Biagio Di Micco. η π0γγ, η/η' mixing angle and status of η mass measurement at KLOE. for the KLOE collaboration

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1 η π0γγ, η/η' mixing angle and status of η mass measurement at KLOE Workshop on production and decay of η and η' mesons Krakow Septemeber 2005 Biagio Di Micco * for the KLOE collaboration * Università degli Studi di Roma Tre I.N.F.N sezione di Roma III

2 Integrated luminosity s = MΦ = GeV σ( ) 3 µb Int. Lum. pb e+e- in two separate rings with crossing angle 25mrad at IP (small Φ momentum pφ 13MeV) end data taking December Decay φ Κ+ Κ φ ΚS ΚL φ π+π π0 φ ηγ BR(%) on tape φ Κ± KSKL η

3 The KLOE detector Electromagnetic Calorimeter (EMC) Fine sampling Pb (0.5 mm thick) / Scifi (1 mm ø) Hermetical coverage High efficiency for low energy photons σe/e = 5.7%/ E(GeV) σt = 54ps/ E(GeV) Central drift chamber (DCH) Large detection volume Uniform tracking and vertexing in all volume Helium based gas mixture σv = 1 mm σpt /pt= 0.5% σr,φ =200 µm σz = 2 mm Quadrupoles' calorimeter (QCAL) Pb/Sci tile calorimeter covering quads inside KLOE

4 Outline Br(φ η'γ)/br(φ ηγ) with π+ π 7γ final state; Br(η π0 γγ) measurement; η mass measurement.

5 Br(f h' g)/br(f hg) event selection φ η'γ, η' π+ π η, η 3π0,π0 γγ η' π0 π0η, η π+ π π0,π0 γγ φ ηγ, η 3π0, π0 γγ Signal selection select particle coming from the I.P charged vertex in a cylinder with a 4 cm radius and a 16 cm height around the interaction point; 7 prompt photons t r/c < 5σt; 21 qg anti KSKL tag. identification of photons coming from the I.P (powerful thanks to the optimum calorimeter time resolution) Background source together beam background.

6 Signal extraction φ η'γ, η' π+ π 6γ n. obs. events n. estim. bkg n. signal (Nobs - Nbkg) wrong combination ± 65stat ± 28syst η' mass distribution after subtraction Ks π+ πkl π0 π0 π0 Ks π0 π0 Kl π+ π- π0 Ks π+ π- γ Kl π0 π0 π0 Signal Mη (MeV) Mη (MeV)

7 Preliminary result ε MC BR (η 3 π ) BR ( φ η γ ) N R = = ηγ BR ( φ ηγ ) N BRcrg ε crgmc + BRntr ε ntrmc η γ ηγ 0 [ ηγ ] BRcrg = BR (η π +π η ) BR (η π 0 π 0 π 0 ) ) n. h 3p0 where BRnrt = BR (η π 0 π 0 η ) BR (η π + π π 0 3 R = ( ± ± 0.20 ) 10 ε F / E RD η γ ε F / E RD Kρ Previous KLOE result Br(φ η'γ)/br(φ ηγ) = 4.70 ± 0.47± 0.31 Phys. Lett. B541 (2002) % 1.3 % % 0. 4 % 1.5 % 3 % Filfo-EVCL TRK ϕ P = ( ) VTX Bg εη/εη' χ2 BR s y s t. do m in ate d by th e u n ce rtain tie s o n Br(η ηπ+ π- ) an d Br(η ηπ0 π0 ) We w ill m e as u re th e m w ith 2 fb - 1

8 Br(h p0 gg) background and selection π0 e+ φ η 5γ final state eselection 5 prompt photons Total energy > 800 MeV 21º <θ < 159º γ kinematic fit with energy momentum conservation Prompt photon t r/c < min(5σt,2 n s ) not associated to a charged track Main background f f0( p0p0)g, f a0( hp0) g e + e - w( p0g)p0 f h( 3p0)g with lost and merging of photons

9 Kinematic fit effect before kinematic fit The most energetic photon is in the main part of cases that coming from the φ ηγ decay (363 MeV) after kinematic fit We build the invariant mass m4γ of the 4 least energetic photon. DATA MC comparison DATA MC the π0 peak is well reproduced mπ(mc) = ± 0.04 MeV/c2 mπ(data) = ± 0.07 MeV/c2

