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Slide 1
GlueX + Exotic Hadron Spectroscopy 1. Hadrons 101 2. Exotica:
glueballs, hybrids and multiquarks/molecules 3. Hybrids:
theoretical expectations and experimental status 4. GlueX@JLAB;
prod of (hybrid) exotics Ted Barnes Physics Div. ORNL Dept. of
Physics and Astronomy, U.Tenn. GlueX PAC @ JLAB 23 Aug 2010
Slide 2
Hadrons 101
Slide 3
QCD flux tube (LGT, G.Bali et al.; hep-ph/010032) LGT
simulation showing the QCD flux tube QQ R = 1.2 [fm] funnel-shaped
V QQ (R) Coul. (OGE) linear conft. (str. tens. = 16 T) Color
singlets and QCD exotica confinement happens.
Slide 4
Physically allowed hadron states (color singlets) (nave,
valence) qq q3q3 Conventional quark model mesons and baryons. q 2 q
2, q 4 q, multiquarks the multiquark fiasco -N.Isgur g 2, g 3,
glueballs maybe 1 e.g. f 0 (1500 or 1710) qqg, q 3 g, hybrids maybe
1-3 e.g.s 1 (1600) best Incl. exotic J PC ! 100s of e.g.s exotica :
ca. 10 6 e.g.s of (q 3 ) n, maybe 1-3 others X(3872) = DD*! (q 3 )
n, (qq)(qq), (qq)(q 3 ), nuclei / molecules _ Basis state mixing
may be very important in some sectors. (q 2 q 2 ),(q 4 q),
multiquark clusters dangerous: may not exist as resonances
e.g.
Slide 5
Parity P qq = ( ) (L+1) C-parity C qq = ( ) (L+S) 1S: 3 S 1 1 ;
1 S 0 0 2S: 2 3 S 1 1 ; 2 1 S 0 0 1P: 3 P 2 2 ; 3 P 1 1 ; 3 P 0 0 ;
1 P 1 1 2P 1D: 3 D 3 3 ; 3 D 2 2 ; 3 D 1 1 ; 1 D 2 2 2D J PC
forbidden to qq are called J PC -exotic quantum numbers : 0 ; 0 ; 1
; 2 ; 3 x Plausible J PC -exotic candidates = hybrids (have all J
PC ), glueballs (high mass), maybe multiquarks (fall-apart decays).
The resulting qq N,L states N 2S+1 L J have J PC = qq mesons
quantum numbers Quarkonia:q
Slide 6
s = 0.5538 b = 0.1422 [GeV 2 ] m c = 1.4834 [GeV] = 1.0222
[GeV] Fitted and predicted cc spectrum Coulomb (OGE) + linear
scalar conft. potential model blue = expt, red = theory. S*S OGE
L*S OGE L*S conft, T OGE Quarkonia: cc e.g.
Slide 7
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: J PC
exotics (non-qq) cc cc hybrids (?) Exotic cc-H 1 4300(50),
Nonexotic cc-H 1 4400(60).
Slide 8
J.J.Dudek, R.G.Edwards and C.E.Thomas, Exotic and excited-state
radiative transitions in charmonium from lattice QCD PRD79, 094504
(2009), arXiv:0902.2241 [hep-ph]. Paper quotes c exotic J keV.
non-exotic hybrid rad. trans. A typical robust cc radiative width.
GlueX is justified. Radiative widths of exotics = ? (The BIG
question for GlueX.)
Slide 9
Approx. status, light (u,d,s) qq spectrum to ca. 2.1 GeV.
States are well known to ca. 1.5 GeV, poorly known above (except
for larger-J). n.b. ss is poorly known generally. Strong decays
give M, , J PC of qq candidates. Several recent candidates, e.g. a
1 (1700), a 2 (1750). I=1 shown, dashed boxes = expected Status of
light meson spectroscopy (I=1 e.g.) Quarkonia: nn e.g.
Slide 10
Theor. guides for expt qq searches: Extensive strong decay
tables S.Godfrey and N.Isgur, PRD32, 189 (1985). T.Barnes,
F.E.Close, P.R.Page and E.S.Swanson, PRD55, 4157 (1997). [u,d
mesons] T.Barnes, N.Black and P.R.Page, PRD68, 054014 (2003).
[strange mesons] [43 states, all 525 modes, all 891 amps.]
T.Barnes, S.Godfrey and E.S.Swanson, PRD72, 054026 (2005).
[charmonia: 1 st 40 cc mesons, all open-charm strong decay amps,
all E1 and many M1 transitions] F.E.Close and E.S.Swanson, PRD72,
094004 (2005). [open-charm mesons: D and D s ] qq meson decays: qqq
baryon decays: S.Capstick and N.Isgur, PRD34, 2809 (1986).
