1. |
- Anastasi, A., et al.
(författare)
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Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector
- 2017
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Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 767, s. 485-492
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the running of the effective QED coupling constant alpha(s) in the time-like region 0.6 < root s < 0.975 GeV with the KLOE detector at DA Phi NE using the Initial-State Radiation process e(+) e(-) -> mu(+) mu(-)gamma. It represents the first measurement of the running of alpha(s) in this energy region. Our results show a more than 5 sigma significance of the hadronic contribution to the running of alpha(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e(+) e(-) -> pi(+) pi(-) cross section measured by KLOE, the real and imaginary parts of the shift Delta alpha(s) have been extracted. From a fit of the real part of Delta alpha(s) and assuming the lepton universality the branching ratio BR(omega -> mu(+) mu(-)) = (6.6 +/- 1.4(stat) +/- 1.7(syst)) (.) 10 (5)has been determined.
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2. |
- Archilli, F., et al.
(författare)
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Search for a vector gauge boson in phi meson decays with the KLOE detector KLOE-2 Collaboration
- 2012
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 706:4-5, s. 251-255
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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3. |
- Anastasi, A., et al.
(författare)
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Limit on the production of a low-mass vector boson in e(+)e(-) -> U gamma, U -> e(+)e(-) with the KLOE experiment
- 2015
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 750, s. 633-637
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Tidskriftsartikel (refereegranskat)abstract
- 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 DA Phi NE e(+)e(-) collider. Using an integrated luminosity of 1.54 fb(-1), we studied the process e(+)e(-) -> U gamma, 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, epsilon(2), at 10(-6)-10(-4) in the 5-520 MeV/c(2) mass range.
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4. |
- Anastasi, A., et al.
(författare)
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Limit on the production of a new vector boson in e+e− → Uγ, U → π+π− with the KLOE experiment
- 2016
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 757, s. 356-361
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in e + e − → U γ , U → π + π − based on 28 million e + e − → π + π − γ events collected at DAΦNE by the KLOE experiment. The π + π − production by initial-state radiation compensates for a loss of sensitivity of previous KLOE U → e + e − , μ + μ − searches due to the small branching ratios in the ρ – ω resonance region. We found no evidence for a signal and set a limit at 90% CL on the mixing strength between the photon and the dark photon, ε 2 , in the U mass range between 527 and 987 MeV . Above 700 MeV this new limit is more stringent than previous ones.
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5. |
- Anastasi, A., et al.
(författare)
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Precision measurement of the η → π + π − π 0 Dalitz plot distribution with the KLOE detector
- 2016
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5
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Tidskriftsartikel (refereegranskat)abstract
- Using 1.6 fb−1 of e + e − → ϕ → ηγ data collected with the KLOE detector at DAΦNE, the Dalitz plot distribution for the η → π + π − π 0 decay is studied with the world’s largest sample of ∼ 4.7 · 106 events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables X and Y . The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a gX 2 Y term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.
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6. |
- Anastasi, A., et al.
(författare)
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Search for dark Higgsstrahlung in e(+0)e(-) -> mu(+)mu(-) and missing energy events with the KLOE experiment
- 2015
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 747, s. 365-372
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Tidskriftsartikel (refereegranskat)abstract
- We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h', with the KLOE detector at DA Phi NE. We investigated the case of h' lighter than U, with U decaying into a muon pair and h' producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m(mu) < m(U) < 1000 MeV, m(h') < m(U). (C) 2015 The Authors. Published by Elsevier B.V.
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7. |
- Babusci, D., et al.
(författare)
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A new limit on the CP violating decay K-S -> 3 pi(0) with the KLOE experiment
- 2013
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 723:1-3, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- 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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8. |
- Babusci, D., et al.
(författare)
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Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector
- 2013
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 720:1-3, s. 111-115
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Tidskriftsartikel (refereegranskat)abstract
- We present a new limit on the production of a light dark-force mediator with the KLOE detector at DA Phi NE. This boson, called U, has been searched for in the decay phi -> eta U, U -> e(+)e(-), analyzing the. decay eta -> pi(0)pi(0)pi(0) 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 eta -> pi(+)pi(-)pi(0), 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 alpha'/alpha < 1.7 x 10(-5) for 30 < M-U < 400 MeV and alpha'/alpha <= 8 x 10(-6) for the sub-region 50 < M-U <210 MeV. This result assumes the Vector Meson Dominance expectations for the phi eta gamma* transition form factor. The dependence of this limit on the transition form factor has also been studied.
