55 research outputs found
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
Search for the Lepton Flavor Violation Processes and
The lepton flavor violation processes and are
searched for using a sample of 5.8 events collected with
the BESII detector. Zero and one candidate events, consistent with the
estimated background, are observed in and
decays, respectively. Upper limits on the branching ratios are determined to be
and at the 90% confidence level (C.L.).Comment: 9 pages, 2 figure
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
Measurement of Branching Ratios for Hadronic Decays
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five decay channels: , , (with
), (with ) and . From
these signals, we determine ,
, ,
and .Comment: 8 pages, 1 figures and 4 table. Submitted to Phys. Lett.
Search for K_S K_S in J/psi and psi(2S) decays
The CP violating processes J/psi-->K_S K_S and psi(2S)-->K_S K_S are searched
for using samples of 58 million J/psi and 14 million psi(2S) events collected
with the Beijing Spectrometer at the Beijing Electron Positron Collider. No
signal is observed, and upper limits on the decay branching ratios are
determined to be BR(J/psi-->K_S K_S) K_S K_S) <
4.6x10^{-6} at the 95% confidence level.Comment: 6 pages, 4 figures, submitted to Phys. Lett.
Measurements of J/psi --> p \bar{p}
The process J/\psi --> p \bar{p} is studied using 57.7 X 10^6 J/\psi events
collected with the BESII detector at the Beijing Electron Positron Collider.
The branching ratio is determined to be Br(J/\psi --> p \bar{p})=(2.26 +- 0.01
+- 0.14) X 10^{-3}, and the angular distribution is well described by
\frac{dN}{d cos\theta_p}=1+\alpha\cos^2\theta_p with \alpha = 0.676 +- 0.036 +-
0.042, where \theta_p is the angle between the proton and beam directions. The
value of \alpha obtained is in good agreement with the predictions of
first-order QCD.Comment: 6 pages, 2 figures, RevTex4, Submitted to Phys.Lett.
A Study of J/psi-->gamma gamma V(rho,phi) Decays with the BESII Detector
Using a sample of events collected with the BESII
detector, radiative decays , where or ,
are studied. A resonance around 1420 MeV/c (X(1424)) is observed in the
mass spectrum. Its mass and width are measured to be MeV/c and MeV/c,
respectively, and its branching ratio is determined to be . A
search for yields a 95% C.L. upper limit .Comment: 10 pages, 5 figures, submitted to PL
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