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Studies of radiative  meson decays with KLOE

Studies of radiative  meson decays with KLOE . P.Gauzzi (La Sapienza University and INFN – Rome) Contributed papers : ABS183, ABS184, ABS185. 31 st International Conference on High Energy Physics 24-31 July 200 2 , Amsterdam. Outline Scalars:  f 0 (980)  a 0 (980)

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Studies of radiative  meson decays with KLOE

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  1. Studies of radiative  meson decays with KLOE P.Gauzzi (La Sapienza University and INFN – Rome) Contributed papers: ABS183, ABS184, ABS185 31st International Conference on High Energy Physics 24-31 July 2002, Amsterdam • Outline • Scalars: f0(980) • a0(980) • Pseudoscalars:    • Conclusions

  2. DANE • Frascati -factory: e+e- collider • s 1020 MeV  M ; peak3000 nb • 2001 performance:peak average • L(cm2 s1)5·1031 3.5·1031 • day L dt (pb1)3 1.8 • 2002 data taking started on • May 1st :same luminosity of 2001, background reduction of a factor 2—3 • Collected data: • 2000: 25 pb-1  7.5 x 107f • (analysis completed) • 2001: 190 pb-1  5.7 x 108f • (analysis in progress)

  3. KLOE • Drift chamber: • gas: He-iC4H10 • dpT/pT= 0.4% • xy150 m ; z2 mm • E.m. calorimeter (Pb-Sci.Fi.): • sE/E = 5.7% / (E(GeV)) • st = 54 ps/(E(GeV))50 ps • 98% of 4 Magnetic field:0.52 T

  4. f0(980) (I=0) f000+-  = 40—100 MeV • a0(980) (I=1) a0 “ “ • not easily interpreted as mesons (3P0 nonet) • Other interpretations: states (Jaffe ’77) • molecules (Weinstein-Isgur ’90) • Br(f0(980)) and Br(a0(980)) and the mass spectra are • sensitive to the nature of these scalar particles: Scalar mesons (JPC= 0++) Br(f0) 5  10-5 3  10-4 10-5 Br(a0) 2  10-5 2  10-4 10-5 • Studied decays (data sample: 16 pb-1 from the 2000 data,~5107) • f0 ; f000  5  final state • a0 ; a00  (39%)  5  • a0 ; a00 +-0 (23%)  2 ch. tracks +5  • first observation  Previous meas. at VEPP2M

  5. 5  final state • cross sect.(nb) • Signal: 00 (f0 ; (500) ; 00) ~ 0.35 •  00  0 • 0 ( a0 ;  00) ~ 0.1 •   • Background: e+e-0 00 (0) ~ 0.5 • 3 (with accidental ’s) (~17) •  000 (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

  6.  0 0 00 • Constrained kinematic fit • to improve resolutions • Photon pairing • |M - M| < 5(M) • Reject events with: • |M - M| < 3(M) •  3102 events • <> = 40% 1+cos2 Estimated backgr. (~20%) e+e-0 00 33924 0 16616  000 15912

  7. radiative g radiative g gKK gf0KK gf0 f  0 0 K+ f g f0 K- 0 0 Fit to M spectrum • 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)) • Two fits: • Fit A : | (f0) + (00 )|2 • Fit B : | (f0)+ () + (00 )|2 • Free parameters: Mf0, g2f0KK, g2f0/g2f0KK, g and • Br(0000)

  8.  contribution negligible • Br(00) = (1.09  0.03  0.05)  10-4 (Fit B) • (SND: (1.220.10 0.06)  10-4 ; CMD-2: (1.080.170.09)  10-4) Fit results A B 2/ndf 109.5/33 43.2/32 Mf0 (MeV) 9624 973 1 g2f0KK/(4) 1.290.14 2.79 0.12 (GeV2) g2f0KK/g2f0 3.220.29 4.000.14 g — 0.060 0.008 • Large f0- destructive interference at M < 700 MeV (see also the work of Gokalp and Yilmaz (Phys.Rev.D64(2001)on the SND spectrum)

  9. Events cos 0 (with ) • Constrained kinematic fit • to improve resolutions • Photon pairing: (1) 00 ; (2) 0 •  reject00 events • M  < 760 MeV (reject f0 events) • |M - M| < 3(M) •  916 events <> = 32 % Events M (MeV/c2) • Estimated backgr.: (~30%) • e+e-0 00 546 • 00 15216 •  000 9810 •   52 • Data —MC Br(0)=(8.510.510.57) 10-5 SND :(8.8 1.40.9)  10 –5 ;CMD-2: (9.0 2.41.0)  10 –5

  10. 0 +-5 (+-0) • No background with the same final state • Backgr.: 2 Tracks + 3/4 photons (e+e-0 ; +-0) • ( ; +-0) • 2 Tracks + 6 photons • (KSKL+-000) • 1 vertex in IR with 2 tracks • 5 prompt  (E>10 MeV, |cos|<0.93) • Constrainedkinematic fit • M+-< 425 MeV (reject KS  p+p-) •  197 events <>=19% • estimated backgr. 44 events Br(0)=(7.960.600.47)  10-5

