5,921 research outputs found
A Unified Approach to the Classical Statistical Analysis of Small Signals
We give a classical confidence belt construction which unifies the treatment
of upper confidence limits for null results and two-sided confidence intervals
for non-null results. The unified treatment solves a problem (apparently not
previously recognized) that the choice of upper limit or two-sided intervals
leads to intervals which are not confidence intervals if the choice is based on
the data. We apply the construction to two related problems which have recently
been a battle-ground between classical and Bayesian statistics: Poisson
processes with background, and Gaussian errors with a bounded physical region.
In contrast with the usual classical construction for upper limits, our
construction avoids unphysical confidence intervals. In contrast with some
popular Bayesian intervals, our intervals eliminate conservatism (frequentist
coverage greater than the stated confidence) in the Gaussian case and reduce it
to a level dictated by discreteness in the Poisson case. We generalize the
method in order to apply it to analysis of experiments searching for neutrino
oscillations. We show that this technique both gives correct coverage and is
powerful, while other classical techniques that have been used by neutrino
oscillation search experiments fail one or both of these criteria.Comment: 40 pages, 15 figures. Changes 15-Dec-99 to agree more closely with
published version. A few small changes, plus the two substantive changes we
made in proof back in 1998: 1) The definition of "sensitivity" in Sec. V(C).
It was inconsistent with our actual definition in Sec. VI. 2) "Note added in
proof" at end of the Conclusio
Observation of decays into vector meson pairs , , and
Decays of to vector meson pairs , and
are observed for the first time using
\psip events accumulated at the BESIII detector at the BEPCII
collider. The branching fractions are measured to be , , and , for , , and ,
respectively. The observation of decays into a pair of vector
mesons , and indicates that the hadron
helicity selection rule is significantly violated in decays. In
addition, the measurement of gives the rate of doubly
OZI-suppressed decay. Branching fractions for and
decays into other vector meson pairs are also measured with improved precision.Comment: 4 pages, 2 figure
First Observation of the Decays chi_{cJ} -> pi^0 pi^0 pi^0 pi^0
We present a study of the P-wave spin -triplet charmonium chi_{cJ} decays
(J=0,1,2) into pi^0 pi^0 pi^0 pi^0. The analysis is based on 106 million
\psiprime decays recorded with the BESIII detector at the BEPCII electron
positron collider. The decay into the pi^0 pi^0 pi^0 pi^0 hadronic final state
is observed for the first time. We measure the branching fractions B(chi_{c0}
-> pi^0 pi^0 pi^0 pi^0)=(3.34 +- 0.06 +- 0.44)*10^{-3}, B(chi_{c1} -> pi^0 pi^0
pi^0 pi^0)=(0.57 +- 0.03 +- 0.08)*10^{-3}, and B(chi_{c2} -> pi^0 pi^0 pi^0
pi^0)=(1.21 +- 0.05 +- 0.16)*10^{-3}, where the uncertainties are statistical
and systematical, respectively.Comment: 7 pages, 3 figure
Study of radiative decays into a vector meson
The decays () are studied with
a sample of radiative \psip\to\gamma\chi_{cJ} events in a sample of
(1.06\pm0.04)\times 10^{8} \psip events collected with the BESIII detector.
The branching fractions are determined to be: , , and . The decay is observed for the first time. Upper limits at the 90% confidence
level on the branching fractions for and \chict decays into these
final states are determined. In addition, the fractions of the transverse
polarization component of the vector meson in decays
are measured to be for , for , and for , respectively. The first errors are statistical and the second
ones are systematic.Comment: 8 pages, 3 figure
Study of and
The decays and have been
investigated with a sample of 225.2 million events collected with the
BESIII detector at the BEPCII collider. The branching fractions are
determined to be and . Distributions of the angle
between the proton or anti-neutron and the beam direction are well
described by the form , and we find
for and
for . Our branching-fraction
results suggest a large phase angle between the strong and electromagnetic
amplitudes describing the decay.Comment: 16 pages, 13 figures, the 2nd version, submitted to PR
Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi' -> pi+pi-pi0
We study the decays of the J/psi and psi' mesons to pi+pi-pi0 using data
samples at both resonances collected with the BES III detector in 2009. We
measure the corresponding branching fractions with unprecedented precision and
provide mass spectra and Dalitz plots. The branching fraction for J/psi ->
pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.)
