We have searched for a light vector boson U, the possible carrier of a “dark force”, with the KLOE detector at the DAΦNE e+e− collider, motivated by astrophysical evidence for the presence of dark ...matter in the Universe. Using e+e− collisions collected with an integrated luminosity of 239.3 pb−1, we look for a dimuon mass peak in the reaction e+e−→μ+μ−γ, corresponding to the decay U→μ+μ−. We find no evidence for a U vector boson signal. We set a 90% CL upper limit for the mixing parameter squared between the photon and the U boson of 1.6×10−5 to 8.6×10−7 for the mass region 520<mU<980 MeV.
We report on a search for a heavy Majorana neutrino in the decays τ^{-}→π^{-}ν_{h}, ν_{h}→π^{±}ℓ^{∓}, ℓ=e, μ. The results are obtained using the full data sample of 988 fb^{-1} collected with the ...Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider, which contains 912×10^{6} ττ pairs. We observe no significant signal and set 95% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional standard model left-handed neutrinos in the mass range 0.2-1.6 GeV/c^{2}. This is the first study of a mixed couplings of heavy neutrinos to τ leptons and light-flavor leptons.
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CMK, CTK, FMFMET, NUK, UL
High-pressure monitored drift tube (MDT) chambers are used as precision tracking detectors in the Muon Spectrometer of the ATLAS experiment at the Large Hadron Collider. MDT chambers, operated at 3 ...bar absolute pressure with 93% argon 7% carbon dioxide gas mixture, were tested with cosmic rays at the Roma TRE test site, and their properties upon variations of the operating conditions are discussed. The improvement of spatial resolution using the measurement of a fraction of the collected charge, exploiting the final version of the MDT electronics, is considered
We have measured the running of the effective QED coupling constant α(s) in the time-like region 0.6<s<0.975 GeV with the KLOE detector at DAΦNE using the Initial-State Radiation process e+e−→μ+μ−γ. ...It represents the first measurement of the running of α(s) in this energy region. Our results show a more than 5σ significance of the hadronic contribution to the running of α(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e+e−→π+π− cross section measured by KLOE, the real and imaginary parts of the shift Δα(s) have been extracted. From a fit of the real part of Δα(s) and assuming the lepton universality the branching ratio BR(ω→μ+μ−)=(6.6±1.4stat±1.7syst)⋅10−5 has been determined.
A
bstract
We report a search for the charged-lepton flavor violation in Υ(2
S
) →
ℓ
∓
τ
±
(
ℓ
=
e, μ
) decays using a 25 fb
−
1
Υ(2
S
) sample collected by the Belle detector at the KEKB
e
+
e
−
...asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions (
B
) at 90% confidence level. We obtain the most stringent upper limits:
B
(Υ(2
S
)
→ μ
∓
τ
±
)
<
0
.
23
×
10
−
6
and
B
(Υ(2
S
)
→ e
∓
τ
±
)
<
1
.
12
×
10
−
6
.
The existence of a light dark force mediator has been tested with the KLOE detector at DA Phi NE. This particle, called U. is searched for using the decay chain phi -> eta U, eta -> ...pi(+)pi(-)pi(0), U -> e(+)e(-). No evidence is found in 1.5 fb(-1) of data. The resulting exclusion plot covers the mass range 5 < M-U < 470 MeV, setting an upper limit on the ratio between the U boson coupling constant and the One structure constant, alpha'/alpha, of <= 2 x 10(-5) at 90% C.L. for 50 < M-U < 420 MeV.
Based on a sample of 300 million KS mesons produced in ϕ→KLKS decays recorded by the KLOE experiment at the DAΦNE e+e− collider we have measured the branching fraction for the decay KS→πμν. The KS ...mesons are identified by the interaction of KL mesons in the detector. The KS→πμν decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of KL→πμν decays. A fit to the reconstructed muon mass distribution finds 7223±180 signal events. Normalising to the KS→π+π− decay events the result for the branching fraction is B(KS→πμν)=(4.56±0.11stat±0.17syst)×10−4. It is the first measurement of this decay mode and the result allows an independent determination of |Vus| and a test of the lepton-flavour universality.
A
bstract
We measure the cross section of
e
+
e
−
→
η
c
J/ψ
at the Υ(
nS
)(
n
= 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector ...with an integrated luminosity of 955 fb
−
1
. We also search for double charmonium production in
e
+
e
−
→
η
c
J/ψ
via initial state radiation near the
η
c
J/ψ
threshold. No evident signal of the double charmonium state is found, but evidence for the
e
+
e
−
→ η
c
J/ψ
process is found with a statistical significance greater than 3
.
3
σ
near the
η
c
J/ψ
threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.
We have measured the overall detection efficiency to neutrons of a small prototype of the KLOE Pb-scintillating fiber calorimeter in the kinetic energy range 5-175 MeV using the neutron beam facility ...of The Svedberg Laboratory, TSL, Uppsala. The measurement of the neutron detection efficiency of a NE110 scintillator provided a reference calibration. At the lowest trigger threshold, the overall calorimeter efficiency ranges from 28% to 33%. This value largely exceeds the estimated ~8% expected if the response were proportional only to the scintillator equivalent thickness. A detailed simulation of the calorimeter and of TSL beamline has been performed with the FLUKA Monte Carlo code. The simulated response of the detector to neutrons is presented together with first data to Monte Carlo comparison. The results show an overall neutron efficiency of about 35%. The reasons for such an efficiency enhancement, in comparison with the typical scintillator-based neutron counters, are explained, opening the road to a novel neutron detector.
Radiographic assessment of marginal bone height is included in longitudinal control of osseointegrated implants. However, accurate and reproducible results are difficult to obtain. The aim of the ...present study was to examine the differences between linear measurements in digitized radiographs (DR) and digital subtraction images (DSI) around endosseous implants and the interobserver variability.
The bone height around 30 implants in 22 patients was assessed by 5 observers. Standardized periapical radiographs were obtained just after the surgery and 4 months later. The radiographs were digitized and manipulated by means of EMAGO software, and linear and logarithmic DSIs were produced. Furthermore, the logarithmic subtraction was enhanced with the use of a filter. The observers had the DRs and three methods of subtraction to assess bone height. ANOVA statistical procedures were applied to analyse differences between the observers in the four assessed images and the Tukey test was used to evaluate the differences between the images.
Comparison of the bone height assessments indicated significantly (P<0.05) higher values in the DR than the three methods of DSI. The observers also had a statistically significant variability in this assessment (P=0.00003).
DSI demonstrated lower values of linear measurements of the bone height around endosseous implants, compared with DR. Interobserver variability should be considered when comparing values from follow-up studies.
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