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2 Collaboration

Publications and source records attributed to 2 Collaboration.

50 records · Page 3Linked to original sources
arXiv2005

Observation of a cusp-like structure in the pizero-pizero invariant mass distribution from K+- ==> pi+- pizero pizero decay and determination of the pi-pi scattering lengths

We report the results from a study of ~23 Million K+- ==> pi+- pizero pizero decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the pizero pizero invariant mass distribution in the region around 2m+, where m+ is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process pi+ pi- ==> pizero pizero in K+- ==> pi+- pi+ pi- decay. It provides a precise determination of a0 - a2, the difference between the pi-pi scattering lengths in the isospin I=0 and I=2 states.

hep-ex↗
arXiv2005

Neutrino Oscillation Effects in Soudan-2 Upward-stopping muons

Upward-going stopping muons initiated by atmospheric \numu and \anumu interactions in the rock below the Soudan 2 detector have been isolated, together with a companion sample of neutrino-induced single muons, created within the detector, which travel downwards and exit. The downward-going sample is consistent with the atmospheric-neutrino flux prediction, but the upward-going sample exhibits a sizeable depletion. Both are consistent with previously reported Soudan-2 neutrino-oscillation results. Inclusion of the two samples in an all-event likelihood analysis, using recent 3D-atmospheric-neutrino-flux calculations, reduces both the allowed oscillation parameter region and the probability of the no-oscillation hypothesis.

hep-ex↗
arXiv2005

Study of the $ρ$ and $ω$ meson decays into pseudoscalar meson and $e^+e^-$ pair with the CMD-2 detector

Using 3.3 pb$^{-1}$ of data collected with the CMD-2 detector in the 720 -- 840 MeV c.m. energy range, the branching fraction of the conversion decay $ω\toπ^0e^+e^-$ has been measured: $\mathcal{B}(ω\toπ^0e^+e^-)=(8.19\pm0.71\pm0.62)\cdot10^{-4}$. The upper limits for the branching fractions of the following conversion decays have been obtained at the 90% confidence level: $\mathcal{B}(ρ\toπ^0e^+e^-)<1.6\cdot10^{-5}$, $\mathcal{B}(ρ\toηe^+e^-)<0.7\cdot10^{-5}$ and $\mathcal{B}(ω\toηe^+e^-)<1.1\cdot10^{-5}$.

hep-ex↗
arXiv2003

Study of the Process e+ e- --> omega pi0 --> pi0 pi0 gamma in c.m. Energy Range 920--1380 MeV at CMD-2

The cross section of the process e+ e- --> omega pi0 --> pi0 pi0 gamma has been measured in the c.m. energy range 920-1380 MeV with the CMD-2 detector. Its energy dependence is well described by the interference of the rho(770) and rho'(1450) mesons decaying to omega pi0. Upper limits for the cross sections of the direct processes e+ e- --> pi0 pi0 gamma, eta pi0 gamma have been set.

hep-ex↗
arXiv2001

Precision Measurement of Muon g-2 at BNL

The Muon (g-2) Experiment (E821) at Brookhaven National Laboratory (BNL) has measured the anomalous magnetic moment of the positive muon to an unprecedented precision of 1.3 parts per million. The result, a_{μ^+} = (g-2)/2 = 11 659 202(14)(6) X 10^{-10}, is based on data recorded in 1999 and is in good agreement with previous measurements. Upcoming analysis of data recorded in 2000 and 2001 will substantially reduce the uncertainty on this measurement. Comparison of the new world average experimental value with the most comprehensive Standard Model calculation, a_μ(SM) = 11 659 159.6(6.7) X 10^{-10}, yields a difference of a_μ(exp)-a_μ(SM) = 43(16) X 10^{-10}.

hep-ex↗
arXiv2001

Measurement of the $ϕ$ meson parameters with CMD-2 detector at VEPP-2M Collider

About 300 000 $e^+e^-\to ϕ\to K^0_L K^0_S$ events in the center of mass energy range from 984 to 1040 MeV were used for the measurement of the $ϕ$ meson parameters. The following results have been obtained: $σ_0 = (1367 \pm 15 \pm 21) nb, m_ϕ=(1019.504 \pm 0.011 \pm 0.033) MeV/c^2, Γ_ϕ=(4.477 \pm 0.036 \pm 0.022) MeV, Γ_{e^+e^-}\cdot B(ϕ\to K^0_L K^0_S) = (4.364 \pm 0.048 \pm 0.065)\cdot 10^{-4}$ MeV.

hep-ex↗
arXiv2000

Study of the process e+e- to pi+pi-pi+pi-pi0 with CMD-2 detector

The process e+e- to pi+ pi- pi+ pi- pi0 has been studied in the center of mass energy range 1280 -- 1380 MeV using 3.0 1/pb of data collected with the CMD-2 detector in Novosibirsk. Analysis shows that the cross section of the five pion production is dominated by the contributions of the eta pi+pi- and omega pi+pi- intermediate states.

hep-ex↗
arXiv2000

Observation of the phi to pi+pi-pi+pi- Decay

Using 11.6 pb^{-1} of data collected in the energy range 0.984--1.06 GeV by CMD-2 at VEPP-2M, the cross section of the reaction e+e- to pi+pi-pi+pi- has been studied. For the first time an interference pattern was observed in the energy dependence of the cross section near the phi meson. The branching ratio of the phi to pi+pi-pi+pi- decay double suppressed by the G-parity and OZI rule is measured Br(phi to pi+pi-pi+pi-) = (3.93 +- 1.74 +- 2.14) \cdot 10^{-6}. The upper limits have been placed for the decays phi to pi+pi-pi+pi-pi0 and phi to eta pi+pi- Br(phi to pi+pi-pi+pi-pi0) < 4.6 \cdot 10^{-6} 90% CL, Br(phi to eta pi+pi-) < 1.8 \cdot 10^{-5} 90% CL.