  11. a0 shape dBr/dm10-6 (MeV-1) Fit to the M spectra • Same model as for the f0 (kaon loop) • Combined fit, relative normalization fixed • to Br()/Br(+-0) • Free parameters: • g2a0KK, ga0/ga0KK and Br(000) • Ma0=984.8 MeV (PDG) fixed • 2/ndf 27.2/25 • g2a0KK/(4) (GeV2) 0.40  0.04 • ga0/ga0KK1.35  0.09 • Br(000) (0.5  0.5)  10-5 5 +-5 Br(a00)= (7.4  0.7)  10-5 M (MeV/c2)

  12. f0 parameters are compatible with model • a0 parameters seem not compatible with model Summary of fit results • Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989) KLOE f0 model g2f0KK/(4) 2.790.12 2.3 (=g2a0KK/4) 0.15 (=g2a0KK/4) 0.3 (=2g2a0KK/4) (GeV2) gf0 /gf0KK 0.500.01 0.3—0.5 2 0.5 Br(00)1041.090.07 ~ 1 ~ 0.15 ~ 0.2 a0 model g2a0KK/(4) 0.400.04 2.3 (=g2f0KK/4) 0.15 (=g2f0KK/4) (GeV2) ga0/ga0KK 1.350.09 0.91 1.53 Br( a0)1040.740.07 ~ 2 ~ 0.2

  13.  /  • The mass eigenstates ,  are related to the 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) • Pcan be extracted from the ratio(Bramon et al., Eur.Phys.J.C7(1999)) : • Br() can probe the gluonic content of 

  14.  /  • Same final state +- 3: • ;+-0;0 Br  3  10-3 •  ; +- ;  Br  2  10-5 • Backgr.: KLKS(with KLdecaying near the IP), +-0 • Data sample : 16 pb-1 from the 2000 data (~5107 ) • 1 vertex in IR with 2 tracks • 3 prompt  (E>10 MeV, |cos|<0.93) • Constrainedkinematic fit • : • 320 < Erad<400 MeV • E++E-< 550 MeV (reject +-0) •  N() = 50210  220 events  = 37 %

  15.  /  • : • Main background is  • Selection: elliptic cut in the plane • of the two most energetic photons N() = 120 12 5 events  = 23 % • F =0.95 (interference with e+e-( ) M (MeV)

  16. (2) (1)  /  • Mixing angle: P=(41.8  1.7) •  P=(-12.9 1.7) • Using Br() = (1.297  0.003) % (PDG) •  Br() = (6.10 0.67  0.45)  10-5 • PDG : (6.7 )  10-5 • Gluonic content of : • Consistency check: if Z=0  |Y|=cosP • other constraints on X and Y from: • (1) /(0 • (2) /(0 • 

  17. Conclusions • With the 2000 data KLOE studied the radiative decays of the •  into scalar and pseudoscalar mesons • We measured the branching ratios of : • 00  Phys.Lett.B537(2002) • 0  “ “ B536(2002) • reducing the experimental uncertainties • We evaluated the couplings of f0 (a0) to KK and to  () from • the fit to the invariant mass spectra • Pseudoscalar mixing angle in the quark flavor basis, • and best measurement of Br()  Phys.Lett.B541(2002) • Other KLOE results: KSe (Phys. Lett.B535(2002)), • (KS+-()) / (KS00) (Phys.Lett.B538(2002)) • Analysis on 2001 data (190 pb-1) is in progress, • results on f0+- are also expected, other 300 pb-1 from 2002 • data taking are foreseen

  18. Comparison with other experiments  decays other f0KLOE SND(1) CMD-2(1) WA102(2) E791(3) Mf0 (MeV)9731 9705 9757 9878 9774 g2f0KK/(4) 2.790.12 2.470.73 1.480.32 0.390.06 0.020.05 (GeV2) g2f0KK/g2f04.000.14 4.60.8 3.610.62 1.630.46 0.20.5 g0.060 0.008 a0KLOE SND E852(4) Crystal Barrel(5) Ma0 (MeV)984.8 (fixed) 995 9913 9996 g2a0KK/(4) 0.400.04 1.4 0.220.03 (GeV2) ga0/ga0KK 1.350.09 0.750.52 1.050.06 0.93—1.07 • f0   ;  contribution negligible (CMD2: combined f000f0+-) • (2) WA102 (CERN): centrally produced K+K-,+- in pp at 450 GeV/c • (3) E791 (Fermilab): f0 production in DS-+ • (4) E852 (BNL): a0 production in -p+-n and -p0n at 18.3 GeV/c • (5)

  19.  f0(980) a0(980) are not easily interpreted as qq mesons • Other interpretations: qqqq states (Jaffe ’77) • KK molecules (Weinstein-Isgur ’90) Scalar mesons (JPC= 0++) • f0(980) (I=0) f000+-  = 40—100 MeV • sizeable ss contents; strongly coupled to KK • a0(980) (I=1) a0 “ “ • coupled to KK • Possible interpretation (3P0 nonet): • f0-a0 mass degeneracy • f0 decay is OZI suppressed • small  partial width (0.3—0.4 keV) • small masses wrt the 3P2 nonet ( ~ 1500 MeV) • other candidates for the 3P0 nonet (a0(1450), f0(1370), f0(1710))

  20. 00 rejection Data • 0 • 000 • 00 |M(1)- M (2)| (MeV) M (MeV) (0 wrong pairing) • Parabolic cut to reject 0 •  M < 760 MeV to reject f0 + 0 wrong pairing • 00 MC-simulation with the experimental M spectrum

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