Engineering topics
Andreassen, R.
Publications and source records attributed to Andreassen, R..
Search for new π 0 -like particles produced in association with a τ -lepton pair
Not Available
Search for a Dark Photon in e + e - Collisions at BaBar
Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A'), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e + e - →γA', A'→e + e - , μ + μ - using 514 fb -1 of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of10 -4 -10 -3 for dark photon masses in the range 0.02–10.2 GeV We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon.
Measurements of direct C P asymmetries in B → X s γ decays using sum of exclusive decays
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Study of χ b meson production in pp collisions at $\sqrt{s}=$ 7 and 8 TeV and observation of the decay χ b (3P) → $\Upsilon$(3S)$\gamma$
A study of χ b meson production at LHCb is performed on proton–proton collision data, corresponding to 3.0 fb -1 of integrated luminosity collected at centre-of-mass energies $\sqrt{s}$ = 7 and 8 TeV. The fraction of $\Upsilon \mathrm {(nS)}$ mesons originating from χ b decays is measured as a function of the $\Upsilon$ transverse momentum in the rapidity range 2.0 < y $\Upsilon$ < 4.5. The radiative transition of the χ b (3P) meson to $\Upsilon$ (3S) is observed for the first time. The χ b1 (3P) mass is determined to be $\begin{aligned} m_{χ_{{\mathrm {b}} 1}\mathrm {(3P)}} = 10\,511.3 \pm 1.7 \pm 2.5{\mathrm {\,MeV}/c^2}, \end{aligned}$ where the first uncertainty is statistical and the second is systematic.
Measurement of the Ξ b – and Ω b – baryon lifetimes
Using a data sample of pp collisions corresponding to an integrated luminosity of 3 fb -1 , the Ξ b – and Ω b – baryons are reconstructed in the Ξ b – →J/ψΞ - and Ω b – →J/ψΩ - decay modes and their lifetimes measured to be τ( Ξ b – )=1.55$^{+0.10}_{-0.09}$(stat)±0.03(syst)ps, τ( Ω b – )=1.54$^{+0.26}_{-0.21}$(stat)±0.05(syst)ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.
Measurement of charged particle multiplicities and densities in pp collisions at √s = 7 TeV in the forward region
Charged particle multiplicities are studied in proton–proton collisions in the forward region at a centre-of-mass energy of √s = 7 TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of 2.0 < η < 4.8 in pseudorapidity, momenta greater than 2 GeV/c and transverse momenta greater than 0.2 GeV/c. The measurements are performed using events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.
Measurement of J/ψ polarization in pp collisions at $\sqrt{s}=7\ \mathrm{TeV}$
An angular analysis of the decay J/ψ→μ + μ – is performed to measure the polarization of prompt J/ψ mesons produced in pp collisions at √s=7 TeV. The dataset corresponds to an integrated luminosity of 0.37 fb –1 collected with the LHCb detector. The measurement is presented as a function of transverse momentum, p T , and rapidity, y, of the J/ψ meson, in the kinematic region 2 < p T < 15 GeV/c and 2.0<y<4.5.
Observation of the Decay B c + → B s 0 π +
The result of a search for the decay B c + → B s 0 π + is presented, using the B s 0 → D s - π + and B s 0 → J /ψφ channels. The analysis is based on a data sample of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of 1 fb -1 taken at a center-of-mass energy of 7 TeV, and 2 fb -1 taken at 8 TeV. The decay B c + → B s 0 π + is observed with significance in excess of 5 standard deviations independently in both decay channels. The measured product of the ratio of cross sections and branching fraction is [σ (B c + )/σ (B s 0 )] × B ( B c + → B s 0 π + ) =[2.37±0.31 (stat) ± 0.11 (syst)$ +0.17\atop{-0.13} $(τ$_B{_c^+}$)]×10 -3 , in the pseudorapidity range 2<η(B)<5, where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the $B{_c^+}$ lifetime. This is the first observation of a B meson decaying to another B meson via the weak interaction.
Measurement of CP-violating asymmetries in B^0 \to (rho-pi)^0 Decays using a Time-dependent Daltiz Plot Analysis
Abstract Not Provided
Search for C P Violation in B 0 - B ¯ 0 Mixing Using Partial Reconstruction of B 0 → D * - X ℓ + ν ℓ and a Kaon Tag
We present results of a search for CP violation in B 0 -B¯ 0 mixing with the BABAR detector. We select a sample of B 0 →D* - Xℓ+ν decays with a partial reconstruction method and use kaon tagging to assess the flavor of the other B meson in the event. We determine the CP violating asymmetry ACP≡[N(B 0 B 0 )-N(B¯ 0 B¯ 0 )]/[N(B 0 B 0 )+N(B¯ 0 B¯ 0 )]=(0.06±0.17+0.38-0.32)%, corresponding to ΔCP=1-|q/p|=(0.29±0.84 +1.88 -1.61 )×10 -3 .
Search for a light Higgs boson decaying to two gluons or ss̄ in the radiative decays of Υ(1S)
We search for the decay Υ(1S)→γA⁰, A⁰→gg or ss̄, where A⁰ is the pseudoscalar light Higgs boson predicted by the next-to-minimal supersymmetric Standard Model. We use a sample of (17.6±0.3)×10⁶ Υ(1S) mesons produced in the BABAR experiment via e⁺e⁻→Υ(2S)→π⁺π⁻Υ(1S). We see no significant signal and set 90%-confidence-level upper limits on the product branching fraction B(Υ(1S)→γA⁰)·B(A⁰→gg or ss̄) ranging from 10⁻⁶ to 10⁻² for A⁰ masses in the range 0.5–9.0 GeV/c².
Search for B \to K(*)nunubar and Invisible Quarkonium Decays
Abstract Not Provided
Observation of direct CP violation in the measurement of the Cabibbo-Kobayashi-Maskawa angle gamma with B+- to D(*)K(*)+- decays
Abstract Not Provided