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Register a new userLimit on the production of a low-mass vector boson in $mathrm{e}^{+}mathrm{e}^{-} to mathrm{U}gamma$, $mathrm{U} to mathrm{e}^{+}mathrm{e}^{-}$ with the KLOE experiment
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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 $mathrm{U}$ boson, with the KLOE detector at the DA$Phi$NE $mathrm{e}^{+}mathrm{e}^{-}$ collider. Using an integrated luminosity of 1.54 fb$^{-1}$, we studied the process $mathrm{e}^{+}mathrm{e}^{-} to mathrm{U}gamma$, with $mathrm{U} to mathrm{e}^{+}mathrm{e}^{-}$, 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, $varepsilon^2$, at $10^{-6}$--$10^{-4}$ in the 5--520~MeV/c$^2$ mass range.
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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 ${rm e^+ e^-}rightarrow {rm U}gamma$, U$rightarrow pi^+pi^-$ based on 28 million $mathrm{e^+ e^-} rightarrow pi^+ pi^-gamma$ events collected at DA$Phi$NE by the KLOE experiment. The $pi^+ pi^-$ production by initial-state radiation compensates for a loss of sensitivity of previous KLOE ${rm U} rightarrow mathrm{e^+ e^-}$, $mu^+mu^-$ searches due to the small branching ratios in the $rho-omega$ 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, $varepsilon^2$, in the U mass range between $527$ and $987$~MeV. Above 700 MeV this new limit is more stringent than previous ones.
We present a precise measurement of double-polarization asymmetries in the $^3vec{mathrm{He}}(vec{mathrm{e}},mathrm{e}mathrm{d})$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in $^3mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasi-elastic kinematics at $Q^2 = 0.25,(mathrm{GeV}/c)^2$ for missing momenta up to $270,mathrm{MeV}/c$. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on $p_mathrm{m}$ and $omega$, but are systematically offset. Beyond the region of the quasi-elastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two- and/or three-body dynamics is required.
We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3mathrm{He}$ proceeding to $mathrm{pd}$ and $mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25,(mathrm{GeV}/c)^2$ for missing momenta up to $250,mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of $^3mathrm{He}$ and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of $^3mathrm{He}$ unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought.
We perform a beam-beam parameter study for a TeV-scale PWFA (particle-driven plasma wakefield acceleration) $mathrm{e}^+$$mathrm{e}^-$ linear collider using GUINEA-PIG simulations. The study shows that the total luminosity follows the $1/sqrt{sigma_z}$-scaling predicted by beamstrahlung theory, where $sigma_z$ is the rms beam length, which is advantageous for PWFA, as short beam lengths are preferred. We also derive a parameter set for a 3 TeV PWFA linear collider with main beam parameters optimised for luminosity and luminosity spread introduced by beamstrahlung. Lastly, the study also compare the performance for scenarios with reduced positron beam charge at 3 TeV and 14 TeV with CLIC parameters.
We extract the $e^+e^-rightarrow pi^+pi^-$ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb$^{-1}$ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor $|F_pi|^2$ as well as the contribution of the measured cross section to the leading order hadronic vacuum polarization contribution to $(g-2)_mu$. We find this value to be $a_mu^{pipi,rm LO}(600-900;rm MeV) = (368.2 pm 2.5_{rm stat} pm 3.3_{rm sys})cdot 10^{-10}$.
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