Exotic States of Matter

Peter KimSLAC

U. of Hawaii Physics ColloquiumNov. 12, 2015

What is the world made of?• 450 BC: water (Thales), earth (Xenophanes),

air (Anaximenes), fire (Heraclitus) + aether (Aristotle)Empedocles, Plato, Aristotle

[Physical states or Types: liquid, solid, gas, energy or light]

Atomos (indivisible) of Democritus – rejected by Aristotle

• 1612: Etienne de Clave arrested for heresy. 2 elements (water, earth) + 3 substances (mercury, sulfur, salt)

• 19th Century: Atomic theory (Dalton) Periodic Table (Mendeleev)

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Building blocks of matter• electron (1897), proton (1917), neutron (1932)

+ few basic elements, we can describe the world we live in!

• Anti-particles: positron (1932), antiproton (1955)• Mesons and baryons: pion (1947), kaon (1947), (1950) • Leptons: muon (1936), neutrino (1956), muon neutrino (1962)• A deluge of meson and baryon resonances …

“The finder of a new particle used to be awarded by a Nobel prize, butsuch a discovery ought to be punished by a $10,000 fine” - Willis Lamb

• Fermi-Yang: nucleon-antinucleon bound states, e.g., + = (p n)• Sakata Model: p, n, as the constituents of mesons and baryons

• Quark Model (Gell-Mann, Zweig)Fractionally charged quarks,: u, d, s (shift Sakata particle charges by -1/3)

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Quark Model

A simpler and more elegant scheme can be constructed if we allow non-integral values for the charges. We can dispense entirely with the basic baryon b if we assign to the triplet t the following properties: spin 1/3, z = 1/3, and baryon number 1/3. We then refer to the members u 2/3, d -1/3, and s 1/3 of the triplet as "quarks" q and the members of the anti-triplet as anti-quarks q-bar.

Baryons can now be constructed from quarks by using the combinations (qqq), (qqq q q-bar), etc., while mesons are made out of (q q-bar), (q q q-bar q-bar), etc. It is assuming that the lowest baryon configuration (qqq) gives just the representations 1, 8, and 10 that have been observed, while the lowest meson configuration (q q-bar) similarly gives just 1 and 8.

"A schematic model of baryons and mesons", M. Gell-Mann (1964).

Does the Nature prefer the simplest configuration?

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Quarks discovered in deep inelastic scattering (e p) at SLAC (1968)

Point-like particles (Bjorken); Partons (Feynman)

Quantum Chromodynamics (QCD)

• SU(3) color gauge field theory of strong interaction- Inspired by success of U(1) gauge group in QED- Quarks and gluons carry the 3 color charges

• QCD (Gross, Wilczek, Politzer)ConfinementAsymptotic freedom

• Very successful in describing Strong Interaction at many energy scales.

• Perturbative nature of gauge field theory calculationsAt low energy (nucleons level), non-perturbative method is required.

• Is there more to Strong Interactions than QCD theory?

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QCD is a precise and beautiful theory. – F. Wilczek

How well do we know the proton?• Mass

Constituent u and d quark masses via Higgs coupling = few MeV1 GeV proton mass mostly comes from the QCD gluons inside the proton; E= mc2

Our visible Universe is made of QCD gluon energy…

• Proton Spin CrisisConstituent quarks not the source of the proton spin? (EMC experiment, 1987)Large contributions from constituent quark angular momentum and gluonsAfter almost 30 years it’s still an open question.

• Proton charge radiusrp = 0.84087(39) fm, muon hydrogen atom 2S-2P Lamb shift at PSI/CREMA (2010,2013)

4% (7 ) smaller than from precision spectroscopy of electron hydrogenUnexpected QCD corrections? New physics? Problem with electronic hydrogen analysis?The proton charge radius problem remains a main problem.

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Lattice QCD

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Quark fields on sites

Gluon fieldson links

Heavy quarks in lattice QCD: non-relativistic techniques on the lattice; efficient way for numerical calculations on the lattice

4-quark XYZ mass spectrum has been attempted using Lattice QCD5-quark calculations were limited to light pentaquark candidates 10 years ago.

Feynman Path Integrals on a 4D grid in Eucledian Space

Lattice spacing a = 0.05-0.10 fmTeraflop scale computing power

Very successful in calculating:Hadron spectroscopy Decay constants of hadronsExtraction of quark masses

Exotic States in QCD

• QCD predicts states beyond the mesons (qq) and baryons (qqq):Glueballs (gg or ggg), Hybrids (qqg), Tetraquarks (qqqq), Pentaquarks (qqqqq), Hexaquarks (qqqqqq; di-baryons), etc.

• Glueballs (gg)- Extensively searched in radiative J/psi decays (and rad. Upsilon decays) - Many candidates, (1440), (1720), (2220), but not truly convincing.- Observation of states beyond the nominal meson spectra not enough;

Exotic JPC states will provide a definite answer.

