(A Few) Recent Developments in Hadron Spectroscopy

(setting the stage for subsequent spectroscopy talks)

Topics:

I. Basic hadronicsII. Some exciting areas of current

research:a. Charm hadronsb. Exotics

III. Future

Ted BarnesPhysics Div. ORNL

ICHEP2010 Paris, 23 July 2010

1. Basic hadronics

QCD flux tube (LGT, G.Bali et al.;hep-ph/010032)

LGT simulation showing the QCD flux tube

Q Q

R = 1.2 [fm]

“funnel-shaped” VQQ(R)

Coul. (OGE)

linear conft.(str. tens. = 16 T)

Color singlets and QCD exotica

“confinement happens”.

Physically allowed hadron states (color singlets) (naïve, valence)

qq

q3 Conventional quark modelmesons and baryons.

q2q2, q4q,…

multiquarks

g2, g3,…

glueballs

maybe 1 e.g. :f0 (1500)

qqg, q3g,…

hybrids

maybe 1-3 e.g.s1 is “solid” : p

1(1600)

100s of e.g.s

“exotica” :ca. 106 e.g.s of (q3)n, maybe 1-3 others X(3872) = DD*!

(q3)n, (qq)(qq), (qq)(q3),…

nuclei / molecules

(q2q2),(q4q),…

multiquark clusters

dangerouse.g. (1540)Q

_

Basis state mixing may be very important in some sectors.

Parity Pqq

= (-1) (L+1)

C-parity Cqq

= (-1) (L+S)

qq mesons: quantum numbers

1S: 3S1 1 - - ; 1S

0 0 - + 2S: 23S

1 1 - - ; 21S

0 0 - + 3D …

1P: 3P2 2 + + ; 3P

1 1 + + ; 3P

0 0 + + ; 1P

1 1 + - 2P …

1D: 3D3 3 - - ; 3D

2 2 - - ; 3D

1 1 - - ; 1D

2 2 - + 2D …

The resulting qq N,L states N2S+1LJ have JPC =

qq (allowed): N

L

2.a. Charm hadrons

Charmonium (cc)A nice example of a QQ spectrum.

Expt. states (blue) are shown with the usual L classification.

Above 3.73 GeV:Open charm strong decays(DD, DD* …):broader statesexcept 1D

2 2- +, 2- -

3.73 GeV

Below 3.73 GeV: Annihilation and EM decays.

(rp, KK* , gcc, gg, l+l-..):narrow states.

Minimal quark potential model physics:

OGE + linear scalar confinement;

Schrödinger eqn (often relativized) for wfns.

Spin-dep. forces, O(v2/c2), treated perturbatively.

Here…

Contact S*S from OGE;Implies S=0 and S=1 c.o.g. degenerate for L > 0.(Not true for vector confinement.)

as = 0.5538

b = 0.1422 [GeV2]m

c = 1.4834 [GeV]

s = 1.0222 [GeV]

Fitted and predicted cc spectrumCoulomb (OGE) + linear scalar conft. potential

model blue = expt, red = theory.

S*S OGE

L*S OGE – L*S conft, T OGE

Fitted and predicted cc spectrumCoulomb (OGE) + linear scalar conft. potential

model blue = expt, red = theory.

Two narrow states are expected,with JPC = 2- + and 2- -. The 1D multiplet is theoreticallyclose to degenerate, near the 3D

1 y(3770).

Best recent LQCD refs for cc and cc-hybrid spectroscopy.(Summary of JLAB LQCD group results.) For references see:

“Charmonium excited state spectrum in lattice QCD.”J.J.Dudek, R.G.Edwards, N.Mathur and D.G.Richards,

Phys. Rev. D77, 034501 (2008) and PRD78, 094504 (2008) n.b. PRD79, 094504 (again) (2009) includes rad. transitions!)

Results for cc still rather difficult to distinguish from quark model.

Final LQCD predictions fm JLAB:

Exotic cc-H 1- + 4300(50), Nonexotic cc-H 1- - 4400(60).

J PC exotics(non-qq)

The new “XYZ” states:2P cc? 3S cc? Molecules? cc hybrids?

Nonresonant enhancements? Experimental errors?How to test these possibilities?

