Experimental Measurement of the Φ meson radiative decays into scalars and pseudoscalars mesons

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1 Experimental Measurement of the Φ meson radiative decays into scalars and pseudoscalars mesons The KLOE Coll. presented by by Camilla Di Di Donato I.N.F.N. Naples International Conference on the Structure and Interactions of the Photon

2 KLOE data collected 1999 run run :: pb pb -1-1 machine and detector studies 2000 run run :: pb pb x φ published results 2001 run: run: pb pb x φ analysis in in progress 2002 run: run: 300 pb pb x φ analysis in in progress

3 KLOE Drift chamber: δp/p < 0.4% σ xy 150 µm ; σ z 2 mm E.m. calorimeter: σ Ε /E = 5.4% / (E(GeV)) σ t = 55 ps/ (E(GeV)) 40 ps 98% of 4π Magnetic field: 0.52 T

4 Φ radiative decays Analysis of 2000 data: Ldt = 16 pb -1 Φ η γ / ηγ Phys. Lett. B541 (2002), Φ π 0 π 0 γ Phys. Lett. B537 (2002), Φ η π 0 γ Phys. Lett. B537 (2002), 209

5 Φ radiative decays Pseudoscalar mesons (J PC = 0 -+ ) η (547) (I=0) η (958) (I=0) Scalar mesons (J PC = 0 ++ ) f 0 (980) (I=0) a 0 (980) (I=1)

6 φ η γ / φ ηγ The mass eigenstates η, η are related to SU(3) octet-singlet η 8, η 1 through the mixing angle ϑ P Recent studies based on χpt 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 (ϕ P ) η = cosϕ η = sinϕ P P uu + dd uu + dd sinϕ P + cosϕ P ss ss

7 φ η γ / φ ηγ ϕ P can be extracted from the ratio (Bramon et al., Eur.Phys.J.C7(1999)) : R Br( φ η γ) m tg p m 2 s ϕ V η = = cotg ϕ 1 ; s P = m Br( φ ηγ) m sin2ϕ P 2 p η Br(φ η γ) can probe the gluonic content of η η = X 1 uu + dd + Y ss + Z η 2 η η glue

8 φ η γ / φ ηγ Decays with π + π - 3γ final state: φ ηγ ; η π + π - π 0 ; π 0 γγ Br φ η γ ; η π + π - η ; η γγ Br Background from φ π + π - π 0 and φ K L K S (with K L decaying near the IP) Analysis cut: 1 vertex in IR with 2 tracks 3 prompt γ (E>10 MeV, cosϑ <0.93) Constrained kinematic fit topological cuts on the energy of particles ε tot (ηγ) = 37 % ε tot (η γ) = 23 % φ ηγ φ ηγ φ η γ φ η γ

9 φ η γ / φ ηγ Main background is φ ηγ Selection: elliptic cut in the plane of the two most energetic photons Phys. Lett. B 541 (2002), 45 M ππγγ (MeV) N(η γ) = 120 ±12 N ±5 ε events; N(ηγ) = ± 220 events R = N η γ ηγ ε ηγ η γ Br(η π π π ) Br(π γγ) F + Br(η π π η) Br(η γγ) R = Br(φ η γ)/br(φ ηγ) = (4.70 ± 0.47 ± 0.31) 10 F ρ =0.95 (interference with e + e - ρ η(η )γ ) 3 ρ =

10 φ η γ / φ ηγ Using PDG value for Br(φ ηγ): Br(φ η γ) = (6.10±0.61±0.43) 10-5 Pseudoscalar mixing angle: ϕ P = (41.8 ± 1.7) ϑ P = (-12.9 ±1.7) (flavor) (octet-singlet) Gluonic content of η : η = X 1 uu + dd + Y ss + Z η 2 η η glue Consistency check: if Z η =0 Y η =cosϕ P other constraints on X η and Y η from: (1) Γ(η ργ)/γ(ω π 0 γ) (2) Γ(η γγ)/γ(π 0 γγ) X η + Yη = (1) (2)

11 100 pb -1 (2001) 100 pb -1 (2001) φ η γ / φ ηγ M ππγγ (MeV)

12 φ η γ π + π 7γ dn/de Selection: dn/de Ks π 0 π 0 Kl π + π π 0 Ks π + π γ Kl π 0 π 0 π 0 data preliminary preliminary Ks π 0 π 0 Kl π + π π 0 Ks π + π γ Kl π 0 π 0 π 0 data N(η γ) = 153 ±12 Eγ (MeV) Eπ + +Eπ - (MeV) Eπ + +Eπ - (MeV) Br(φ η γ) = (7.05± /-0.46)x10-5