• Searches for Hybrids (e.g. GlueX at Jlab)

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X Y Z States

• First evidence for 4-quark states (c c q q) ? (Belle)

• Z+ states: Charmonium-like, but charged!Z+(4430), Z1

+(4050), Z2+(4250) Belle

Z+(3900), Z+(4020) BESIII Zb states also observed in the bottomonium mass range

• Interpretations:Conventional Quarkonium States or HybridsMultiquark States: Molecule, TetraquarkRescattering of resonances; Cusps, Thresholds

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U.Hawaii – Center of XYZ studies!

• 2016 Panofsky prize (Steve Olson)“For leadership in the BaBar and Belle experiments, which established the violation of CP asymmetry in B-meson decay, and furthered our understanding of quark mixing and quantum chromodynamcs.”

• Recent reviews in U of Hawaii Colloquia:F. Harris (2013), S. Godfrey (2015), D.Kornicer (2015)

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(E. Braaten)

15 neutral cc mesons

5 charged cc mesons

Bodwin et al, arXiv: 1307.7425

New Charmonium like X Y Z states

New Bottomonium like states

1neutral bb meson

2charged bb mesons

Bodwin et al, arXiv: 1307.7425

Beginning of a new area of spectroscopyin QCD

Pentaquarks • Previous round of Pentaquark observations were not verified by other

experiments+ K0p, K+n from LEPS at SPring-8 (M=1.54 GeV, =10 MeV)c0 D*-p from H1 at HERA (M =3.10 GeV, =12 MeV)

-- - - NA-49 at CERN SPS (M =1.862 GeV, <18 MeV)

• Searches by BaBar/Belle/BES in B decays and e+e- collisions“Prospects for Pentaquark Production at Meson Factories”

(Browder, Klebanov, Marlow) http://arxiv.org/abs/hep-ph/0401115

The Rise and Fall of Pentaquarks in Experiments, R. Schumacher, AIP Conf. Proc. 842, 409 (2006); On the conundrum of the pentaquarks, K.Hicks, Eur. Phys. J. H37 (2012) 1.

Another resurrection of pentaquarks at CERN – LHCb experiment (July, 2015)

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LHCb Detector

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Dedicated single-arm Forward spectrometer with 1.8 < < 4.9.Proton-Proton collisions at LHC in Run 1:

2011: 1/fb at 7 TeV2012: 2/fb at 8 TeVHigh bb̄ and c c̄ cross-sections: (pp bb̄) = 286 µb at 7 TeV

VeLo detectorSilicon detector with two retractable halves7 mm away from the beam line when closedB lifetime resolution: 50 fs

RICH Particle ID K / separation in [2,100] GeV/c

Muon detectors: 97% efficiency, < 2.5% µ mis-ID

(B. Dey, SSI 2015)

Pentaquarks, LHCb, T. Skwarnicki LP2015

LHCb b0 J/ K-p

LHCb-PAPER-2015-029, arXiv:1507.03414, PRL 115, 07201

26,007±166b candidates0

Run Ifb-13

The backgroundis only 5.4% in thesignal region!

The sidebanddistributions are flat

no major reflections from the other b-hadrons after the selection

b0• The decay first observed by LHCb and used to measure lifetime:– LHCb-PAPER-2013-032 (PRL 111, 102003)

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Pentaquarks, LHCb, T. Skwarnicki LP2015

b0 J/ pK-: unexpected structure in mJ/ p

Pc+ J/ p?

*’s K-(1520) and other p ••

Unexpected, narrow peak in m J/ p

Many checks done to ensure it is notLHCban–

“artifact” of selection:Veto Bs J/ K-K+ & B0 J/ K- + after changing p to K, or K toClone and ghost tracks carefully eliminatedExclude b decays as a possible source

––

• Could it be a reflection of interfering*’s p K- ?

– Proper amplitude analysis absolutelynecessary!PRL 115, 07201 (2015)

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LHCb Tetra- and Penta-quarks,T. Skwarnicki

Amplitude Analysis of b J pK-, J

1cnK 2 Pc *

D , ( P , * ,0)

* 1, P , P

*, , ,Pc( , ,0) R(m | M n , )D ( , ,0)

c

P n p

b Pcn

nP Pcc cnp c b c cn pPc c

J

p P PDA

Pc

n Pc 1,0,1b , p ,M Pc A b P

n n * *

, *

*

b , p ,

2

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d 2 Pc ,

b 1/ 2, 1/ 2 p 1/ 2, 1/ 2 1,1 p 1/2, 1/ 2

,

, Pc ,

M (mKp , | M )

( )M

, A, A, , J , A , APc p b n n pKp

b Pc KP n P n n n pc c Pc Pc

c

p pPc b p

ip

PeM

3-4 independent complex helicitycouplings per Pc resonancen

Pentaquarks, LHCb, T. Skwarnicki LP2015

with *’s two Pc+ J pFit and states

Pc(4450)+

Pc(4380)+

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Max. Likelihood Fit with 2 signal and 12 * componentsBest fit has JP=(3/2-, 5/2+), also (3/2+, 5/2-) & (5/2+, 3/2-) are preferred

Pentaquarks, LHCb, T. Skwarnicki LP2015

Argand diagrams PRL 115, 07201 (2015)

Pc+ amplitudes for 6 mJ/ p bins between + & - around the resonance mass

Breit-WignerBreit-

Wigner

of Pc(4450)+••

Good evidence for the resonantThe errors for Pc(4380)+ are too

characterlarge to be conclusive

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(E. Braaten)

Molecular forces via an exchange of a pion

Spin 5/2+ can’t be made in a S-wave molecule; L=1 state is likely not bound

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Baryon-meson molecule vs. compact Pentaquark

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Can accommodate 5/2+

with a diquark in L=1 state

Pc(4450)+

Tightly bound Pentaquark is favored!

