Apr 14th, 2025
BESIII Collab.
Based on (2712.4 ± 14.3)×106 ψ(3686) events collected by the BESIII detector operating at the BEPCII storage ring, we perform a search for the baryon- and lepton-number violating decay J/ψ→pe−+c.c. via ψ(3686)→π+π− J/ψ. No significant signal is found. An upper limit on the branching fraction of B(J/ψ→pe−+c.c.)<3.1×10−8 at 90% confidence level.
ATLAS Collab.
Higgs boson production cross-sections via gluon-gluon fusion and vector-boson fusion in proton-proton collisions are measured in the H→WW*→ℓνℓν decay channel. The Large Hadron Collider delivered proton-proton collisions at a centre-of-mass energy of 13TeV between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of 140fb−1. The total cross-sections for Higgs boson production by gluon-gluon fusion and vector-boson fusion times the H→WW* branching ratio are measured to be 12.4+1.3−1.2 pb and 0.79+0.18−0.16 pb, respectively, in agreement with the Standard Model predictions. Higgs boson production is further characterised through measurements of Simplified Template Cross-Sections in a total of fifteen kinematic fiducial regions. A new scheme of kinematic fiducial regions has been introduced to enhance the sensitivity to CP-violating effects in Higgs boson interactions. Both schemes are used to constrain CP-even and CP-odd dimension-six operators in the Standard Model effective field theory.
ATLAS Collab.
A measurement of off-shell Higgs boson production is performed in the H*→WW channel. The measurement uses a proton-proton collision dataset with an integrated luminosity of 140 fb−1 collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Final states in which both W bosons decay leptonically are targeted, and events are categorised based on the flavour of the final-state leptons, the jet multiplicity, and the output of neural network-based classifiers. The data are found to be compatible with the Standard Model expectation. An observed (expected) upper limit at 95% confidence level is set on the rate of off-shell Higgs boson production at a value of 3.4 (4.4) times the Standard Model prediction. These results are combined with the results from the measurement of on-shell Higgs boson production with the same final states to obtain an observed (expected) upper limit at 95% confidence level on the Higgs boson total width of 13.1 (17.3) MeV.
ATLAS Collab.
A reconstructed electron (purple line) with pT = 390 GeV can be seen leaving a significant energy deposit in the calorimeter, and a muon (red line) with pT = 236 GeV can be seen propagating through the muon spectrometer. The reconstructed missing energy vector is illustrated as a white dotted line, with an associated pTmiss of 156 GeV. In the inner detector SCT hits are shown to highlight the large multiplicity of particles in the inner detector.
LHCb Collab.
The first observation of the Σ+→pμ+μ− decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 5.4fb−1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV. A yield of 237 ± 16 Σ+→pμ+μ− decays is obtained, where the uncertainty is statistical only. A branching fraction of (1.08±0.17)×10−8 is measured, where the uncertainty includes statistical and systematic sources. No evidence of resonant structures is found in the dimuon invariant-mass distribution. All results are compatible with Standard Model expectations. This represents the rarest decay of a baryon ever observed.
LHCb Collab.
LHCb Collab.
LHCb Collab.
LHCb Collab.
C. A. Lindstrøm
Beam-driven plasma-wakefield acceleration (PWFA) has emerged as a transformative technology with the potential to revolutionize the field of particle acceleration, especially toward compact accelerators for high-energy and high-power applications. Charged particle beams are used to excite density waves in plasma with accelerating fields reaching up to 100 GV/m, thousands of times stronger than the fields provided by radio-frequency cavities. Plasma-wakefield-accelerator research has matured over the span of four decades from basic concepts and proof-of-principle experiments to a rich and rapidly progressing sub-field with dedicated experimental facilities and state-of-the-art simulation codes. We review the physics, including theory of linear and nonlinear plasma wakefields as well as beam dynamics of both the wakefield driver and trailing bunches accelerating in the plasma wake, and address challenges associated with energy efficiency and preservation of beam quality. Advanced topics such as positron acceleration, self-modulation, internal injection, long-term plasma evolution and multistage acceleration are discussed. Simulation codes and major experiments are surveyed, spanning the use of electron, positron and proton bunches as wakefield drivers. Finally, we look ahead to future particle colliders and light sources based on plasma technology.