13 φ f 0 (980) γ / a 0 (980) γ The scalar mesons f 0 (980) a 0 (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 qq qqqq KK Br(φ f 0 γ) Br(φ a 0 γ)

14 Models Predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989) ff 0 0 model s s(uu + dd)/ 2 (u u + dd)/ 2 ss g 2 2 f0kk/(4π) (GeV 2 2 )) (=g (=g 2 2 a0kk a0kk /4π) /4π) (=g (=g 2 2 a0kk a0kk /4π) /4π) (=2g (=2g 2 2 a0kk a0kk /4π) /4π) g f0ππ f0ππ /g /g f0kk f0kk Br(φ π 0 0 π 0 0 γ) 10 γ) ~ 1 ~ ~ a 0 0 model s s(uu dd)/ 2 (uu dd)/ 2 g 2 2 a0kk/(4π) (GeV 2 2 )) (=g (=g 2 2 f0kk/4π) (=g (=g 2 2 f0kk/4π) g a0ηπ a0ηπ /g /g a0kk a0kk Br(φ a 0 0 γ) ~ 2 ~

15 Scalar mesons (J PC PC = 0 ++ ) ++ ) f 0 (980) (I=0) f 0 π 0 π 0, π + π - a 0 (980) (I=1) a 0 ηπ Studied decays (data sample: 16 pb -1 from the 2000 data,~ φ) φ f 0 γ ; f 0 π 0 π 0 5 γ final state φ a 0 γ ; a 0 ηπ 0 η γγ (39%) 5 γ Previous meas. at VEPP2M φ a 0 γ ; a 0 ηπ 0 η π + π - π 0 (23%) 2 ch. tracks +5 γ first observation

16 5 γ final states cross sect.(nb) Signal: φ π 0 π 0 γ (φ f 0 γ ; φ σ(500)γ ; φ ρ 0 π 0 ) ~ 0.35 π 0 π 0 π 0 γ φ ηπ 0 γ (φ a 0 γ ; φ ρ 0 π 0 ) ~ 0.1 ηγ Background: e + e - ωπ 0 π 0 π 0 γ ~ 0.5 φ ηγ 3γ (with accidental γ s) (~17) φ ηγ π 0 π 0 π 0 γ (with 2γ lost) (~14) Sample selection: exactly 5 prompt photons E γ > 7 MeV cosϑ < 0.93 to avoid the quadrupole region 5 E i > 700 MeV to reject φ K L K S neutrals

17 Constrained kinematic fit to improve resolutions Photon pairing M γγ -M π < 5σ(M π ) Reject events with: M πγ -M ω < 3σ(M ω ) 3102 events <ε> = 40% φ π 0 π 0 γ Estimated backgr. (~20%) e + e - ωπ 0 π 0 π 0 γ 339±24 φ ηπ 0 γ 166±16 φ ηγ π 0 π 0 π 0 γ 159±12 1+cos 2 ϑ γ ψ π 0 π 0

18 radiative γ Fit to M ππ ππ spectrum φ K + f 0 Model : 1) φ f 0 γ dominated by kaon loop (Achasov-Ivanchenko, Nucl.Phys.B315(1989)) 2) f 0 propagator with finite width corrections 3) σ(500) B-W with M σ =478 MeV and Γ σ =324 MeV (Fermilab E791-Phys.Rev.Lett.86(2001)770) 4) point-like coupling of σ(500) to φ (Gokalp,Yilmaz,Phys.Rev.D64(2001)) 5) ρπ + interference term parameterizations from Achasov-Gubin, (Phys.Rev.D63(2001)) Two fits: Fit A : (φ f 0 γ)+ (φ ρ 0 π 0 ) 2 Fit B : (φ f 0 γ)+ (φ σγ)+ (φ ρ 0 π 0 ) 2 Free parameters: M f0, g 2 f0kk, g 2 f0ππ/g 2 f0kk, g φσγ and (g φρπ g ρπγ ) 2 K - π 0 π 0 g φkk g f0kk g f0ππ

19 Fit results A B χ 2 /ndf 109.5/ /32 M f0 (MeV) 962±4 973 ±1 g 2 f0kk/(4π) 1.29± ±0.12 (GeV 2 ) g 2 f0kk/g 2 f0ππ 3.22± ±0.14 g φσγ ±0.008 ( ρπ contribution negligible ) Br(φ π 0 π 0 γ) = (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 ) Large f 0 -σ Br(φ f destructive 00 γ)= (4.47 interference ± 0.21) at M ππ < 700 MeV

20 φ ηπ 0 γ (with η γγ) Constrained kinematic fit to improve resolutions Photon pairing: (1) π 0 π 0 γ ; (2) ηπ 0 γ reject π 0 π 0 γ events M ππ < 760 MeV (reject f 0 γ events) M γγ -M η < 3σ(M η ) 916 events <ε> = 32 % Estimated backgr.: (~30%) e + e - ωπ 0 π 0 π 0 γ 54±6 φ π 0 π 0 γ 152±16 φ ηγ π 0 π 0 π 0 γ 98±10 φ ηγ γγγ 5±2 Events Events M ηπ (MeV/c 2 ) Data MC Br(φ ηπ 00 γ)=(8.51±0.51±0.57) SND :(8.8 ±1.4±0.9) 10 5 ;CMD-2: (9.0 ±2.4±1.0) 10 5 cosϑ

21 φ ηπ 0 γ π γ + π -- +5γ (η π + π -- π 0 ) No background with the same final state Backgr.: 2 Tracks + 3/4 photons (e + e - ωπ 0 ; ω π + π - π 0 ) (φ ηγ ; η π + π - π 0 ) 2 Tracks + 6 photons (φ K S K L π + π - π 0 π 0 π 0 ) 1 vertex in IR with 2 tracks 5 prompt γ (E>10 MeV, cosϑ <0.93) Constrained kinematic fit M π+π- < 425 MeV (reject K S π + π ) 197 events <ε>=19% estimated backgr. 4±4 events Br(φ ηπ 00 γ)=(7.96±0.60±0.47)

22 Fit to M ηπ ηπ spectrum Same model as for the f 0 (kaon loop) Combined fit, relative normalization fixed to Br(η γγ)/br(η π + π - π 0 ) Free parameters: g 2 a0kk, g a0ππ /g a0kk and Br(φ ρ 0 π 0 ηπ 0 γ) M a0 =984.8 MeV (PDG) fixed χ 2 /ndf 27.2/25 g 2 a0kk/(4π) (GeV 2 ) 0.40 ± 0.04 g a0ηπ /g a0kk 1.35 ± 0.09 Br(φ ρ 0 π 0 ηπ 0 γ) (0.5 ± 0.5) γ π + π - 5γ Br(φ a 00 γ ηπ 00 γ)= (7.4 ± 0.7)

23 Summary of fit results Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989) KLOE s s(uu + dd)/ 2 (u u + dd)/ 2 ff 0 0 model ss g 2 2 f0kk/(4π) 2.79± (GeV 2 2 )) (=g (=g 2 2 a0kk a0kk /4π) /4π) (=g (=g 2 2 a0kk a0kk /4π) /4π) (=2g (=2g 2 2 a0kk a0kk /4π) /4π) g f0ππ f0ππ /g /g f0kk f0kk 0.50± Br(φ π 0 0 π 0 0 γ) 10 γ) ±0.07 ~ 1 ~ ~ a 0 0 model ss(uu dd)/ 2 (uu dd)/ 2 g 2 2 a0kk/(4π) 0.40± (GeV 2 2 )) (=g (=g 2 2 f0kk/4π) (=g (=g 2 2 f0kk/4π) g a0ηπ a0ηπ /g /g a0kk a0kk 1.35± Br(φ a 0 0 γ) ±0.07 ~ 2 ~ ff 00 parameters are compatible with qqqq model a 00 parameters seem not compatible with qqqq model

24 φ f 0 (980) γ / a 0 (980) γ 200 Phys. Lett. B 537 (2002), data 2000 data Phys. Lett. B 536 (2002), M ππ (MeV) Mηπ 0 (MeV)

25 Conclusions First KLOE published papers on φ radiative decays, 2000 events: Br(φ η γ) = (6.10±0.61±0.43) 10-5 ϕ P = (41.8 ± 1.7) (flavor) Br(φ π 0 π 0 γ) = (1.09 ± 0.03 ± 0.05) 10-4 Br(φ f 0 γ) = (4.47 ± 0.21) 10-4 Br(φ a 0 γ) = (7.4 ± 0.7) 10-5 Analysis in progress on events 500pb -1 : more statistic and models with more free parameters

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27 ================================================== ==== 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. ==================================================