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Strong Decays and Couplings

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Making new hadrons (hit things together) Glueballs and hybrids (gluonic excitations) ... Physicists are cautious about leaping onto the pentaquark bandwagon ... – PowerPoint PPT presentation

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Title: Strong Decays and Couplings


1
Monday Quarks and QCD.
Quarks and gluons QCD, another gauge
theory! Basic physics of QCD Quarks and their
properties The strong interaction mesons and
baryons
2
Today (mainly) mesons recent discoveries.
QCD reminder Conventional qq mesons (cc) Making
new hadrons (hit things together) Glueballs and
hybrids (gluonic excitations) MOST RECENT
ARE Trouble in charmed mesons Molecules,
multiquarks and pentaquarks
3
QCD The Theory of the Strong Interaction
QCD quantum chromodynamics, ca. 1973 Theory of
the strong nuclear force. Its due to the
exchange of spin-1 particles gluons g between
spin-1/2 matter particles, quarks q and
antiquarks q. Similar to QED (quantum
electrodynamics), spin-1 photons g are exchanged
between spin-1/2 electrons e- and positrons
e. The basic rules of interaction Feynman
vertices in this non-Abelian quantum field
theory are that quarks and antiquarks can
emit/absorb gluons, and novel gluons interact
with gluons.
4
Comparing QED and QCD. (lagrangians)
Its déjà vu all over again. -Y.Berra
5
basic physics of QCD


Small qq separation
Large qq separation
6
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)
The QCD flux tube (LGT, G.Bali et al
hep-ph/010032)
7
Quarks Minimal solution for quarks needed to
explain the known light hadrons (1964,
Gell-Mann, Zweig Neeman)
All JP ½ (fermions)
u Q 2/3 e (u,d very similar in mass) d
Q -1/3 e s Q -1/3 e (somewhat heavier)
Thus p uud, n udd, D uuu, L uds,
p ud, K us, etc.
8
qqq baryons The lightest qqq baryon
octet. (SU(3) symmetry.)
3 x 3 x 3 10 8 8 1
9
qq meson The lightest qq meson octet. (SU(3)
symmetry.)
3 x 3 8 1
10
The six types or flavors of quarks . Gens.
I,II,III.
  • Label Name Q/e I Iz ca.
    mass habitat
  • u up 2/3 ½ ½ 5
    MeV p(938)uud, n(940)udd,
  • d down -1/3 ½ -½ 10
    MeV p(135)ud p-(135)du,
  • s strange -1/3 0 (etc) 150
    MeV strange hadrons Luds,Kus,
  • c charm 2/3 1500
    MeV y family (cc)

  • open charm hadrons

  • Do cu, Dcd
    Dscs Lcudc,
  • b bottom -1/3
    5 GeV U family (bb) open b hadrons
  • t top 2/3
    175 GeV t decays too quickly to hadronize

11
Naïve physically allowed hadrons (color
singlets)
_
Conventional quark model mesons and baryons.
qq
q3
100s of e.g.s
exotica
12
qq mesons states
First, some conventional hadrons (qq mesons) to
illustrate forces.
  • The quark model treats conventional mesons as qq
    bound states.
  • Since each quark has spin-1/2, the total spin is
  • Sqq tot ½ x ½
    1 0
  • Combining this with orbital angular momentum Lqq
    gives states
  • of total
  • Jqq
    Lqq spin singlets
  • Jqq Lqq1, Lqq,
    Lqq-1 spin triplets

13
qq mesons quantum numbers
  • Parity Pqq (-1) (L1)
    C-parity Cqq (-1) (LS)

The resulting qq NL states N2S1LJ have JPC
1S 3S1 1- - 1S0 0 - 2S 23S1 1- -
21S0 0 - 1P 3P2 2 3P1 1 3P0
0 1P1 1 - 2P 1D 3D3
3- - 3D2 2- - 3D1 1- - 1D2 2-
2D
JPC forbidden to qq are called JPC-exotic
quantum numbers 0
- - 0 - 1 - 2 - 3 -

