ D−π+, which

predominantly proceeds through the colour-allowed tree topology. The measured value

of B(B0 → D−_s K+) is in good agreement with existing measurements from the BaBar

collaboration [9], and is larger than the result published by the Belle collaboration [10] with

a significance of more than three standard deviations.

Acknowledgments

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); 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 Sk lodowska-Curie Actions and

ERC (European Union), Conseil g´en´eral de Haute-Savoie, Labex ENIGMASS and OCEVU,

R´egion Auvergne (France), RFBR (Russia), XuntaGal and GENCAT (Spain), Royal Society

and Royal Commission for the Exhibition of 1851 (United Kingdom).

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

JHEP05(2015)019

References

[1] R. Aleksan, I. Dunietz and B. Kayser, Determining the CP-violating phase gamma,Z. Phys. C 54 (1992) 653[INSPIRE].

[2] R. Fleischer, New strategies to obtain insights into CP-violation through

Bs→ D±sK∓, Ds∗±K∓, ... and Bd → D±π∓, D∗±π∓, ... decays,Nucl. Phys. B 671 (2003) 459 [hep-ph/0304027] [INSPIRE].

[3] LHCb collaboration, Measurement of CP asymmetry in B0s→ D∓sK± decays,JHEP 11 (2014) 060[arXiv:1407.6127] [INSPIRE].

[4] K. De Bruyn et al., Exploring Bs→ D (∗)±

s K∓ Decays in the Presence of a Sizable Width Difference ∆Γs,Nucl. Phys. B 868 (2013) 351[arXiv:1208.6463] [INSPIRE].

[5] R. Fleischer, N. Serra and N. Tuning, Tests of Factorization and SU(3) Relations in B Decays into Heavy-Light Final States,Phys. Rev. D 83 (2011) 014017[arXiv:1012.2784] [INSPIRE].

[6] CDF collaboration, T. Aaltonen et al., First observation of ¯B0s→ D±sK∓ and measurement of the ratio of branching fractions B( ¯B0

s → Ds±K∓) /B( ¯Bs0→ D+sπ−),Phys. Rev. Lett. 103 (2009) 191802[arXiv:0809.0080] [INSPIRE].

[7] Belle collaboration, R. Louvot et al., Measurement of the Decay Bs0→ Ds−π+ and Evidence for Bs0 → Ds± K± in e+e− Annihilation at

√

s ∼ 10.87 GeV,Phys. Rev. Lett. 102 (2009) 021801[arXiv:0809.2526] [INSPIRE].

[8] LHCb collaboration, Measurements of the branching fractions of the decays Bs0→ Ds∓K± and B0

s → D−sπ+,JHEP 06 (2012) 115[arXiv:1204.1237] [INSPIRE].

[9] BaBar collaboration, B. Aubert et al., Measurement of the Branching Fractions of the Rare Decays B0→ D(∗)+s π−, B0→ Ds(∗)+ρ− and B0→ D(∗)−s K(∗)+,Phys. Rev. D 78 (2008) 032005[arXiv:0803.4296] [INSPIRE].

[10] Belle collaboration, A. Das et al., Measurements of Branching Fractions for B0_{→ D}+ sπ− and ¯B0→ D+

sK−,Phys. Rev. D 82 (2010) 051103[arXiv:1007.4619] [INSPIRE].

[11] M. Gronau and J.L. Rosner, B decays dominated by ω−φ mixing,Phys. Lett. B 666 (2008) 185[arXiv:0806.3584] [INSPIRE].

[12] LHCb collaboration, The LHCb Detector at the LHC,2008 JINST 3 S08005[INSPIRE].

[13] V.V. Gligorov and M. Williams, Efficient, reliable and fast high-level triggering using a bonsai boosted decision tree,2013 JINST 8 P02013[arXiv:1210.6861] [INSPIRE].

[14] T. Sj¨ostrand, S. Mrenna and P.Z. Skands, PYTHIA 6.4 Physics and Manual,JHEP 05 (2006) 026[hep-ph/0603175] [INSPIRE].

[15] T. Sj¨ostrand, S. Mrenna and P.Z. Skands, A Brief Introduction to PYTHIA 8.1,Comput. Phys. Commun. 178 (2008) 852[arXiv:0710.3820] [INSPIRE].

[16] I. Belyaev et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework,IEEE Nucl. Sci. Symp. Conf. Rec. (NSS/MIC) (2010) 1155.

[17] D.J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Meth. A 462 (2001) 152[INSPIRE].

