Search results for " ANN"
showing 10 items of 1343 documents
Measurement of initial-state–final-state radiation interference in the processese+e−→μ+μ−γande+e−→π+π−γ
2015
Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma is measured using 232 fb-1 of data collected with the BABAR detector at center-of-mass energies near 10.58 GeV. An observable is introduced and shown to be very robust against detector asymmetries while keeping a large sensitivity to the physical charge asymmetry that results from the interference between initial and final state radiation. The asymmetry is determined as afunction of the invariant mass of the final-state tracks from production threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e- --> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A clear interfe…
Structure at 2175 MeV ine+e−→ϕf0(980)observed via initial-state radiation
2006
We study the initial-state-radiation processes e+e-→K+K-π+π- γ and e+e-→K+K-π0π0γ using an integrated luminosity of 232fb-1 collected at the Υ(4S) mass with the BABAR detector at SLAC. Even though these reactions are dominated by intermediate states with excited kaons, we are able to study for the first time the cross section for e+e-→ (1020)f0(980) as a function of center-of-mass energy. We observe a structure near threshold consistent with a 1 - resonance with mass m=2.175±0. 010±0.015GeV/c2 and width Γ=58±16±20MeV. We observe no Y(4260) signal and set a limit of BY→ π+π-•ΓeeY<0. 4eV (90% confidence level), which excludes some models. © 2006 The American Physical Society.
Thee+e−→3(π+π−),2(π+π−π0)andK+K−2(π+π−)cross sections at center-of-mass energies from production threshold to 4.5 GeV measured with initial-state rad…
2006
We study the processes e^+e^- → 3(π^+π^-)γ, 2(π^+π^-π^0)γ and K^+K^-2(π^+π^-)γ, with the photon radiated from the initial state. About 20 000, 33 000 and 4000 fully reconstructed events, respectively, have been selected from 232 fb^(-1) of BABAR data. The invariant mass of the hadronic final state defines the effective e^+e^- center-of-mass energy, so that these data can be compared with the corresponding direct e^+e^- measurements. From the 3(π^+π^-), 2(π^+π^-π^0) and K^+K^-2(π^+π^-) mass spectra, the cross sections for the processes e^+e^- → 3(π^+π^-), e^+e^- → 2(π^+π^-π^0) and e^+e^- → K^+K^-2(π^+π^-) are measured for center-of-mass energies from production threshold to 4.5 GeV. The unc…
Evidence forηc→γγand measurement ofJ/ψ→3γ
2013
The decay of J/psi to three photons is studied using psi (3686) -> pi(+) pi(-) J/psi in a sample of 1.0641 X 10(8) psi (3686) events collected with the BESIII detector. Evidence of the direct decay of eta(c) to two photons, eta(c) -> gamma gamma, is reported, and the product branching fraction is determined to be B(J/psi -> gamma eta(c,) eta(c) -> gamma gamma = (4.5 +/- 1.2 +/- 0.6) X 10(-6), where the first error is statistical and the second is systematic. The branching fraction for J/psi -> 3 gamma is measured to be (11.3 +/- 1.8 +/- 2.0) X 10(-6) with improved precision. DOI: 10.1103/PhysRevD.87.032003
Measurements ofe+e−→K+K−η,K+K−π0, andKs0K±π∓cross sections using initial state radiation events
2008
This paper reports measurements of processes: e+e-→γKS0K±π∓, e+e-→γK+K-π0, e+e-→γϕη, and e+e-→γϕπ0. The initial-state radiated photon allows to cover the hadronic final state in the energy range from thresholds up to ≈4.6 GeV. The overall size of the data sample analyzed is 232 fb-1, collected by the BABAR detector running at the PEP-II e+e- storage ring. From the Dalitz plot analysis of the KS0K±π∓ final state, moduli, and relative phase of the isoscalar and the isovector components of the e+e-→KK*(892) cross section are determined. Parameters of ϕ and ρ recurrences are also measured, using a global fitting procedure which exploits the interconnection among amplitudes, moduli, and phases…
Improved measurements of the branching fractions forB0→π+π−andB0→K+π−, and a search forB0→K+K−
2007
We present measurements of the branching fractions for the charmless two-body decays B0→π+π- and B0→K+π-, and a search for the decay B0→K+K-. We include the effects of final-state radiation from the daughter mesons for the first time, and quote branching fractions for the inclusive processes B0→h+h′-nγ, where h and h′ are pions or kaons. The maximum value of the sum of the energies of the n undetected photons, Eγmax, is mode-dependent. Using a data sample of approximately 227×106 Υ(4S)→BB decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we measure: B(B0→π+π-nγ;Eγmax =150MeV)=(5.1±0.4±0.2) ×10-6, B(B0→K+π-nγ;Eγmax =105MeV)=(18.1±0. 6±0.6)×10-6, …
Measurement of the proton form factor by studyinge+e−→pp¯
2015
Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of e(+)e(-) -> p (p) over tilde at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal (vertical bar G(E)vertical bar = vertical bar G(M)vertical bar). In addition, the ratio of electric to magnetic form factors, vertical bar G(E)/G(M)vertical bar, and vertical bar G(M)vertical bar are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at root s = 2232.4 and 240…
Weak magnetic dipole moments in two-Higgs-doublet models
1995
We investigate the effects of the new scalars in a two-Higgs-doublet model on the weak magnetic dipole moments of the fermions at the $Z$ peak. Proportionality of the Yukawa couplings to the fermion masses, and to $\tan{\beta}$, makes such effects more important for the third family, and potentially relevant. For the $\tau$ lepton, the new diagrams are suppressed by $v_\tau = 2 \sin^2 \theta_W - 1/2$, or by powers of $m_\tau/M_Z$, but may still be comparable to the SM electroweak contributions. In contrast, we find that the new contributions for the bottom quark may be much larger than the SM electroweak contributions. These new effects may even compete with the gluonic contribution, if the…
Experimental results on the electroweak interaction
1999
Recent results from the four experiments ALEPH, DELPHI, L3 and OPAL at the Large Electron-Positron collider, LEP at CERN, and by the SLD collaboration at the Stanford Linear Collider, SLC, are reviewed. Analyses from an integrated luminosity of about 150 pb− recorded by each experiment at LEP, taken at different centre-of-mass energies within ±3 GeV around the peak of the Z resonance during the years 1989 to 1995 are available now. Repeated accurate calibrations of the beam energy lead to precise measurements of the mass and of the total width of the Z boson. These results are complemented by measurements at the Z resonance with polarised beams at Stanford. First results from an integrated …
CP violation and electric-dipole moment at low energy tau production with polarized electrons
2006
10 pages, 2 figures.-- ISI Article Identifier: 000243912400014.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0610135