Scalar Mesons Physics with the KLOE detector C

Scalar Mesons Physics with the KLOE detector C. Bini Universita’ “La Sapienza” and INFN Roma For the KLOE collaboration Outline 1. Status of the KLOE experiment 2. “Hadron Physics” at a f - factory 3. Scalar Mesons at a f - factory : 4. Results 4. 1 p+p-g 4. 2 p 0 p 0 g 4. 3 hp 0 g 5. Summary and perspectives

1) Status of the KLOE experiment These days: end of f –peak run 2 fb-1 collected in the last two years. f 6 × 109 K+ - K- 3 × 109 KL - KS 2 × 109 h 6 × 107 f 0 , a 0 6 × 105 h’ 5 × 105 ANALYZED Program now: energy scan around the f + off-peak run s = 1 Ge. V: KLOE end by spring 2006

2) “Hadron Physics” at a f - factory Preview: analysis done and in progress (non Kaon physics) f hp 0 g Study of a 0(980) f p 0 g Study of f 0(980) + f 0(600) f hg , h’g h / h’ mixing f p+p-p 0 r+, -, 0 line shapes + “direct term” h ggg / h p+p- Upper limit on C, P, CP violating decays f e+e- / f m+m- f leptonic widths: lepton universality e+e- p+p- (rad. ret, ) Hadronic contribution to g-2 f p+p-g Study of f 0(980) + f 0(600) h p+p-p 0 Fit of Dalitz plot: Ch. PT test h p 0 gg Ch. PT test @ p 6 h, K 0 masses

3) Scalar Mesons at a f - factory How a f-factory can contribute to the understanding of the scalar mesons Mass (Me. V/c 2) f(1020) 1000 a 0(980) f 0(980) K*0(800) “k” 500 f 0(600) “s” 0 I=1/2 I=1 Scalar Mesons Spectroscopy: f 0(980), f 0(600) and a 0(980) are accessible (k not accessible) through f Sg; Questions: 1. Is f 0(600) needed to describe the mass spectra ? 2. “couplings”of f 0(980) and a 0(980) to f |ss> and to KK, pp and hp. 4 -quark vs. 2 -quark states

How to detect these radiative decays f f 0(980)g f a 0(980)g f f 0(600)g p+p-g p 0 g K+K-g [ 2 m(K)~m(f 0)~m(f) ] expected BR ~ 10 -6 K 0 g “ “ ~ 10 -8 hp 0 g K+K-g expected BR ~ 10 -6 K 0 g “ ~ 10 -8 p+p-g p 0 g General Comments: fits of mass spectra are needed to extract the signals: this requires a parametrization for the signal shape; the unreducible background is not fully known: a parametrization is required and some parameters have to be determined from the data themselves; sizeable interferences between signal and background;

How to extract the signal: 1. Electric Dipole Transitions: G(E 1) Eg 3 × |Mif(Eg)|2 2. Distortions due to KK thresholds (Flatte’-like). Kaon-loop (by N. N. Achasov): for each scalar meson S: g. Spp, g. SKK, MS No-Structure (by G. Isidori and L. Maiani): a modified BW + a polynomial continuum: gf. Sg, g. Spp, g. SKK, MS + pol. cont. parameters Scattering Amplitudes (by M. E. Boglione and M. R. Pennington) A (a 1+b 1 m 2+c 1 m 4) T(pp pp) + (a 1+b 1 m 2+c 1 m 4) T(pp KK) pole residual gf

Definition of the relevant couplings (S=f 0 or a 0): S to f gf. Sg (Ge. V-1) S to kaons g. SKK=g. SK+K-=g. SK 0 K 0 (Ge. V) f 0 to pp (I=0) gf 0 pp=√ 3/2 gf 0 p+p-=√ 3 gf 0 p 0 p 0 (Ge. V) a 0 to hp (I=1) ga 0 hp (Ge. V) Coupling ratio Rf 0=(gf 0 KK/ gf 0 p+p-)2 Ra 0=(ga 0 KK/ ga 0 hp)2 Kaon-loop K+ f p+ g K- p+ f 0, a 0 p- No-structure f f 0, a 0 pg

The unreducible backgrounds Unreducible backgrounds: (p+p- ): huge backgrounds: Initial state radiation (ISR) Final state radiation (FSR) f r±p± with r ± p±g (p 0 p 0): large backgrounds: e+e- wp 0 with w p 0 g f r 0 p 0 with r 0 p 0 g (hp 0): small backgrounds: e+e- wp 0 with w hg f r 0 p 0 with r 0 hg (p+p-) vs. (p 0 p 0): search for the “same amplitude” with a completely different background ! (hp 0) is the “cleanest” sample

4. 1) The p+p-g analysis I - Event selection: (a) 2 tracks with qt>45 o; missing momentum qpp>45 o (Large Angle); (b) Each track is pion-like (tracking, To. F and Shower shape): (c) 1 photon matching the missing momentum Particle identification: p vs. e and m (Likelihood: Tof and Shower shape) pions, muons (“trackmass”) pions muons electrons

II – The data sample 6. 7 × 105 events / 350 pb-1 @ √s = Mf 2. 2 × 104 events / 11 pb-1 “off-peak” m(pp) spectra: (blue) “Small angle” qpp<15 o; (red) “Large angle” qpp>45 o; “Large angle”: clear f 0(980) signal f 0(980) region m(pp) (Me. V) photon efficiency m(pp) (Me. V)

III - Fit to the m(pp) spectrum (491 bins, 1. 2 Me. V wide, 420 to 1009 Me. V) F= ISR + FSR + rp + scalar ± interference KL fit NS fit KL and NS fits: Good description in both cases of signal and background (KS); “negative” interference; f 0(600) doesn’t help.

