 0  (search for a 0 (980))

1. 0(search for a0(980)) C.Bini,P.Gauzzi,D.Leone • Channel 1: 05 () • Channel 2: 0+-5 (+-0) • Combined fit to the M spectra • Conclusions • KLOE General Meeting 20/12/2001 – Roma 3

2. 5  channel • Signal: • (a0+00)0 • Background: S/B • e+e-0 00 0.2 • (f0+00)00 0.3 • 3 1.5 (0.4% = fraction of 5 events) •  000 0.3 (2.5% = fraction of 5 events)

3. Analysis scheme • Preliminary selection: no tracks, 5 prompt photons (5t), • Eprompt> 700 MeV, > 21o • First kinematic fit: 30 parameters with 9 constraints 9 ndf • Best photon pairing in the following hypotheses: • 1) 0 • 2) 00 • 3) 000 ( mass , E0=218 MeV in the selection 2) • 4) 3 ( mass , Erad=363 MeV in the selection 2) • Second kinematic fit : 30 parameters, 11 constraints • ( 9 +  and 0 masses for 1) or two 0 masses for 2) 3) ) • For each event this fit is performed three times •  hyp. 1) , 2) and 3) • Final cuts • All the events pass through the whole chain: cuts are applied • at the end

4.  rejection • 0 • 00 •  E (MeV) Data M (MeV) M (MeV) • Photon pairing in the 3 hyp. •  rejection : Erad<340 MeV • To reduce the sample: |M-M| < 3 • cut at 2/ndf < 3to reject  000

5. MC: 00 sample • 00 • 0 •  E (MeV) Events M (MeV) • Get spectrum from data: • |M-M|>3 to get a clean • 00 sample • Alternative way: use the spectrum • from Simona’s analysis M (MeV)

6. MC: 00 sample  • Correct for efficiency • Get scale factors bin by bin • from the ratio of the • experimental spectrum to the • MC generated one • It takes into account for both • f0 and 00 00 • No need for MC • 0000 M (MeV)

7. 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 (equivalent to 2 cut on M) •  M < 760 MeV to reject f0 + 0 wrong pairing

8. Data-MC comparison • Data • — MC • — bckg • Data • — MC Events Events 2/ndf Etot/E • Second fit: 2/ndf >3 dominated by background • (mainly 000)  cut at 2/ndf < 3

9. Data-MC comparison • Data • — MC • — bckg Events • 3  cut on M removed • Good agreement up to 10  (M-547)/ (M-135)/

10. Final sample • Data • — 00 • —000  • —000 • — • Data • — MC Events Events M (MeV) cos • 916 events in the final sample

11. Efficiency and luminosity  Efficiency: Average efficiency = 32.4% • Luminosity: • Run number range: 15174 – 17330 • Integrated luminosity: (16.45 0.33) pb-1 • use VLAB, uncertainty 2% • if there is no VLAB, use LAB x (1 – 1.2%) • if there is no LAB use TRGLUMI, • uncertainty  5% M (MeV) LVLAB = 15.78 pb-1 LLAB = 0.58 pb-1 LTRG = 0.09 pb-1

12. Background subtraction Rej. factor Cross sect. or Br.(*) Expected events e+e-0 00 140  = 0.460.05 nb 54  6 00 40 Br = 10-4  10% 152  16   6  104  = 17.2  0.6 nb5  2  000 2.5  103  = 13.8  0.4 nb98 10 ——— tot. bckg. 309  20 The errors include MC statistics and cross section (or Br) uncertainties ((*) Only KLOE measurements) Signal (0) : 916 – 309 = 607 events with =(3.370.12) b (from  ) and Br() = (39.33 0.25) % (PDG 2000) Br(0) = (8.51  0.43 (stat.)) x 10 -5

13. Systematics • Analysis cuts: evaluated by moving the cuts by 1 on the variable • and cuts on 2 by 1 • Cut Uncertainty • >21o (1o) 1.5 % • first fit 2 1.2 % • 3  on M 4.0 % • E < 340 MeV 2.0 % • Parabolic cut (M) 3.0% • M < 760 MeV 1.7 % • second fit 2 1.2 % • ——— • Combining in quadrature 6 %

14. Uncertainty summary • Absolute (10-5 units) Relative • Statistics 0.43 5.0 % • Bckg subtraction 0.28 3.3 % • Analysis cuts 0.51 6.0 % • Luminosity 0.17 2.0 % • cross section 0.31 4.0% (L contribution subtracted) Br() 0.05 0.6 % Trigger to be evaluated ( negligible) Photon counting to be evaluated (1—2 % ?) Br(0) = (8.510.51(stat.+bckg))0.62(syst.)) x 10 –5 Br(0) = (8.8 1.40.9) x 10 –5 SND (2000) Br(0) = (9.0 2.41.0) x 10 –5 CMD-2 (1999)

