The PENTAQUARK Is It Magic?

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The PENTAQUARK is it magic? R. Landua July 2015 1 - Reminder: quarks, colour, J/휓 2 - Bound states of quarks - simple and complex states 3 - Why to search for a pentaquark? 4 - Production of b quarks in LHCb 5 - The decay of a Λb 6 - Some of the observations 7 - The analysis and interpretation PARTICLE SPECTRUM 1963 REMINDER FROM LECTURES SU(3) - Classification scheme based on ‘quarks’ 1) 3 types of “quarks” : up, down, strange u d s 2) Carry electric charges: +2/3, -1/3, -1/3 +2/3 e -1/3 e -1/3 e 3) Appear in combinations: Meson = quark+antiquark Baryon = quark(1) + quark(2) + quark(3) Gell-Mann, 1963 (G. Zweig, 1963, CERN) PARTICLE SPECTRUM this has nothing to do with our visible colours, Quantum Chromo Dynamics just an analogy Theory constructed in analogy to QED QCD: 3 different charges (“colour charge”) [red, green, blue]* ‘Strong force’ between quarks is transmitted by (8) gluons Dogma of QCD: Only colour-neutral bound states are allowed MESONS = Quark-Antiquark BARYONS = 3-Quark states 1974 Discovery of the ‘charm’ quark in 1974 NOVEMBER REVOLUTION (11 November 1974) 'Psi' am SLAC (Burt Richter) 'J' at Brookhaven (Sam Ting) Compromise: J/Psi “Extremely” long lifetime (~10-20 sec) Decay only possible through electroweak interaction 2 - Bound states of quarks - simple and complex states QCD: only ‘white’ states can exist “50 shades of white” MESON + = white Colour Anti-Colour SIMPLEST STATES BARYON = white + + Blue Green Red 2 - Bound states of quarks - simple and complex states More complex bound states also allowed: Four quark state + = white + Colour Anti-Colour COMPLEX BOUND STATES Five quark state Colour Anti-Colour “Pentaquark” = white Blue Green Red 3 - Why to search for a pentaquark? Better understanding of QCD at low energy This … or this ? 4 - Production of b quarks in LHCb J/휓 p K- Secondary vertex -12 Lifetime Λb : 1.4 · 10 sec ~ 435 µm Mass Λb : 5619.5 MeV 5 - The decay of a Λb Mass Λb : 5619.5 MeV 6 - Some of the observations M = 4380 MeV, Width = 205 MeV M = 4450 MeV, Width =40 MeV Two Penta-Quark states 7 - Analysis and interpretation Complex partial wave analysis based on “Dalitz plot” Best fit results: Spin 3/2 (broad state), Spin 5/2 (narrow state) J/휓 p J/휓 p More studies are necessary to find out more about these states..

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