[18] GEANT4 collaboration, J. Allison et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270.

JHEP05(2015)019

[19] GEANT4 collaboration, S. Agostinelli et al., GEANT4: A Simulation toolkit,Nucl. Instrum.

Meth. A 506 (2003) 250[INSPIRE].

[20] LHCb collaboration, The LHCb simulation application, Gauss: Design, evolution and experience,J. Phys. Conf. Ser. 331 (2011) 032023 [INSPIRE].

[21] Particle Data Group, K.A. Olive et al., Review of particle physics,Chin. Phys. C 38 (2014) 090001.

[22] L. Breiman, J.H. Friedman, R.A. Olshen, and C.J. Stone, Classification and regression trees, Wadsworth international group, Belmont, California, U.S.A. (1984).

[23] R.E. Schapire and Y. Freund, A decision-theoretic generalization of on-line learning and an application to boosting,J. Comp. Syst. Sci. 55 (1997) 119.

[24] M. Pivk and F.R. Le Diberder, SPlot: A Statistical tool to unfold data distributions,Nucl. Instrum. Meth. A 555 (2005) 356[physics/0402083] [INSPIRE].

[25] T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, [DESY-F31-86-02].

JHEP05(2015)019

The LHCb collaboration

R. Aaij41, B. Adeva37, M. Adinolfi46, A. Affolder52, Z. Ajaltouni5, S. Akar6, J. Albrecht9, F. Alessio38_{, M. Alexander}51_{, S. Ali}41_{, G. Alkhazov}30_{, P. Alvarez Cartelle}37_{, A.A. Alves Jr}25,38_, S. Amato2_{, S. Amerio}22_{, Y. Amhis}7_{, L. An}3_{, L. Anderlini}17,g_{, J. Anderson}40_{, R. Andreassen}57_, M. Andreotti16,f_{, J.E. Andrews}58_{, R.B. Appleby}54_{, O. Aquines Gutierrez}10_{, F. Archilli}38_, A. Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, M. Baalouch5, S. Bachmann11, J.J. Back48_{, A. Badalov}36_{, C. Baesso}60_{, W. Baldini}16_{, R.J. Barlow}54_{, C. Barschel}38_{, S. Barsuk}7_, W. Barter47_{, V. Batozskaya}28_{, V. Battista}39_{, A. Bay}39_{, L. Beaucourt}4_{, J. Beddow}51_{, F. Bedeschi}23_, I. Bediaga1, L.J. Bel41, S. Belogurov31, K. Belous35, I. Belyaev31, E. Ben-Haim8, G. Bencivenni18, S. Benson38_{, J. Benton}46_{, A. Berezhnoy}32_{, R. Bernet}40_{, A. Bertolin}22_{, M.-O. Bettler}47_,

M. van Beuzekom41_{, A. Bien}11_{, S. Bifani}45_{, T. Bird}54_{, A. Bizzeti}17,i_{, P.M. Bjørnstad}54_{, T. Blake}48_, F. Blanc39_{, J. Blouw}10_{, S. Blusk}59_{, V. Bocci}25_{, A. Bondar}34_{, N. Bondar}30,38_{, W. Bonivento}15_, S. Borghi54, A. Borgia59, M. Borsato7, T.J.V. Bowcock52, E. Bowen40, C. Bozzi16, D. Brett54, M. Britsch10_{, T. Britton}59_{, J. Brodzicka}54_{, N.H. Brook}46_{, A. Bursche}40_{, J. Buytaert}38_, S. Cadeddu15_{, R. Calabrese}16,f_{, M. Calvi}20,k_{, M. Calvo Gomez}36,p_{, P. Campana}18_, D. Campora Perez38_{, L. Capriotti}54_{, A. Carbone}14,d_{, G. Carboni}24,l_{, R. Cardinale}19,38,j_, A. Cardini15, L. Carson50, K. Carvalho Akiba2,38, RCM Casanova Mohr36, G. Casse52, L. Cassina20,k_{, L. Castillo Garcia}38_{, M. Cattaneo}38_{, Ch. Cauet}9_{, R. Cenci}23,t_{, M. Charles}8_, Ph. Charpentier38_{, M. Chefdeville}4_{, S. Chen}54_{, S.-F. Cheung}55_{, N. Chiapolini}40_{, M. Chrzaszcz}40,26_, X. Cid Vidal38, G. Ciezarek41, P.E.L. Clarke50, M. Clemencic38, H.V. Cliff47, J. Closier38,