Recommended reading:

“The New Heavy Mesons: A Status Report”E.S.Swanson, Phys. Reports 429, 243-305 (2006).

“What’s new with the XYZ mesons?”S.L.Olsen, arXiv:0801.1153v3 [hep-ex]13 Feb 2008.

“The Exotic XYZ Charmonium-like Mesons.” S.Godfrey and S.L.Olsen, arXiv:0801.3867 [hep-ph] Jan 2008.

submitted to Ann. Rev. Nucl. Part. Phys.

“Selections from…”

(Godfrey and Olsen review, list of new states):

cc spectrum, potential models (dashed: nonrel L, Godfrey-Isgur R) vs data

Possible new cc states at these masses and elsewhere! “XYZ” states

2P or not 2P?

Reminder:Three as yet unknown 1D states.Predicted to have G < 1 MeV!

BGS, hep-ph/0505002, PRD72, 054026 (2005).

e+e- collisions: Initial state radiation (ISR)

The traditional approach, s-channel annihilation, but can use higher energy beams.

Still restricted to JPC = 1 - - .

J/y

Y(4260)

a (nonexotic) charmonium hybrid?

Y(4260) e+e- -> Y(4260)ISR

, Y -> p+p-J/y

log scale

Not seen in R.Hmmm?!

[ref] = BaBar, PRL95, 142001 (2005).closed-flavor decay mode !?

cc spectrum, potential models (dashed: nonrel L, Godfrey-Isgur R) vs data

Possible 1- - state Y(4260).Note no plausible cc assignment exists.A 1- - charmonium hybrid??

QQ-hybrid closed-flavor decays predicted by LGT:

We are hoping that closed-flavor decays are a signature for charmonium hybrids (and not charmonia).

If so, nature has been kind. This is a nice experimental signature.

Searches for other decay modes of the Y(4260) are in progress…

e+e- collisions: Double charmonium production.

The traditional approach, s-channel annihilation, but can now make C=(+) charmonia!

JPC = JP+

J/y

C=(+) cc

hc’

c0

hc

X(3943)

An interesting new charmoniumproduction mechanism!

Allows access to C=(+) cc states in e+e- w/o using gg.

No c1

or c2

!?

X(3943)

[ref] = Belle, hep-ex/0507019, 8 Jul 2005. n.b. Eichten: X(3943) may be the 31S0 cc h

c’’.

X(3872)

a charmed meson molecule?

B+ / - -> K+ / - p+p- J / Y

( M Do + D*o) = 3871.5 +- 0.5 MeV

Accidental agreement?X = cc (2- + or 2- - or …),or a DD* molecule?

< 2.3G MeV

Alas the known (y 3770) = 3D1 cc

fixes the mass scale of 1D cc states.

If the X(3872) is 1D cc, an L-excited multiplet is split much more than expected assuming scalar confinement.

n.b. ( M D+ + D*-) = 3879.5 +- 0.7 MeV

= 3872.0 +- 0.6 +- 0.5 M MeV

Belle Collab. K.Abe et al, hep-ex/0308029;S.-K.Choi et al, hep-ex/0309032, PRL91 (2003) 262001.X(3872) from

KEK

Charm in nuclear physics???

The trouble with multiquarks: “Fall-Apart Decay” (actually not a decay at all: no H

I)

Multiquark models found thatmost channels showed short distance repulsion:

E(cluster) > M1 + M

2.

Thus no bound states.

Only 1+2 repulsive scattering.

nuclei and hypernuclei

weak int-R attraction allows “molecules”

E(cluster) < M1 + M

2,

bag model:

u2d2s2 H-dibaryon, MH - M

LL = - 80 MeV.

n.b. LL

hypernuclei exist, so this H was wrong.

Exceptions:

VNN

(R)

-2mN

R R

“VLL

(R)”

-2mL

Q2q2 (Q = b, c?)

2)

1)

3) Heavy-light

Interesting prediction of molecule decay modes:

E.S.Swanson: 1+ + DoD*o molecule - maximally isospin violating!with additional comps. due to rescattering.

J/y“w”J/yro

Predicted total width ca. = expt limit (2 MeV).

Very characteristic mix of isospins: comparable J/yro and J/y“w” decay modes expected. Appears to be confirmed experimentally!

