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Transcript of Averages of b-hadron, c-hadron, and -lepton ific.uv.es/~oyangur/tempo/ Averages of b-hadron,...

  • Averages of b-hadron, c-hadron, and τ -lepton properties as of summer 2016

    Heavy Flavor Averaging Group (HFAG):

    N. Body1

    1Authors will be de�ned later

    May 22, 2017

    Abstract

    This article reports world averages of measurements of b-hadron, c-hadron, and τ -lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through summer 2016. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays and CKM matrix elements.

    1

  • Contents

    1 Introduction 3

    2 D decays 5 2.1 Interplay of direct and indirect CP violation . . . . . . . . . . . . . . . . . . . . 6 2.2 Semileptonic decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

    2.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2 D→P`ν` decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.3 Form factor parameterizations . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.4 Simple pole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.5 z expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.6 Three-pole formalism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.7 Experimental techniques and results . . . . . . . . . . . . . . . . . . . . 12 2.2.8 Combined results for the D → K`ν` channel . . . . . . . . . . . . . . . . 14 2.2.9 Combined results for the D → π`ν` channel . . . . . . . . . . . . . . . . 16 2.2.10 Vcs and Vcd determination . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.11 D→V `ν` decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.2.12 Form factor measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 21

    2.3 Excited D(s) mesons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.4 Rare and forbidden decays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

    References 44

    2

  • 1 Introduction

    Flavor dynamics is an important element in understanding the nature of particle physics. The accurate knowledge of properties of heavy �avor hadrons, especially b hadrons, plays an essential role for determining the elements of the Cabibbo-Kobayashi-Maskawa (CKM) weak-mixing matrix [1,2]. The operation of the Belle and BABAR e+e− B factory experiments led to a large increase in the size of available B-meson, D-hadron and τ -lepton samples, enabling dramatic improvement in the accuracies of related measurements. The CDF and D0 experiments at the Fermilab Tevatron have also provided important results in heavy �avour physics, most notably in the B0s sector. In the D-meson sector, the dedicated e

    +e− charm factory experiments CLEOc and BESIII have made signi�cant contributions. Run I of the CERN Large Hadron Collider delivered high luminosity, enabling the collection of even higher statistics samples of b and c hadrons, and thus a further leap in precision in many areas, at the ATLAS, CMS, and (especially) LHCb experiments. With the LHC Run II ongoing, further improvements are keenly anticipated.

    The Heavy Flavor Averaging Group (HFAG) was formed in 2002 to continue the activities of the LEP Heavy Flavor Steering group [3]. This group was responsible for calculating averages of measurements of b-�avor related quantities. HFAG has evolved since its inception and currently consists of seven subgroups:

    • the �B Lifetime and Oscillations� subgroup provides averages for b-hadron lifetimes, b- hadron fractions in Υ (4S) decay and pp or pp collisions, and various parameters governing B0-B0 and Bs�B

    0 s mixing;

    • the �Unitarity Triangle Parameters� subgroup provides averages for time-dependent CP asymmetry parameters and studies of B → DK decays, and resulting determinations of the angles of the CKM unitarity triangle;

    • the �Semileptonic B Decays� subgroup provides averages for inclusive and exclusive B- decay branching fractions, and subsequent determinations of the CKM matrix elements |Vcb| and |Vub|;

    • the �B to Charm Decays� subgroup provides averages of branching fractions for B decays to �nal states involving open charm or charmonium mesons;

    • the �Rare Decays� subgroup provides averages of branching fractions and CP asymmetries for charmless, radiative, leptonic, and baryonic B-meson and b-baryon decays;

    • the �Charm Physics� subgroup provides averages of numerous quantities in the charm sector, including branching fractions properties of charm baryons and of excited D∗∗ and DsJ mesons, averages of D

    0-D0 mixing and CP and T violation parameters, and an average value for the Ds decay constant fDs .

