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SUMMARY:Modern Meson Spectroscopy: The Importance of Unitarity for Experim
 ent\, Lattice & Models
DTSTART;VALUE=DATE-TIME:20181129T113000Z
DTEND;VALUE=DATE-TIME:20181129T123000Z
DTSTAMP;VALUE=DATE-TIME:20181012T165300Z
UID:indico-event-486@indico.lip.pt
DESCRIPTION:The most fundamental cornerstone of the PDG tables is the uniq
 ueness of\nS-matrix pole positions of unstable particles\, as a consequenc
 e of\nquantum-field-theory principles. Therefore\, the unitarity property 
 of\nthe S-matrix should ideally be respected in whatever description of\nh
 adronic resonances in experiment\, on the lattice\, and in quark models.\n
 Unfortunately\, simple Breit-Wigner (BW) parametrisations continue to be\n
 widely used in data analyses of hadronic processes\, while lattice and\nmo
 del calculations are often still done by ignoring strong decay and\nits dy
 namical effects. All such approaches manifestly violate\nunitarity.\n\nIn 
 the present talk I shall show how a BW description of a resonance\nproduce
 s a wrong pole position\, even in the elastic case\, while for\ninelastic 
 decays the error can become huge\, in excess of 100 MeV.\nIts consequences
  for meson spectroscopy and possible remedies will be\ndiscussed. As for t
 he lattice\, some recent calculations of meson\nresonances will be present
 ed that do satisfy unitarity\, by using\nLuescher's method to compute scat
 tering phase shifts in a Euclidean\nframework. These calculations lend str
 ong support to earlier model\ndescriptions of enigmatic resonances like th
 e light scalar mesons\, as\nwell as the puzzling states Ds0(2317)\, Ds0(24
 60)\, and X(3872). Finally\,\na case is made for considering non-resonant\
 , threshold-related\nenhancements\, which are a consequence of extended un
 itarity in\nproduction processes. Typical examples of such enhancements wi
 ll be\ndiscussed\, as e.g. X(4260)\, X(4660)\, and Upsilon(10580).\n \n\n
 https://indico.lip.pt/event/486/
LOCATION:LIP seminar room 311
URL:https://indico.lip.pt/event/486/
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