A New Dynamical Picture for the Production and Decay of the X, Y, Z, and P c Charmoniumlike Exotics Richard Lebed Modern Exotic Hadrons Institute for Nuclear Theory November, 2015 X(3872) Z(4475) Y(4260) LHCb CMS BES III BELLE B A B AR CLEO CDF, DØ

Outline 1)Discovery of the exotic hadrons X,Y,Z, P c 2)How are the tetraquarks X,Y,Z assembled? 3)A new dynamical picture for the X,Y,Z 4)Puzzles resolved by the new picture 5)The pentaquarks P c 6)Conclusions

Whenever teaching the Particle & Nuclear Physics undergraduate survey class, I always say: “Quarks and gluons are never seen in isolation, a phenomenon called color confinement. Instead, they are always found in compounds called hadrons, either as quark-antiquark pairs (mesons), or triples of quarks (baryons).” because color charge provides two distinct ways to make color-neutral states R = red color G = green color B = blue color

Every now and then, a really sharp student asks: “Aren’t there any other ways to make other color-neutral states?” Sure; they are called exotics: (g = gluon, q = quark) gg, ggg, … (glueball) qq̄g, qq̄gg, … (hybrid meson) qq̄qq̄, qq̄qq̄qq̄, … (tetraquark, hexaquark, …) qqqqq̄, qqqqqqqq̄, … (pentaquark, octoquark, …) i.e., (# of q) – (# of q̄) = 0 mod 3, any number of g except one by itself

“So why haven’t they been found?”

…Until 2003: X Belle Collaboration (S.-K. Choi et al., PRL [2003])

…And in 2005: Y B A B AR Collaboration (B. Aubert et al., PRL 95, [2005]) Figure from Nielsen et al., Phys. Rept. 497 (2010) 41 = photon

…And in 2013: Z BESIII Collaboration [Beijing] (M. Ablikim et al., PRL 110, [2013]), Belle Collaboration (Z. Liu et al., PRL 110, [2013])

…And in 2014: Resonance LHCb Collaboration (R. Aaij et al., PRL 112, [2014])

…And now in 2015: P c LHCb Collaboration [R. Aaij et al., PRL 115 (2015) ]

Our limited nomenclature

Charmonium: November 2014 Esposito et al., Int. J. Mod. Phys. A30 (2014) NeutralCharged Black: Observed conventional cc̄ states Blue: Predicted conventional cc̄ states Red: Exotic cc̄ states

How are tetraquarks assembled? Image from Godfrey & Olsen, Ann. Rev. Nucl. Part. Sci. 58 (2008) 51 c̄ c c u u hadrocharmonium _ cusp effect: Resonance created by rapid opening of meson-meson threshold

Trouble with the dynamical pictures

The hadron molecular picture

Prompt production

Amazing (well-known) fact about color:

A new tetraquark picture Stanley J. Brodsky, Dae Sung Hwang, RFL Physical Review Letters 113, (2014) CLAIM: At least some of the observed tetraquark states are bound states of diquark-antidiquark pairs BUT the pairs are not in a static configuration; they are created with a lot of relative energy, and rapidly separate from each other Diquarks are not color neutral! They cannot, by confinement, separate asymptotically far They must hadronize via large-r tails of mesonic wave functions, which suppresses decay widths

A new tetraquark picture Stanley J. Brodsky, Dae Sung Hwang, RFL Physical Review Letters 113, (2014) CLAIM: At least some of the observed tetraquark states are bound states of diquark-antidiquark pairs BUT the pairs are not in a static configuration; they are created with a lot of relative energy, and rapidly separate from each other Diquarks are not color neutral! They cannot, by confinement, separate asymptotically far They must hadronize via large-r tails of mesonic wave functions, which suppresses decay widths Want to see this in action? Time for some cartoons!

Nonleptonic B 0 meson decay B.R.~22% b b d̄d̄ d̄d̄ c c W─W─ s s c̄ _

What happens next? Option 1: Color-allowed B.R.~5% (& similar 2-body) d̄d̄ d̄d̄ c c D (*)+ s s c̄ D s (*)- ―

What happens next? Option 1: Color-allowed B.R.~5% (& similar 2-body) d̄ c c D (*)0 s s c̄c̄ c̄c̄ D s (*)- ― Each has P ~1700 MeV

What happens next? Option 2: Color-suppressed B.R.~2.3% d̄ c c s s c̄

What happens next? Option 2: Color-suppressed B.R.~2.3% c c c̄ d̄ s s charmonium K̄ (*)0

