International Conference on the Structure and Interactions of the Photon

Experimental Measurement

of the meson radiative decays into scalars and pseudoscalars mesons

Experimental Measurement

of the meson radiative decays into scalars and pseudoscalars mesonsThe KLOE Coll. presented byCamilla Di Donato I.N.F.N. NaplesThe KLOE Coll. presented byCamilla Di Donato I.N.F.N. Naples

KLOE data collected KLOE data collected

1999 run : 2.5 pb-1 machine and detector studies

2000 run : 25 pb-1 7.5x107 published results 2001 run: 190 pb-1 5.7x108 analysis in progress

2002 run: 300 pb-1 9.0x108 analysis in progress

1999 run : 2.5 pb-1 machine and detector studies

2000 run : 25 pb-1 7.5x107 published results 2001 run: 190 pb-1 5.7x108 analysis in progress

2002 run: 300 pb-1 9.0x108 analysis in progress

KLOEKLOE

Drift chamber:• p/p < 0.4%• xy150 m ; z2 mm

E.m. calorimeter:•/E = 5.4% / (E(GeV))• t = 55 ps/(E(GeV))40 ps • 98% of 4

Magnetic field: 0.52 T

radiative decays radiative decays

•Analysis of 2000 data: Ldt = 16 pb-1

Phys. Lett. B541 (2002), 45

Phys. Lett. B537 (2002), 21

Phys. Lett. B537 (2002), 209

•Analysis of 2000 data: Ldt = 16 pb-1

Phys. Lett. B541 (2002), 45

Phys. Lett. B537 (2002), 21

Phys. Lett. B537 (2002), 209

radiative decays radiative decays

Pseudoscalar mesons (JPC= 0-+)

• (547) (I=0) • (958) (I=0)

Scalar mesons (JPC= 0++)

• f0(980) (I=0)

• a0(980) (I=1)

/ / / /

• The mass eigenstates , are related to SU(3) octet-singlet 8, 1 through the mixing angle P

• Recent studies based on PT and phenomenological analyses suggested a two mixing angle scenario

• In the quark flavour basis the two mixing angles are almost equal mixing is described by only one parameter (P)

sscosdduu2

1sinη

sssindduu2

1cosη

PP

PP

• P can be extracted from the ratio

(Bramon et al., Eur.Phys.J.C7(1999)) :

• Br() can probe the gluonic content of

/ / / /

1.45m

sm

; p

p

sin2

tg

m

m1cotg

ηγ)Br(

γ)ηBr(R

3

η

η

2

P

VsP

2

glueZssYdduuXη ηη21

η

/ / / /

• Decays with +- 3 final state: ;+-0;0 Br 310-3

; +- ; Br 210-5

Background from +-0 and KLKS (with KL decaying near the IP)

Analysis cut:• 1 vertex in IR with 2 tracks• 3 prompt (E>10 MeV, cos|<0.93)

• Constrained kinematic fit • topological cuts on the energy of particles

tot () = 37 % tot () = 23 %

´́ ´́

M (MeV)N() = 120 12 5 events; N() = 50210 220 events

• Main background is • Selection: elliptic cut in the plane of the two most energetic photons

R = Br()/Br()

Phys. Lett. B 541 (2002), 45

/ / / /

3

ρ

00

γη

ηγ

ηγ

γη

100.31)0.47(4.70

Fγγ)Br(η η)ππηBr(

γγ)Br(π )πππBr(η

ε

ε

N

NR

• F =0.95 (interference with e+e-( )

• Using PDG value for Br(): Br() = (6.100.610.43)10-5

• Pseudoscalar mixing angle: P = (41.8 1.7) (flavor)

P = (-12.9 1.7) (octet-singlet)

•Gluonic content of :

Consistency check: if Z=0 |Y|=cosP

other constraints on X and Y from: (1) /(0 (2) /(0

glueZssYdduuXη ηη21

η glueZssYdduuXη ηη21

η

0.060.09

2η

2η 0.94YX

(1)

(2)

/ / / /

M (MeV)

100 pb-1 (2

001)

100 pb-1 (2

001)

/ / / /

N() = 153 12

• Selection:

Br() = (7.05±0.50+0.53/-0.46)x10-5

Ks Kl Ks Kl

data

Ks Kl Ks Kl

data

77 77

E++E- (MeV)

dN

/dE

E(MeV)

prelim

inary

prelim

inary

200020012002

E++E- (MeV)

dN

/dE

Br(f0) 5 10-5 3 10-4 10-5

Br(a0) 2 10-5 2 10-4 10-5

fa fa•The scalar mesons f0 (980) a0 (980) are not easily interpreted as qq states

