5,052 research outputs found
1/f noise of Josephson-junction-embedded microwave resonators at single photon energies and millikelvin temperatures
We present measurements of 1/f frequency noise in both linear and
Josephson-junction-embedded superconducting aluminum resonators in the low
power, low temperature regime - typical operating conditions for
superconducting qubits. The addition of the Josephson junction does not result
in additional frequency noise, thereby placing an upper limit for fractional
critical current fluctuations of (Hz) at 1 Hz for
sub-micron, shadow evaporated junctions. These values imply a minimum dephasing
time for a superconducting qubit due to critical current noise of 40 -- 1400
s depending on qubit architecture. Occasionally, at temperatures above 50
mK, we observe the activation of individual fluctuators which increase the
level of noise significantly and exhibit Lorentzian spectra
Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut
We compute the first two moments of the final hadronic invariant mass in
inclusive semileptonic B decay, in the presence of a cut on the charged lepton
energy. These moments may be measured directly by experiments at the
Upsilon(4S) using the neutrino reconstruction technique, which requires such a
cut. Measurement of these moments will place constraints on the nonperturbative
parameters \bar\Lambda and \lambda_1, which are relevant for extracting the
quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of
order \alpha_s^2\beta_0 and 1/m_b^3 in the operator product expansion, and use
the latter to estimate the theoretical uncertainty in the extraction of
\bar\Lambda and \lambda_1.Comment: 13 pages, 5 figures, REVTe
1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-
Using a known result by Falk et al. for the 1/m_b^2 correction to the
dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we
calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry
in this decay. Employing an up-to-date range of values for the non-perturbative
parameter \lambda_1, we find that the correction is much smaller than it should
have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear
in Physical Review D. The complete postscript file is also available from URL
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g
Conclusions from CDF Results on CP Violation in D^0 \to \pi^+\pi^-, K^+K^- and Future Tasks
Within the Standard Model (SM) one predicts both direct and indirect CP
violation in D^0 \to \pi^+\pi^-, K^+K^- transitions, although the effects are
tiny: Indirect CP asymmetry cannot exceed O(10^{-4}), probably even O(10^{-5});
direct effects are estimated at not larger than 10^{-4}. At B factories direct
and indirect asymmetries have been studied with /\tau_{D^0} ~ 1; no CP
asymmetry was found with an upper bound of about 1%. CDF has shown intriguing
data on CP violation in D^0 \to \pi^+\pi^- [K^+K^-] with /\tau_{D^0} ~ 2.4
[2.65]. Also, CDF has not seen any CP violation. For direct CP asymmetry, CDF
has a sensitivity similar to the combination of the B factories, yet for
indirect CP violation it yields a significantly smaller sensitivity of
a_{cp}^{ind}=(-0.01 +- 0.06_{stat} +- 0.05_{syst})% due to it being based on
longer decay times. New Physics models (NP) like Little Higgs Models with
T-Parity (LHT) can produce an indirect CP asymmetry up to 1%; CDF's findings
thus cover the upper range of realistic NP predictions ~ 0.1 - 1%. One hopes
that LHCb and a Super-Flavour Factory will probe the lower range down to
~0.01%. Such non-ad-hoc NP like LHT cannot enhance direct CP violation
significantly over the SM level in D^0 \to \pi^+\pi^-, K^+K^- and D^{\pm} \to
\pi^{\pm}K^+K^- transitions, but others might well do so.Comment: 11 pages, 1 figure. V2 has minor corrections and corresponds to the
published versio
- …