Study of ordered hadron chains with the ATLAS detector

Abstract

The analysis of the momentum difference between charged hadrons in high-energy proton-proton collisions is performed in order to study coherent particle production. The observed correlation pattern agrees with a model of a helical QCD string fragmenting into a chain of ground-state hadrons. A threshold momentum difference in the production of adjacent pairs of charged hadrons is observed, in agreement with model predictions. The presence of low-mass hadron chains also explains the emergence of charge-combination-dependent two-particle correlations commonly attributed to Bose-Einstein interference. The data sample consists of 190 μb −1 of minimum-bias events collected with proton-proton collisions at a center-of-mass energy ffiffi ffi s p ¼ 7 TeV in the early low-luminosity data taking with the ATLAS detector at the LHC.

Ultraperipheral nuclear interactions

“…For example, pairs of muons produced in ultraperipheral collisions are observed at LHC [37,38,39,40,41]. The light-by-light scattering described theoretically by the loop of charged particles is also detected at LHC [42,43,44]. Some neutral C-even bosons composed of quark-antiquark pairs can be produced in the two-photon interactions.…”

New physics with boosted single top production at the LHC and future colliders

“…The cross section and shape of the dominant tt background can be reliably predicted [26] and the efficiencies for event selection are determined from control regions and sidebands. Current searches in the much more demanding dijet final states, either with the use of jet substructure techniques [27,28] or without it [29,30], already use control regions to determine directly the background from data.…”

Dark matter mass from relic abundance, an extra U(1) gauge boson, and active-sterile neutrino mixing

“…where n c = 3 when f stands for quarks and n c = 1 when f stands for leptons and s ≈ In figure 3 we have shown the allowed region of M X and m ψ 1 for above mentioned two values of ∆. In plotting the figure we have considered the constraint coming from relic abundance on dark matter from Planck 2017 Ωh 2 ∈ (0.1188, 0.1212) [13] and also have considered constraint on g X and M X given by ATLAS [14,15] at LHC. We have also varied g X over the range 0.001 to 0.7 as considered by ATLAS.…”

“…Mass M X of the extra gauge boson in above expressions is given by equation (6) [14] and figure (5a) of [15] at 95% confidence level. However, these two figures in reference [14] and [15] don't differ too much. We have considered the allowed region of g X and M X in figure (5a) of ref [15] in our numerical analysis.…”