Parameter uncertainties are dominated by the systematic errors: Comments: Mass value OK [ PDG 980 ± 10 Me. V ] R > 1 in both fits (in agreement with published values p 0 p 0 g) KL couplings >> NS couplings: effect of polynomial continuum NS suggests “large” coupling to the f (see following)

Scattering Amplitude Fit gf = 6. 6 × 10 -4 BR(f f 0(980)g) × BR(f 0(980) p+p-) ~ 3 × 10 -5 [ similar conclusion from BP analysis of p 0 p 0 g data (KLOE + SND)] Summarizing: The peak at ~980 Me. V is well interpreted in both KL and NS approaches as due to the decay f f 0(980)g with a negative interference with FSR. The couplings suggest the f 0(980) to be strongly coupled to kaons and to the f. No space for f 0(600). Scattering Amplitude gives a marginal agreement.

IV - The Forward-Backward asymmetry: A = (N(q+>90 o) – N(q+<90 o)) / sum p+p- system: Cross-section: A(ISR) C-odd A(FSR) & A(scalar) C-even |A(tot)|2 = |A(ISR)|2 + |A(FSR)|2 + |A(scalar)|2 + 2 Re[A(ISR) A(FSR)] + 2 Re[A(ISR) A(scalar)] + 2 Re[A(FSR) A(scalar)] Pion polar angle distributions (Red) = p+ (Blue) = p- Effect of the scalar amplitude on the charge asymmetry: Plot of A in slices of m(pp); Comparison with simulation with and without the scalar amplitude.

FB asymmetry vs. m(pp): Clear signal ~ 980 Me. V Interesting comparison with simulation: Data Simulation FSR+ISR+ scalar(KL) The simulation provides a “qualitative” description of: f 0(980) region behaviour (the signal is reproduced); Low mass behaviour (low mass tail of the signal. Remarkable result: not a fit but an absolute prediction

V – Cross section dependence on √s: Absolute prediction based on KL fit parameters Data: on-peak Data: off-peak KL absolute prediction Based on fit parameters Concluding remark: p+p-g is a powerful tool to test scalar production: mass spectrum, FB asym. and s dependence KLOE has now collected 2 fb-1 at f factor 6 more. Is now starting a finer energy scan around the f

4. 2) The p 0 p 0 g analysis I - event selection: 5 photons with qg>21 o ; no tracks; Kinematic fit energy-momentum conservation; Kinematic fit p 0 masses: choice of the pairing. 4 × 105 events / 450 pb-1 2002 analysis scheme: 1. Reject wp 0 events interference is neglected; 2. 1 -dim analysis: fit with KL The spectrum is dominated by w p 0 g KLOE PLB 537 (2002) 21

New analysis scheme: 1. Removed the m(w) cut : wp 0 are now in the sample 2. Bi-dimensional analysis [ Dalitz-plot m(p 0 p 0) – m(p 0 g) ] 3. New treatment of systematics [ pairing problem. . . ] 4. Improved VDM parametrization of wp 0

II – Fit of the Dalitz plot (still preliminary results) KL and NS fits in progress Residuals vs. DP position Comments: Data- fit comparison (on projections) 1. VDM part still not perfect (see residuals); 2. Scalar part ok BUT f 0(600) is still needed in KL fit [p(c 2) ~ 10 -4 30% !]; 3. f 0(980) parameters agree with p+p-g analysis again R > 1 (gf. KK > gfp+p-).

4. 3) The hp 0 g analysis I – The data samples: out of 400 pb-1 : Statistics of PLB 536 (2002) 209 × 20 (h gg) Improved reducible background subtraction: 2. 2 × 104 events [ ½ are signal] Red = signal Other colors= bck (h p+p-p 0) almost “background free” 4100 events [ bck < 3%] Full pts. = “ 20 pb-1” data Empty pts. = “ 400 pb-1” data M(hp) (Me. V)

II – The combined fit Simultaneous fit of h gg and h p+p-p 0 channels: ratio of BR is fixed Pts. = data, hist = fit (including smearing) KL fit NS fit The spectra are dominated by the a 0 production: both models are able to reproduce them

Preliminary results of the fits (KL and NS): KL fit gfa 0 g (Ge. V-1) NS fit 1. 9 ga 0 K+K- (Ge. V) 2. 3 1. 9 Ga 0 hp (Ge. V) 2. 6 2. 2 Comments: gfa 0 g ~ in agreement with f 0 value Ra 0= 0. 78 (KL) and 0. 74 (NS) < 1

5) Summary and Perspectives The KLOE scalar analysis is not yet completed. However: 1. f 0(600): required in the p 0 p 0 channel not in the p+p- one: no clear answer by now. 2. Couplings: both NS and KL fits indicate Rf 0 =(gf 0 K+K-/ gf 0 p+p-)2 = 2 ÷ 4 Ra 0 = (ga 0 K+K-/ ga 0 hp-)2 = 0. 7 ÷ 0. 8 from NS analysis: large couplings to the f gff 0 g = 1. 2 ÷ 2. 0 gfa 0 g ~ 1. 9 (unc. evaluation in progress) in any case >> gfpg gfh’g = (0. 1 0. 7).

KLOE perspectives on scalar mesons 1. Conclude analysis on 2001 -2002 data sample for f 0(980) (neutral final states) and a 0(980). 2. With 2000 pb-1 @ f peak: improvement expected for f 0 → p+pcombined fit p+p- AND p 0 p 0 search for f 0, a 0 KK 3. With new forthcoming energy scan data improved study of the √s-dependence of the cross-section; Off-peak: “test run” of gg p 0 p 0