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.
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.
We have studied the vector to pseudoscalar conversion decay phi -> eta e(+)e(-), with.. eta -> pi(0)pi(0)pi(0), with the KLOE detector at DA phi NE. The data set of 1.7 fb(-1) of e(+)e(-) ...collisions at root s similar to M-phi contains a clear conversion decay signal of similar to 31,000 events from which we measured a value of BR(phi -> eta e(+)e-) = (1.075 +/- 0.007 +/- 0.038) x 10(-4). The same sample is used to determine the transition form factor by a fit to the e(+)e(-) invariant mass spectrum, obtaining b(phi eta)=( 1.28 +/- 0.10(-0.08)(+0.09)) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.
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 K sub(S) arrow right 3 pi super(0)KS arrow right 3 pi 0 with 1.7 fb super(-1) of e super(+)e super(-)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 5.910 super(8)5.9108K sub(S)K sub(L)KSKL events tagging the K sub(S)KS by means of the K sub(L)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 K sub(S)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 K sub(S) arrow right 2 pi super(0)KS arrow right 2 pi 0 events in the same sample, we set the upper limit on BR(K sub(S) arrow right 3 pi super(0))el2.610 super(-8)BR(KS arrow right 3 pi 0)el2.610-8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta sub(000) eta 000 parameter, | eta sub(000)|el0.0088| eta 000|el0.0088 at 90% C.L., improving by a factor two the latest direct measurement.
We have measured the ratio I (e + e - a pi + pi - gamma ) / I (e + e - a mu + mu - gamma ) , with the KLOE detector at DAIBBNE for a total integrated luminosity of similar to 240 pb - 1 . From this ...ratio we obtain the cross section I (e + e - a pi + pi -) . From the cross section we determine the pion form factor | F pi | 2 and the two-pion contribution to the muon anomaly a mu for 0.592 < M pi pi < 0.975 GeV , I pi pi a mu = (385.1 +/- 1.1 stat +/- 2.7 sys + theo) X 10 - 10 . This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.
Measurement of with the KLOE detector Babusci, D; Badoni, D; Balwierz-Pytko, I ...
Physics letters. B,
01/2013, Letnik:
718, Številka:
3
Journal Article
Recenzirano
The ratio R IDT = Phi (IDT a pi + pi - gamma ) / Phi (IDT a pi + pi - pi 0) has been measured by analysing 22 million I a IDT gamma decays collected by the KLOE experiment at DAIBBNE, corresponding ...to an integrated luminosity of 558 pb-1. The IDT a pi + pi - gamma proceeds both via the I resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R IDT = 0.1856 +/- 0.0005 stat +/- 0.0028 syst , points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the IDT a pi + pi - gamma decay could be described in a model-independent approach in terms of a single free parameter, alpha . The determined value of the parameter alpha is alpha = (1.32 +/- 0.08 stat - 0.09 syst + 0.10 +/- 0.02 theo) GeV - 2 .
We have studied the vector to pseudoscalar conversion decay ϕ→ηe+e−, with η→π0π0π0, with the KLOE detector at DAΦNE. The data set of 1.7 fb−1 of e+e− collisions at s∼Mϕ contains a clear conversion ...decay signal of ∼31,000 events from which we measured a value of BR(ϕ→ηe+e−)=(1.075±0.007±0.038)×10−4. The same sample is used to determine the transition form factor by a fit to the e+e− invariant mass spectrum, obtaining bϕη=(1.28±0.10−0.08+0.09) GeV−2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.
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.
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