405 research outputs found
Exclusive rare B -> K*e+e- decays at low recoil: controlling the long-distance effects
We present a model-independent description of the exclusive rare decays B->
K* e+e- in the low recoil region (large lepton invariant mass q^2 ~ m_b^2). In
this region the long-distance effects from quark loops can be computed with the
help of an operator product expansion in 1/Q, with Q={m_b, \sqrt{q^2}}.
Nonperturbative effects up to and including terms suppressed by Lambda/Q and
mc^2/mb^2 relative to the short-distance amplitude can be included in a
model-independent way. Based on these results, we propose an improved method
for determining the CKM matrix element |V{ub}| from a combination of rare and
semileptonic B and D decays near the zero recoil point. The residual
theoretical uncertainty from long distance effects in this |V{ub}|
determination comes from terms in the OPE of order alpha_s(Q)\Lambda/mb,
alpha_s^2(Q), mc^4/mb^4$ and duality violations and is estimated to be below
10%.Comment: 21 pages RevTex, 2 figures; v3: extensive numerical changes in the
NLL analysis, with improved stability under scale dependence. Typos fixed,
version to appear in Phys.Rev.
Anatomy of beyond the Standard Model
We present for the first time a model-independent anatomy of the ratio
in the context of the effective
theory with operators invariant under QCD and QED and in the context of the
Standard Model Effective Field Theory (SMEFT) with the operators invariant
under the full SM gauge group. Our goal is to identify the new physics
scenarios that are probed by this ratio and which could help to explain a
possible deviation from the SM that is hinted by the data. To this end we
derive a master formula for , which can be applied to
any theory beyond the Standard Model (BSM) in which the Wilson coefficients of
all contributing operators have been calculated at the electroweak scale. The
relevant hadronic matrix elements of BSM operators are from the Dual QCD
approach and the SM ones from lattice QCD. Within SMEFT, the constraints from
and mixing as well as electric dipole moments limit significantly
potential new physics contributions to . Correlations
of with decays are briefly
discussed. Building on our EFT analysis and the model-independent constraints,
we discuss implications of a possible deviation from the SM in
for model building, highlighting the role of the new
scalar and tensor matrix elements in models with scalar mediators.Comment: 47 pages, 4 figures. v3: signs in tables 6-10 corrected, numerical
results and conclusions unchange
Cornering New Physics in b --> s Transitions
We derive constraints on Wilson coefficients of dimension-six effective
operators probing the b --> s transition, using recent improved measurements of
the rare decays Bs --> mu+mu-, B --> K mu+mu- and B --> K* mu+mu- and including
all relevant observables in inclusive and exclusive decays. We consider
operators present in the SM as well as their chirality-flipped counterparts and
scalar operators. We find good agreement with the SM expectations. Compared to
the situation before winter 2012, we find significantly more stringent
constraints on the chirality-flipped coefficients due to complementary
constraints from B --> K mu+mu- and B --> K* mu+mu- and due to the LHCb
measurement of the angular observable S_3 in the latter decay. We also list the
full set of observables sensitive to new physics in the low recoil region of B
--> K* mu+mu-.Comment: 18 pages, 6 figures, 4 tables. v3: typos correcte
Complete Anatomy of B -> K*ll and its angular distribution
We present a complete and optimal set of observables for the exclusive 4-body
B meson decay B -> K*(->K pi) l+l- in the low dilepton mass region, that
contains a maximal number of clean observables. This basis of observables is
built in a systematic way. We show that all the previously defined observables
and any observable that one can construct, can be expressed as a function of
this basis. This set of observables contains all the information that can be
extracted from the angular distribution in the cleanest possible way. We
provide explicit expressions for the full and the uniangular distributions in
terms of this basis. The conclusions presented here can be easily extended to
the large-q^2 region. We study the sensitivity of the observables to
right-handed currents and scalars. Finally, we present for the first time all
the symmetries of the full distribution including massive terms and scalar
contributions.Comment: 37 pages, 12 Figures. Corrected typo in Eqs. (29) and (44). Results
and conclusions unchange
Bayesian Fit of Exclusive Decays: The Standard Model Operator Basis
We perform a model-independent fit of the short-distance couplings
within the Standard Model set of and operators. Our analysis of , and decays is the first to harness the full
power of the Bayesian approach: all major sources of theory uncertainty
explicitly enter as nuisance parameters. Exploiting the latest measurements,
