140 research outputs found
Study of the Cabibbo-suppressed decay modes D0-->Pi-pi+ and D0-->K-K+
Using data from the FOCUS (E831) experiment at Fermilab, we present a new
measurement for the branching ratios of the Cabibbo-suppressed decay modes
D0-->Pi-Pi+ and D0-->K-K+. We measured:
Gamma(D0-->K-K+)/Gamma(D0-->Pi-Pi+) = 2.81 +/- 0.10(stat) +/- 0.06(syst),
Gamma(D0-->K-K+)/Gamma(D0-->K-Pi+) = 0.0993 +/- 0.0014(stat) +/- 0.0014(syst),
and Gamma(D0-->Pi-Pi+)/Gamma(D0-->K-Pi+) = 0.0353 +/- 0.0012 (stat) +/-
0.0006(syst).
These values have been combined with other experimental data to extract the
ratios of isospin amplitudes and the phase shifts for the D-->KK and D-->PiPi
decay channels.Comment: 12 pages, 1 Figure, accepted for publication in Phys.Lett.
Study of the decay mode D^0 -> K-K-K+pi+
Using data from the FOCUS (E831) experiment at Fermilab, we present a new
measurement of the branching ratio for the Cabibbo-favored decay mode . From a sample of fully reconstructed events, we measure .
A coherent amplitude analysis has been performed to determine the resonant
substructure of this decay mode. This analysis reveals a dominant contribution
from and states.Comment: 15 pages, 4 figures, to be submitted to Physics Letters
The first ultracompact Roche lobe-filling hot subdwarf binary
We report the discovery of the first short period binary in which a hot subdwarf star (sdOB) fills its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic Plane named the Zwicky Transient Facility and exhibits a period of Porb=39.3401(1) min, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of Teff=42,400±300 K and a surface gravity of log(g)=5.77±0.05. A high-signal-to noise GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass MsdOB=0.337±0.015 Mâ and a white dwarf accretor with a mass MWD=0.545±0.020 Mâ. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5â2.8 Mâ star lost its envelope when crossing the Hertzsprung Gap. To match its current Porb, Teff, log(g), and masses, we estimate a post-common envelope period of Porbâ150 min, and find the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of â0.1 Mâ and will merge with its carbon/oxygen white dwarf companion after â17 Myr and presumably explode as a thermonuclear supernova or form an R CrB star
Light-Ion-Induced Multifragmentation: The ISiS Project
An extensive study of GeV light-ion-induced multifragmentation and its
possible interpretation in terms of a nuclear liquid-gas phase transition has
been performed with the Indiana Silicon Sphere (ISiS)4 pi detector array.
Measurements were performed with 5-15 GeV/c p, pbar, and pion beams incident on
Au and 2-5 GeV He incident on Ag and Au targets.
Both the reaction dynamics and the subsequent decay of the heavy residues have
been explored. The data provide evidence for a dramatic change in the reaction
observables near an excitation energy of E*/A = 4-5 MeV per residue nucleon. In
this region, fragment multiplicities and energy spectra indicate emission from
an expanded/dilute source on a very short time scale (20-50 fm/c). These
properties, along with caloric curve and scaling-law behavior, yield a pattern
that is consistent with a nuclear liquid-gas phase transition.Comment: 67 pages, 44 figures, all included in tar fil
Study of the decay mode D^0 -> K-K+pi-pi+
Using data from the FOCUS (E831) experiment at Fermilab, we present a new
measurement of the branching ratio for the Cabibbo-favored decay mode . From a sample of fully reconstructed events, we measure .
A coherent amplitude analysis has been performed to determine the resonant
substructure of this decay mode. This analysis reveals a dominant contribution
from modes.Comment: 19 pages, 6 figures, to be submitted to Physics Letters
A new class of Roche lobeâfilling hot subdwarf binaries
We present the discovery of the second binary with a Roche lobeâfilling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of T eff = 33,700 ± 1000 K and a surface gravity of log(g) = 5.54 ± 0.11. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of M sdOB = 0.41 ± 0.04 M â and a WD mass of M WD = 0.68 ± 0.05 M â. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius R WD = 0.0148 ± 0.0020 R â as expected for a WD of such high temperature. The He-sdOB star is likely undergoing hydrogen shell burning and will continue transferring mass for â1 Myr at a rate of 10â9 M â yrâ1, which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in â30 Myr. We suggest that Galactic reddening could bias discoveries toward preferentially finding Roche lobeâfilling systems during the short-lived shell-burning phase. Studies using reddening-corrected samples should reveal a large population of helium coreâburning hot subdwarfs with T eff â 25,000 K in binaries of 60â90 minutes with WDs. Though not yet in contact, these binaries would eventually come into contact through gravitational-wave emission and explode as a subluminous thermonuclear supernova or evolve into a massive single WD
Measurement of the View the tt production cross-section using eÎŒ events with b-tagged jets in pp collisions at âs = 13 TeV with the ATLAS detector
This paper describes a measurement of the inclusive top quark pair production cross-section (ÏttÂŻ) with a data sample of 3.2 fbâ1 of protonâproton collisions at a centre-of-mass energy of âs = 13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electronâmuon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously ÏttÂŻ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be:
ÏttÂŻ = 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb,
where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented
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