In the last ten years, there has been great progress in calculations of decays of
B
and
D
mesons, and baryons containing a heavy
b
or
c
quark. One propelling factor has been the measurement of ...several anomalies in
b
→
s
and
b
→
c
transitions, these are one of the only signs of physics beyond the Standard Model. The deviations included measurements of branching ratios, angular observables and lepton universality ratios. Another factor is the exclusive-inclusive discrepancy in the determination of the CKM elements
V
ub
and
V
cb
. We will first review recent calculations involving
b
→
s
and
c
→
u
transitions that could shed light on the neutral current anomalies. We will then summarise the progress the determination of the CKM elements,
V
ub
and
V
cb
. Finally we will discuss the current theoretical status and experimental prospects for the lepton universality ratios in
b
→
s
and
b
→
c
semileptonic decays.
By analyzing 2.93 fb−1 data collected at the center-of-mass energy with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D+ → K̅0 e+νe to be ℬ(D+ → K̅0 e+νe) ...= (8.59 ± 0.14 ± 0.21)% using , where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties..
By analyzing 2.93 fb(-1) data collected at the center-of-mass energy root s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D+ -> (K) ...over bar (0)e(+)nu(e) to be B(D (+) -> (K) over bar (0)e(+)nu(e)) = (8.59 +/- 0.14 +/- 0.21)% using (K) over bar (0) -> K-S(0) -> pi(0) pi(0), where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties..
We use three-flavour hard pion Chiral Perturbation Theory (HPChPT) in both the heavy meson and a relativistic formulation to calculate the chiral logarithms
m
2
log
(
m
2
/
μ
2
)
contributing to the ...formfactors of the
B
(
s
)
→
π
,
K
,
η
and
D
(
s
)
→
π
,
K
,
η
transitions at momentum transfer
q
2
away from the endpoint
q
max
2
=
(
m
B
−
m
M
)
2
. We compare our results with CLEO
D
→
π
and
D
→
K
data. We also calculate the Isgur–Wise function of the
B
(
s
)
→
D
(
s
)
semileptonic decay away from the endpoint and the chiral logarithms for the pion and kaon electromagnetic formfactor.
In two-flavour HPChPT we calculate the chiral logarithms for the pion vector and the scalar formfactors at
s
≫
m
π
2
. This allows us to test hard pion ChPT using the existing two-loop calculations for these quantities.
Rare B meson decays mediated by flavour changing neutral current (FCNC) transition play interesting role to probe the flavour sector of the standard model (SM). Generally at the tree level, FCNC ...processes are not allowed in the SM but occurs at the loop levels. This gives an excellent hunting ground for new physics (NP). From various experimental studies it is found that the FCNC processes having quark level transition
b
→
s
are challenging. Here, we investigate different kinematic observables like forward-backward asymmetry, differential branching ratio and lepton polarization asymmetry for semileptonic rare B decay modes
B
s
→
φl
+
l
−
and
B
+
→
K
+
l
+
l
−
(
l
=
μ
,
τ
) considering the contribution of Z-mediated FCNC. A noticeable deviation of the observables for these decay channels from the SM value is found because of non-universal
Z
−
bs
coupling.
Like the two-photon and two-gluon decays of the P-wave charmonium state for which the Born term produces a very simple decays amplitude, the Born term for the processes cd‾→(π,K)ℓν and bd‾→(π,K)ℓν, ...could also produce a simple expression for D and B meson semileptonic decays with a light meson π, K in the final state. The pole term at q2=mB2+mπ2 for B → π and at q2=mD2+mK2 for D → K form factor, are generated by the Born term and given as: f+(0)/(1−q2/(mH2+mπ2)), with H = D, B for D, B → π form factors, and f+(0)/(1−q2/(mH2+mK2)) for B, D → K form factor. These pole dominance terms describe rather well the q2-behavior of the form factors observed in the BaBar, Belle and BESIII measurements and in lattice simulation. In particular, the D → K form factors are in good agreement with the measured values in the whole range of q2 showing evidence for S U(3) breaking with the presence of the mK2 term in the quark propagator, but some corrections to the Born term are needed at large q2 for D, B → π form factors.
Flavor Changing Neutral Current transitions b→sγ and b→sl+l− provide an excellent laboratory for the search for physics beyond the Standard Model. Standard Model tests are performed through ...measurements of the B→Xsl+l− branching ratio, the B→Xsl+l− and B→Xsγ direct CP asymmetries, and the B0→Ks0π−π+γ time-dependent CP asymmetry.
Strong constraints on the (tanβ,mH+) plane in the two-Higgs doublet models scenario are obtained from the measurements of the B+→τ+ν branching ratio and of the branching fractions ratio R(D(⁎))=B(B¯→D(⁎)τ−ντ¯)/B(B¯→D(⁎)l−νl¯), where l refers to either an electron or a muon.
A direct CP asymmetry in inclusive semileptonic B(s) decays vanishes by CPT to lowest order in weak interactions. Calculating the asymmetry at second-order-weak interactions in the ...Cabibbo–Kobayashi–Maskawa framework we find Asl=(−3.2±0.9)×10−9. A maximal asymmetry which is two orders of magnitude larger is estimated in a left–right-symmetric model. This quite generic upper bound implies negligible effects on wrong-sign lepton asymmetries in B0 and Bs decays.
Measurement of Kμ30 form factors Lai, A.; Marras, D.; Bevan, A. ...
Physics letters. B,
04/2007, Letnik:
647, Številka:
5-6
Journal Article
Recenzirano
This Letter reports on a new high precision measurement of the form factors of the KL→π±μ∓νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. ...Studying the Dalitz plot density we measured a linear, λ+′=(20.5±2.2stat±2.4syst)×10−3, and a quadratic, λ+″=(2.6±0.9stat±1.0syst)×10−3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0=(9.5±1.1stat±0.8syst)×10−3. Using a linear fit our results were: λ+=(26.7±0.6stat±0.8syst)×10−3 and λ0=(11.7±0.7stat±1.0syst)×10−3. A pole fit of the form factors yields: mV=(905±9stat±17syst) MeV/c2 and mS=(1400±46stat±53syst) MeV/c2.
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