591 research outputs found

    Acceleration by Strong Interactions

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    Beyond the attractive strong potential needed for hadronic bound states, strong interactions are predicted to provide repulsive forces depending on the color charges involved. The repulsive interactions could in principle serve for particle acceleration with highest gradients in the order of GeV/fm. Indirect evidence for repulsive interactions have been reported in the context of heavy meson production at colliders. In this contribution, we sketch a thought experiment to directly investigate repulsive strong interactions. For this we prepare two quarks using two simultaneous deep inelastic scattering processes off an iron target. We discuss the principle setup of the experiment and estimate the number of electrons on target required to observe a repulsive effect between the quarks.Comment: 6 pages, 7 figure

    Reliability and accuracy of single-molecule FRET studies for characterization of structural dynamics and distances in proteins

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    Single-molecule Förster-resonance energy transfer (smFRET) experiments allow the study of biomolecular structure and dynamics in vitro and in vivo. We performed an international blind study involving 19 laboratories to assess the uncertainty of FRET experiments for proteins with respect to the measured FRET efficiency histograms, determination of distances, and the detection and quantification of structural dynamics. Using two protein systems with distinct conformational changes and dynamics, we obtained an uncertainty of the FRET efficiency ≀0.06, corresponding to an interdye distance precision of ≀2 Å and accuracy of ≀5 Å. We further discuss the limits for detecting fluctuations in this distance range and how to identify dye perturbations. Our work demonstrates the ability of smFRET experiments to simultaneously measure distances and avoid the averaging of conformational dynamics for realistic protein systems, highlighting its importance in the expanding toolbox of integrative structural biology

    Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at √s = 13 TeV

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    Abstract The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d̂ t) and chromomagnetic (Ό̂ t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable AFB(1) is used to approximate the asymmetry. Candidate t t ÂŻ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t t ÂŻ final states. The values found for the parameters are AFB(1)=0.048−0.087+0.095(stat)−0.029+0.020(syst),Ό̂t=−0.024−0.009+0.013(stat)−0.011+0.016(syst), and a limit is placed on the magnitude of | d̂ t| < 0.03 at 95% confidence level. [Figure not available: see fulltext.

    Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV