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Studies of radiative meson decays with KLOE P.Gauzzi (La Sapienza University and INFN – Rome) Contributed papers: ABS183, ABS184, ABS185 Outline • Scalars: f0(980) a0(980) • Pseudoscalars: • Conclusions 31st International Conference on High Energy Physics 24-31 July 2002, Amsterdam DANE • Frascati -factory: e+e- collider s 1020 MeV M ; peak3000 nb • 2001 performance: peak average L(cm2 s1) 5·1031 3.5·1031 day L dt (pb1) 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 107 (analysis completed) 2001: 190 pb-1 5.7 x 108 (analysis in progress) KLOE Drift chamber: • gas: He-iC4H10 • dpT/pT = 0.4% • xy150 m ; z2 mm E.m. calorimeter (Pb-Sci.Fi.): • E/E = 5.7% / (E(GeV)) • t = 54 ps/(E(GeV))50 ps • 98% of 4 Magnetic field: 0.52 T Scalar mesons (JPC= 0++) • f0(980) (I=0) f000+ = 40—100 MeV • a0(980) (I=1) a0 “ “ not easily interpreted as q q mesons (3P0 nonet) • Other interpretations: q q q q states (Jaffe ’77) KK molecules (Weinstein-Isgur ’90) • Br(f0(980)) and Br(a0(980)) and the mass spectra are sensitive to the nature of these scalar particles: Br(f0) Br(a0) qq 5 10-5 2 10-5 qqqq 3 10-4 2 10-4 KK 10-5 10-5 • Studied decays (data sample: 16 pb-1 from the 2000 data,~5107) Previous meas. f0 ; f000 5 final state at VEPP2M a0 ; a00 (39%) 5 a0 ; a00 +-0 (23%) 2 ch. tracks +5 first observation 5 final state • Signal: 00 (f0 ; (500) ; 00) 00 0 0 ( a0 ; 00) • Background: e+e-0 00 (0) 3 (with accidental ’s) 000 (with 2 lost) cross sect.(nb) ~ 0.35 • Sample selection: – exactly 5 prompt photons – E > 7 MeV – |cos| < 0.93 to avoid the quadrupole region – 5Ei > 700 MeV to reject KLKS neutrals ~ 0.1 ~ 0.5 (~17) (~14) 00 • Constrained kinematic fit to improve resolutions • Photon pairing • |M - M| < 5(M) • Reject events with: |M - M| < 3(M) 3102 events <> = 40% Estimated backgr. (~20%) e+e-0 00 33924 0 16616 000 15912 1+cos2 0 0 Fit to M spectrum • Model : 1) f0 dominated by kaon loop radiative K+ f0 0 0 K- (Achasov-Ivanchenko, Nucl.Phys.B315(1989)) gKK gf0KK gf0 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 radiative (Gokalp,Yilmaz,Phys.Rev.D64(2001)) 5) + interference term parameterizations from Achasov-Gubin, (Phys.Rev.D63(2001)) • Two fits: Fit A : | (f0) + (00 )|2 Fit B : | (f0) + () + (00 )|2 Free parameters: Mf0, g2f0KK, g2f0/g2f0KK, g and Br(0000) 0 0 g Fit results A B 2/ndf 109.5/33 43.2/32 Mf0 (MeV) 9624 973 1 g2f0KK/(4) 1.290.14 2.79 0.12 (GeV2) g2f0KK/g2f0 3.220.29 4.000.14 g — 0.060 0.008 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) Large f0- destructive interference at M < 700 MeV (see also the work of Gokalp and Yilmaz (Phys.Rev.D64(2001)on the SND spectrum) • 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) <> = 32 % • Estimated backgr.: (~30%) e+e-0 00 546 00 15216 000 9810 52 Events 916 events Events 0 (with ) M (MeV/c2) • Data —MC Br(0)=(8.510.510.57) 10-5 SND :(8.8 1.40.9) 10 –5 ;CMD-2: (9.0 2.41.0) 10 –5 cos 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+-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) 10-5 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(000) Ma0=984.8 MeV (PDG) fixed Br(a00)= (7.4 0.7) 10-5 +-5 dBr/dm10-6 (MeV-1) 2/ndf 27.2/25 g2a0KK/(4) (GeV2) 0.40 0.04 ga0/ga0KK 1.35 0.09 Br(000) (0.5 0.5) 10-5 5 a0 shape M (MeV/c2) Summary of fit results • Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989) KLOE ss ss(uu dd)/ 2 (uu dd)/ 2 f0 model g2f0KK/(4) 2.790.12 2.3 (=g2a0KK/4) 0.15 (=g2a0KK/4) 0.3 (=2g2a0KK/4) (GeV2) gf0 /gf0KK 0.500.01 0.3—0.5 2 0.5 Br(00)104 1.090.07 ~1 ~ 0.15 ~ 0.2 a0 model g2a0KK/(4) (GeV2) ga0/ga0KK Br( a0)104 ss(uu dd)/ 2 0.400.04 1.350.09 0.740.07 (uu dd)/ 2 2.3 (=g2f0KK/4) 0.15 (=g2f0KK/4) 0.91 ~2 1.53 ~ 0.2 • f0 parameters are compatible with q q q q model • a0 parameters seem not compatible with q q q q model / • 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) 1 η cos P uu dd sin P s s η sin P 2 1 uu dd cos P s s 2 P can be extracted from the ratio (Bramon et al., Eur.Phys.J.C7(1999)) : m s tg V Br( ηγ) 2 R cotg P 1 Br( ηγ) m sin2 P 2 p η p η 3 • Br() can probe the gluonic content of ms ; 1.45 m / • Same final state +- 3: ;+-0 ;0 ; +- ; Br 3 10-3 Br 2 10-5 • Backgr.: KLKS (with KL decaying near the IP) , +-0 • Data sample : 16 pb-1 from the 2000 data (~5107 ) • 1 vertex in IR with 2 tracks • 3 prompt (E>10 MeV, |cos|<0.93) • Constrained kinematic fit : • 320 < Erad<400 MeV • E++E-< 550 MeV (reject +-0) N() = 50210 220 events = 37 % / : • Main background is • Selection: elliptic cut in the plane of the two most energetic photons N() = 120 12 5 events = 23 % N ηγ ε ηγ Br(η π π π 0 ) Br(π 0 γγ) R Fρ N ηγ ε ηγ Br( η π π η) Br(η γγ) (4.70 0.47 0.31) 10 3 • F =0.95 (interference with e+e-() ) M (MeV) / • 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 53..31 ) 10-5 • Gluonic content of : η X η 1 2 u u d d Yη s s Z η glue Consistency check: if Z=0 |Y|=cosP other constraints on X and Y from: (1) )/(0) (2) )/(0) (2) (1) X2η Yη2 0.940.06 0.09 Conclusions • With the 2000 data KLOE studied the radiative decays of the into scalar and pseudoscalar mesons • We measured the branching ratios of : 00 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: KSe (Phys. Lett.B535(2002)), (KS+-()) / (KS00) (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 Comparison with other experiments decays f0 KLOE SND(1) CMD-2(1) Mf0 (MeV) 9731 9705 9757 g2f0KK/(4) 2.790.12 2.470.73 1.480.32 (GeV2) g2f0KK/g2f0 4.000.14 4.60.8 3.610.62 g 0.060 0.008 a0 KLOE SND 52 Ma0 (MeV) 984.8 (fixed) 995 10 g2a0KK/(4) 0.400.04 1.490..49 (GeV2) ga0/ga0KK 1.350.09 0.750.52 (1) (2) (3) (4) (5) other WA102(2) E791(3) 9878 9774 0.390.06 0.020.05 1.630.46 0.20.5 E852(4) Crystal Barrel(5) 9913 9996 0.220.03 1.050.06 0.93—1.07 f0 ; contribution negligible (CMD2: combined f000 f0+-) WA102 (CERN): centrally produced K+K-,+- in pp at 450 GeV/c E791 (Fermilab): f0 production in DS-+ E852 (BNL): a0 production in -p+-n and -p0n at 18.3 GeV/c pp π 0 π0 η Scalar mesons (JPC= 0++) • f0(980) (I=0) f000+ = 40—100 MeV sizeable ss contents; strongly coupled to KK • a0(980) (I=1) a0 “ “ coupled to KK • Possible interpretation (3P0 nonet): f0 s s ; a 00 12 (u u dd ) • 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)) f0(980) a0(980) are not easily interpreted as qq mesons • Other interpretations: qqqq states (Jaffe ’77) KK molecules (Weinstein-Isgur ’90) |M(1) - M (2) | (MeV) 00 rejection • 0 • 000 •00 (0 wrong pairing) Data M (MeV) • Parabolic cut to reject 0 M < 760 MeV to reject f0 + 0 wrong pairing • 00 MC-simulation with the experimental M spectrum