Transcript Slide 1

QCHS06 – Ponta Delgada
Experimental Review on Light Meson Physics
Cesare Bini
Universita’ “La Sapienza” and INFN Roma
(1)
(2)
(3)
(4)
(5)
Outline
Overview
Pseudoscalars
Vectors
Scalars
The 1  2 GeV region
(1) Overview: mass spectra of mesons below 1 GeV
Pseudoscalar multi-plet:
qq states with L=0; S=0  JPC=0-+
Vector multi-plet:
qq states with L=0; S=1  JPC=1--
Scalar multi-plet:
s(500), k(700), f0(980), a0(980)
qq states with L=1; S=1  JPC=0++ (??)
BUT: provided s and k are there
the scalars have an “Inverted Spectrum”
This talk will review:
 Recent measurements on P and V
(“refinement” measurements)
 Several recent measurements on S
(many open questions)
(2) Pseudoscalars-I: the h – h’ mixing angle
2 recent results on the mixing angle:
 KLOE measures
R = BR(f h’) / BR(fh) [Phys.Lett.B541(2002)45 + new preliminary]
 BES measures
R = BR(J/ h’) / BR(J/h) [Phys.Rev.D73,052008(2006)]
KLOE extracts the angle in the flavor basis
[according to A.Bramon et al. Eur. Phys. J. C7 (1999)]
R

ms Z NS t anV
BRφ  ηγ 
 cot2  P 
1




BRφ  ηγ
m Z S sin 2 P





P  41.4  0.3stat  0.7sys  0.6th 
2
 pη 


 p 
 η 
3
BES extracts the angle in the octet-singlet basis
[according to D.Gross,S.Treiman, F.Wilczek, Phys.Rev.D19 (1979)2188]
R
BRJ /  h  
BRJ /  h 


 mh2' 2 cos P  sin  P
 2

 mh cos P  2 sin  P
 P  15.9  1.2


2
  ph  

 



