LHCb results on Tetra- and Penta-Quark candidates Tomasz Skwarnicki - PowerPoint PPT Presentation

LHCb results on Tetra- and Penta-Quark candidates Tomasz Skwarnicki Syracuse University Nov 10, 2015 at

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 2 Quark hypothesis – SU(3) flavor symmetry “Eightfold Way” symmetry – Gell-Mann 1961 (Y=S+A) Y=S+1/3 Y=S Q -electric charge Q +1 +1 S= Strangeness d u 0 I = ½ 0 0 Ι z Ι z -1 I = 0 s -1 -1 -1 0 1 -1 0 1 Isospin Isospin Meson octet Quark triplet J = 0 (also J=1/2 baryon octet and J=3/2 decuplet) • Quarks initially treated as mathematical abstractions

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 3 “Exotic” mutiquark states conceived already at the birth of Quark Model … … Nobel Prize 1969 Murray Gell-Mann George Zweig 1929- 1937- US US

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 4 Charmonium – narrow (i.e. long-lived) states Non-relativistic quantum mechanics! Linear potential is confining � � � quarks to stay inside hadrons L J = L + S s 1 − ≤ ≤ L S J L+S r n cc c L+1 P = (-1) s 2 � � L+S C = (-1) � c Coulomb potential n 2S+1 l J S=s +s 1 2 “ionization threshold” Forces between quarks ψ ’ 1974 are 10-100 times stronger Threshold for (cd)(cd) decay i.e. DD � c 1975 than between nucleons! � c ’ 1974 November revolution : 750 MeV 2002 Fine splitting h c � � � � 2005 • Quark Model and qq ⋅ L S , spin-orbit � � � � � � � � � � hypothesis for mesons � � J �� 1974 ⋅ ⋅ − ⋅ s r s r s s firmly established! 1 2 1 2 • However, near mass large Hyperfine splitting equality of light quarks � � for l= 0 states � c • s s was coincidental 1 2 1980

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 5 SU(3) color symmetry • Fundamental parts of SU(3) flavor symmetry discovered by Gell-Mann & Zweig: – Quark flavor independence of strong interactions – Rules for making hadrons out of quarks – led to development of exact theory of strong interactions, QCD based on SU(3) color symmetry Breaking of color field flux tube by popping of qq pair: Strength of color interactions raises with separation of color charges → confinement of color charge → hadrons must be color neutral i.e. “white” (qq, qqq, ….)

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 6 Mesons from quarks & antiquarks in QCD color octet 1 i − 2 2 color color color i 1 singlet antitriplet 2 triplet 2 1 1 i 1 2 − _ − 3 2 2 2 6 3 8 = ⊗ ⊕ 1 3 1 1 i 1 1 1 1 3 − 3 2 6 6 2 2 quark antiquark attractive color force i 1 − q 2 q 2 (qq) meson i 1 e.g. K + + + + 2 2 _ Color flux tube s repulsive color force stretched between quark and antiquark quarks will pull apart in any _ with attractive octet configuration u potential gluons happen to belong to the color octet

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 7 (Colored) diquarks in QCD color (antisymmetric) sextet color (symmetric) antitriplet 1 2 color color 1 1 1 triplet triplet 2 2 2 1 _ 1 − − 1 1 2 2 3 = ⊗ 1 2 2 ⊕ 6 1 3 3 2 1 2 1 2 − 2 quark quark 1 1 1 q q repulsive color force attractive color force _ quarks will pull apart in any (half as strong as in the meson) sextet configuration (qq) diquark Color flux tube _ stretched between Not a particle, just a the quarks and s u building block in extending to other QCD color partners

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 8 Baryons from quarks and diquarks color singlet color color antitriplet 1 triplet 6 1 1 1 − 2 2 6 1 _ 1 − − 2 2 = ⊗ 3 ⊕ ... 1 1 1 1 3 2 6 6 1 1 1 − − − 6 6 2 Color flux tube stretched between attractive color force the diquark and the quark (q(qq)) baryon third quark attractive color force q (qq) diquark s u e.g. Λ Λ Λ Λ d

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 9 Baryons directly from 3 quarks color singlet color color color 1 triplet triplet triplet 3 = ⊗ ⊗ ⊕ 1 ... 3 3 3 1 1 3 3 q q q Color flux tube in QCD gluons can attractive color force stretched between couple to each other three quarks (qqq) baryon Different forms of quark configurations in a baryon can s u coexist. Relative importance of diaquarks can depend on quark flavors. d