Plausible JPC-exotic candidates hybrids,
glueballs (high mass), maybe multiquarks
(fall-apart decays).
14
How to make new hadrons (strongly int. particles)
Hit things together. A B -gt
final state You may see evidence for a new
resonance in the decay products.
J/y and other 1-- cc
Some reactions are clean, like ee- -gt
hadrons.
e.g.s SLAC, DESY 1970s Now CLEO-c, BES
cc B-factories bb (SLAC, KEK) W,Z machines
(LEP_at_CERN)
15
  • 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 states except 1D2 2- , 2- -
3.73 GeV
Below 3.73 GeV Annihilation and EM decays. (rp,
KK , gcc, gg, ll-..) narrow states.
16
Fitted and predicted cc spectrum Coulomb (OGE)
linear scalar conft. potential model blue
expt, red theory.
LS OGE LS conft, T OGE
as 0.5538 b 0.1422 GeV2 mc 1.4834
GeV s 1.0222 GeV
SS OGE
17
cc from LGT
What about LGT??? An e.g. X.Liao and T.Manke,
hep-lat/0210030 (quenched no decay
loops) Broadly consistent with the cc potential
model spectrum. No radiative or strong decay
predictions yet.
lt- 1- exotic cc-H at 4.4 GeV
Small L2 hfs.
oops 1 - cc has been withdrawn.
18
Sector of the 1st shocking new discovery
cs
S
P
19
LGT 0 2.44 - 2.47 GeV.
P
S
20
Where it all started. BABAR
DsJ(2317) in Ds p0
D.Aubert et al. (BABAR Collab.), PRL90, 242001
(2003).
M 2317 MeV (2 Ds channels), G lt 9 MeV (expt.
resolution)
Who ordered that !? - I.I.Rabi
(about the m- )
Since confirmed by CLEO, Belle and FOCUS.
(Theorists expected L1 cs states, e.g. JP0,
but with a LARGE width and at a much higher
mass.)
21
And another! CLEO
DsJ(2463) in Ds p0
D.Besson et al. (CLEO Collab.), PRD68, 032002
(2003).
M 2463 MeV, G lt 7 MeV (expt. resolution)
Since confirmed by BABAR and Belle. M 2457 MeV.
A JP1partner of the possibly 0 DsJ(2317) cs
?
22
(Godfrey and Isgur potential model.)
Prev. (narrow) expt. states in gray.
DK threshold
23
Theorists responses to the BaBar states
  • Approx. 100 theoretical papers have been
    published since
  • the discovery. There are two general schools of
    thought
  • 1) They are cs quark model mesons, albeit at a
    much lower mass than expected by the usual
    NRQPMs. Fermilab
  • 2) They are multiquark states.
  • (DK molecules) UT,Oxon,Weiz.
  • 3) They are somewhere between 1) and 2).
    reality

24
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25
2. They are multiquark states (DK molecules)
UT,Oxon,Weiz.
T.Barnes, F.E.Close, H.J.Lipkin, hep-ph/0305025,
PRD68, 054006 (2003).
3. reality
Recall Weinstein and Isgurs KKbar molecules.
26
X(3872)
Another recent shock to the system
Belle Collab. K.Abe et al, hep-ex/0308029 S.-K.Ch
oi et al, hep-ex/0309032, PRL91 (2003) 262001.
B / - -gt K / - pp- J / Y
(From ee- collisions at KEK.)
cc sector
y(3770) 3D1 cc. If the X(3872) is 1D cc, an
L-multiplet is split much more than expected
assuming scalar conft.
G lt 2.3 MeV
M 3872.0 - 0.6 - 0.5 MeV
27
Fitted and predicted cc spectrum Coulomb (OGE)
linear scalar conft. potential model blue
expt, red theory.
X(3872)
not cc ???
28
X(3872) confirmation (from Fermilab)
CDF II Collab. D.Acosta et al, hep-ex/0312021,
PRL to appear
G.Bauer, QWG presentation, 20 Sept. 2003.
n.b. most recent CDF II M 3871.3 pm 0.7 pm
0.4 MeV
X(3872) also confirmed by D0 Collab. at
Fermilab. Perhaps also seen by BaBar
OK, its real
29
X(3872)
n.b. M( D D-) 3879.5 - 0.7 MeV
Charm in nuclear physics???
30
Glueballs Theor. masses (LGT)
The glueball spectrum from an anisotropic lattice
study Colin Morningstar, Mike Peardon Phys. Rev.
D60 (1999) 034509 The spectrum of glueballs
below 4 GeV in the SU(3) pure-gauge theory is
investigated using Monte Carlo simulations of
gluons on several anisotropic lattices with
spatial grid separations ranging from 0.1 to 0.4
fm.
31
How to make new hadrons (strongly int. particles)
(II)
Hit more things together. A B
-gt 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.
All light-q and g mesons, incl. qq, glueballs,
hybrids, multiquarks.
e.g.s BNL p-p -gt mesons baryon LEAR (CERN) pp
annih.
32
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33
Glueball discovery? Crystal Barrel expt.
(LEAR_at_CERN, ca. 1995)
pp -gt p0 p0 p0
Evidence for a scalar resonance, f0(1500) -gt
p0 p0
n.b. Some prefer a different scalar, f0(1710)
-gt hh, KK.
PROBLEM Neither f0 decays in a naïve glueball
flavor-symmetric way to pp, hh, KK. qq lt-gt G
mixing?
34
Hybrid meson? JPC 1- exotic. (Cant be
qq.) E852_at_BNL, ca. 1996
p-p -gt (p-h) p
(Current best of several reactions and claimed
exotics.)
p1(1600)
Follow up expts planned at a new meson
facility at CEBAF HallD or GlueX.
a2(1320) qq
exotic
35
(Too?) exciting news the pentaquark at CLAS
(CEBAF).
nK (udd)(us) u2d2s. Cant be a 3 quark
baryon! A flavor exotic multiquark (if it
exists).
( gt 200 papers)
36
An experiment expressly designed to detect
pentaquarks confirms the existence of these
exotic physics particles, researchers
reported Sunday. Physicists are cautious
about leaping onto the pentaquark
bandwagon because of past bad experiences

