We present a new limit on the production of a light dark-force mediator with the KLOE detector at DAΦNE. This boson, called U, has been searched for in the decay ϕ→ηU, U→e+e−, analyzing the decay ...η→π0π0π0 in a data sample of 1.7 fb−1. No structures are observed in the e+e− invariant mass distribution over the background. This search is combined with a previous result obtained from the decay η→π+π−π0, increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of α′/α<1.7×10−5 for 30<MU<400 MeV and α′/α⩽8×10−6 for the sub-region 50<MU<210 MeV. This result assumes the Vector Meson Dominance expectations for the ϕηγ⁎ transition form factor. The dependence of this limit on the transition form factor has also been studied.
A
bstract
The ratio
R
= Γ(
K
S
→ πeν
)
/
Γ(
K
S
→ π
+
π
−
) has been measured with a sample of 300 million
K
S
mesons produced in
ϕ → K
L
K
S
decays recorded by the KLOE experiment at the DAΦNE
e
+
e
...−
collider.
K
S
→ πeν
events are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of
K
L
→ πeν
decays are used to evaluate signal selection efficiencies. With 49647
±
316 signal events we measure
R
= (1
.
0421
±
0
.
0066
stat
±
0
.
0075
syst
)
×
10
−
3
. The combination with our previous measurement gives
R
= (1
.
0338
±
0
.
0054
stat
±
0
.
0064
syst
)
×
10
−
3
. From this value we derive the branching fraction
B
(
K
S
→ πeν
) = (7
.
153
±
0
.
037
stat
±
0
.
044
syst
)
×
10
−
4
and
f
+
(0)
|V
us
|
= 0
.
2170
±
0
.
009.
A
bstract
Using 1.63 fb
−1
of integrated luminosity collected by the KLOE experiment about 7 × 10
4
K
S
→
π
±
e
∓
ν
decays have been reconstructed. The measured value of the charge asymmetry for this ...decay is
A
S
= (−4.9 ± 5.7
stat
± 2.6
syst
) × 10
−3
, which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives
A
S
= (−3.8 ± 5.0
stat
± 2.6
syst
) × 10
−3
and, together with the asymmetry of the
K
L
semileptonic decay, provides significant tests of the
CPT
symmetry. The obtained results are in agreement with
CPT
invariance.
The existence of a light dark force mediator has been tested with the KLOE detector at DAΦNE. This particle, called U, is searched for using the decay chain ϕ→ηU, η→π+π−π0, U→e+e−. No evidence is ...found in 1.5 fb−1 of data. The resulting exclusion plot covers the mass range 5<MU<470 MeV, setting an upper limit on the ratio between the U boson coupling constant and the fine structure constant, α′/α, of ⩽2×10−5 at 90% C.L. for 50<MU<420 MeV.
Investigation at a
φ
-factory can shed light on several debated issues in particle physics. We discuss: (i) recent theoretical development and experimental progress in kaon physics relevant for the ...Standard Model tests in the flavor sector, (ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled-kaon states, (iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and
η
/
η
′ mesons, (iv) the contribution to understand the nature of light scalar mesons, and (v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the
e
+
e
−
physics in the continuum with the measurements of (multi)hadronic cross sections and the study of
γ
γ
processes.
The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the ...light vector mediator of this dark force, the U boson, with the KLOE detector at the DAΦNE e+e− collider. Using an integrated luminosity of 1.54 fb−1, we studied the process e+e−→Uγ, with U→e+e−, using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, ε2, at 10−6–10−4 in the 5–520 MeV/c2 mass range.
Flavor physics in the quark sector Asner, D.M.; Bauer, D.; Becher, T. ...
Physics Reports,
2010, Volume:
494, Issue:
3
Journal Article, Conference Proceeding
Peer reviewed
Open access
In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical ...interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved; apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral
K
mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral
B
mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of
K
,
D
, and
B
mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model.
In the near future, there will be a transition from the current to a new generation of experiments; thus a review of the status of quark flavor physics is timely. This report is the result of the work of physicists attending the 5th CKM workshop, hosted by the University of Rome “La Sapienza”, September 9–13, 2008. It summarizes the results of the current generation of experiments that are about to be completed and it confronts these results with the theoretical understanding of the field which has greatly improved in the past decade.
A
bstract
The quantum interference between the decays of entangled neutral kaons is studied in the process
ϕ
→ K
S
K
L
→
π
+
π
−
π
+
π
−
, which exhibits the characteristic Einstein-Podolsky-Rosen ...correlations that prevent both kaons to decay into
π
+
π
−
at the same time. This constitutes a very powerful tool for testing at the utmost precision the quantum coherence of the entangled kaon pair state, and to search for tiny decoherence and
CPT
violation effects, which may be justified in a quantum gravity framework.
The analysed data sample was collected with the KLOE detector at DAΦNE, the Frascati
ϕ
-factory, and corresponds to an integrated luminosity of about 1.7 fb
−
1
, i.e. to about 1
.
7 × 10
9
ϕ
→ K
S
K
L
decays produced. From the fit of the observed ∆
t
distribution, being ∆
t
the difference of the kaon decay times, the decoherence and
CPT
violation parameters of various phenomenological models are measured with a largely improved accuracy with respect to previous analyses.
The results are consistent with no deviation from quantum mechanics and
CPT
symmetry, while for some parameters the precision reaches the interesting level at which — in the most optimistic scenarios — quantum gravity effects might show up. They provide the most stringent limits up to date on the considered models.
Neutral kaon pairs produced in ϕ decays in anti-symmetric entangled state can be exploited to search for violation of CPT symmetry and Lorentz invariance. We present an analysis of the CP-violating ...process ϕ→KSKL→π+π−π+π− based on 1.7 fb−1 of data collected by the KLOE experiment at the Frascati ϕ-factory DAΦNE. The data are used to perform a measurement of the CPT-violating parameters Δaμ for neutral kaons in the context of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are:Δa0=(−6.0±7.7stat±3.1syst)×10−18 GeV,ΔaX=(0.9±1.5stat±0.6syst)×10−18 GeV,ΔaY=(−2.0±1.5stat±0.5syst)×10−18 GeV,ΔaZ=(3.1±1.7stat±0.5syst)×10−18 GeV. These are presently the most precise measurements in the quark sector of the Standard Model Extension.
We searched for the μ+μ− decay of a light vector gauge boson, also known as dark photon, in the e+e−→μ+μ−γISR process by means of the Initial State Radiation (ISR) method. We used 1.93 fb−1 of data ...collected by the KLOE experiment at the DAΦNE ϕ-factory. No structures have been observed over the irreducible μ+μ− background. A 90% CL limit on the ratio ε2=α′/α between the dark coupling constant and the fine structure constant of 3×10−6–2×10−7 has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in e+e−→π+π−γISR events. The combined 90% CL limit increases the sensitivity especially in the ρ–ω interference region and excludes ε2 greater than (13−2)×10−7. For dark photon masses greater than 600 MeV the combined limit is lower than 8 ×10−7 resulting more stringent than present constraints from other experiments.
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