Upload
tod
View
37
Download
0
Tags:
Embed Size (px)
DESCRIPTION
QCHS06 – Ponta Delgada. Experimental Review on Light Meson Physics. Cesare Bini Universita’ “La Sapienza” and INFN Roma. Outline (1) Overview (2) Pseudoscalars (3) Vectors (4) Scalars (5) The 1 2 GeV region. (1) Overview : mass spectra of mesons below 1 GeV. - PowerPoint PPT Presentation
Citation preview
Experimental Review on Light Meson Physics
Cesare BiniUniversita’ “La Sapienza” and INFN Roma
Outline(1) Overview(2) Pseudoscalars(3) Vectors(4) Scalars (5) The 1 2 GeV region
QCHS06 – Ponta Delgada
qq states with L=1; S=1 JPC=0++ (??) BUT: provided and are there
the scalars have an “Inverted Spectrum”
Pseudoscalar multi-plet:qq states with L=0; S=0 JPC=0-+
Vector multi-plet:qq states with L=0; S=1 JPC=1--
(1) Overview: mass spectra of mesons below 1 GeV
Scalar multi-plet:(500), (700), f0(980), a0(980)
This talk will review: Recent measurements on P and V (“refinement” measurements) Several recent measurements on S(many open questions)
(2) Pseudoscalars-I: the – ’ mixing angle
32
2
2'
sin2cos
sincos2
/
/
p
p
m
m
JBR
JBRR
PP
PP
thsysstatP .... 607030441
KLOE extracts the angle in the flavor basis [according to A.Bramon et al. Eur. Phys. J. C7 (1999)]
2 recent results on the mixing angle: KLOE measures R = BR( ’) / BR() [Phys.Lett.B541(2002)45 + new preliminary] BES measures R = BR(J ’) / BR(J) [Phys.Rev.D73,052008(2006)]
BES extracts the angle in the octet-singlet basis [according to D.Gross,S.Treiman, F.Wilczek, Phys.Rev.D19 (1979)2188]
2.19.15P
32
2
2sin
tan1cot
η
η
P
V
S
NSsP p
p
Z
Z
m
m
ηγφBR
γηφBRR
KLOE vs. BES comparison: translate KLOE P P [caveat see T.Feldmann hep-ph/9907491]
0.13.13)(KLOEP 1.7 discrepancy <P> ~ -14.6o
(2) Pseudoscalars-II: the ’ gluonium contentAllow the ’ (not the ) to have a gluonium content Z’ (new KLOE analysis preliminary)
Consistency check of the hyp. Z’ =0 X2
’ +Y2’ = 0.93 ± 0.06
Introduce a further angle G and extract it using all available data
GGPGP
PP
ZYX
YX
sin;coscos;cossin
sin;cos
'''
Work is in progress:3 experimental constraints for 2 angles2 fit worse P resolution, estimate of G
Space to improve the check ?(’) is poorly known, at~8%BR(’), BR(’0) known at 10% and 3%(’), () known at 3.5% and 7%(0) known at 3%
(2) Pseudoscalars-III: the mass3 recent “precision” measurements done with different methods: NA48 (CERN) high statistics, invariant mass of decay [Phys.Lett.B533,196 (2002)]
GEM (Julich) production through: p+d 3He + [Phys.Lett.B619,281 (2005)]
KLOE (Frascati) decay using position photon directions [new preliminary]
GEM
NA48NA48 vs. GEM == 8 discrepancy:KLOE result (preliminary) is in agreementwith NA48 and in disagreement with GEM
mass (MeV)
KLOE
NA48
GEM
(2) Pseudoscalars-IV: planned experiments
KLOE@DAFNE: [data taken in 2004-2006 – analysis in progress]e+e- , ‘ : ~ 3 ×105 /day + 2 × 103 ‘/day (simultaneously)rare , ´ 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]pp , ’p , +n, on 2H liquid target: ~ 107 /dayrare , ´ decays, tests of ChPT and C-invariancepion polarizabilities, further test of ChPT
WASA@COSY: [start in 2007]pppp , pp’ study of production and decays of and ’: ~108 /dayor 106 ’/dayisospin simmetry breaking in (’) 3 sin
(3) Vectors-I: precision measurementsPrecision measurements done (mostly at Novosibirsk) on , and parameters:
pion form factor (e+e- ) – line shape + 0 – mixing e+e- cross-section + depolarization method and parameters
CMD2 (prelim.)
SND
CMD-2
Summary [see Eidelman, talk Novosibirsk 2006]
(3) Vectors-II: modifications in nuclear mediumLine-shapes of vector meson produced in dense nuclear mediumMass shift and broadening expected [see the talk by B.Kaempfer]Several experiments: positive evidences reported:
KEK PS-E325 [R.Muto et al., J.Phys.G30 S1023 (2004)]
p (12 GeV) + A VM + X (VM e+e-) on C and CuExcess in the – region -9% mass
g4 Jlab preliminary results [see the talk by C.Djalali]
TAPS (Bonn-Elsa) [D.Trnka et al., Phys.Rev.Lett.94(2005) 192303]
+A +X (0+) on Nb and liquid 2H targetsM(*) = ( 722 4stat (+35/-5)syst ) MeV (~-160 MeV)
Q=0 Q=0 Q=1 Q=-1 (the f0(980) and
a0(980))
duud
dusdduusdsudsuud
susddsusdssdsuus
I3=0 Q=0 (the (500))
Q=0 Q=1 Q=0 Q=-1 (the (800))add 1Quark s
add 2Quarks s
“Building Rule”Mass
2 important consequences: if 4q hipothesys is correct the (500) and the (800) have to be firmly established the s-quark content of f0 and a0 should be sizeable f0 and a0 couplings with (ss) and with kaons
[N.N.Achasov and V.Ivanchenko, Nucl.Phys.B315,465(1989)]
(4) Scalars-I: the inverted spectrum hint of 4-quark
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-II: the 4-quark hipothesys
(4) Scalars-III: are there the (500) and the (800) ?
