Transcript Strong Decays and Couplings - UTK Department of Physics

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
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
QCD: The Theory of the Strong Interaction
QCD = quantum chromodynamics, ca. 1973
Theory of the strong “nuclear” force. It’s 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.
Comparing QED and QCD.
“It’s déjà vu all over again.” -Y.Berra
(lagrangians)
basic physics of QCD
Small qq
separation
Large qq
separation
LGT simulation showing
the QCD flux tube
Q
Q
R = 1.2 [fm]
“funnel-shaped” VQQ(R)
Coul.
(OGE)
The QCD flux tube
(LGT, G.Bali et al; hep-ph/010032)
linear conft.
(str. tens. = 16 T)
Quarks
Minimal solution for quarks needed to explain the known light hadrons:
(1964, Gell-Mann, Zweig; Ne’eman):
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.
qqq baryons
The lightest
qqq baryon octet.
(SU(3) symmetry.)
3x3x3=
10 + 8 + 8 + 1
qq meson
The lightest
qq meson octet.
(SU(3) symmetry.)
3x3=8+1
The six types or “flavors” of quarks . Gens. I,II,III.
Label Name
Q/|e|
I
Iz
ca. mass
u
d
up
down
+2/3
-1/3
½
½
+½
-½
5 MeV
10 MeV
s
c
strange -1/3
charm +2/3
0 (etc)
150 MeV
1500 MeV
habitat
p(938)=uud, n(940)=udd,…
p+(135)=ud p-(135)=du,…
strange hadrons; L=uds,K+=us,…
y family (cc);
open charm hadrons;
Do =cu, D+=cd; Ds+=cs Lc+=udc, …
b
t
bottom -1/3
top
+2/3
5 GeV
175 GeV
U family (bb); open b hadrons
t decays too quickly to hadronize
“Naïve” physically allowed hadrons (color singlets)
_
3
qq
Conventional quark model
mesons and baryons.
q
100s of e.g.s
“exotica” :
2
3
g , g ,…
glueballs
maybe 1 e.g.
3
qqg, q g,…
hybrids
maybe 1-3 e.g.s
2 2
4
q q , q q,…
multiquarks
First, some conventional hadrons (qq mesons) to illustrate forces.
qq mesons
states
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 = Lqq+1, Lqq, Lqq-1
spin triplets
qq mesons
Parity Pqq = (-1)
quantum numbers
(L+1)
C-parity Cqq = (-1)
(L+S)
The resulting qq NL states N2S+1LJ have JPC =
1S: 3S1 1- - ;
1
S0 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).
How to make new hadrons (strongly int. particles):
Hit things together.
A + B -> final state
You may see evidence for a new resonance in the decay products.
Some reactions are “clean”,
like e+e- -> hadrons.
e.g.s
SLAC, DESY 1970s
Now:
CLEO-c, BES cc
B-factories bb
(SLAC, KEK)
W,Z machines (LEP@CERN)
J/y and other 1-- cc
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, l l ..):
narrow states.
Fitted and predicted cc spectrum
Coulomb (OGE) + linear scalar conft. potential model
blue = expt, red = theory.
L*S OGE – L*S conft,
T OGE
S*S OGE
as = 0.5538
2
b = 0.1422 [GeV ]
mc = 1.4834 [GeV]
s = 1.0222 [GeV]
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.
<- 1
Small
L=2 hfs.
oops…
+1 cc has
been withdrawn.
-+
exotic cc-H at 4.4 GeV
Sector of the 1st
shocking new discovery: cs
S
P
LGT 0+: 2.44 - 2.47 GeV.
S
P
Where it all started.
BABAR:
D.Aubert et al. (BABAR Collab.),
PRL90, 242001 (2003).
M = 2317 MeV (2 Ds channels),
G < 9 MeV (expt. resolution)
“Who ordered that !?”
- I.I.Rabi
(about the m- )
Since confirmed by
CLEO, Belle and FOCUS.
(Theorists expected L=1 cs states, e.g.
P
+
J =0 , but with a LARGE width and at a
much higher mass.) …
D*
sJ(2317)
+
in Ds
+ 0
p
And another!
D.Besson et al. (CLEO Collab.),
PRD68, 032002 (2003).
M = 2463 MeV,
G < 7 MeV (expt. resolution)
Since confirmed by BABAR and Belle.
M = 2457 MeV.
P
+
A J =1 partner of the possibly
+
+
0 D*sJ(2317) cs ?
CLEO:
+
+ 0
D*sJ(2463) in Ds*
p
(Godfrey and Isgur potential model.)
Prev. (narrow) expt. states in gray.
DK threshold
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]
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 Isgur’s “KKbar molecules”.