V. Coco38_{, J. Cogan}6_{, E. Cogneras}5_{, V. Cogoni}15_{, L. Cojocariu}29_{, G. Collazuol}22_{, P. Collins}38_, A. Comerma-Montells11_{, A. Contu}15,38_{, A. Cook}46_{, M. Coombes}46_{, S. Coquereau}8_{, G. Corti}38_, M. Corvo16,f_{, I. Counts}56_{, B. Couturier}38_{, G.A. Cowan}50_{, D.C. Craik}48_{, A.C. Crocombe}48_, M. Cruz Torres60, S. Cunliffe53, R. Currie53, C. D’Ambrosio38, J. Dalseno46, P. David8, P.N.Y. David41_{, A. Davis}57_{, K. De Bruyn}41_{, S. De Capua}54_{, M. De Cian}11_{, J.M. De Miranda}1_, L. De Paula2_{, W. De Silva}57_{, P. De Simone}18_{, C.-T. Dean}51_{, D. Decamp}4_{, M. Deckenhoff}9_, L. Del Buono8, N. D´el´eage4, D. Derkach55, O. Deschamps5, F. Dettori38, B. Dey40, A. Di Canto38, A Di Domenico25, F. Di Ruscio24, H. Dijkstra38, S. Donleavy52, F. Dordei11, M. Dorigo39,

A. Dosil Su´arez37_{, D. Dossett}48_{, A. Dovbnya}43_{, K. Dreimanis}52_{, G. Dujany}54_{, F. Dupertuis}39_, P. Durante38_{, R. Dzhelyadin}35_{, A. Dziurda}26_{, A. Dzyuba}30_{, S. Easo}49,38_{, U. Egede}53_,

V. Egorychev31, S. Eidelman34, S. Eisenhardt50, U. Eitschberger9, R. Ekelhof9, L. Eklund51, I. El Rifai5_{, Ch. Elsasser}40_{, S. Ely}59_{, S. Esen}11_{, H.-M. Evans}47_{, T. Evans}55_{, A. Falabella}14_, C. F¨arber11_{, C. Farinelli}41_{, N. Farley}45_{, S. Farry}52_{, R. Fay}52_{, D. Ferguson}50_{, V. Fernandez Albor}37_, F. Ferreira Rodrigues1_{, M. Ferro-Luzzi}38_{, S. Filippov}33_{, M. Fiore}16,f_{, M. Fiorini}16,f_{, M. Firlej}27_, C. Fitzpatrick39, T. Fiutowski27, P. Fol53, M. Fontana10, F. Fontanelli19,j, R. Forty38, O. Francisco2, M. Frank38_{, C. Frei}38_{, M. Frosini}17_{, J. Fu}21,38_{, E. Furfaro}24,l_{, A. Gallas Torreira}37_{, D. Galli}14,d_, S. Gallorini22,38_{, S. Gambetta}19,j_{, M. Gandelman}2_{, P. Gandini}59_{, Y. Gao}3_{, J. Garc´ıa Pardi˜nas}37_, J. Garofoli59, J. Garra Tico47, L. Garrido36, D. Gascon36, C. Gaspar38, U. Gastaldi16, R. Gauld55, L. Gavardi9, G. Gazzoni5, A. Geraci21,v, E. Gersabeck11, M. Gersabeck54, T. Gershon48, Ph. Ghez4, A. Gianelle22_{, S. Gian`ı}39_{, V. Gibson}47_{, L. Giubega}29_{, V.V. Gligorov}38_{, C. G¨obel}60_{, D. Golubkov}31_, A. Golutvin53,31,38_{, A. Gomes}1,a_{, C. Gotti}20,k_{, M. Grabalosa G´andara}5_{, R. Graciani Diaz}36_, L.A. Granado Cardoso38, E. Graug´es36, E. Graverini40, G. Graziani17, A. Grecu29, E. Greening55, S. Gregson47_{, P. Griffith}45_{, L. Grillo}11_{, O. Gr¨unberg}63_{, B. Gui}59_{, E. Gushchin}33_{, Yu. Guz}35,38_, T. Gys38_{, C. Hadjivasiliou}59_{, G. Haefeli}39_{, C. Haen}38_{, S.C. Haines}47_{, S. Hall}53_{, B. Hamilton}58_, T. Hampson46_{, X. Han}11_{, S. Hansmann-Menzemer}11_{, N. Harnew}55_{, S.T. Harnew}46_{, J. Harrison}54_, J. He38, T. Head39, V. Heijne41, K. Hennessy52, P. Henrard5, L. Henry8, J.A. Hernando Morata37, E. van Herwijnen38_{, M. Heß}63_{, A. Hicheur}2_{, D. Hill}55_{, M. Hoballah}5_{, C. Hombach}54_,