Latest experimental “observation” of by BES [Phys.Lett.B598 (2004) 149]
J/ M = 541 ± 39 – i(252 ± 42) MeV( 472 ± 35 according to a refined analysis including scattering data and KLOE data [D.Bugg hep-ph/0608081])
Evidence of
Evidence of
Latest theoretical evaluation: [I.Caprini, G.Colangelo,H.Leutwyler Phys.Rev.Lett.96 (2006) 132001]
as the lowest resonance in QCD
M = 441+16-8 – i(272+9
-12) MeV
Experimental “observation” of BES [Phys.Lett.B633 (2006) 681]
J/ K*K+-
M = 841 ± 30+81-73 – i(309 ± 45+48
-72) MeV
(4) Scalars-IV: another hint for 4q: f0(980), a0(980)
ssdduu
dduudduu
00
00
f;2
a
2f;
2aIf are qq
states:
Mass degeneracy ; very small “coupling” with large coupling with and (OZI rule argument)
Expected mass difference; different “couplings” of f0 and a0 to and .
If are 4q states:
ssdduu
ssdduu
2f;
2a 00 Mass degeneracy; large coupling to
Look at f0 and a0 “affinity” to the == content of quark s in the wavefunction:radiative decays (CMD-2, SND, KLOE)
0
000
00
f
f
a
KLOE observation of f0(980): fit of mass spectrum Dalitz plot analysis
(4) Scalars-V: results from 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( f0(980) ) = (1.07 ± 0.07) ×10-4 (includes a small contribution from (500))
BR( f0(980) ) = (2.1 2.4) ×10-4
BR( a0(980) ) = (0.70 ± 0.07) ×10-4
Few remarks: BR( f0(980) ) ~ 2 × BR( f0(980) ) as expected (Isospin) BR( f0(980)) ~ 4 5 × BR( 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 ( from the fit [G.Isidori et al. JHEP 0605:049(2006)]) gM(M any meson)
2/3
2
222
3M
m
mmg MM
Meson gM (GeV-1)
0 0.12
0.66
’ 0.70
f0 1.2 2.0
a0 > 1.0 (prel.)
(c) Coupling to meson pairs: gfKK >> gf
gaKK ~ ga
A Sizeable coupling to KKis found for both
(4) Scalars-VI: results from J/ decays
(500) f0(980)
J/
J/
f0(980)
BES data: Phys.Rev. D68 (2003) 52003, Phys.Lett. B607 (2005) 243, Phys.Lett. B603 (2004) 138
J/K+K-
J/K+K-
Message: (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 compared to f2(1270) and a2(1320) [PDG 2004 values]:
(f0(980)) = 0.39 ± 0.13 keV(a0(980)) = 0.30 ± 0.10 keV(f2(1270)) = 2.60 ± 0.24 keV(a2(1320)) = 1.00 ± 0.06 keVLarge 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): for W>700 MeVf0(980) peak is observed.(f0(980)) ~ 0.15 keV[N.N.Achasov and G.N.Shestakov, Phys.Rev.D72,013007 (2005)]
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]
A recent estimate of ((500)) = 4.3 keV[M.R.Pennington Phys.Rev.Lett.97,0011601 (2006)]
(4) Scalars-VIII: summary and outlookMost 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- and e+e- f0(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]
1. again: hint of an inverted spectrum 4-quark structure2. 3 I=0 states: probably one is a glueball (Maiani, Piccinini, Polosa, Riquer hep-ph/0604018)
3. Ratio [f0(1370)KK]/[f0(1370)] sensitive to the quark structure andto the glueball-tetraquark mixing scheme.
(5) 1 ÷ 2 GeV region-I: the second scalar multi-plet
(5) 1 ÷ 2 GeV region-II: around the nucleon threshold
BES: J/ radiative decays:Threshold effect on ppPeak in ’ (7.7)Threshold effect in Consistent masses and widthsNot a vector: (0-+ or 0++)Properties similar to ’[BES-II coll., Phys.Rev.Lett. 95 (2005) 262001
Phys.Rev.Lett. 96 (2006) 162002]
M = 1830.6 6.7 MeV
= 0 93 MeV
M = 1833.7 7.2 MeV
= 68 22 MeV
BABAR: e+e- hadrons through ISR confirms a vector state around 2Mp
Experim.
process M(MeV) (MeV)
DM2 6 ~1930 ~35
FENICE Mh ~1870 ~10
E687 3+3- 1910 ± 10
33 ± 13
BABAR-1
3+3- 1880 ± 50
130 ± 30
BABAR-2
2+2-
20
1860 ± 20
160 ± 20
BABAR-3
2+2- 1880 ± 10
180 ± 20
BABAR-4
+-20 1890 ± 20
190 ± 20
BABAR-1 BABAR-3[BABAR coll., Phys.Rev.D73:052003 (2006)]
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 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.