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Article
Report number arXiv:2212.06588 ; CERN-EP-2022-283
Title First measurement of prompt and non-prompt D+ vector meson spin alignment in pp collisions at s=13 TeV
Author(s) ALICE Collaboration  ყველა 1039 ავტორის ჩვენება
Publication 2023-09-20
Imprint 09 Dec 2022
Number of pages 15
Note 23 pages, 6 captioned figures, 1 table, authors from page 18, published version, figures at http://alice-publications.web.cern.ch/node/8858
In: Phys. Lett. B 846 (2023) 137920
DOI 10.1016/j.physletb.2023.137920 (publication)
Subject category Nuclear Physics - Experiment ; Particle Physics - Experiment
Accelerator/Facility, Experiment CERN LHC ; ALICE
Free keywords QCD ; relativistic heavy ion physics ; B physics ; charm physics ; heavy quark production ; experimental results
Abstract This letter reports the first measurement of spin alignment, with respect to the helicity axis, for D+ vector mesons and their charge conjugates from charm-quark hadronisation (prompt) and from beauty-meson decays (non-prompt) in hadron collisions. The measurements were performed at midrapidity (|y|<0.8) as a function of transverse momentum (pT) in proton-proton (pp) collisions collected by ALICE at the centre-of-mass energy s=13 TeV. The diagonal spin density matrix element ρ00 of D+ mesons was measured from the angular distribution of the D+D0(Kπ+)π+ decay products, in the D+ rest frame, with respect to the D+ momentum direction in the pp centre of mass frame. The ρ00 value for prompt D+ mesons is consistent with 1/3, which implies no spin alignment. However, for non-prompt D+ mesons an evidence of ρ00 larger than 1/3 is found. The measured value of the spin density element is ρ00=0.455±0.022(stat.)±0.035(syst.) in the 5<pT<20 GeV/c interval, which is consistent with a PYTHIA 8 Monte Carlo simulation coupled with the EVTGEN package, which implements the helicity conservation in the decay of D+ meson from beauty mesons. In non-central heavy-ion collisions, the spin of the D+ mesons may be globally aligned with the direction of the initial angular momentum and magnetic field. Based on the results for pp collisions reported in this letter it is shown that alignment of non-prompt D+ mesons due to the helicity conservation coupled to the collective anisotropic expansion may mimic the signal of global spin alignment in heavy-ion collisions.
Copyright/License Publication: © 2023-2024 CERN (License: CC BY 4.0), sponsored by SCOAP³
Preprint: © 2022-2024 CERN (License: CC-BY-4.0)



Corresponding record in: Inspire
Email contact: javier.castillo.castellanos@cern.ch


 ჩანაწერი შექმნილია 2022-12-09, ბოლოს შესწორებულია 2024-11-27


სრული ტექსტი:
2212.06588 - სრული ტექსტის ჩამოტვირთვაPDF
Publication - სრული ტექსტის ჩამოტვირთვაPDF
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