+0.027-0.026 (norm.))*10-2, and the branching fraction for psi' -> pi+pi-pi0 is
measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4.
The J/psi decay is found to be dominated by an intermediate rho(770) state,
whereas the psi' decay is dominated by di-pion masses around 2.2 GeV/c2,
leading to strikingly different Dalitz distributions.Comment: 15 pages, 2 figure
Higher-order multipole amplitude measurement in
Using events collected with the BESIII detector at
the BEPCII storage ring, the higher-order multipole amplitudes in the radiative
transition are measured.
A fit to the production and decay angular distributions yields
and , where the first
errors are statistical and the second systematic. Here denotes the
normalized magnetic quadrupole amplitude and the normalized electric
octupole amplitude. This measurement shows evidence for the existence of the
signal with statistical significance and is consistent with
the charm quark having no anomalous magnetic moment.Comment: 14 pages, 4 figure
Observation and study of the decay
We report the observation and study of the decay
using events
collected with the BESIII detector. Its branching fraction, including all
possible intermediate states, is measured to be
. We also report evidence for a structure,
denoted as , in the mass spectrum in the GeV/
region. Using two decay modes of the meson ( and
), a simultaneous fit to the mass spectra is
performed. Assuming the quantum numbers of the to be , its
significance is found to be 4.4, with a mass and width of MeV/ and MeV, respectively, and a
product branching fraction
. Alternatively, assuming , the
significance is 3.8, with a mass and width of MeV/ and MeV, respectively, and a product
branching fraction
. The angular distribution of
is studied and the two assumptions of the
cannot be clearly distinguished due to the limited statistics. In all
measurements the first uncertainties are statistical and the second systematic.Comment: 10 pages, 6 figures and 4 table
Measurement of proton electromagnetic form factors in in the energy region 2.00-3.08 GeV
The process of is studied at 22 center-of-mass
energy points () from 2.00 to 3.08 GeV, exploiting 688.5~pb of
data collected with the BESIII detector operating at the BEPCII collider. The
Born cross section~() of is
measured with the energy-scan technique and it is found to be consistent with
previously published data, but with much improved accuracy. In addition, the
electromagnetic form-factor ratio () and the value of the
effective (), electric () and magnetic () form
factors are measured by studying the helicity angle of the proton at 16
center-of-mass energy points. and are determined with
high accuracy, providing uncertainties comparable to data in the space-like
region, and is measured for the first time. We reach unprecedented
accuracy, and precision results in the time-like region provide information to
improve our understanding of the proton inner structure and to test theoretical
models which depend on non-perturbative Quantum Chromodynamics
First observation of the M1 transition
Using a sample of 106 million \psi(3686) events collected with the BESIII
detector at the BEPCII storage ring, we have made the first measurement of the
M1 transition between the radially excited charmonium S-wave spin-triplet and
the radially excited S-wave spin-singlet states: \psi(3686)\to\gamma\eta_c(2S).
Analyses of the processes \psi(2S)\to \gamma\eta_c(2S) with \eta_c(2S)\to
\K_S^0 K\pi and K^+K^-\pi^0 gave an \eta_c(2S) signal with a statistical
significance of greater than 10 standard deviations under a wide range of
assumptions about the signal and background properties. The data are used to
obtain measurements of the \eta_c(2S) mass (M(\eta_c(2S))=3637.6\pm
2.9_\mathrm{stat}\pm 1.6_\mathrm{sys} MeV/c^2), width
(\Gamma(\eta_c(2S))=16.9\pm 6.4_\mathrm{stat}\pm 4.8_\mathrm{sys} MeV), and the
product branching fraction (\BR(\psi(3686)\to \gamma\eta_c(2S))\times
\BR(\eta_c(2S)\to K\bar K\pi) = (1.30\pm 0.20_\mathrm{stat}\pm
0.30_\mathrm{sys})\times 10^{-5}). Combining our result with a BaBar
measurement of \BR(\eta_c(2S)\to K\bar K \pi), we find the branching fraction
of the M1 transition to be \BR(\psi(3686)\to\gamma\eta_c(2S)) = (6.8\pm
1.1_\mathrm{stat}\pm 4.5_\mathrm{sys})\times 10^{-4}.Comment: 7 pages, 1 figure, 1 tabl
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