the fit reveals a flipped-sign solution in addition to a Standard-Model-like
solution for the couplings . Each solution contains about half of the
posterior probability, and both have nearly equal goodness of fit. The Standard
Model prediction is close to the best-fit point. No New Physics contributions
are necessary to describe the current data. Benefitting from the improved
posterior knowledge of the nuisance parameters, we predict ranges for currently
unmeasured, optimized observables in the angular distributions of .Comment: 42 pages, 8 figures; v2: Using new lattice input for f_Bs,
considering Bs-mixing effects in BR[B_s->ll]. Main results and conclusion
unchanged, matches journal versio
Supersymmetric constraints from Bs -> mu+mu- and B -> K* mu+mu- observables
We study the implications of the recent LHCb limit and results on Bs ->
mu+mu- and B -> K* mu+mu- observables in the constrained SUSY scenarios. After
discussing the Standard Model predictions and carefully estimating the
theoretical errors, we show the constraining power of these observables in
CMSSM and NUHM. The latest limit on BR(Bs -> mu+mu-), being very close to the
SM prediction, constrains strongly the large tan(beta) regime and we show that
the various angular observables from B -> K* mu+mu- decay can provide
complementary information in particular for moderate tan(beta) values.Comment: 30 pages, 14 figure
The Benefits of B ---> K* l+ l- Decays at Low Recoil
Using the heavy quark effective theory framework put forward by Grinstein and
Pirjol we work out predictions for B -> K* l+ l-, l = (e, mu), decays for a
softly recoiling K*, i.e., for large dilepton masses sqrt{q^2} of the order of
the b-quark mass m_b. We work to lowest order in Lambda/Q, where Q = (m_b,
sqrt{q^2}) and include the next-to-leading order corrections from the charm
quark mass m_c and the strong coupling at O(m_c^2/Q^2, alpha_s). The leading
Lambda/m_b corrections are parametrically suppressed. The improved Isgur-Wise
form factor relations correlate the B -> K* l+ l- transversity amplitudes,
which simplifies the description of the various decay observables and provides
opportunities for the extraction of the electroweak short distance couplings.
We propose new angular observables which have very small hadronic
uncertainties. We exploit existing data on B -> K* l+ l- distributions and show
that the low recoil region provides powerful additional information to the
large recoil one. We find disjoint best-fit solutions, which include the
Standard Model, but also beyond-the-Standard Model ones. This ambiguity can be
accessed with future precision measurements.Comment: 31 pages, 8 figures; Instability near minimal recoil from numerics
removed, Fig. 1 replaced and minor shifts in short distance uncertainties in
SM predictions; typos corrected and references added; main results and
conclusions unchange
in the Two Higgs Doublet Model up to Next-to-Next-to-Leading Order in QCD
We compute three-loop matching corrections to the Wilson coefficients
and in the Two Higgs Doublet Model by applying expansions for small,
intermediate and large charged Higgs boson masses. The results are used to
evaluate the branching ratio of to next-to-next-to
leading order accuracy, and to determine an updated lower limit on the charged
Higgs boson mass. We find \mhplus \ge 380 GeV at 95% confidence level when
the recently completed BABAR data analysis is taken into account. Our results
for the charged Higgs contribution to the branching ratio exhibit considerably
weaker sensitivity to the matching scale , as compared to previous
calculations.Comment: 20 pages, 15 figures; v2: minor modifications, matches published
version in JHE
Angular analysis of B --> V (--> P_1 P_2) l^+ l^- decays
The angular analysis of exclusive rare B-meson decays via intermediate vector
mesons V into 4-body final states of two pseudo-scalars P_1, P_2 and a pair of
light leptons l = e, mu offers a large set of observables. They can be used to
test the electroweak short-distance couplings in the Standard Model and to
search for New Physics. The two kinematic regions of low and high dilepton mass
depend on short-distance physics in complementary ways and can be expanded in
powers of Lambda_QCD/m_b. These expansions guide towards suitable combinations
of observables allowing to i) reduce the hadronic uncertainties in the
extraction of the short-distance couplings or ii) test the lattice QCD (B -> V)
form factors in short-distance independent combinations. Several such
possibilities of CP-averaged and CP-asymmetric (T-even and T-odd) quantities
are presented for B_d^0 --> K^*0 (-> K pi) l^+ l^- and time-integrated
CP-asymmetries without tagging for (anti-B_s, B_s) --> phi (--> K^- K^+) l^+
l^- decays in view of the latest B-factory and CDF results and the forthcoming
LHCb measurements.Comment: 9 pages, 4 figures; Talk given at Discrete '10: Symposium on
Prospects in the Physics of Discrete Symmetries, Rome, Italy, 6-11 Dec 201
- …