Observation of triple J-psi Meson Production

The J/ψ meson (J/psi meson or psion) is a flavor-neutral meson about three times more massive than a proton.

This particle consists of a charm and an anti-charm pair held together tightly via the strong force.

It was discovered in two experiments unexpectedly in 1974, in the so-called ‘November Revolution’ of particle physics. This, in turn, led to the discovery of the charm quark, a heavier cousin of the up quark.

It fetched the pioneers of the experiments — Burton Richter and Samuel Ting — the Physics Nobel prize in 1976, and, importantly, opened a new window in the field of high-energy physics.

ATLAS, CMS and LHCb experiments have previously seen one or two J/ψ particles coming out of a single particle collision, but never before have they seen the simultaneous production of three J/ψ particles — until the new CMS analysis.

The rarity of this process is reflected in the number of events found, which is a meager 5, out of almost 100 billion proton-proton interactions that occurred during the Run-2 operation of the LHC spanning 2015-2018.

The new result, published on the CERN CDS information server, has a statistical significance of more than five standard deviations — the threshold used to claim the observation of a particle or process in particle physics.

“This result provides a novel independent approach to study the evolution of the transverse density of quarks and gluons inside the proton by exploiting, for the first time, the production of three J/ψ particles,” said CMS physicist Dr. Stefanos Leontsinis and his colleagues.

“In the next 20 years, the LHC experiments expect to accumulate data samples of proton-proton collisions that are 20 times larger than those analyzed by our team.”

“Future studies will thus allow us to measure more precisely the triple production of the J/ψ particle — and other heavier particles — and thereby improve greatly our understanding of the proton structure at the highest energy scales ever probed.”

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CMS Collaboration. 2021. Observation of triple J/ψ meson production in proton-proton collisions at s√= 13 TeV. CMS-PAS-BPH-21-004

© Karam OUHAROU. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

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