JHEP05(2015)019

W. Hulsbergen41_{, N. Hussain}55_{, D. Hutchcroft}52_{, D. Hynds}51_{, M. Idzik}27_{, P. Ilten}56_{, R. Jacobsson}38_,

A. Jaeger11_{, J. Jalocha}55_{, E. Jans}41_{, A. Jawahery}58_{, F. Jing}3_{, M. John}55_{, D. Johnson}38_, 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,k,

C. Khurewathanakul39_{, S. Klaver}54_{, K. Klimaszewski}28_{, O. Kochebina}7_{, M. Kolpin}11_{, I. Komarov}39_, R.F. Koopman42_{, P. Koppenburg}41,38_{, M. Korolev}32_{, L. Kravchuk}33_{, K. Kreplin}11_{, M. Kreps}48_, G. Krocker11, P. Krokovny34, F. Kruse9, W. Kucewicz26,o, M. Kucharczyk20,26,k, V. Kudryavtsev34, K. Kurek28_{, T. Kvaratskheliya}31_{, V.N. La Thi}39_{, D. Lacarrere}38_{, G. Lafferty}54_{, A. Lai}15_,

D. Lambert50_{, R.W. Lambert}42_{, G. Lanfranchi}18_{, C. Langenbruch}48_{, B. Langhans}38_{, T. Latham}48_, C. Lazzeroni45_{, R. Le Gac}6_{, J. van Leerdam}41_{, J.-P. Lees}4_{, R. Lef`evre}5_{, A. Leflat}32_{, J. Lefran¸cois}7_, O. Leroy6, T. Lesiak26, B. Leverington11, Y. Li7, T. Likhomanenko64, M. Liles52, R. Lindner38, C. Linn38_{, F. Lionetto}40_{, B. Liu}15_{, S. Lohn}38_{, I. Longstaff}51_{, J.H. Lopes}2_{, P. Lowdon}40_,

D. Lucchesi22,r_{, H. Luo}50_{, A. Lupato}22_{, E. Luppi}16,f_{, O. Lupton}55_{, F. Machefert}7_, 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. M¨arki}39_{, J. Marks}11_{, G. Martellotti}25_{, M. Martinelli}39_{, D. Martinez Santos}42_, F. Martinez Vidal65_{, D. Martins Tostes}2_{, A. Massafferri}1_{, R. Matev}38_{, Z. Mathe}38_{, C. Matteuzzi}20_, A. Mazurov45, M. McCann53, J. McCarthy45, A. McNab54, R. McNulty12, B. McSkelly52,

B. Meadows57_{, F. Meier}9_{, M. Meissner}11_{, M. Merk}41_{, D.A. Milanes}62_{, M.-N. Minard}4_{, N. Moggi}14_, J. Molina Rodriguez60_{, S. Monteil}5_{, M. Morandin}22_{, P. Morawski}27_{, A. Mord`a}6_{, M.J. Morello}23,t_, J. Moron27_{, A.-B. Morris}50_{, R. Mountain}59_{, F. Muheim}50_{, K. M¨uller}40_{, M. Mussini}14_{, B. Muster}39_, P. Naik46, T. Nakada39, R. Nandakumar49, I. Nasteva2, M. Needham50, N. Neri21, S. Neubert38, N. Neufeld38_{, M. Neuner}11_{, A.D. Nguyen}39_{, T.D. Nguyen}39_{, C. Nguyen-Mau}39,q_{, M. Nicol}7_, V. Niess5_{, R. Niet}9_{, N. Nikitin}32_{, T. Nikodem}11_{, A. Novoselov}35_{, D.P. O’Hanlon}48_,

A. Oblakowska-Mucha27, V. Obraztsov35, S. Ogilvy51, O. Okhrimenko44, R. Oldeman15,e,

C.J.G. Onderwater66, M. Orlandea29, B. Osorio Rodrigues1, J.M. Otalora Goicochea2, A. Otto38, P. Owen53_{, A. Oyanguren}65_{, B.K. Pal}59_{, A. Palano}13,c_{, F. Palombo}21,u_{, M. Palutan}18_{, J. Panman}38_, A. Papanestis49,38_{, M. Pappagallo}51_{, L.L. Pappalardo}16,f_{, C. Parkes}54_{, C.J. Parkinson}9,45_,