Another recent shock
to the system:
X(3872)
Belle Collab. K.Abe et al, hep-ex/0308029;
S.-K.Choi et al, hep-ex/0309032, PRL91 (2003) 262001.
B
+/-
-> K
+/-
+ -
p p J/Y
(From e+e- collisions at KEK.)
cc sector
y(3770) =
3
D1 cc.
If the X(3872) is 1D cc,
an L-multiplet is split much more
than expected assuming
scalar conft.
G < 2.3 MeV
M = 3872.0 +- 0.6 +- 0.5 MeV
Fitted and predicted cc spectrum
Coulomb (OGE) + linear scalar conft. potential model
blue = expt, red = theory.
X(3872)
not cc ???
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, it’s real…
X(3872)
M = 3872.0 +- 0.6 +- 0.5 MeV
M( Do + D*o) = 3871.5 +- 0.5 MeV
n.b. M( D+ + D*-) = 3879.5 +- 0.7 MeV
Accidental agreement?
-+
-If not cc 2 or 2 or …,
a molecular (DD*) state?
Charm in nuclear physics???
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.
How to make new hadrons (strongly int. particles) (II):
Hit more 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 p -> mesons + baryon
LEAR (CERN) pp annih.
All light-q and g mesons,
incl. qq, glueballs, hybrids, multiquarks.
Glueball discovery? Crystal Barrel expt. (LEAR@CERN, ca. 1995)
pp -> p0 p0 p0
Evidence for a
scalar resonance,
f0(1500)
-> p0 p0
n.b.
Some prefer a different scalar,
f0(1710)
>
hh,
PROBLEM:
KK.Neither f0 decays in a naïve glueball flavor-symmetric way to pp,
qq <-> G mixing?
hh, KK.
Hybrid meson? JPC = 1-+ exotic. (Can’t be qq.)
E852@BNL, ca. 1996
p-p -> (p-h’) p
(Current best of
several reactions
and claimed exotics.)
Follow up expts
planned at a new
meson facility
at CEBAF;
“HallD” or GlueX.
p1(1600)
a2(1320)
exotic
qq
(Too?) exciting news: the pentaquark at CLAS (CEBAF).
nK+ = (udd)(us) = u2d2s.
Can’t be a 3 quark baryon!
A “flavor exotic” multiquark (if it exists).
( > 200 papers)
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
The multiquark fiasco
“These are very serious charges you’re making,
and all the more painful to us, your elders, because
we still have nightmares from five times before.”
Frankenstein”
village elder, “Young
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.
2 2
qq
“baryonia”
6
“dibaryons”
4
“Z*” for q = s …
now “pentaquarks”
q
qq
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,…)
The simplest e.g. of had-had scat: I=2 pp.
(A flavor-exotic 27 channel, no s-channel qq resonances,
I=2
S-wave
so no qq annihilation. Similar to the NN pp
and BB’ problems.)
d
I=2
0
Q = +2 channel
No qq states.
2 2
ud?
[deg]
2 2
Mpp [GeV]
No I=2 q q resonance at 1.2 GeV.
(Bag model prediction, would give
Dd = + 180 [deg] there.)
Expt sees only repulsive pp scat.
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) > M1 + M2.
Thus no bound states.
Only 1+2 repulsive scattering.
Exceptions:
2)
1)
VNN(R)
-2mN
bag model:
2 2 2
u d s H-dibaryon, MH - MLL = - 80 MeV.
nuclei and hypernuclei
weak int-R attraction allows
“molecules”
E(cluster) < M1 + M2,
“VLL(R)”
n.b.
LLhypernuclei
exist, so this H was wrong.
-2mL
R
R
3)
Heavy-light
2 2
Q q (Q=b, c?)
Post-fiasco
physically
allowed
hadrons
(color
singlets)
“Naïve” physically
allowed
hadrons
(color
singlets)
_
3
qq
Conventional quark model
mesons and baryons.
q
100s of e.g.s
3 n
3
(q ) , (qq)(qq), (qq)(q ),…
Basis state mixing may be
very important in some sectors.
nuclei / molecules
”exotica” :
2
3
g , g ,…
glueballs
maybe 1 e.g.
6
3 n
ca. 10 e.g.s of (q ) , maybe 1-3 others
3
qqg, q g,…
hybrids
maybe 1-3 e.g.s
22 22
4 4
(qqq, ),(q
q),…
q
q q,…
multiquark clusters ???
multiquarks
controversial
e.g. Q(1542)?
Does it exist? ca. 10 expt. refs confirm and 10 don’t (incl. HEP).
Follow-up expts. at CLAS (CEBAF)
in progress. They aren’t talking
(in public).
Sell now.
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.