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9. |
- Babusci, D., et al.
(författare)
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Measurement of eta meson production in gamma gamma interactions and Gamma(eta -> gamma gamma) with the KLOE detector
- 2013
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :1, s. 119-
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Tidskriftsartikel (refereegranskat)abstract
- We present a measurement of eta meson production in photon-photon interactions produced by electron-positron beams colliding with root s = 1 GeV. The measurement is done with the KLOE detector at the phi-factory DA Phi NE with an integrated luminosity of 0.24 fb(-1). The e(+)e(-) -> e(+)e(-)eta cross section is measured without detecting the outgoing electron and positron, selecting the decays eta -> pi(+)pi(-)pi(0) and eta -> pi(0)pi(0)pi(0). The most relevant background is due to e(+)e(-) -> eta gamma when the monochromatic photon escapes detection. The cross section for this process is measured as sigma(e(+)e(-) -> eta gamma) = (856 +/- 8(stat) +/- 16(syst)) pb. The combined result for the e(+)e(-) -> e(+)e(-)eta cross section is sigma(e(+)e(-) -> e(+)e(-)eta) = (32.72 +/- 1.27(stat) +/- 0.70(syst)) pb. From this we derive the partial width Gamma(eta -> gamma gamma) = (520 +/- 20(stat) +/- 13(syst)) eV. This is in agreement with the world average and is the most precise measurement to date.
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10. |
- Babusci, D., et al.
(författare)
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Measurement of Γ(η→π+π-γ)/Γ(η→π+π-π0) with the KLOE detector
- 2013
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 718:3, s. 910-914
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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11. |
- Babusci, D., et al.
(författare)
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Precision measurement of sigma (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) ->mu(+)mu(-)gamma) and determination of the pi(+)pi(-) contribution to the muon anomaly with the KLOE detector
- 2013
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 720:4-5, s. 336-343
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the ratio cr (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) -> mu(+)mu(-)gamma), with the KLOE detector at DA Phi NE for a total integrated luminosity of similar to 240 pb(-1). From this ratio we obtain the cross section sigma (e(+)e(-) -> pi(+)pi(-)gamma). From the cross section we determine the pion form factor vertical bar F-pi vertical bar(2) and the two-pion contribution to the muon anomaly a(mu) for 0.592< M-pi pi < 0.975 GeV, Delta(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. (c) 2013 Elsevier B.V. All rights reserved.
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12. |
- Babusci, D., et al.
(författare)
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Search for light vector boson production in e(+)e(-) -> mu(+)mu(-)gamma interactions with the KLOE experiment
- 2014
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 736, s. 459-464
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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13. |
- Babusci, D., et al.
(författare)
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Study of the Dalitz decay phi -> eta e(+)e(-) with the KLOE detector
- 2015
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 742, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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14. |
- Babusci, D., et al.
(författare)
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Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment
- 2014
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 730, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- Neutral kaon pairs produced in phi 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 phi -> KSKL -> pi(+)pi(-)pi(+)pi(-) based on 1.7 fb(-1) of data collected by the KLOE experiment at the Frascati phi-factory DA Phi NE. The data are used to perform a Measurement of the CPT-violating parameters Delta a(mu) for neutral kaons in the context of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are: Delta a(0) = (-6.0 +/- 7.7(stat)+/- 3.1(syst)) X 10(-18) GeV, Delta a(x) = (0.9 +/- 1.5(stat)+/- 0.6(syst)) X 10(-18) GeV, Delta a(y) = (-2.0 +/- 1.5(stat)+/- 0.5(syst)) X 10(-18) GeV, Delta a(z) = (3.1 +/- 1.7(stat)+/- 0.5(syst)) X 10(-18) GeV. These are presently the most precise measurements in the quark sector of the Standard Model Extension. (C) 2014 The Authors. Published by Elsevier B.V.
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15. |
- Babuscih, D., et al.
(författare)
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Measurement of the absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay with the KLOE detector
- 2014
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 738, s. 128-133
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Tidskriftsartikel (refereegranskat)abstract
- The absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay, inclusive of final-state radiation, has been measured using similar to 17 million tagged K+ mesons collected with the KLOE detector at DA Phi NE, the Frascati phi-factory. The result is: BR(K+ -> pi(+) pi(-) pi(+) (gamma)) = 0.05565 +/- 0.00031(stat) +/- 0.00025(syst) a factor similar or equal to 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.
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