USA Today

3 May 2004
37
The multiquark fiasco
These are very serious charges youre making,
and all the more painful to us, your elders,
because we still have nightmares from five times
before. - village elder,
Young Frankenstein
38
The dangerous 1970s multiquark logic (which led
to the multiquark fiasco)
The known hadron resonances, qq and qqq (and
qqq) exist because they are color
singlets. Therefore all higher Fock space
multiquark color singlet sectors will also
possess hadron resonances.
q2q2 baryonia q6 dibaryons q4q
Z for q s now pentaquarks
MANY theoretical predictions of a very rich
spectrum of multiquark resonances followed in the
1970s/early 1980s. (Bag model, potential
models, QCD_SRs, color chemistry,)
39
The simplest e.g. of had-had scat I2 pp. (A
flavor-exotic 27 channel, no s-channel qq
resonances, so no qq annihilation. Similar to the
NN and BB problems.)
Q 2 channel No qq states. u2d2?
I2 pp S-wave
d 0I2 deg
No I2 q2q2 resonance at 1.2 GeV. (Bag model
prediction, would give Dd 180 deg
there.) Expt sees only repulsive pp scat.
Mpp GeV
40
Why are there no multiquark resonances?
Fall-Apart Decay (actually not a decay at
all no HI )
Most multiquark models found that most channels
showed short distance repulsion
E(cluster) gt M1 M2. Thus no bound
states. Only 12 repulsive scattering.
Exceptions
2)
E(cluster) lt M1 M2, bag model u2d2s2
H-dibaryon, MH - MLL - 80 MeV. n.b.
LLhypernuclei exist, so this H was wrong.
1)
nuclei and hypernuclei weak int-R attraction
allows molecules
VLL(R)
VNN(R) -2mN
-2mL
3)
Heavy-light
R
R
Q2q2 (Qb, c?)
41
Naïve physically allowed hadrons (color
singlets)
Post-fiasco physically allowed hadrons (color
singlets)
_
Conventional quark model mesons and baryons.
qq
q3
100s of e.g.s
Basis state mixing may be very important in some
sectors.
exotica
42
Does it exist? ca. 10 expt. refs confirm and 10
dont (incl. HEP).
Follow-up expts. at CLAS (CEBAF) in progress.
They arent talking (in public).
Sell now.
43
Summary and conclusions
  • 1) We now understand EM, weak and strong forces
    as a single theory, called the standard model
    (SM). Gravity is not yet included.
  • 2) Both SM components (electroweak and strong
    int) are very similar renormalizable QFTs of the
    type known as non-Abelian gauge theories.
  • 3) The strong int is described by QCD, a gauge
    theory of quarks and gluons. Recent developments
    are concerned with the possible existence of
    exotica - glueballs, hybrids and multiquarks,
  • and charmed mesons much at lower masses
    than expected.
  • Derivation of nuclear forces (e.g. NN)
    from QCD is an interesting, open topic.
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