Potential Searches at e+e- B-factories

• ISR production of [J/ p p-bar] at E_CM just above mass threshold

• Inclusive search for Pc(4450) J/ p in continuum data

• Inclusive search for Pc(4450) J/ p in Y(nS) data- Hadronic decays are dominated by 3-gluon decay- No suppression of strange quark or diquark production; high rate

of baryons- Relative proximity in physical space and momentum & wave

function overlap- BaBar/Belle: 100’s of million events at Y(1S), Y(2S), and Y(3S)

• Exclusive search in Y(nS) dataY(nS) J/ p p-bar

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Run 2 and beyond

LHCb and Belle II

Complementarity with Belle II. CMS/Atlas also coming into thefold.

Integrated Luminosity

muon, exclusive, baryons

electron, neutrino,tagging, inclusive modes

August, 2015Biplab Dey Recent results from LHCb (SSI 2015)

Summary of LHCb pentaquarks• Strong evidence for bound state of a J/ and a proton,

Pc(4450)

• The spin assignment 5/2+ makes it a very good candidate for a compact QCD pentaquark.

• LHCb searches in additional decay modes and other pentaquark states are expected.

• Confirmation could come from CMS at LHC, or the Belle/BaBar e+e- data.

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Di-baryons (6-quarks)• 64 Combinations from 8 N and Strange baryons: n, p, , , 0,

+, , 0

• Deuteron (np): Binding Energy of 2.225 MeV- (pp) and (nn) are not bound.

• Hyper-deuterons: p p, p or n n, n - Extensive study of hyper-nuclei in Nuclear Physics (since

1960’s)

- Lowest mass hypernuclei observed is ( np)

• H di-baryon ( )• More 6-quark combinations

e.g., (uuuuuu) – Brodsky, arXiv:1308.6404• Charmed hyper-nuclei (or Supernuclei): Charm baryon + N

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Binding Energy of Nucleons

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• M(neutron) – M(proton) = 1.29 MeV• Deuteron: p-n bound state with binding energy of 2.225 MeV

(p-p and n-n combinations are not bound)• Elements production in stars: Triple – production of C and C-N-O cycle

• What if?M(neutron) < M(proton): No hydrogen atomProton-proton is bound -> quick burning of hydrogen in early UniverseNo excited state of 12C near (8Be + 4He) energy -> No production of heavier elements

• A curious case of strangelets (bound states of u, d, and s quarks)“Will relativistic heavy-ion colliders destroy out planet?” Fear of strangelet production in heavy on collisions at RHIC

- Negative charge strangelet interacting with nucleus and grow!Ruled out from examination of Cosmic ray “experiments”

Our existence depends on these fine details!

Antideuterons • Antideuterons observed in Y(nS) data by ARGUS (1985,

1990), CLEO (2007), and BaBar (2014): B.F. of ~2.5 x 10-5

• Leading theory is deuteron wave-function overlap with the neutron proton pair in close space and momentum ranges, a la coalescence model.

• Theoretical details are uncertain how the 6 quarks are arranged internally; treated as composition of Fock States: p n color singlet state, p n color octet state, , or multi-diquark state.

• Search for antideuteron from dark matter interactions, AMS-02

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H di-baryon • Searches at fixed target and ion collision experiments, and Belle - PRL 110, 222002 (2013)

Needs More Data!• If loosley-bound above threshold, H -> • If bound tightly, leading decay modes depend on the Binding energy

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If the binding energy is large, M_H = 1.5-1.7 GeV, it becomes very stable -- Dark Matter candidate (G. Farrar)

Lattice QCD: binding energy, 30-40 MeV HAL QCD Coll., PRL, 106, 162002 (2011).

Schaffner-Bielich et al.,PRL 84, 4305 (2000)

Low energy QCD in the LHC Era

• Study of hadronic properties:Hadron masses and decaysStructural propertiesSpectroscopy of mesons, baryons, and exotics

• Study of multi-quark states (formation, spectroscopy, and decay) can provide a testing ground for precision QCD calculations in Lattice QCD.

Our knowledge of the true nature of the theory of stronginteractions is still limited and uncertain. - Ken Wilson

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Summary

• Most exotic states predicted in QCD are not confirmed, even after ~40 years of QCD success in describing the Strong Interactions.

• Recent observation LHCb pentaquark and further X Y Z states are most welcome!

• We expect to see in 5-10 years precision tests of QCD via Lattice QCD aided by supercomputers.

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