92 research outputs found
Factorization in B -> K pi e+e- decays
We derive factorization relations for the transverse helicity amplitudes in
the rare decays B-> K\pi l+l- at leading order in Lambda/m_b, in the
kinematical region with an energetic kaon and a soft pion. We identify and
compute a new contribution of leading order in Lambda/m_b to the B->K\pi l+l-
amplitude, which is not present in the one-body decay B-> K*l+l-. As an
application we study the forward-backward asymmetry (FBA) of the lepton
momentum angular distribution in B-> K\pi l+l- decays away from the K*
resonance. The FBA in these decays has a zero at q0^2 = q0^2(M_{Kpi}), which
can be used, in principle, for determining the Wilson coefficients C_{7,9} and
testing the Standard Model. We point out that the slope of the q0^2(M_{Kpi}^2)
curve contains the same information about the Wilson coefficients as the
location of the zero, but is less sensitive to unknown nonperturbative
dynamics. We estimate the location of the zero at leading order in
factorization, and using a resonant model for the B -> K\pi l+l-
nonfactorizable amplitude.Comment: 16 pages, 5 figures. Version to appear in Physical Review D. One new
observable introduced and considered - the slope of the zero of the
forward-backward asymmetry as function of the K\pi invariant mas
Factorization in exclusive semileptonic radiative B decays
We derive a new factorization relation for the semileptonic radiative decay B
-> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda
and an energetic photon E_\gamma >> \Lambda, working at leading order in
\Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element
appearing in this relation can be computed using chiral perturbation theory. We
present a phenomenological study of this decay, which may be important for a
precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde
The CP asymmetry in B^0(t) -> K_S \pi^0 \gamma in the Standard Model
The time-dependent CP asymmetry in exclusive B^0(t) -> K^{*0}\gamma decays
has been proposed as a probe of new physics in B decays. Recently, this method
was extended to radiative decays into multibody hadronic final states such as
B^0(t)-> K_S\pi^0\gamma and B^0(t)-> \pi^+\pi^-\gamma. The CP asymmetry in
these decays vanishes to the extent that the photon is completely polarized. In
the Standard Model, the photon emitted in b-> s\gamma has high left-handed
polarization, but right-handed contamination enters already at leading order in
\Lambda/m_b even for vanishing light quark masses. We compute here the
magnitude of this effect and the time dependent CP asymmetry parameter S_{K_S
\pi^0\gamma}. We find that the Standard Model can easily accomodate values of S
as large as 10%, but a precise value cannot be obtained at present because of
strong interactions uncertainties.Comment: 11 pages, 4 figures. Final version to appear in Physical Review
Subleading corrections to the V_ub determination from exclusive B decays
It has been proposed to determine the CKM matrix element |V_ub| in a
model-independent way from a combination of rare and semileptonic B and D
decays near the zero recoil point. An essential ingredient in such a
determination is a heavy quark symmetry relation connecting the form-factors
appearing in B -> K* e+e- to semileptonic form factors relevant for B -> rho
e\nu. We estimate the leading corrections to this symmetry relation, of order
\alpha_s(m_b) and \Lambda/m_b, pointing out that they can be as large as 20%,
depending on the value of the matrix element of a dimension-4 operator.
Dimensional analysis estimates of this matrix element give a corresponding
uncertainty in |V_ub| of the order of a few percent.Comment: 8 page
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.
Chiral symmetry and exclusive B decays in the SCET
We describe a chiral formalism for processes involving both energetic hadrons
and soft Goldstone bosons, which extends the application of soft-collinear
effective theory to multibody B decays. The nonfactorizable helicity amplitudes
for heavy meson decays into multibody final states satisfy symmetry relations
analogous to the large energy form factor relations, which are broken at
leading order in Lambda/mb by calculable factorizable terms. We use the chiral
effective theory to compute the leading corrections to these symmetry relations
in B -> M_n pi ell\bar\nu and B -> M_n pi e+e- decays.Comment: 6 pages, 1 figure; typos correcte
Refund to Savings (R2S): Insight From the Field, 2012
Refund to Savings (R2S): Insight From the Field, 201
COVID-19 Educational Inequities: Shining a Light on Disparities in a Graduate School of Social Work
In the wake of COVID-19, universities and schools of social work face unprecedented challenges and uncertainty in aligning their academic models with public heath protocols and best practices, while prioritizing the safety and well-being of their students. In order to best respond to these challenges and uncertainty, more research is needed to advance a greater understanding of (1) what challenges students face, (2) who is most at risk and impacted by these challenges, and (3) how universities can best support students. Through a survey administered during the spring 2020 semester at a large research university in the Midwest, we explored the attitudes, experiences, and needs of graduate students in social work, public health, and social policy programs. We observed notable disparities by race and ethnicity, international student status, first-generation student status, and gender. Additionally, our survey results suggest that protective factors, such as university and social supports, may inform how students navigate and cope with the challenges related to or exacerbated by the pandemic. In addition to advancing a better understanding of student experiences during COVID-19, our findings build on the previous research that highlights the distinct needs and disparate impacts of vulnerable student populations in higher education.
Acknowledgements: An original survey instrument was created at Hebrew University and was modified and shared openly with other interested Universities
The photon polarization in B -> X gamma in the standard model
The standard model prediction for the decay amplitude
with a right-handed photon is believed to be tiny, suppressed by ,
compared to the amplitude with a left-handed photon. We show that this
suppression is fictitious: in inclusive decays, the ratio of these two
amplitudes is only suppressed by , and in exclusive decays by
. The suppression is not stronger in decays
than it is in . We estimate that the time dependent CP
asymmetries in , , , and
are of order 0.1 and that they have significant
uncertainties.Comment: Clarifications in the exclusive section, references adde
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