G. Passaleva17, G.D. Patel52, M. Patel53, C. Patrignani19,j, A. Pearce54,49, A. Pellegrino41, G. Penso25,m_{, M. Pepe Altarelli}38_{, S. Perazzini}14,d_{, P. Perret}5_{, L. Pescatore}45_{, E. Pesen}67_, K. Petridis53_{, A. Petrolini}19,j_{, E. Picatoste Olloqui}36_{, B. Pietrzyk}4_{, T. Pilaˇr}48_{, D. Pinci}25_, A. Pistone19_{, S. Playfer}50_{, M. Plo Casasus}37_{, F. Polci}8_{, A. Poluektov}48,34_{, I. Polyakov}31_, E. Polycarpo2, A. Popov35, D. Popov10, B. Popovici29, C. Potterat2, E. Price46, J.D. Price52, J. Prisciandaro39_{, A. Pritchard}52_{, C. Prouve}46_{, V. Pugatch}44_{, A. Puig Navarro}39_{, G. Punzi}23,s_, W. Qian4_{, R Quagliani}7,46_{, B. Rachwal}26_{, J.H. Rademacker}46_{, B. Rakotomiaramanana}39_, M. Rama23, 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. Robbe}7_{, A.B. Rodrigues}1_{, E. Rodrigues}54_{, P. Rodriguez Perez}54_{, S. Roiser}38_, V. Romanovsky35_{, A. Romero Vidal}37_{, M. Rotondo}22_{, J. Rouvinet}39_{, T. Ruf}38_{, H. Ruiz}36_,

P. Ruiz Valls65, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B. Saitta15,e,

V. Salustino Guimaraes2_{, C. Sanchez Mayordomo}65_{, B. Sanmartin Sedes}37_{, R. Santacesaria}25_, C. Santamarina Rios37_{, E. Santovetti}24,l_{, A. Sarti}18,m_{, C. Satriano}25,n_{, A. Satta}24_,

D.M. Saunders46_{, D. Savrina}31,32_{, M. Schiller}38_{, H. Schindler}38_{, M. Schlupp}9_{, M. Schmelling}10_, B. Schmidt38, O. Schneider39, A. Schopper38, M.-H. Schune7, R. Schwemmer38, B. Sciascia18, A. Sciubba25,m_{, A. Semennikov}31_{, I. Sepp}53_{, N. Serra}40_{, J. Serrano}6_{, L. Sestini}22_{, P. Seyfert}11_, M. Shapkin35_{, I. Shapoval}16,43,f_{, Y. Shcheglov}30_{, T. Shears}52_{, L. Shekhtman}34_{, V. Shevchenko}64_, A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, I. Skillicorn51,

JHEP05(2015)019

M.D. Sokoloff57_{, F.J.P. Soler}51_{, F. Soomro}39_{, D. Souza}46_{, B. Souza De Paula}2_{, B. Spaan}9_,

P. Spradlin51_{, S. Sridharan}38_{, F. Stagni}38_{, M. Stahl}11_{, S. Stahl}11_{, O. Steinkamp}40_{, O. Stenyakin}35_, F Sterpka59, S. Stevenson55, S. Stoica29, S. Stone59, B. Storaci40, S. Stracka23,t, M. Straticiuc29, U. Straumann40, R. Stroili22, L. Sun57, W. Sutcliffe53, K. Swientek27, S. Swientek9,

V. Syropoulos42_{, M. Szczekowski}28_{, P. Szczypka}39,38_{, T. Szumlak}27_{, S. T’Jampens}4_{, M. Teklishyn}7_, G. Tellarini16,f_{, F. Teubert}38_{, C. Thomas}55_{, E. Thomas}38_{, J. van Tilburg}41_{, V. Tisserand}4_, M. Tobin39, J. Todd57, S. Tolk42, L. Tomassetti16,f, D. Tonelli38, S. Topp-Joergensen55, N. Torr55, E. Tournefier4_{, S. Tourneur}39_{, M.T. Tran}39_{, M. Tresch}40_{, A. Trisovic}38_{, A. Tsaregorodtsev}6_, P. Tsopelas41_{, N. Tuning}41_{, M. Ubeda Garcia}38_{, A. Ukleja}28_{, A. Ustyuzhanin}64_{, U. Uwer}11_, C. Vacca15_{, V. Vagnoni}14_{, G. Valenti}14_{, A. Vallier}7_{, R. Vazquez Gomez}18_{, P. Vazquez Regueiro}37_, C. V´azquez Sierra37, S. Vecchi16, J.J. Velthuis46, M. Veltri17,h, G. Veneziano39, M. Vesterinen11, JVVB Viana Barbosa38_{, B. Viaud}7_{, D. Vieira}2_{, M. Vieites Diaz}37_{, X. Vilasis-Cardona}36,p_, A. Vollhardt40_{, D. Volyanskyy}10_{, D. Voong}46_{, A. Vorobyev}30_{, V. Vorobyev}34_{, C. Voß}63_,

