358 research outputs found
Multiwavelength Study of M8.9/3B Solar Flare from AR NOAA 10960
We present a multi-wavelength analysis of a long duration white-light solar
flare (M8.9/3B) event that occurred on 4 June 2007 from NOAA AR 10960. The
flare was observed by several spaceborne instruments, namely SOHO/MDI,
Hinode/SOT, TRACE and STEREO/SECCHI. The flare was initiated near a small,
positive-polarity, satellite sunspot at the centre of the AR, surrounded by
opposite-polarity field regions. MDI images of the AR show considerable amount
of changes in a small positive-polarity sunspot of delta configuration during
the flare event. SOT/G-band (4305 A) images of the sunspot also suggest the
rapid evolution of the positive-polarity sunspot with highly twisted penumbral
filaments before the flare event, which were oriented in the counterclockwise
direction. It shows the change in orientation and also remarkable disappearance
of twisted penumbral filaments (~35-40%) and enhancement in umbral area
(~45-50%) during the decay phase of the flare. TRACE and SECCHI observations
reveal the successive activations of two helical twisted structures associated
with this sunspot, and the corresponding brightening in the chromosphere as
observed by the time-sequence images of SOT/Ca II H line (3968 A). The
secondary-helical twisted structure is found to be associated with the M8.9
flare event. The brightening starts 6-7 min prior to the flare maximum with the
appearance of secondary helical-twisted structure. The flare intensity
maximizes as this structure moves away from the AR. This twisted flux-tube
associated with the flare triggering, is found to be failed in eruption. The
location of the flare is found to coincide with the activation site of the
helical twisted structures. We conclude that the activations of successive
helical twists in the magnetic flux tubes/ropes plays a crucial role in the
energy build-up process and triggering of M-class solar flare without a CME.Comment: 22 pages, 12 figures, Accepted for Publication in Solar Physic
Search for Exotic Mesons in pi- P Interactions at 18 GeV/c
The recent search for non mesons in interactions at
Brookhaven National Laboratory is summarized. Many final states such as , , , , , ,
which are favored decay modes of exotics, are under investigation.Comment: 9 pages, PostScript, Presented at the International School of Nuclear
Physics, Erice, Sicily, Italy, September 199
A Parametric Study of Erupting Flux Rope Rotation. Modeling the "Cartwheel CME" on 9 April 2008
The rotation of erupting filaments in the solar corona is addressed through a
parametric simulation study of unstable, rotating flux ropes in bipolar
force-free initial equilibrium. The Lorentz force due to the external shear
field component and the relaxation of tension in the twisted field are the
major contributors to the rotation in this model, while reconnection with the
ambient field is of minor importance. Both major mechanisms writhe the flux
rope axis, converting part of the initial twist helicity, and produce rotation
profiles which, to a large part, are very similar in a range of shear-twist
combinations. A difference lies in the tendency of twist-driven rotation to
saturate at lower heights than shear-driven rotation. For parameters
characteristic of the source regions of erupting filaments and coronal mass
ejections, the shear field is found to be the dominant origin of rotations in
the corona and to be required if the rotation reaches angles of order 90
degrees and higher; it dominates even if the twist exceeds the threshold of the
helical kink instability. The contributions by shear and twist to the total
rotation can be disentangled in the analysis of observations if the rotation
and rise profiles are simultaneously compared with model calculations. The
resulting twist estimate allows one to judge whether the helical kink
instability occurred. This is demonstrated for the erupting prominence in the
"Cartwheel CME" on 9 April 2008, which has shown a rotation of \approx 115
degrees up to a height of 1.5 R_sun above the photosphere. Out of a range of
initial equilibria which include strongly kink-unstable (twist Phi=5pi), weakly
kink-unstable (Phi=3.5pi), and kink-stable (Phi=2.5pi) configurations, only the
evolution of the weakly kink-unstable flux rope matches the observations in
their entirety.Comment: Solar Physics, submitte
Observation of a New J(PC)=1(+-) Isoscalar State in the Reaction Pi- Proton -> Omega Eta Neutron at 18 GeV/c
Results are presented on a partial wave analysis of the Omega Eta final state
produced in Pi- Proton interactions at 18 GeVc where Omega -> Pi+ Pi- Pi0, Pi0
-> 2 Gammas, and Eta -> 2 Gammas. We observe the previously unreported decay
mode Omega(1650) -> Omega Eta and a new 1(+-) meson state h1(1595) with a mass
M=1594(15)(+10)(-60) MeV/c^2 and a width Gamma=384(60)(+70)(-100) MeV/c^2. The
h1(1595) state exhibits resonant-like phase motion relative to the Omega(1650).Comment: Submitted to Physics Letters B Eight total pages including 11 figures
and 1 tabl
Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2
The hadronic structure function of the photon F_2^gamma is measured as a
function of Bjorken x and of the factorisation scale Q^2 using data taken by
the OPAL detector at LEP. Previous OPAL measurements of the x dependence of
F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of
F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted
by QCD, the data show positive scaling violations in F_2^gamma. Several
parameterisations of F_2^gamma are in agreement with the measurements whereas
the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001,
Ascona, Switzerlan
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons
We report the first observation of Z/gamma* production in Compton scattering
of quasi-real photons. This is a subprocess of the reaction e+e- to
e+e-Z/gamma*, where one of the final state electrons is undetected.
Approximately 55 pb-1 of data collected in the year 1997 at an e+e-
centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been
analysed. The Z/gamma* from Compton scattering has been detected in the
hadronic decay channel. Within well defined kinematic bounds, we measure the
product of cross-section and Z/gamma* branching ratio to hadrons to be
(0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV,
dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60
GeV, dominated by (e)egamma* production, this product is found to be
(4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo
event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays
The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where
Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL
detector at LEP. Lambda_b are selected by the presence of energetic Lambda
particles in bottom events tagged by the presence of displaced secondary
vertices. A fit to the momenta of the Lambda particles separates signal from B
meson and fragmentation backgrounds. The measured product branching ratio is
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))%
Combined with a previous OPAL measurement, one obtains
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European
Physical Journal
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