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 10 Tetraquarks from diquarks and diantiquarks color color color singlet antitriplet triplet 1 1 2 2 1 _ 1 − − 2 = 2 1 3 ⊗ ⊕ ... 1 1 2 2 1 1 − − 2 2 3 1 1 attractive color force 2 2 1 Color flux tube 1 − − stretched between 2 ((qq)(qq)) tetraquark 2 the diquark and _ diantiquark _ _ s u attractive color force attractive color force (qq) diquark (qq) diantiquark s d

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 11 Pentaquark directly from two diquarks and antiquark color color color color singlet antitriplet antitriplet antitriplet 1 1 1 − 1 − − − 2 2 2 2 1 _ 1 _ 1 1 _ 2 3 2 2 3 2 = ⊗ 3 ⊗ 1 1 − − 2 2 1 1 2 2 q antiquark attractive color force attractive color force attractive color force Color flux tube s u stretched between (qq) diquark (qq) diquark the diquarks and _ antiquark Different forms of quark configurations in a pentaquark s can coexist. Modeling of pentaquarks is complicated. d u ((qq)(qq)q) pentaquark

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 12 Hexaquark directly from three diquarks color color color color singlet antitriplet antitriplet antitriplet 1 1 1 1 − − − − 2 2 2 2 1 1 1 _ 1 _ 1 1 _ 2 2 2 2 3 2 3 2 3 1 1 1 − − − ⊗ 2 2 ⊗ = 2 1 1 1 2 2 2 attractive color force attractive attractive attractive color force color force color force d u (qq) diquark (qq) diquark (qq) diquark d u s u ((qq)(qq)(qq)) hexaquark (dibaryon)

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 13 Tightly and loosely bound multiquark states ((q(sq))(qq)) ((sq)(sq)) ((q(sq))(q(sq))) (((sq)(sq))(qq)) pentaquark tetraquark hexaquark hexaquark _ _ _ _ u s u d s u u s _ _ d u d d d d s s u s u s u _ dihyperon Any of these states would be predicted by Jaffe to be stable considered an “exotic” hadron. PRL 38,195(1977) Λ _ _ Λ d s s u _ π + s _ K − _ u d u u d Λ Λ Λ π π π π K + d s d _ s _ s d _ u s u u u Bayronium (q(sq)) (qq)) (q(sq)) (q(sq)) (q(sq)) (q(sq)) (sq) (sq) Λπ + molecule K + K − molecule ΛΛ molecule ΛΛ molecule

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 14 Tightly versus loosely bound multiquark systems p (q(qq)) (q(qq)) (((qq)(qq))(qq)) molecule d s hexaquark (dibaryon) e.g. deuteron u These quarks d u pop-out of gluon π 0 The same d u field, later annihilate quark content _ d u d s d Quite different d u spectroscopy n • Rich excitation spectrum, in Molecular forces can be described principle, possible: as exchange of a pion – n, l, S – hundreds of MeV in energy between Difficult to get more than different excitations one state ( n=1, l =0 ). � = � + � � values possible high � – M = M 1 +M 2 – (a few MeV) Such structures may be extremely unstable (wide). J P = (J 1 ± J 2 ) P1*P2 ⊗ No firm input from lattice QCD (yet) which, if any, multiquark structures form Γ ~ max( Γ 1 , Γ 2 ) well defined bound states.

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 15 Two waves of past pentaquark claims (with s) Last mention of 2 nd pentaquark wave: PDG 2006 e.g. PDG 1976 Found/debunked by looking for “bumps” in mass spectra … Last mention of baryonic Z*’s PDG 1992 …

LHCb Tetra- and Penta-quarks, T. Skwarnicki SLAC, Nov 2015 16 LHCb: first dedicated b,c detector at hadronic collider Advantages over e + e - LHCb • CMS B-factories (Belle, RICH2 BaBar): RICH1 – ~1000x larger b VELO production rate – produce b- baryons at the same time as B- � mesons – long visible lifetime of b-hadrons (no backgrounds from the other b-hadron) • Advantages over (B) (B) µ − ATLAS, CMS, CDF, VELO D0: p – RICH detectors for ( π + ) π /K/p discrimination µ + (smaller K - backgrounds) – Small event size allows large trigger bandwidth (up to 5 kHz in Run I); all devoted to flavor physics The LHCb detector described in JINST 3 (2008) S08005