  ph 
3
KLOE vs. BES comparison: translate KLOE fP  P [caveat see T.Feldmann hep-ph/9907491]
 P (KLOE)  13.3  1.0
 1.7 s discrepancy  <P> ~ -14.6o
(2) Pseudoscalars-II: the h’ gluonium content
Allow the h’ (not the h) to have a gluonium content Zh’ (new KLOE analysis preliminary)
1
| uu  dd  Yh | ss 
2
1
h   Xh '
| uu  dd  Yh ' | ss   Zh ' | glue 
2
h  Xh
 Consistency check of the hyp. Zh’ =0
 X2h’ +Y2h’ = 0.93 ± 0.06
Introduce a further angle fG
and extract it using all available data
X h  cos P ; Yh  sin  P
X h '  sin  P cosG ; Yh '  cos P cosG ; Zh '  sin G
Work is in progress:
3 experimental constraints for 2 angles
c2 fit  worse fP resolution, estimate of fG
Space to improve the check ?
G(h’) is poorly known, at~8%
BR(h’w), BR(h’r0) known at 10% and 3%
G(h’), G(p0) known at 3.5% and 7%
G(wp0) known at 3%
(2) Pseudoscalars-III: the h mass
3 recent “precision” measurements done with different methods:
 NA48 (CERN) high statistics, invariant mass of h p0p0p0 decay [Phys.Lett.B533,196 (2002)]
 GEM (Julich) h production through: p+d  3He + h [Phys.Lett.B619,281 (2005)]
 KLOE (Frascati) decay f  h   using position photon directions [new preliminary]
NA48
NA48 vs. GEM == 8s discrepancy:
KLOE result (preliminary) is in agreement
with NA48 and in disagreement with GEM
KLOE
GEM
NA48
GEM
h mass (MeV)
(2) Pseudoscalars-IV: planned experiments
KLOE@DAFNE: [data taken in 2004-2006 – analysis in progress]
e+e-  f  h , h‘ : ~ 3 ×105 h/day + 2 × 103 h‘/day (simultaneously)
rare h, h´ decays, tests of ChPT, C and Isospin invariance
+ Expression of Interest for KLOE2 with 10 x KLOE   widths also
CRYSTAL BALL+TAPS@MAMI: [started in 2004 – data taking in progress]
php , h’p , p+n, on 2H liquid target: ~ 107 h/day
rare h, h´ decays, tests of ChPT and C-invariance
pion polarizabilities, further test of ChPT
WASA@COSY: [start in 2007]
pppph , pph’ study of production and decays of h and h’: ~108 h/day
or 106 h’/day
isospin simmetry breaking in h(h’) 3p  sinph
(3) Vectors-I: precision measurements
Precision measurements done (mostly at Novosibirsk) on r, w and f parameters:
 pion form factor (e+e-  pp)  r – line shape + r0 – w mixing
 e+e-  ppp0 cross-section + depolarization method  w and f parameters
CMD-2
Summary [see Eidelman, talk Novosibirsk 2006]
CMD2 (prelim.)
SND
(3) Vectors-II: modifications in nuclear medium
Line-shapes of vector meson produced in dense nuclear medium
Mass shift and broadening expected [see the talk by B.Kaempfer]
Several experiments: positive evidences reported:
TAPS (Bonn-Elsa) [D.Trnka et al., Phys.Rev.Lett.94(2005) 192303]
+A w+X (wp0+) on Nb and liquid 2H targets
M(w*) = ( 722  4stat (+35/-5)syst ) MeV (~-160 MeV)
KEK PS-E325 [R.Muto et al., J.Phys.G30 S1023 (2004)]
p (12 GeV) + A  VM + X (VM  e+e-) on C and Cu
Excess in the r – w region  -9% r mass
 g4 Jlab preliminary results [see the talk by C.Djalali]
(4) Scalars-I: the inverted spectrum  hint of 4-quark
Mass
add 2
Quarks s
add 1
Quark s
“Building Rule”
usu s sd sd ussd sd u s 
Q=0
Q=0
Q=1
Q=-1
(the f0(980)
and a0(980))
udu s udsd usu d sd u d 
Q=0
Q=1
Q=0
udu d 
Q=-1 (the k(800))
I3=0 Q=0 (the s(500))
2 important consequences: if 4q hipothesys is correct
 the s(500) and the k(800) have to be firmly established
 the s-quark content of f0 and a0 should be sizeable
 f0 and a0 couplings with f (ss) and with kaons
[N.N.Achasov and V.Ivanchenko, Nucl.Phys.B315,465(1989)]
(4) Scalars-II: the 4-quark hipothesys
Renewed interest after B-factory results:
new scalar meson “zoology” above 2.3 GeV
 reconsider the low mass spectrum
Assuming 2 quarks interacting by a single
gluon exchange. Find other configurations:
 Color triplet diquarks and anti-diquarks
 Attractive interaction between diquark and anti-diquark
giving a color singlet [R.L.Jaffe, Phys.Rev.D15,267(1977)]
 it is possible to build up 4-quarks scalar meson
(4) Scalars-III: are there the s(500) and the k(800) ?
Latest theoretical evaluation: [I.Caprini,
G.Colangelo,H.Leutwyler Phys.Rev.Lett.96 (2006) 132001]
s as the lowest resonance in QCD
Ms = 441+16-8 – i(272+9-12) MeV
 Latest experimental “observation” of s
by BES [Phys.Lett.B598 (2004) 149]
J/  wpp
 Ms = 541 ± 39 – i(252 ± 42) MeV
(
472 ± 35 according to a refined
analysis including pp scattering data and
f  p0p0 KLOE data [D.Bugg hep-ph/0608081])
Evidence of s
Evidence of k
 Experimental “observation” of k:BES [Phys.Lett.B633 (2006) 681]
J/  K*K+p Mk = 841 ± 30+81-73 – i(309 ± 45+48-72) MeV
(4) Scalars-IV: another hint for 4q: f  f0(980), a0(980)
If are qq
states:
If are 4q
states:
uu  dd
uu  dd
; f0 
2
2
uu  dd
a0 
; f 0  ss
2
a0 
 uu  dd
a 0  
2

Mass degeneracy ; very small “coupling” with f
large coupling with r and w (OZI rule argument)
Expected mass difference; different “couplings”
of f0 and a0 to f r and w.

 uu  dd
ss ; f 0  
2



ss

Mass degeneracy; large coupling to f
Look at f0 and a0 “affinity” to the f == content of quark s in the wavefunction:
f radiative decays (CMD-2, SND, KLOE)
f  a 0  hp 
0
f  f 0  p 0p 0
f  f 0  p  p  
KLOE observation of f0(980):
pp  fit of mass spectrum
p0p0  Dalitz plot analysis
pp
p0p0
(4) Scalars-V: results from f radiative decays
The signal due to the scalar is “lost” in a large and partly unknown background:
 Fit needed to extract the relevant amplitude  model dependence
(a) Branching Ratios ( integral of the scalar spectrum) [KLOE analysis – model dependent]:
[Phys.Lett.B536,209(2002),Phys.Lett.B537,21(2002),Phys.Lett.B634,148(2006)]
BR(f  f0(980)  p0p0) = (1.07 ± 0.07) ×10-4 (includes
BR(f  f0(980)  pp) = (2.1  2.4) ×10-4
BR(f  a0(980)  hp0) = (0.70 ± 0.07) ×10-4
a small contribution from s(500))
Few remarks:
 BR(f  f0(980)  pp) ~ 2 × BR(f  f0(980)  p0p0) as expected (Isospin)
 BR(f  f0(980)) ~ 4  5 × BR(f  a0(980)) (assuming f0, a0 KK negligible)
both too large to be compatible to qq states [Achasov, Ivanchenko, Nucl.Phys.B315,465(1989)]
(b) Couplings to the f ( from the fit [G.Isidori et al. JHEP 0605:049(2006)]) gfM (M any meson)
Gf  M   g
  mf  m 
2
2
fM
3 
2
M
mf2
3/ 2


