2,857 research outputs found

### Extracting |V_{ub}| from the Hadronic Mass Spectrum of Inclusive B decays

Following a strategy introduced earlier by the authors, we show that it is
possible to extract |V_{ub}| from the cut hadronic mass spectrum of B decays
without large systematic errors which usually arise from having to model the
Fermi motion of the heavy quark. We present a closed form expression for
|V_{ub}|/|V_{ts}| which is accurate up to corrections of order \alpha_s^2,
\alpha_s \rho, (\Lambda/m_b)^2/\rho, where \rho is the experimental cut
(s_c/m_b^2) on the hadronic mass used to veto charmed decays. Modulo duality
violation errors, which are intrinsic to all inclusive predictions, we estimate
the theoretical error in the extraction to be at the 5% level.Comment: 11 pages, 1 figur

### A Comment on the Extractions of V_{ub} from Radiative Decays

We present a model independent closed form expression for |V_{ub}|^2/|V_{tb}
V_{ts}^*|^2, which includes the resummation of large endpoint logarithms as
well as the interference effects from the operators $O_2$ and $O_8$. We
demonstrate that the method to extract |V_{ub}| presented by the authors in
hep-ph/9909404, and modified in this letter to include interference effects, is
not just a refinement of the method introduced in hep-ph/9312311. We also
discuss the model dependence of the latter proposal. Furthermore, we show that
the resummation is not negligible and that the Landau pole does not introduce
any significant uncertainties.Comment: 10 pages, 3 figures; one figure added, one reference added, expanded
discussion

### Enhanced subleading structure functions in semileptonic B decay

The charged lepton spectrum in semileptonic $B\to X_u \ell\bar\nu$ decay near
maximal lepton energy receives important corrections from subleading structure
functions that are formally suppressed by powers of $\Lambda_{QCD}/m_b$ but are
enhanced by numerical factors. We investigate the series of higher order terms
which smear over a region of width $\Delta E_\ell \sim \Lambda_{QCD}$ near the
endpoint the contributions proportional to $\delta(E_\ell - m_b/2)$ times (i)
the matrix element of the chromomagnetic operator, and (ii) four-quark
operators. These contribute to the total rate at the few percent level, but
affect the endpoint region much more significantly. Implications for the
determination of $|V_{ub}|$ are discussed.Comment: 12 page

### $1/f^{\beta}$ noise for scale-invariant processes: How long you wait matters

We study the power spectrum which is estimated from a nonstationary signal.
In particular we examine the case when the signal is observed in a measurement
time window $[t_w,t_w+t_m]$, namely the observation started after a waiting
time $t_w$, and $t_m$ is the measurement duration. We introduce a generalized
aging Wiener-Khinchin theorem which relates between the spectrum and the time-
and ensemble-averaged correlation function for arbitrary $t_m$ and $t_w$.
Furthermore we provide a general relation between the non-analytical behavior
of the scale-invariant correlation function and the aging $1/f^{\beta}$ noise.
We illustrate our general results with two-state renewal models with sojourn
times' distributions having a broad tail

### Mutual Enrichment in Ranked Lists and the Statistical Assessment of Position Weight Matrix Motifs

Statistics in ranked lists is important in analyzing molecular biology
measurement data, such as ChIP-seq, which yields ranked lists of genomic
sequences. State of the art methods study fixed motifs in ranked lists. More
flexible models such as position weight matrix (PWM) motifs are not addressed
in this context. To assess the enrichment of a PWM motif in a ranked list we
use a PWM induced second ranking on the same set of elements. Possible orders
of one ranked list relative to the other are modeled by permutations. Due to
sample space complexity, it is difficult to characterize tail distributions in
the group of permutations. In this paper we develop tight upper bounds on tail
distributions of the size of the intersection of the top of two uniformly and
independently drawn permutations and demonstrate advantages of this approach
using our software implementation, mmHG-Finder, to study PWMs in several
datasets.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013

### Semileptonic Lambda_b decay to excited Lambda_c baryons at order Lambda_{QCD}/m_Q

Exclusive semileptonic Lambda_b decays to excited charmed Lambda_c baryons
are investigated at order Lambda_{QCD}/m_Q in the heavy quark effective theory.
The differential decay rates are analyzed for the J^\pi=1/2^- Lambda_c(2593)
and the J^\pi=3/2^- \Lambda_c(2625). They receive 1/m_{c,b} corrections at zero
recoil that are determined by mass splittings and the leading order Isgur-Wise
function. With some assumptions, we find that the branching fraction for
Lambda_b decays to these states is 2.5-3.3%. The decay rate to the helicity \pm
3/2 states, which vanishes for m_Q \to \infty, remains small at order
Lambda_{QCD}/m_Q since 1/m_c corrections do not contribute. Matrix elements of
weak currents between a Lambda_b and other excited Lambda_c states are analyzed
at zero-recoil to order Lambda_{QCD}/m_Q. Applications to baryonic heavy quark
sum-rules are explored.Comment: 27 pages, 1 fig., minor changes, version to appear in Phys.Rev.

- â€¦