S.Capstick and W.Roberts, PRD49, 4570 (1994); PPNP 45, S241-S331
(2000). [BPs, BV modes of u,d baryons] Mainly light (u,d,s) hadrons
in f.-t. or 3 P 0 models. A few references:
Slide 11
Exotica: G/H/M
Slide 12
The glueball spectrum from an anisotropic lattice study Colin
Morningstar, Mike Peardon Phys. Rev. D60 (1999) 034509 Theor.
masses (LQCD) Glueballs No J PC -exotics until 4 GeV ! 1 GeV 2 GeV
3 GeV G = new I=0 mesons starting with an extra scalar at ca. 1.6
GeV. Then no new G states until > 2 GeV. No J PC - exotic G
until > 4 GeV. (= forget it)
Slide 13
G = 1 extra I=0 scalar meson at ca. 1.6 GeV. f 0 (~1600) = The
worst possible quantum numbers experimentally! Several broad
overlapping states. Then no new G states until > 2 GeV. No J PC
- exotic G until > 4 GeV. (= forget it) Glueballs
Slide 14
How to make new (u,d,s,g) hadrons: Hit things together. A + B
final state You may see evidence for a new resonance in the decay
products. Reactions between hadrons (traditional approach) are rich
but usually poorly understood. e.g.s BNL - p -> mesons + baryon
LEAR (CERN) pp annih. All light-q and g mesons, incl. qq,
glueballs, hybrids, multiquarks.
Slide 15
Slide 16
Glueball discovery? Crystal Barrel expt. (LEAR@CERN, ca. 1995)
pp 0 0 0 Evidence for a scalar resonance, f 0 0 n.b. Some prefer a
different scalar, f PROBLEM: Neither f 0 decays in a nave glueball
flavor-symmetric way to . qq G mixing?
Slide 17
Extra hadrons just below two-hadron thresholds. S-waves easiest
look for quantum numbers of an S-wave pair. Nuclei are examples
MANY molecules exist! Cant predict molecules w/o understanding soft
hadron scattering. Add X(3872) to the list? Molecules
Slide 18
X(3872 ) Belle Collab. K.Abe et al, hep-ex/0308029; S.-K.Choi
et al, hep-ex/0309032, PRL91 (2003) 262001. J D D* MeV MeV n.b. D
D* MeV MeV Charm in nuclear physics??? A DD* molecule???
Molecules
Slide 19
The trouble with multiquarks: Multiquark models found that most
channels showed short distance repulsion: E(cluster) > M 1 + M
2. Thus no bound states. (Remember (1540) ! ) Only 1+2 repulsive
scattering (continuum) in this sector of Hilbert space. nuclei and
hypernuclei weak int-R attraction allows molecules If E(cluster)
< M 1 + M 2 bag model: u 2 d 2 s 2 H-dibaryon, M H - M = 80 MeV.
n.b. hypernuclei exist, so this H was wrong. Exceptions: V NN (R)
2m N RR V (R) 2m 2) 1) Q 2 q 2 (Q = b; c?) 3) Heavy-light n.b.
multiquark.ne. molecule Fall-Apart Decay (actually not a decay at
all: no H I )
Slide 20
(Light; u,d,s) Hybrids: Theory and Experiment
Slide 21
[flux-tube model] New RICH band of meson excitations expected,
starting at ca. 1.9 GeV. Flavor nonets x 8 J PC = 72 states.
Includes 0 , 1 and 2 J PC -exotics. [bag model] ca. 1.5 GeV. Lowest
exotic is 1 (TE gluon) 0 and 2 are at higher mass (TM) Hybrids
Slide 22
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 QCD arXiv: 1004.4930v1 Most
recent LQCD results for light exotics, J PC = 1 , 2 , 0 . m q incr.
u,d 2.5 GeV 2.0 GeV 1.5 GeV 1.0 GeV n.b. All 3 of these exotic J PC
s were degen. in the flux-tube model. In the bag model, 1 is
lighter.
Slide 23
N.Isgur, R.Kokoski and J.Paton, PRL54, 869 (1985). Gluonic
Excitations of Mesons: Why They Are Missing and Where to Find Them
b f S+P S+P modes (poorly studied exptally; multimeson final
states) 1 exotic is observably narrow! some hybrids are predicted
to be VERY broad Hybrid Meson Decays: flux-tube model Hybrids
Slide 24
hybrid hybrid; b mode Close and Page: some notably narrow
nonexotic hybrids in the f-t model F.E.Close and P.R.Page, NPB443,
233 (1995).