J.A. de Vries41, R. Waldi63, C. Wallace48, R. Wallace12, J. Walsh23, S. Wandernoth11, J. Wang59, D.R. Ward47, N.K. Watson45, D. Websdale53, M. Whitehead48, D. Wiedner11, G. Wilkinson55,38, M. Wilkinson59_{, M.P. Williams}45_{, M. Williams}56_{, H.W. Wilschut}66_{, F.F. Wilson}49_{, J. Wimberley}58_, J. Wishahi9_{, W. Wislicki}28_{, M. Witek}26_{, G. Wormser}7_{, S.A. Wotton}47_{, S. Wright}47_{, K. Wyllie}38_, Y. Xie61, Z. Xing59, Z. Xu39, Z. Yang3, X. Yuan3, O. Yushchenko35, M. Zangoli14,

M. Zavertyaev10,b_{, L. Zhang}3_{, W.C. Zhang}12_{, Y. Zhang}3_{, A. Zhelezov}11_{, A. Zhokhov}31_{, L. Zhong}3_.

1 _{Centro Brasileiro de Pesquisas F´ısicas (CBPF), Rio de Janeiro, Brazil} 2

Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

3

Center for High Energy Physics, Tsinghua University, Beijing, China

4 _{LAPP, Universit´e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France} 5

Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France

6

CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France

7 _{LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France} 8

LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France

9 _{Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany} 10

Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany

11

Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany

12 _{School of Physics, University College Dublin, Dublin, Ireland} 13

Sezione INFN di Bari, Bari, Italy

14

Sezione INFN di Bologna, Bologna, Italy

15 _{Sezione INFN di Cagliari, Cagliari, Italy} 16

Sezione INFN di Ferrara, Ferrara, Italy

17 _{Sezione INFN di Firenze, Firenze, Italy} 18

Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy

19

Sezione INFN di Genova, Genova, Italy

20 _{Sezione INFN di Milano Bicocca, Milano, Italy} 21

Sezione INFN di Milano, Milano, Italy

22

Sezione INFN di Padova, Padova, Italy

JHEP05(2015)019

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, Krak´ow, Poland} 27 _{AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science,}

Krak´ow, 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 F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland} 40

Physik-Institut, Universit¨at Z¨urich, Z¨urich, 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 _{Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated}

to2

JHEP05(2015)019

62 _{Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to}8

63 _{Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to} 11 64

National Research Centre Kurchatov Institute, Moscow, Russia, associated to31

65

Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to36

66

Van Swinderen Institute, University of Groningen, Groningen, The Netherlands, associated to 41

67

Celal Bayar University, Manisa, Turkey, associated to38

a

Universidade Federal do Triˆangulo Mineiro (UFTM), Uberaba-MG, Brazil

b

P.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia

c

Universit`a di Bari, Bari, Italy

d

Universit`a di Bologna, Bologna, Italy

e

Universit`a di Cagliari, Cagliari, Italy

f

Universit`a di Ferrara, Ferrara, Italy

g _{Universit`a di Firenze, Firenze, Italy</sub> h <sub>Universit`a di Urbino, Urbino, Italy}

i _{Universit`a di Modena e Reggio Emilia, Modena, Italy</sub> j <sub>Universit`a di Genova, Genova, Italy}

k _{Universit`a di Milano Bicocca, Milano, Italy</sub> l <sub>Universit`a di Roma Tor Vergata, Roma, Italy} m _{Universit`a di Roma La Sapienza, Roma, Italy}

n

Universit`a della Basilicata, Potenza, Italy

o

AGH - University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Krak´ow, Poland

p

LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

q

Hanoi University of Science, Hanoi, Viet Nam

r

Universit`a di Padova, Padova, Italy

s

Universit`a di Pisa, Pisa, Italy

t

Scuola Normale Superiore, Pisa, Italy

u

Universit`a degli Studi di Milano, Milano, Italy