2,254 research outputs found

### Factorization of the charge correlation function in $B^0\bar B^0$ oscillations

Extraction of the mass difference $\Delta m$ from $B^0\bar B^0$ oscillations
involves tagging of bottom flavour at production and at decay. We show that the
asymmetry between the unmixed and mixed events factorizes into two parts, one
depending on the production-tag and the other on the decay-tag.Comment: 6 pages, Latex, no figure

### B Mixing

The neutral $B$ mesons, $B^0$ and $B_s$, can oscillate between their particle
and antiparticle states owing to flavor-changing weak interactions. In recent
years, techniques to detect these oscillations as a function of the meson's
decay time have been developed. In this article the physics of flavor
oscillations is reviewed and theoretical predictions are summarized. The many
observations that demonstrate the time-dependence of B^0-\B0bar oscillations
are presented along with a combined measurement of its frequency, $\delta m_d$.
The attempts to measure the $B_s$ oscillation frequency, both directly and
indirectly, are then summarized. Finally, values for the CKM elements
$|V_{td}|$ and $|V_{ts}/V_{td}|$ are extracted

### ALEPH Tau Spectral Functions and QCD

Hadronic $\tau$ decays provide a clean laboratory for the precise study of
quantum chromodynamics (QCD). Observables based on the spectral functions of
hadronic $\tau$ decays can be related to QCD quark-level calculations to
determine fundamental quantities like the strong coupling constant, quark and
gluon condensates. Using the ALEPH spectral functions and branching ratios,
complemented by some other available measurements, and a revisited analysis of
the theoretical framework, the value \asm = 0.345 \pm 0.004_{\rm exp} \pm
0.009_{\rm th} is obtained. Taken together with the determination of \asZ from
the global electroweak fit, this result leads to the most accurate test of
asymptotic freedom: the value of the logarithmic slope of $\alpha_s^{-1}(s)$ is
found to agree with QCD at a precision of 4%. The value of \asZ obtained from
$\tau$ decays is \asZ = 0.1215 \pm 0.0004_{\rm exp} \pm 0.0010_{\rm th} \pm
0.0005_{\rm evol}
= 0.1215 \pm 0.0012.Comment: 14 pages, 5 figures, invited talk at the Tau06 International
Workshop, Pisa, September 19-22 200

### Measurement of the photon structure function at ALEPH

The photon structure function F2gamma has been measured with data taken by
the ALEPH collaboration at LEP centre-of-mass energies sqrt s = 91 GeV with <
Q^2 > of 9.9, 20.7 and 284 GeV^2 and sqrt s = 183 GeV with of 13.7 and
56.5 GeV^2. For the data at sqrt s = 183 GeV a two-dimensional unfolding method
employing the principle of maximum entropy is used, which reduces the errors
compared to one-dimensional methods.Comment: 5 pages, 5 figures, To be published in proceedings "PHOTON99

### Vector and Axial-Vector Spectral Functions and QCD

We present new results of the tau hadronic spectral function analysis using
data accumulated by the ALEPH detector at LEP during the years 1991-94. In
addition to the vector spectral functions, the axial-vector spectral functions
and, separately, the tau --> 3pi nu as well as the tau --> pi 2pi0 nu spectral
functions are determined from their respective unfolded, i.e., physical
invariant mass spectra. The spectral functions are applied to QCD chiral sum
rules in order to extract information about saturation at the tau mass scale.
Using the the semi-leptonic tau decay rate for vector and axial-vector currents
in addition to spectral moments, we obtain precise measurements of the strong
coupling constant alpha_s(M_tau) and the contributing non-perturbative power
terms. The evolution to the Z mass yields alpha_s(M_Z) = 0.1219 +/- 0.0019.Comment: 15 pages, 12 figures, LaTex, Talk given at the Fourth International
Workshop on Tau Lepton Physics (TAU96), Colorado, September 199

### Chiral-invariant CP-violating Effective Interactions in Z Decays to three Jets

Tests of CP violation by appropriate momentum correlations in $Z\to 3$ jets
and in particular in $Z\to b\bar bX$ probe CP-violating effective couplings --
that manifest themselves as form factors -- which conserve the quark chirality
and quark flavour. By giving two examples we show that such couplings can be
induced at one-loop order in extensions of the Standard Model with CP violation
beyond the Kobayashi-Maskawa phase. In one of the models we compute the
chirality-conserving part of the CP-violating $Zb{\bar b}$-gluon amplitude for
massless $b$ quarks, determine the resulting effective dimension $d=6$
couplings in the local limit, and discuss the possible size of the effects.
Finally we show that in models with excited quarks the chiral-invariant
CP-violating effective interactions could be quite large if appropriate
couplings are of a size characteristic of a strong interactionComment: 14 pages, LaTeX with 4 postscript figures, epsf macro include

### SVD Approach to Data Unfolding

Distributions measured in high energy physics experiments are usually
distorted and/or transformed by various detector effects. A regularization
method for unfolding these distributions is re-formulated in terms of the
Singular Value Decomposition (SVD) of the response matrix. A relatively simple,
yet quite efficient unfolding procedure is explained in detail. The concise
linear algorithm results in a straightforward implementation with full error
propagation, including the complete covariance matrix and its inverse. Several
improvements upon widely used procedures are proposed, and recommendations are
given how to simplify the task by the proper choice of the matrix. Ways of
determining the optimal value of the regularization parameter are suggested and
discussed, and several examples illustrating the use of the method are
presented.Comment: 22 page

### Nucleosynthesis constraints on heavy tau-neutrino in the presence of annihilations to majorons

We show that in the presence of sufficiently strong $\nu_\tau$ annihilations
to majorons, primordial nucleosynthesis constraints can not rule out any values
of the $\nu_\tau$ mass up the present laboratory limit.Comment: Talk given at TAUP 95, Toledo, Sept. 1995; 5 pages, LaTex file + 2
figures, all compressed by uufile

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