What happens next? Option 3: Diquark formation d̄ c c s s c̄ c̄d̄ ūū ūū u u cu K (*)‾

What happens next? Option 3: Diquark formation s s ūū ūū cu K (*)‾ c̄d̄

Driven apart by kinematics, yet bound together by confinement, our star-crossed diquarks must somehow hadronize as one cucu cucu c̄ d̄ charmonium Ψ(2S) π+π+ Z + (4475)

Why doesn’t this just happen? It’s called baryonium cdcd cdcd c̄ d̄ ū u u

How far apart do the diquarks actually get? cucu cucu c̄ d̄

Fascinating Z(4475) fact: cucu cucu c̄ d̄

The large-r wave function tails and resonance widths

For one thing, Diquark-antidiquark pairs create their own bound-state spectroscopy [L. Maiani et al., PRD 71 (2005) ] – Simple Hamiltonian with spin-spin interactions among the four quarks – Once one bound state is found, a whole multiplet arises – Then compare predicted spectrum to experiment Original version predicts states with quantum numbers and multiplicities not found to exist (XYZ phenomenology not very well developed then), but a new version of the model [L. Maiani et al., PRD 89 (2014) ] appears to be much more successful – Crucial revision: Dominant spin-spin couplings are within each diquark – e.g., Z(4475) is radial excitation of Z(3900); Y states are L=1 color flux tube excitations

And furthermore,

The Cusp Im Π(s) Re Π(s) (Normalized to unity at s th )

How closely can cusps attract thresholds?

Example cusp effects S. Blitz & RFL, Phys. Rev. D 91 (2015) M 0 : Bare resonant pole mass S th : Threshold s value [here (3.872 GeV) 2 ] M pole : Shifted pole mass Relative size of pole shift (about 0.12% near S th, or 5 MeV) At the charm scale, a cusp from an opening diquark pair threshold is more effective than one from a meson pair!..

Does the dynamical diquark picture have anything to say about the P c states? Yes. RFL, Phys. Lett. B 749 (2015) 454

Nonleptonic Λ b baryon decay b b c c W─W─ s s c̄ u u d d ud

What happens next? Diquark and triquark formation ud c c s s c̄ c̄ud ūū ūū u u cu K (*)‾

What happens next? Diquark and triquark formation s s ūū ūū cu K (*)‾ c̄ud

The same color triplet mechanism, supplemented with the fact that the ud in Λ baryons themselves act as diquarks, predicts a rich spectrum of pentaquarks cucu cucu c̄ ud J/Ψ p

Any quantitative work? Yes. Zhu & Qiao,

QCD counting rules for cross sections S. Brodsky and RFL, Phys. Rev. D 91 (2015)

Why not ss̄ pentaquarks?

Conclusions The past two years have provided confirmation of the existence of the tetraquark and observation of the pentaquark, the third and fourth classes of hadron Over 20 such states (X, Y, Z, P C ) have thus far been observed All of the popular physical pictures for describing their structure seem to suffer some imperfection We propose an entirely new dynamical picture based on a diquark-antidiquark (or triquark) pair rapidly separating until forced to hadronize due to confinement Then several problems, e.g., the widths of X, Y, Z, P C states and their couplings to hadrons, become much less mysterious Much new work is underway, and many opportunities remain!

Backup slides

Quantum Chromodynamics (QCD) QCD is the quantum field theory of the strong nuclear force that holds atomic nuclei together Its fundamental particles of matter are called quarks Its particles responsible for force exchanges are called gluons Quarks exchange gluons because quarks carry color charge Analogy: QED (Quantum Electrodynamics, the quantum field theory of electricity & magnetism) includes electrons among its fundamental matter particles, which interact by exchanging photons, possible because electrons carry electric charge A huge difference: No problem in separating electrons from neutral atoms, but quarks cannot be separated from the compounds (hadrons) in which they occur: color confinement

Quantum Chromodynamics (QCD)

The Breit-Wigner resonance

Belle Leads the Way Confirmed states (by > 1 experiments or > 1 modes) Belle confirms? X(3823) = ψ 2 (1D)? X(3872) Z c + (3885)/Z c + (3900) Z c 0 (3885)/Z c 0 (3900) χ c0 (3915) Y(4260) Y(4360) Z + (4430) Y(4660) Z b (10610) Z b (10650) Only seen, or best seen, at Belle X(3940) Y(4008) Z + (4050) X(4160) Z + (4200) Z + (4250) (also LHCb?) X(4350) X(4630) Y b (10888)

The large-r wave function tails and resonance widths

What determines cusp shapes?

Can the counting rules be used for cross sections as well?