2,590 research outputs found
Measurement of B(t->Wb)/B(t->Wq) at the Collider Detector at Fermilab
We present a measurement of the ratio of top-quark branching fractions R= B(t
-> Wb)/B(t -> Wq), where q can be a b, s or a d quark, using lepton-plus-jets
and dilepton data sets with integrated luminosity of ~162 pb^{-1} collected
with the Collider Detector at Fermilab during Run II of the Tevatron. The
measurement is derived from the relative numbers of t-tbar events with
different multiplicity of identified secondary vertices. We set a lower limit
of R > 0.61 at 95% confidence level.Comment: 7 pages, 2 figures, published in Physical Review Letters; changes
made to be consistent with published versio
Hot spots and waves in Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks -a study by Low Temperature Scanning Laser Microscopy
Recently, it has been shown that large stacks of intrinsic Josephson
junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization
presumably triggered by a cavity resonance. To investigate this effect we use
Low Temperature Scanning Laser Microscopy to image electric field
distributions. Apart from verifying the appearance of cavity modes at low bias
we find that, in a high input power regime, standing-wave patterns are created
through interactions with a hot spot, possibly pointing to a new mode of
generating synchronized radiation in intrinsic Josephson junction stacks.Comment: 6 pages, 5 figures, supplementary information include
Local SiC photoluminescence evidence of non-mutualistic hot spot formation and sub-THz coherent emission from a rectangular BiSrCaCuO mesa
From the photoluminescence of SiC microcrystals uniformly covering a
rectangular mesa of the high transition temperature superconductor
BiSrCaCuO, the local surface temperature
was directly measured during simultaneous sub-THz emission from the
intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents and
low bath temperatures K, the center of a large
elliptical hot spot with jumps dramatically with little
current-voltage characteristic changes. The hot spot doesn't alter the
ubiquitous primary and secondary emission conditions: the ac Josephson relation
and the electromagnetic cavity resonance excitation, respectively. Since the
intense sub-THz emission was observed for high K in
the low bias regime where hot spots are absent, hot spots can not provide
the primary mechanisms for increasing the output power, the tunability, or for
promoting the synchronization of the IJJs for the sub-THz emission, but can
at best coexist non-mutualistically with the emission. No standing
waves were observed
Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays
We report the first reconstruction in hadron collisions of the suppressed
decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the
CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by
the CDF II detector at the Tevatron collider. We reconstruct a signal for the
B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard
deviations, and measure the ratios of the suppressed to favored branching
fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) =
[42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm
2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) =
-0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for
B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for
Publicatio
Search for long-lived doubly charged Higgs bosons in p(p)over-bar collisions at root s=1.96 TeV
We present a search for long-lived doubly charged Higgs bosons (H+/-+/-), with signatures of high ionization energy loss and muonlike penetration. We use 292 pb(-1) of data collected in p (p) over bar collisions at root s=1.96 TeV by the CDF II detector at the Fermilab Tevatron. Observing no evidence of long-lived doubly charged particle production, we exclude H-L(+/-+/-) and H-R(+/-+/-) bosons with masses below 133 GeV/c(2) and 109 GeV/c(2), respectively. In the degenerate case we exclude H+/-+/- mass below 146 GeV/c(2). All limits are quoted at the 95% confidence level
Search for Pair Production of Scalar Top Quarks Decaying to a tau Lepton and a b Quark in ppbar Collisions at sqrt{s}=1.96 TeV
We search for pair production of supersymmetric top quarks (~t_1), followed
by R-parity violating decay ~t_1 -> tau b with a branching ratio beta, using
322 pb^-1 of ppbar collisions at sqrt{s}=1.96 TeV collected by the CDF II
detector at Fermilab. Two candidate events pass our final selection criteria,
consistent with the standard model expectation. We set upper limits on the
cross section sigma(~t_1 ~tbar_1)*beta^2 as a function of the stop mass
m(~t_1). Assuming beta=1, we set a 95% confidence level limit m(~t_1)>153
GeV/c^2. The limits are also applicable to the case of a third generation
scalar leptoquark (LQ_3) decaying LQ_3 -> tau b.Comment: 7 pages, 2 eps figure
Measurement of the ratios of branching fractions B (B-s(0)-\u3e D-s(-) pi(+) pi(+) pi(-))/B(B-0 -\u3e D- pi(+) pi(+) pi(-)) and B(B-s(0) -\u3e D-s(-) pi(+))/B(B-0 -\u3e D- pi(+))
Using 355 pb(-1) of data collected by the CDF II detector in p (p) over bar at collisions at root s = 1.96 TeV at the Fermilab Tevatron, we study the fully reconstructed hadronic decays B-(s)(0) -\u3e D-(s)(-)pi(+) and B-(s)(0) -\u3e D-(s)(-) pi(+)pi(+)pi(-). We present the first measurement of the ratio of branching fractions B(B-s(0) -\u3e D-s(-) pi(+)pi(+)pi(-))/B(B-0 -\u3e D-s(-) pi(+)pi(+)pi(-)) = 1.05 +/- 0.10(stat) +/- 0.22(syst). We also update our measurement of B(B-s(0) -\u3e D-s(-)pi(+))/B(B-0 -\u3e D-pi(+)) to 1.13 +/- 0.08(stat) +/- 0.23(syst), improving the statistical uncertainty by more than a factor of 2. We find B(B-s(0) -\u3e D-s(-)pi(+)) = [3.8 +/- 0.3(stat) +/- 1.3(syst)] x 10(-3) and B(B-s(0) -\u3e D-s(-) pi(+)pi(+)pi(-)) = [8.4 +/- 0.8 (stat) +/- 3.2(syst)] x 10(-3)
Interaction of hot spots and THz waves in Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks of various geometry
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson
junctions a hot spot (a region heated to above the superconducting transition
temperature) coexists with regions still in the superconducting state. In the
``cold'' regions cavity resonances can occur, synchronizing the ac Josephson
currents and giving rise to strong coherent THz emission. We investigate the
interplay of hot spots and standing electromagnetic waves by low temperature
scanning laser microscopy and THz emission measurements, using stacks of
various geometries. For a rectangular and a arrow-shaped structure we show that
the standing wave can be turned on and off in various regions of the stack
structure, depending on the hot spot position. We also report on standing wave
and hot spot formation in a disk shaped mesa structure
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