•Jaffe(1977) suggested qqqq states•Weinstein, Isgur (1990) suggested KK molecule

•Both BR and scalar mass spectra are sensitive to nature

KK qqqq qq

f0 model g2

f0KK/(4) 2.3 0.15 0.3 (GeV2) (=g2

a0KK/4) (=g2a0KK/4) (=2g2

a0KK/4) gf0 /gf0KK 0.3—0.5 2 0.5 Br(00)104 ~ 1 ~ 0.15 ~ 0.2

a0 model g2

a0KK/(4) 2.3 0.15 (GeV2) (=g2

f0KK/4) (=g2f0KK/4)

ga0/ga0KK 0.91 1.53 Br( a0)104 ~ 2 ~ 0.2

f0 model g2

f0KK/(4) 2.3 0.15 0.3 (GeV2) (=g2

a0KK/4) (=g2a0KK/4) (=2g2

a0KK/4) gf0 /gf0KK 0.3—0.5 2 0.5 Br(00)104 ~ 1 ~ 0.15 ~ 0.2

a0 model g2

a0KK/(4) 2.3 0.15 (GeV2) (=g2

f0KK/4) (=g2f0KK/4)

ga0/ga0KK 0.91 1.53 Br( a0)104 ~ 2 ~ 0.2

2)/ddu(uss 2)/ddu(u ss

2)/ddu(uss 2)/ddu(u

ModelsModelsModelsModels

• Predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)

Scalar mesons (JScalar mesons (JPCPC= 0= 0++++))Scalar mesons (JScalar mesons (JPCPC= 0= 0++++))

• Studied decays (data sample: 16 pb-1 from the 2000 data,~5107)f0 ; f000 5 final state a0 ; a00 (39%) 5 a0 ; a00 +-0 (23%) 2 ch. tracks +5

first observation

Previous meas. at VEPP2M

• f0(980) (I=0) f000+-

• a0(980) (I=1) a0

cross sect.(nb)• Signal: 00 (f0 ; (500) ; 00) ~ 0.35 00 0 0 ( a0 ; 00) ~ 0.1 • Background: e+e-0 00 ~ 0.5 3 (with accidental ’s) (~17) 000 (with 2 lost) (~14)

• Sample selection:– exactly 5 prompt photons – E > 7 MeV– |cos| < 0.93 to avoid the quadrupole region– 5Ei > 700 MeV to reject KLKS neutrals

5 5 final states final states5 5 final states final states

00000000

• Constrained kinematic fit to improve resolutions• Photon pairing • |M - M| < 5(M)• Reject events with: |M - M| < 3(M)

3102 events <> = 40%

1+cos2

0 0

Estimated backgr. (~20%)e+e-0 00 339240 16616 000 15912

Fit toFit to M M spectrumspectrumFit toFit to M M spectrumspectrum

• Two fits: Fit A : | (f0) + (00 )|2

Fit B : | (f0) + () + (00 )|2

Free parameters: Mf0, g2f0KK, g2

f0/g2f0KK, g and (gg)2

• Model : 1) f0 dominated by kaon loop (Achasov-Ivanchenko, Nucl.Phys.B315(1989))

2) f0 propagator with finite width corrections 3) (500) B-W with M=478 MeV and =324 MeV (Fermilab E791-Phys.Rev.Lett.86(2001)770)

4) point-like coupling of (500) to (Gokalp,Yilmaz,Phys.Rev.D64(2001))

5) + interference term parameterizations from Achasov-Gubin, (Phys.Rev.D63(2001))

f0

radiative gKK

gf0KK

gf0

0

0

K+

K-

( contribution negligible )

Br(00) = (1.09 0.03 0.05) 10-4 (Fit B) (SND: (1.220.10 0.06) 10-4 ; CMD-2: (1.080.170.09) 10-4)

Fit resultsFit resultsFit resultsFit results

Large f0- destructive interference at M < 700 MeV

A B2/ndf 109.5/33 43.2/32Mf0 (MeV) 9624 973 1 g2

f0KK/(4) 1.290.14 2.79 0.12(GeV2)g2

f0KK/g2f0 3.220.29 4.000.14

g — 0.060 0.008

Br(f0)= (4.47 0.21) 10-4 Br(f0)= (4.47 0.21) 10-4

• Constrained kinematic fit to improve resolutions• Photon pairing: (1) 00 ; (2) 0 reject 00 events• M < 760 MeV (reject f0 events) • |M - M| < 3(M) 916 events <> = 32 %

Eve

nts

cos

Eve

nts

• Data —MC

00 (with (with )) 00 (with (with ))