Nothing about the X(3872) is input: this all follows from OpE and C.I.

D*s0

(2317) and Ds1

(2457)

cs mesons or DK molecules?

(or both)

Not to forget the first of the new discoveries:

The unexpected, very long-lived mesons in the cs sector!

Where the trouble all started: BABAR D*s0

(2317)+ in Ds+

p0

D.Aubert et al. (BABAR Collab.), PRL90, 242001 (2003).

M = 2317 MeV (2 Ds channels),

G < 9 MeV (expt. resolution)

(Theorists expected L=1 cs states, e.g. JP=0+, but with a LARGE width and at a much higher mass.) …

“Who ordered that !?”

- I.I.Rabi, about the m-

Since confirmed by CLEO, Belle and FOCUS.

And another! CLEO: Ds1

(2460)+ in Ds*+

p0

Since confirmed by BABAR and Belle. M = 2457 MeV.

D.Besson et al. (CLEO Collab.), PRD68, 032002 (2003).

M = 2463 MeV,

G < 7 MeV (expt. resolution)

A JP=1+partner of the 0+ D*

s0(2317)+ cs ?

(Godfrey and Isgur potential model.) Prev. (narrow) expt. states in gray.

DK threshold

What caused large downwardsmass shifts? Mixing with 2 mesoncontinuum states? (Believed true.)

2.b. Exotics

qq mesons vs. exotics: quantum numbers

1S: 3S1 1 - - ; 1S

0 0 - + 2S: 23S

1 1 - - ; 21S

0 0 - + …

1P: 3P2 2 + + ; 3P

1 1 + + ; 3P

0 0 + + ; 1P

1 1 + - 2P …

1D: 3D3 3 - - ; 3D

2 2 - - ; 3D

1 1 - - ; 1D

2 2 - + 2D …

JPC-exotic quantum numbers :

Plausible JPC-exotic candidates = hybrids, glueballs (high mass), maybe multiquarks (fall-apart decays).

0 - - 0 + - 1 - + 2 + - 3 - + 4 + -

…

notqq:

qq (allowed):

p1(1600)

p-p -> p-h’ p

E.I.Ivanov et al. (E852)PRL86, 3977 (2001).

p1(1600)

1-+ exotic reported in p-h’

ph’is a nice channel because nn couplingsare weak for once (e.g. the a

2(1320) noted here).

The reported exotic P-wave is dominant!

The (only) strong JPC-exotic H candidate signal.

A.Alekseev et al. (COMPASS Collab.) Observation of a JPC =1-+ exotic resonance in diffractive dissociation of 190 GeV pi- into pi- pi- pi+ArXiv:0910.5842v3 (Sept. 2009)

M = 1660 +-10 +0 -64 MeV , Gamma = 269 +-21+42 -64 MeV.

p1(1600)

JPC exotic

(confirmed)

n.b.

resonant phase motion (confirmed but not shown here)is of course the crucial test

J.J.Dudek, R.G.Edwards, M.J.Peardon, D.G.Richards and C.E.Thomas,([JLAB] Hadron Spectrum Collaboration)

Toward the excited meson spectrum of dynamical QCDarXiv: 1004.4930v1

Most recent LQCD results for light exotics, JPC = 1- + , 2+ - , 0+ - .

mq incr. ->u,d

2.5 GeV

2.0 GeV

1.5 GeV

n.b.

All 3 of these exotic JPCs were degen. in the flux-tube model.

In the bag model, 1-+ is lighter.

p1(1600)

1.0 GeV

3. Future

Future…

Spectroscopy involves an active interplay between theory and experiment.Consequently, future topics will depend on developments in both areas.

Experiment:

BES-III is currently gathering high statistics cc data (J/y and y‘) in e+e-.

COMPASS has reported new results on light exotic spectroscopy in HE hadroproduction.

GlueX will use protoproduction to search for light hybrids (incl. exotic JPC) at JLAB, start ca. 2015.

PANDA will search for cc-hybrids (incl. exotics) at GSI, start ca. 2017.

Theory:

LQCD is being extended to light quarks; we should have accurate JPC-exotic mass estimates and predictions of EM couplings and (open flavor) strong decays in the next few years.

END