Proposal of a revised hadrons naming scheme - CERN Indico

Proposal of a revised hadrons naming scheme Simone Pagan Griso Lawrence Berkeley National Laboratory Review authors: Burkert, S. Eidelman*, C.Hanhart*, B.K. Heltsley, E. Klempt, M.R. Pennington*, L. Tiator, C.G. Wohl and R. Workman * = corresponding authors for the update proposal

Outline: • Motivation • Brief summary of the proposal • Community input process and critical points • Future steps

See also C. Hanhart presentation at PDG collaboration meeting Simone Pagan Griso (LBNL), Page 1

Motivation • With the discovery of X(3872), hadron spectroscopy began a new “era” – Followed by unusual 1– – states (called Y) and charged ones (Z)

• More recently: observation of pentaquarks (Pc) • Many new states with mass and properties incompatible with naive quark model • How should we name them?

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Naming of hadrons • Fundamental principle already in existing names: name assigned based on the quantum numbers

+ naming for baryons and S,C,B = 0 mesons

RPP 2016, “Naming Scheme for Hadrons” last revision: 2004 Simone Pagan Griso (LBNL), Page 3

Naming update proposal • Keep the same principles as in current naming scheme • No distinction between mostly qq and e.g. mostly gluonium – still use quark model whenever possible

• Extend current naming scheme to accommodate “newly” observed mesons – Only concerns S(strangeness) = C(charmness) = B(bottomness) = 0 mesons

• Pentaquarks: use LHCb name Pc(mass) (no other changes for baryons)

W E N Simone Pagan Griso (LBNL), Page 4

Naming update proposal • Keep the same principles as in current naming scheme • No distinction between mostly qq and e.g. mostly gluonium – still use quark model whenever possible Examples:

• Extend current naming scheme to accommodate “newly” observed mesons PDG = C(charmness) PDG = B(bottomness) name in= 0 mesons – Only concerns S(strangeness) old name new name literature • Pentaquarks: use LHCb name Pc(mass) (no other changes for baryons)

X(3872)

c1(3872)

X(3872)

X(4430)

Zc(4430)

Zc(4430)

X(4260)

(4260)

Y(4260)

Note: X(mass) is reserved in PDG for unknown states W E N Simone Pagan Griso (LBNL), Page 5

Community input process • Heavily discussed in the PDG meson team • Presented at international conferences: Quarkonium 2014 and 2016 • Latest iteration sent for feedback to representative of major experiments, as well as relevant experts, active in this field – goal: collect input for proposal discussion at the PDG collaboration meeting

Experimental Collaborations • LHCb • BES-III • Belle-II • BaBar • ATLAS • CMS

Other experts in this field • Theorist (Eric Braaten) • PDG review authors – non qqbar mesons – pentaquarks – C. Patrignani – Matts Roos

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Input received • Every Collaboration contacted responded within deadlines • Clear and shared welcoming of the initiative and overall positive feedback

LHCb BaBar ATLAS • Non-controversial comments already incorporated in proposal text • Some “bonus” suggestion to improve: e.g. clarify role of mass in particle names explicitly in the PDG • Will cover here only the few areas with significant / critical comments – useful to see homogeneity / diversity of opinion in the community

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Exotic mesons and dual names • Explicitly distinguishing exotic meson states – Input: would be nice to be able to identify easily states that do not fit conventional quark model (aka exotic) – Ruled out incorporating that in the new name, but will flag the states with potential exotic nature with a sentence in the data listing

will insert a note here

• Dual names? usage now and in the future – “Old” name to persist in some form at least until community fully transitions – New (spectroscopic) name used as primary name in e.g. decay chains – Current proposal text implies dual-names in data-listing e.g.

– Alternative proposals to include dual-name in a weaker form • e.g. only as comment in the text or as “was: ...” (preferred e.g. by LBL-PDG group)

– Also problem in introducing “two” new names (e.g. Y(4260) is X(4260) in PDG) – Medium-term: “glossary” table in review with historical and new names Simone Pagan Griso (LBNL), Page 8

Choice of particle names BaBar MichaelB Roos j

 c Hc b H b

Jc c Jb b

Pc c Pb b

c b

• Few suggestions on alternative names, main motivation: avoid particle names similar to existing ones, homogeneity of choice • Others expressed instead support for the ones chosen (esp. Zc,b) • Any change would of course need further discussion with community Simone Pagan Griso (LBNL), Page 9

Conclusions and Next steps • Proposal for extending existing meson naming scheme – prompted mostly by the large number of X(/Y/Z) states discovered – particles will keep X(mass) until their quantum numbers are determined

• Need to settle on open points, considering input also from these two days • Work on revised text • Follow-up any action-item (e.g. decide which mesons to “flag” as exotic) • Iterate final proposal within PDG and experimental Collaborations • Foresee to implement proposal for PDG 2018 edition – Implementing technical changes as well – Ensure coherent treatment in PDG listing and reviews

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BACKUP

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