hep-ex↗
arXiv2000

Measurement of omega meson parameters in pi^+pi^-pi^0 decay mode with CMD-2

About 11 200 e^+e^- -> omega -> pi^+pi^-pi^0 events selected in the center of mass energy range from 760 to 810 MeV were used for the measurement of the ωmeson parameters. The following results have been obtained: sigma _{0}=(1457 \pm 23 \pm 19)nb, m_ω=(782.71 \pm 0.07 \pm 0.04) MeV/c^{2}, Γ_ω=(8.68 \pm 0.23 \pm 0.10) MeV, Γ_{e^+e^-}\cdot Br (ω-> pi^+pi^-pi^0)= (0.528 \pm 0.012 \pm 0.007) \cdot 10^{-3} MeV.

hep-ex↗
arXiv1999

First observation of the $ϕ\toπ^+π^-γ$ decay

Radiative decays of the $ϕ$ meson have been studied using a data sample of about 20 million $ϕ$ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected $e^+e^-\toπ^{+}π^{-}γ$ events the $ϕ\toπ^{+}π^{-}γ$ decay has been observed for the first time. \par Under the assumption that the intermediate $f_{0}(980)γ$ state dominates in the $ϕ\to π^+π^-γ$ decay, the corresponding branching ratio is $Br(ϕ\to f_{0}(980)γ)=(1.93\pm 0.46\pm 0.50)\times10^{-4}$. \par Selected $e^+e^-\toμ^+μ^-γ$ events were used to obtain $Br(ϕ\toμ^+μ^-γ) =(1.43\pm 0.45\pm 0.14)\times10^{-5}$ for $E_γ>20$ MeV. \par Using the same data sample, upper limits at 90% CL have been obtained for the C-violating decay of the $ϕ$: $Br(ϕ\toργ) < 1.2\times10^{-5}$; and for the P- and CP-violating decay of the $η$: \par $Br(η\toπ^+π^-) < 3.3\times10^{-4}$.

hep-ex↗
arXiv1999

Study of the $ϕ$ decays into $π^0π^0γ$ and $ηπ^0γ$ final states

Radiative decays of the $ϕ$ meson have been studied using a data sample of about 19 million $ϕ$ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected $e^+e^-\toπ^{0}π^{0}γ$ and $e^+e^-\toηπ^{0}γ$ events the following model independent results have been obtained: \par $Br(ϕ\toπ^{0}π^{0}γ) = (0.92\pm 0.08\pm0.06)\times10^{-4}$ for $M_{π^{0}π^{0}}>700$ MeV, \par $Br(ϕ\toηπ^{0}γ) = (0.90\pm 0.24\pm 0.10)\times10^{-4}$. It is shown that the intermediate mechanism $f_{0}(980)γ$ dominates in the $ϕ\toπ^{0}π^{0}γ$ decay and the corresponding branching ratio is \par $Br(ϕ\to f_{0}(980)γ)=(2.90\pm 0.21\pm1.54)\times10^{-4}$. The systematic error is dominated by the possible model uncertainty. \par Using the same data sample the upper limit has been obtained for the P- and CP-violating decay of $η$ at 90% CL: \par $Br(η\toπ^{0}π^{0}) < 4.3\times10^{-4}$ >.

hep-ex↗
arXiv1997

Search for rare Phi decays in pi+ pi_ gamma final state

A search for phi radiative decays has been performed using a data sample of about 2.0 million phi decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From the selected e+ e- -> pi+ pi- gamma events the following results were obtained: B(phi -> f0(980) gamma) < 1x10-4 for destructive and B(phi -> f0(980) gamma) < 7x10-4 for constructive interference with the Bremsstrahlung process respectively, B(phi -> gamma -> pi+ pi- gamma) < 3x10-5 for E of gamma > 20 MeV, B(phi -> rho gamma) < 7x10-4. From the selected e+ e- -> mu+ mu- gamma events B(phi -> mu+ mu- gamma) = (2.3+-1.0)x10-5 has been obtained for E of gamma> 20 MeV. The upper limit on the P,CP-violating decay eta -> pi+ pi- has also been placed: B(eta -> pi+ pi-) < 9x10-4 . All upper limits are at 90 % C.L.

hep-ex↗
arXiv1997

Study of KS KL Coupled Decays and KL -Be Interactions with the CMD-2 Detector at VEPP-2M Collider

The integrated luminosity about 4000 inverse nanobarn of around phi meson mass ( 5 millions of phi mesons) has been collected with the CMD-2 detector at the VEPP-2M collider. A latest analysis of the KS KL coupled decays based on 30 % of available data is presented in this paper. The KS KL pairs from phi meson decays were reconstructed in the drift chamber when both kaons decayed into two charged particles. From a sample of 1423 coupled decays a selection of candidates to the CP violating KL into pi+ pi- decay was performed. CP violating decays were not identified because of the domination of events with a KL regenerating at the Be beam pipe into KS and a background from KL semileptonic decays. The regeneration cross section of 110 MeV/c KL mesons was found to be 53 +- 17 mb in agreement with theoretical expectations. The angular distribution of KS mesons after regeneration and the total cross section of KL for Be have been measured.

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