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.
The ratio Rη=Γ(η→π+π−γ)/Γ(η→π+π−π0) has been measured by analysing 22 million ϕ→ηγ decays collected by the KLOE experiment at DAΦNE, corresponding to an integrated luminosity of 558 pb−1. The η→π+π−γ ...proceeds both via the ρ resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, Rη=0.1856±0.0005stat±0.0028syst, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η→π+π−γ decay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter α is α=(1.32±0.08stat−0.09syst+0.10±0.02theo) GeV−2.
A
bstract
We present a measurement of
η
meson production in photon-photon interactions produced by electron-positron beams colliding with
GeV. The measurement is done with the KLOE detector at the
ϕ
...-factory DAΦNE with an integrated luminosity of 0.24 fb
−1
. The
e
+
e
−
→
e
+
e
−
η
cross section is measured without detecting the out-going electron and positron, selecting the decays
η
→
π
+
π
−
π
0
and
η
→
π
0
π
0
π
0
. The most relevant background is due to
e
+
e
−
→
ηγ
when the monochromatic photon escapes detection. The cross section for this process is measured as
σ
(
e
+
e
−
→
ηγ
) = (856 ± 8
stat
± 16
syst
) pb. The combined result for the
e
+
e
−
→
e
+
e
−
η
cross section is
σ
(
e
+
e
−
→
e
+
e
−
η
) = (32.72 ± 1.27
stat
± 0.70
syst
) pb. From this we derive the partial width Γ(
η
→
γγ
) = (520 ± 20
stat
± 13
syst
) eV. This is in agreement with the world average and is the most precise measurement to date.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).We present a measurement of eta meson production in photon-photon interactions produced by electron-positron beams ...colliding with ... GeV. The measurement is done with the KLOE detector at the -factory DA Phi NE with an integrated luminosity of 0.24 fb super(-1). The e super(+) e super(-) arrow right e super(+) e super(-) eta cross section is measured without detecting the out-going electron and positron, selecting the decays eta arrow right pi super(+) pi super(-) pi super(0) and eta arrow right pi super(0) pi super(0) pi super(0). The most relevant background is due to e super(+) e super(-) arrow right eta gamma when the monochromatic photon escapes detection. The cross section for this process is measured as sigma (e super(+) e super(-) arrow right eta gamma ) = (856 plus or minus 8 sub(stat) plus or minus 16 sub(syst)) pb. The combined result for the e super(+) e super(-) arrow right e super(+) e super(-) eta cross section is sigma (e super(+) e super(-) arrow right e super(+) e super(-) eta ) = (32.72 plus or minus 1.27 sub(stat) plus or minus 0.70 sub(syst)) pb. From this we derive the partial width Gamma ( eta arrow right gamma gamma ) = (520 plus or minus 20 sub(stat) plus or minus 13 sub(syst)) eV. This is in agreement with the world average and is the most precise measurement to date.
We report the first observation of the rare η→e+e−e+e−(γ) decay based on 1.7 fb−1 collected by the KLOE experiment at the DAΦNE ϕ-factory. The selection of the e+e−e+e− final state is fully inclusive ...of radiation. We have identified 362±29 events resulting in a branching ratio of (2.4±0.2stat+bckg±0.1syst)×10−5.
We have searched for a light vector boson U, the possible carrier of a "dark force", with the KLOE detector at the DA Phi NE 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(-) -> mu(+)mu(-)gamma, corresponding to the decay U -> mu(+)mu(-). 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 x 10(-5) to 8.6 x 10(-7) for the mass region 520 < m(U) < 980 MeV.
We have carried out a new direct search for the CP violating decay KS→3π0 with 1.7 fb−1 of e+e− collisions collected by the KLOE detector at the Φ-factory DAΦNE. We have searched for this decay in a ...sample of about 5.9×108KSKL events tagging the KS by means of the KL interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake KS tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of KS→2π0 events in the same sample, we set the upper limit on BR(KS→3π0)⩽2.6×10−8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the η000 parameter, |η000|⩽0.0088 at 90% C.L., improving by a factor two the latest direct measurement.
We have carried out a new direct search for the CP violating decay K-S -> 3 pi(0) with 1.7 fb(-1) of e(+)e(-) collisions collected by the KLOE detector at the Phi-factory DA Phi NE. We have ...searched for this decay in a sample of about 5.9 x 10(8) KSKL events tagging the K-S by means of the K-L interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake K-S tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of K-S -> 2 pi(0) events in the same sample, we set the upper limit on BR(K-S -> 3 pi(0)) <= 2.6 x 10(-8) at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta(000) parameter, vertical bar eta(000)vertical bar <= 0.0088 at 90% C.L., improving by a factor two the latest direct measurement. (c) 2013 Elsevier B.V. All rights reserved.
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