10 Background composition Background composition obtained by fitting mγγ distribution Correction factors mγγ MeV/c ± ± ± ± ± ± ± 0.06 mγγ MeV/c2 900 bins χ2 = 1.2

11 5g rejection φ f0( π0π0)γ 3 4 φ a0( ηπ0) γ e + e - ω( π0γ)π0 φ ρ0( η γ)π0,ρ0( π0γ)π

12 Merged clusters identification φ ηγφ π π π γ π0 γ1 n.cells π0 π 0 x, y,z, t rms= i x, y, z, t skew = 2 Ei x i x mean n.cells i n.cells i Ei 3 x i x mean n.cells i γ2 L good r=log merged L Ei

13 Preliminary results The shape of background + signal after fit well reproduce the DATA. Pbkg = ± Psig = ± NDATA = 735 Nbkg = 667 ± 36 Νsig=68±23 ε(η π0γγ) = 4.63 ± 0.09 (only stat) Ν(η 3π0) = ε(η π0π0π0) = ± 0.08syst± 0.01stat Br(η π0γγ) = (8.4 ± 2.7stat ± 1.4syst) 10 5 Pr elim in ary

14 Comparison with theory (preliminary) [1] [2] [3] [4] [5] [6] [7] [8] GAMS ( ) KLOE 1 KLOE 2 KLOE 3 O(p 6 ) calcu lat ion s Cry s tal Ball ( ) KLOE Facto r ~ 1 0 le s s th an GAMS Marg in ally co m patible w ith Cry s tal Ball Go o d ag re e m e n t w ith O (p 6 ) calculatio n s

15 η mass actual situation Very good agreement NA48 wrong?

16 Measurement method Using the decays: φ ηγ φ π0 γ γγ γγ E3 cross checking pourpose E1 A kinematic fit is performed imposing: conservation Px,Py,Pz,Etot t-r/c of clusters compatible with light velocity E2 As a consequnce of the kinematic fit the mass measurement is almost independent from the energy of the cluster, it is given by the cluster positions. The φ momentum and the vertex position are very well determined run by run from the study of the Bhabha scattering at large angle e+e- e+e (90000 events for each run).

17 Event selection χ2 fit distribution Cut χ2 < 35 no χ2 cut Dalitz plot E1 < E2 < E3 π0 π η χ2 < 35 0 η

18 Mass extraction Double gaussian fit core gaussian mean ± MeV σcore = 1.66 ± 0.05 MeV Very low background χ2/n.d.f = 304/257 Single gaussian fit Mean ± MeV Sigma ± MeV χ2/n.d.f = 146/161

19 Energy calibration independence Variation of 5% in the calibration constant produces a tiny effect ( 10-6 ) on the measured mass A shift of 10 MeV on the photon energy produces an effect of 4 KeV on the η mass ( 10-6 )

20 Preliminary mass measurement Data-set divided in 8 periods m(π0) = ± 6 s tat ± 30 s ys t KeV m(π0)pdg= ± 0.6 KeV m(η) = ± 5 s t at ± 69 s ys t KeV Syst from sqrt(s), vertex position

21 KLOE PRELIM IN New situation with KLOE NA48 compatibility 0.24 σ Produced at threshold on nuclear target. ARY in vacuum φ ηγ η γγ η 3π0?

22 Conclusions η de cay s : Pre lim inary KLOE Br(η π0 γγ) s m alle r than the pre v io us m e as ure m e nts, final re s ult for the e nd o f this y e ar w ith data, to re do w ith 2 fb - 1 (C. Blo is e talk) η forbidde n de cay s (not include d in this talk) Br(η π+ π- ) < % C.L. [Ph ys.let t.b606 (2005) 276] Br(η γγγ) < % C.L. [Ph ys.let t.b59 1 (20 04) 49] φ η γ in π+ π- + 7 γ final s tate, in agre e m e nt w ith the KLOE pre v io us re s ult in π+ π- + 3 γ final s tate ; η m as s m e as ure m e nt: KLOE pre lim inary re s ult is in agre e m e nt w ith NA4 8 m e as ure m e nt.