    • the �Tau Physics� subgroup provides documentation and averages for a selection of τ lepton quantities that most pro�t from the adoption of the HFAG prescriptions. In particular, the τ lepton branching fractions, uncertainties and correlations are obtained from a global �t of the experimental results, and this information is further elaborated to compute several lepton universality tests and the CKM matrix element |Vus|. The

    3

  • τ lepton-�avor-violating decays are documented and combinations of upper limits are computed.

    The �Lifetime and Oscillations� and �Semileptonic� subgroups were formed from the merger of four LEP working groups. The �Unitary Triangle,� �B to Charm Decays,� and �Rare De- cays� subgroups were formed to provide averages for new results obtained from the B factory experiments (and now also from the Fermilab Tevatron and CERN LHC experiments). The �Charm� and �Tau� subgroups were formed more recently in response to the wealth of new data concerning D and τ physics. Subgroups typically include representatives from Belle, BABAR and LHCb, plus, when relevant, CLEO, CDF and D0.

    This article is an update of the last HFAG preprint, which used results available at least through early 2012 [4]. Here we report world averages using results available at least through summer 2014. In some cases results made available in the latter part of 2014 have been in- cluded.1 In general, we use all publicly available results that have written documentation. These include preliminary results presented at conferences or workshops. However, we do not use preliminary results that remain unpublished for an extended period of time, or for which no publication is planned. Close contacts have been established between representatives from the experiments and members of subgroups that perform averaging to ensure that the data are prepared in a form suitable for combinations.

    In the case of obtaining a world average for which χ2/dof > 1, where dof is the number of degrees of freedom in the average calculation, we do not usually scale the resulting error, as is presently done by the Particle Data Group [5]. Rather, we examine the systematics of each measurement to better understand them. Unless we �nd possible systematic discrepancies between the measurements, we do not apply any additional correction to the calculated error. We provide the con�dence level of the �t as an indicator for the consistency of the measurements included in the average. In case some special treatment was necessary to calculate an average, or if an approximation used in an average calculation might not be su�ciently accurate (e.g., assuming Gaussian errors when the likelihood function indicates non-Gaussian behavior), we include a warning message.

    Chapter ?? describes the methodology used for calculating averages. In the averaging procedure, common input parameters used in the various analyses are adjusted (rescaled) to common values, and, where possible, known correlations are taken into account. Chapters ??� ?? present world average values from each of the subgroups listed above. A brief summary of the averages presented is given in Chapter ??. A complete listing of the averages and plots, including updates since this document was prepared, are also available on the HFAG web site:

    http://www.slac.stanford.edu/xorg/hfag

    1* Particularly important new results have been included whenever possible. The precise cut-o� date for including results in the averages varies between subgroups.

    4

    http://www.slac.stanford.edu/xorg/hfag

  • 2 D decays

    5

  • 2.1 Interplay of direct and indirect CP violation

    In decays of D0 mesons, CP asymmetry measurements have contributions from both direct and indirect CP violation as discussed in Sec. ??. The contribution from indirect CP viola- tion depends on the decay-time distribution of the data sample [6]. This section describes a combination of measurements that allows the extraction of the individual contributions of the two types of CP violation. At the same time, the level of agreement for a no-CP -violation hypothesis is tested. The observables are:

    AΓ ≡ τ(D 0→h+h−)− τ(D0→h+h−) τ(D 0→h+h−) + τ(D0→h+h−)

    , (1)

    where h+h− can be K+K− or π+π−, and

    ∆ACP ≡ ACP(K+K−)− ACP(π+π−), (2)

    where ACP are time-integrated CP asymmetries. The underlying theoretical parameters are:

    adirCP ≡ |AD0→f |2 − |AD 0→f |2

    |AD0→f |2 + |AD 0→f |2 ,

    aindCP ≡ 1

    2

    [(∣∣∣∣qp ∣∣∣∣+ ∣∣∣∣pq

    ∣∣∣∣)x sinφ