Manchester Particle Physics Seminars, Colloquia and Meetings

Mikhail Mikhasenko: Fresh Pentaquarks from LHCb

Friday, 28 June 2019 from to (Europe/London)
at Schuster ( 54-6-6.40 - Niels Bohr Common Room )
Description
The hadronic matter that surrounds us is build from ordinary baryons that contain three quarks.
Ordinary mesons with two quarks appear the cosmic rays and massively produced in collisions at the particle-physics experiments.
The strong-interaction theory, however, does not limit the hadronic formation to the ordinary mesons and baryons.
The pentaquark states that contain 5 valence quarks were strongly anticipated for a long time but did not showed up in the collider experiments until 2015.
In that year two significant enhancements in the (J/psi p) invariant mass spectrum (ccbar+uud) in Lambdab decay were observed by LHCb experiment.

The Run-II data has come with surprises: the reanalysis of the same reaction with an order of magnitude larger statistics nearly doubles the number of established Pentaquarks states.
The fact that new states are very narrow and are located close to the (Sigmac D) threshold hints at their molecular (meson+baryon) nature.
Alternatively, the states are suggested to be compact tightly-bound formations.
In the talk I will discuss the latest LHCb analysis as well as several theoretical investigations on the nature of new states.
I will show how the amplitude analysis and studies of the signal lineshape help understanding the nature of the observed signals.