Slide 25
Hybrid = qqg states (with q=u,d,s) span flavor nonets, hence
there are many experimental possibilities. Models agree that the
lightest hybrid multiplet contains J PC -exotics. f.t. model
predicts 8 J PC x 9 flavors = 72 extra resonances at the hybrid
threshold. 3/8 J PC are exotic, 0 , 1 , 2 . The remainder, 0 , 1 ,
2 , 0 , 1 , 1 are overpopulation rel to the quark model. M estm ca.
1.5 - 2.0 GeV. f.t. 1.9 GeV is famous. LGT mass similar to f.t. for
1 . J PC = 1 with I=1, , is especially attractive. It is predicted
in the f.t. decay model to be relatively narrow and to have unusual
decay modes. Hybrids flux-tube model (Theory Summary)
Slide 26
Spectrum of light (n=u,d) hybrid baryons. S.Capstick and
P.R.Page, nucl-th/0207027, Phys. Rev. C66 (2002) 065204. (flux tube
model) M (MeV) Hybrid baryons Non-exotics in a rich N* background
spectrum
Slide 27
(Light) Hybrids: Experiment
Slide 28
E.I.Ivanov et al. (BNL E852) PRL86, 3977 (2001). 1 exotic
reported in p p is a nice channel because nn couplings are weak for
once (e.g. the a 2 (1320) noted here). The reported exotic P-wave
is dominant! The (only) strong J PC -exotic H candidate signal. p
p
Slide 29
A.Alekseev et al. (COMPASS Collab.) Observation of a J P C =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. J PC exotic (confirmed) n.b.
resonant phase motion (confirmed but not shown here) is of course
the crucial test
Slide 30
Summary regarding meson spectroscopy and exotics: Theorists
expect new types of mesons (glueballs and hybrids) starting at ca.
1.5 - 2 GeV. A few candidates exist. Looking for J PC -exotics is a
good strategy. Also overpopulation - need to better establish the
qq sector above 1.5 GeV and ss! Charm mesons (cs and cc sectors)
have surprised people recently cs low masses hence tiny widths;
also perhaps new molecular states and hybrids. Data on the spectrum
is needed to compare with models and LGT. Strong and EM widths are
also useful information. Strong decays are poorly understood in
terms of QCD. n.b. Exciting discoveries in meson spectroscopy are
often serendipitous: J/ D s0 *(2317) D s1 (2460) X(3872)
Y(4260)
Slide 31
Hybrids: JLAB and elsewhere (final comments)
Slide 32
Existing and planned facilities (the competition?): BES-III
(Beijing) [now] e e to sqrt(s) ca. 4.2 GeV. Mainly very large J/
and event samples. Charmonium decays, in future unusual cc sector
states? Y(4260)? Application to light and exotic spectroscopy?
Could do e.g. rad decays. COMPASS (CERN) [now] High energy beam
available, former E852 people (S.U.Chung) revisiting p but at
higher E (more diffractive). Have seen evidence for the 1 (1600),
will proceed to other interesting final states. PANDA (GSI) [2017+]
Dedicated spectroscopy experiment. Official goal is cc hybrids. pp
annihilation to sqrt(s) ca. 5 GeV (higher energy LEAR). Light
spectroscopy for free. n.b. Lower energy pp produced the f 0 (1500)
glueball candidate, and has a large 1 (1400) signal. * * Not
really. Discovery of unusual hadrons requires confirmation by other
experiments.
Slide 33
GlueX at JLAB: Photoproduction (~new expt approach) accesses
exotic-J PC easily (S=1 beam) plucking the string - Isgur. [or is
it vec dom?] Several production mechanisms, 2 are: t-channel CEX,
e.g. diffr., e.g. P (Also s- and u-channel baryon resonances.) n.b.
You get the poorly explored ss sector for free. Theorists can
contribute by 1. LGT spectroscopy and decays, 2. modeling
photoproduction of both exotic and ordinary (qq) resonances (CLAS
data?).
Slide 34
Recent e.g. of 3pi CEX photoproduction (CLAS), showing a 2
(1320) and 2 (1670) qq states. a2a2 22
Slide 35
The importance of GlueX at JLAB: (Summary. C.Meyer presentation
follows) The light (u,d,s,g) meson spectrum is poorly known above
ca. 1.5 GeV. Theorists expect a rich new spectroscopy of hybrids,
including exotics, starting not far above this mass. Widths and
decay mechanisms are obscure [models], will be explored by LQCD in
the near future. GlueXs goal is to establish the meson spectrum to
ca. 2.5 GeV, and see whats out there. [serendipity in spectroscopy]
Past lessons (4pi detector, hermiticity, neutral and final modes,
studies of all decay modes, robust PWA) have been learned (LEAR,
E852) and are being implemented. It will be very exciting!