• Estimated backgr.: (~30%) e+e-0 00 546 00 15216 000 9810 52

SND :(8.8 1.40.9) 10 –5 ;CMD-2: (9.0 2.41.0) 10 –5

Br(0)=(8.510.510.57) 10-5Br(0)=(8.510.510.57) 10-5

M (MeV/c2)

00 ++--55 ( (++--00))00 ++--55 ( (++--00))• No background with the same final state• Backgr.: 2 Tracks + 3/4 photons (e+e-0 ; +-0) ( ; +-0) 2 Tracks + 6 photons (KSKL+-000)

• 1 vertex in IR with 2 tracks• 5 prompt (E>10 MeV, cos|<0.93)• Constrained kinematic fit • M+-< 425 MeV (reject KS

197 events <>=19% estimated backgr. 44 events

Br(0)=(7.960.600.47) 10-5Br(0)=(7.960.600.47) 10-5

• Same model as for the f0 (kaon loop)• Combined fit, relative normalization fixed to Br()/Br(+-0) • Free parameters: g2

a0KK, ga0/ga0KK and Br(000) Ma0=984.8 MeV (PDG) fixed

2/ndf 27.2/25 g2

a0KK/(4) (GeV2) 0.40 0.04 ga0/ga0KK 1.35 0.09 Br(000) (0.5 0.5) 10-5

5

+-5

Br(a00)= (7.4 0.7) 10-5 Br(a00)= (7.4 0.7) 10-5

Fit toFit to M M spectrumspectrumFit toFit to M M spectrumspectrum

Summary of fit resultsSummary of fit resultsSummary of fit resultsSummary of fit results• Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)

KLOE f0 modelg2

f0KK/(4) 2.790.12 2.3 0.15 0.3(GeV2) (=g2

a0KK/4) (=g2a0KK/4) (=2g2

a0KK/4) gf0 /gf0KK 0.500.01 0.3—0.5 2 0.5Br(00)104 1.090.07 ~ 1 ~ 0.15 ~ 0.2

a0 modelg2

a0KK/(4) 0.400.04 2.3 0.15(GeV2) (=g2

f0KK/4) (=g2f0KK/4)

ga0/ga0KK 1.350.09 0.91 1.53 Br( a0)104 0.740.07 ~ 2 ~ 0.2

KLOE f0 modelg2

f0KK/(4) 2.790.12 2.3 0.15 0.3(GeV2) (=g2

a0KK/4) (=g2a0KK/4) (=2g2

a0KK/4) gf0 /gf0KK 0.500.01 0.3—0.5 2 0.5Br(00)104 1.090.07 ~ 1 ~ 0.15 ~ 0.2

a0 modelg2

a0KK/(4) 0.400.04 2.3 0.15(GeV2) (=g2

f0KK/4) (=g2f0KK/4)

ga0/ga0KK 1.350.09 0.91 1.53 Br( a0)104 0.740.07 ~ 2 ~ 0.2

2)/ddu(uss 2)/ddu(u ss

2)/ddu(uss 2)/ddu(u

• f0 parameters are compatible with model • a0 parameters seem not compatible with model

• f0 parameters are compatible with model • a0 parameters seem not compatible with model

qqqq qqqq

Phys. Lett. B 536 (2002), 209

M0 (MeV)

Phys. Lett. B 537 (2002), 21

f0a0 f0a0

M (MeV)

2001+2002 data2000 data

Conclusions Conclusions

First KLOE published papers on radiative decays, 2000 events:

• Br() = (6.100.610.43)10-5

• P = (41.8 1.7) (flavor)

• Br(00) = (1.09 0.03 0.05) 10-4

• Br(f0) = (4.47 0.21) 10-4

• Br(a0) = (7.4 0.7) 10-5

Analysis in progress on 2001+2002 events 500pb-1:

more statistic and models with more free parameters

====================================================== Author : KLOE Collab. (Speaker: Camilla Di Donato) Type : Experimental Measurement of the Phi meson radiative decays into scalars and pseudoscalars mesons.

The Kloe experiment has measured the radiative decays of the Phi meson into pi0, eta and eta'(958); these measurements are relevant to assess the mixing in the pseudoscalar nonet as well as to evaluate the gluon content in the eta'(958). Moreover also the radiative decays into pi0 pi0 gamma and eta pi0 gamma have been measured. These decays are dominated by the final states f0(980) and a0(980). The measurement of the branching ratios and of the pi0-pi0 or eta-pi0 invariant mass spectrum helps to understand the controversial nature of the above scalar mesons. ==================================================