(c) Coupling to meson pairs:
gfKK >> gfpp
gaKK ~ gahp
A Sizeable coupling to KK is found for both
Meson gfM (GeV-1)
p0
0.12
h
0.66
h’
0.70
f0
1.2  2.0
a0
> 1.0 (prel.)
(4) Scalars-VI: results from J/ decays
BES data: Phys.Rev. D68 (2003) 52003, Phys.Lett. B607 (2005) 243, Phys.Lett. B603 (2004) 138
s(500) f0(980)
f0(980)
J/wK+K-
J/wpp
J/fpp
J/fK+K-
Message: s(500) has a u-d quark structure, f0(980) has large s content
(4) Scalars-VII:  widths
Another “strong” argument in favour of non qq nature of low mass scalars.
f0(980) and a0(980) have small G compared to f2(1270) and a2(1320) [PDG 2004 values]:
G(f0(980))
= 0.39 ± 0.13 keV
G(a0(980))
= 0.30 ± 0.10 keV
G(f2(1270))
= 2.60 ± 0.24 keV
G(a2(1320)) = 1.00 ± 0.06 keV
Large G  compact object promptly annihilating in 2 
BUT: experimentally very “poor” measuraments.  Low Energy  physics still to be done
A recent result by BELLE
(not yet published):
  pp for W>700 MeV
f0(980) peak is observed.
G(f0(980)) ~ 0.15 keV
[N.N.Achasov and G.N.Shestakov,
Phys.Rev.D72,013007 (2005)]
A recent estimate of
G(s(500)) = 4.3 keV
[M.R.Pennington Phys.Rev.Lett.97,0011601 (2006)]
A complete low energy  physics program can be pursued at DAFNE-2
[see F.Ambrosino et al. hep-ex/0603056, see also F.Nguyen, F.Piccinini, A.Polosa hep-ph/0602205]
(4) Scalars-VIII: summary and outlook
Most analyses seem to point to a non q-qbar nature of the low mass scalar mesons:
 Tetraquarks [discussed by many authors...]
 Extended objects: f0(980), a0(980) as K-Kbar molecules [J.Weinstein,N.Isgur,Phys.Rev.D27(1979)588]
They are not elementary particles but are composite objects [V.Baru et al.,Phys.Lett.B586 (2004) 53]
New experimental checks (quark counting):
(1) BABAR – ISR measures e+e-  fh and e+e-  ff0(980) vs. √s  quark counting
[S.Pacetti, talk given at QNP06 Madrid]
 4 elementary fields for f0
 need of data at higher √s
(2) Heavy ions: elliptic-flow counts
the valence quarks
[see M.Lisa talk here]
(5) 1 ÷ 2 GeV region-I: the second scalar multi-plet
1. again: hint of an inverted spectrum  4-quark structure
2. 3 I=0 states: probably one is a glueball (Maiani, Piccinini, Polosa, Riquer hep-ph/0604018)
3. Ratio [f0(1370)KK]/[f0(1370)pp] sensitive to the quark structure and
to the glueball-tetraquark mixing scheme.
(5) 1 ÷ 2 GeV region-II: around the nucleon threshold
BES: J/ radiative decays:
Threshold effect on pp
Peak in pph’ (7.7s)
Threshold effect in fw
Consistent masses and widths
Not a vector: (0-+ or 0++)
Properties similar to h’
M = 1830.6  6.7 MeV
G = 0  93 MeV
M = 1833.7  7.2 MeV
G = 68  22 MeV
[BES-II coll., Phys.Rev.Lett. 95 (2005) 262001
Phys.Rev.Lett. 96 (2006) 162002]
BABAR: e+e-  hadrons through ISR confirms a vector state around 2Mp
[BABAR coll., Phys.Rev.D73:052003 (2006)]
Experim.
process
M(MeV)
G(MeV)
DM2
6p
~1930
~35
FENICE
Mh
~1870
~10
E687
3p+3p-
1910 ± 10
33 ± 13
BABAR-1
3p+3p-
1880 ± 50
130 ± 30
BABAR-2
2p+2p-2p0
1860 ± 20
160 ± 20
BABAR-3
2p+2p-
1880 ± 10
180 ± 20
BABAR-4
p+p-2p0
1890 ± 20
190 ± 20
BABAR-1
BABAR-3
Conclusions
Many other things not mentioned:
 hybrids, 1-+ states, BES f0(1790) ?, new states above 2 GeV,...
The experimental activities are mostly concentrated on the Scalar sector
(the most fundamental and the most elusive) but also on Pseudoscalar
and on Vector states.
SCALARS:
(1) Convergence of theory and experiments on the s as a resonance;
(2) There are now many hints of a non standard (non q-qbar)
structure for the lowest mass scalar multi-plet and some also
for the second scalar multi-plet.
VECTORS and PSEUDOSCALARS: precision measurements are coming.
In all cases the main difficulty is to extract “model-independent”
conclusions from data: a positive collaboration between theorists and
experimentalists is crucial.