15. +-5 channel • No background with exactly the same final state • Main backgrounds: • 2 Tracks + 3/4 photons + splitting/accidental • 2 Tracks + 6 photons + acceptance loss/merging

16. Event selection • ECL (ppfilt) • 1 vtx in IR with 2 tracks • 5 prompt photons E>10 MeV, q>21o • kinematic fit 1 E/p cons., c-speed • Minv(p+p-) < 425 MeV • to reject KSp+p-  M (MeV) Large rejection factors few expected bckg events

17. Data-MC comparison Before cut on Minv(p+p-) • h and w peaks clear. • MC signal + bckg well reproduces • data • gg and ppgg combinations • invariant masses after fit-1 gg and ppgg combinations invariant masses after fit-2 (variables from fit-1) M (MeV) M (MeV) After cut on Minv(p+p-) M (MeV) M (MeV) M (MeV) M (MeV) M (MeV) M (MeV)

18. Final sample 197 events selected: Lint=16.4 pb-1 BR(0)=(7.960.60(stat+bckg) 0.47(syst))  10-5 Statistics 0.58 Bckg subtraction 0.15 Efficiency(*) 0.30 Br(+-0) 0.14 Luminosity 0.16  cross section 0.28 (*)work in progress Raw Minv(hp) spectrum and cos(qg) distribution

19. Fit to the Mspectra • Contributions: • a0(980) with a00 • 00 with 0 • Br() 1/3 Br(0) =1.2  10-5 (PDG) • Br( 0) = 0.54  10-5 (Bramon, Grau, Pancheri, • Phys.Lett.B283(1992),416) • = 5.18  10-5 (Fajfer, Oakes, • Phys.Rev.D42(1990),2392) • 3)e+e-0 with • (e+e-0)  Br()  0.12  10-5  negligible • 1) and 2) can interfere

20.  shape  momentum in the  c.m. Phase space ( angle in the  c.m.) Achasov-Gubin Phys.Rev.D63 094007(2001)

21.  shape a.u. M (MeV) Good agreement with Bramon et al., Phys.Lett.B283,416 (1992)

22. a0 (Flatte’,Phys.Lett.B63,224,(1976)) Above KK threshold Below KK threshold

23. a000 interference (Achasov-Gubin) a0 only a0+ no interf. interference (+) interference (-) M (MeV)

24. Fit method • Combined fit to the two spectra •  shape fixed + Br()/Br(+-0) fixed • Ni = number of events (data) i=1,Nexp bin in Mexp • Mij = smearing matrix, takes into account for resolution and photon • pairing effects j=1,Ngen bin in Mgen (from MC) • f = theoretical function • i2 = 2(data) + stat2(MC) • Free parameters: Br1=Br( 0), Br2=Br(a0), • a0 (PDG: 50—100 MeV) • Fixed : Ma0 = (984.8 1.2) MeV (PDG) ; gk = 0

25. Fit results • Br1(10-5) Br2(10-5) a0(MeV) 2/ndf • Combined 1.780.40 6.220.43 12915 20.3/25 • Only ch. 1 1.310.54 6.520.57 13922 15.5/15 • Only ch. 2 2.450.69 6.000.74 11724 2.7/7 • Comb., +int. 2.200.44 5.920.47 12316 19.7/25 • Comb., - int. 1.510.42 6.620.48 13816 22.3/25 • Br(a0) = (6.220.43(stat+bckg))  10-5 • Agreementbetween the two samples • Very large a0 width, but it is model • dependent • Interference: not significant with this • statistics • Br1 close to Br() 1/3 Br(0)

26. Fit to a0 only (Flatte’) • From Bramon et al., • Br1 = 0.54  10-5 • Try to fit the spectra to a0 only • 2 free parameters: • Br(a0) = (7.650.33)  10-5 • a0 = (192  18) MeV • 2/ndf = 37/26

27. Fit to a0 only (II) • Flatte’ formula has no p3 • dependence, as expected for a • V  V S decay • Try a simple B.W. with p3 and • with a damping factor: • Br(a0) = (7.890.34)  10-5 • a0 = (36.9  5.2) MeV • = (890  100) MeV 2/ndf = 24.3/25

28. Conclusions • The analysis of the two channels is well defined • The two samples are in good agreement • Systematics evaluation is almost done • The combined fit procedure is working: • The two channels are consistent • Separation of the two contribution a0(980) and  0 is difficult, because the fit cannot be performed in a model independent way