Observation of abnormal suppression of f_0(980) production in p-Pb collisions at √s_NN = 5.02 TeV
ALICE Collaboration
Hide abstract | Show figures | Show BibTeX | Show discussion | View PDF | 2311.11786v1
The dependence of f_0(980) production on the final-state charged-particle multiplicity in p-Pb collisions at √s_NN = 5.02 TeV is reported. The production of f_0(980) is measured with the ALICE detector via the f0(980)→π+π− decay channel in a midrapidity region of −0.5<y<0. Particle yield ratios of f_0(980) to π and K∗(892)^0 are found to be decreasing with increasing charged-particle multiplicity. The magnitude of the suppression of the f_0(980)/π and f_0(980)/K∗(892)^0 yield ratios is found to be dependent on the transverse momentum pT, suggesting different mechanisms responsible for the measured effects. Furthermore, the nuclear modification factor Q_pPb of f_0(980) is measured in various multiplicity ranges. The Q_pPb shows a strong suppression of the f_0(980) production in the pT region up to about 4 GeV/c. The results on the particle yield ratios and Q_pPb for f_0(980) may help to understand the late hadronic phase in p-Pb collisions and the nature of the internal structure of f_0(980) particle. Authors' comments: 25 pages, 6 captioned figures, 2 tables, authors from page 19, submitted to PLB, figures at http://alice-publications.web.cern.ch/node/10258
Observation of quantum entanglement in top-quark pairs using the ATLAS detector
[ATLAS Collaboration]
Hide abstract | Show figures | Show BibTeX | Show discussion | View PDF | 2311.07288v2
We report the highest-energy observation of entanglement, in top-antitop quark events produced at the Large Hadron Collider, using a proton-proton collision data set with a center-of-mass energy of √s = 13 TeV and an integrated luminosity of 140/fb recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable D, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top-antitop quark production threshold, where the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D = −0.547±0.002 (stat.)±0.021 (syst.) for 340 < m_{t\bar{t}} < 380 GeV. The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes both the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement to date.
Authors' comments: 45 pages in total, author list starting page 28, 4 figures, 2 tables, submitted to Nature. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2021-24
