PHI PSI 08. Federico Nguyen. International Workshop on e+e- collisions from Phi to Psi

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1 PHI PSI 08 Laboratori Nazionali di Frascati (Roma), April 8 th 008 International Workshop on e+e- collisions from Phi to Psi A precise new KLOE measurement of F! with ISR and extraction of a µ!! for [0.35,0.95] GeV Università degli Studi and Sezione INFN Roma TRE for the KLOE Collaboration 1

2 Outline! Introduction: ISR method! Selection criteria: improvements on new data (4 pb -1 ) with respect to the published (140 pb -1 ) analysis! Results and comparisons! Conclusions and outlook

3 The cross section " e+e-#!+!- from ISR events at a fixed $s, studying Initial State Radiation events, " e+ e- #!+!- (s) is extracted! +! - ISR only: M "" d# e + e $ %" + " $ & = # dm e (M + e $ %" + " $ "" ) ' H(M "",( min ) "" " EVA + PHOKHARA MC Generator (S. Binner, J.H. Kühn, K. Melnikov, PLB459,1999) (H.Czy!, A.Grzeli"ska, J.H Kühn, G.Rodrigo, EPJC7,003) main advantage: no point-to-point errors on beam energy and luminosity main requirement: precise knowledge of ISR radiative corrections 1 st KLOE publication (based on 140 pb -1 ) A. Aloisio et al., PLB606(005)1 3

4 Selection of!!% events at small angle a) tracks with 50 o < & track < 130 o b) small angle % ( &!! < 15 o ) kinematics: r p " = p r miss = #( p r + + p r # ) # high statistics for ISR (~ & - ) # low relative FSR contribution # suppressed ' #! +! -! 0 wrt the signal n. of events 0.01 GeV M!! (GeV ) statistics: 4pb Million Events 4

5 Selection of!!% events: suppress background suppress e + e ( # e + e (! remnant e + e ( # µ + µ (! & "# $ + $ % $ 0!/e separation performed with particle ID based on the cut and estimated as a function of M!! calorimeter e + e (!! +! (! signal region m µ m! m trk (MeV) m trk, defined under the hypothesis of equal mass particles and 1 % in the final state 5

6 Radiative corrections " (!!%) [nb] with F! =1 - ISR-Process calculated at NLO-level PHOKHARA generator (Czy!, Kühn et.al) Precision: 0.5% d$ ""# M "" = $ ( s)! "" H(s) dm "" i) Bare Cross Section divide by Vacuum Polarisation " from F. Jegerlehner relative FSR contribution ii) FSR - Corrections cross section "!! must be inclusive for FSR FSR corrections taken into account in the efficiency evaluation and in M!! # M %) M %* 6

7 Improvements compared to the published analysis error table in the published work Reconstruction filter Background M trk cuts Particle ID Tracking Vertex Trigger Acceptance Unfolding Luminosity (0.5 th * 0.3 exp )% d" ##$ = dm ## PLB606(005)1 0.6% 0.3% 0.% 0.1% 0.3% 0.3% 0.3% 0.3% 0.% 0.6% N obs % N bkg 1 ' ' 1 &M ## ( sel L improved machine conditions (luminosity and background) in the new data set improved offline-event filter reduces systematic uncertainty to < 0.1% improvements (e.g. no vertex requirement) on the selection 30% inefficiency (veto of cosmic rays) recovered by introducing 3 rd level trigger new generator BABAYAGA@NLO, error on " Bhabha from 0.5% to 0.1% 7

8 Trigger improvements + cosmic veto (published data) + L3 trigger (new data) -30% the main source (hardware veto of cosmic rays) of inefficiency in the published result has been removed M!! (GeV ) + trigger (meth 1) + trigger (meth ) trigger efficiency: fractional error given by relative difference of independent methods from data # 0.1% M!! (GeV ) 8

9 Update in the Bhabha cross section: luminosity KLOE measures L with Bhabha scattering 55 < & < 15 acollinearity < 9 p, 400 MeV F. Ambrosino et al. (KLOE Coll.) Eur.Phys.J.C47: ,006 generator used for " eff BABAYAGA (Pavia group): C. M.C. Calame et al., NPB758 (006) see C.M.C. Calame s talk e + new version (BABAYAGA@NLO) gives 0.7% decrease in cross section, and better accuracy: 0.1% e - Theory Systematics on Luminosity 0.1 % % Experiment TOTAL 0.1 % th * 0.3% exp = 0.3% 0.3 % 9

10 Error table and results Background M trk cuts Particle ID Tracking Trigger Acceptance Unfolding L3 Trigger Luminosity (0.1 th * 0.3 exp )% M dep ( %) 0.% 0.3% 0.3% 0.1% M dep (0.1%) 0.% 0.1% 0.3% " ## = #$ 3 % # 3s F # F! resolution effects unfolded experimental fractional error on a µ = 0.7% Radiator H 0.5% total fractional error on a µ = 0.9% M!! (GeV ) 10

11 KLOE results on a µ (1) Dispersion integral for! channel in the mass range 0.35 GeV < M!! < 0.95 GeV a "" µ = GeV & ds #(e + e $ % " + " $ ) K(s) 4" GeV published result (Phys. Lett. B606 (005) 1): a!! µ ([ ] GeV ) = (388.7 ± 0.8 stat ± 3.5 sys ± 3.5 th )! applying update for trigger efficiency and change in theoretical " Bhabha : a!! µ ([ ] GeV ) = (384.4 ± 0.8 stat ± 3.5 sys ± 3.5 th )! new: a µ!! ([ ] GeV ) = (389. ± 0.6 stat ± 3.0 sys ±.0 th )!

12 KLOE results on a µ () 140 pb -1 data 4pb -1 1

13 Results on a µ in the same range: a comparison KLOE result in agreement with CMD and SND 13

14 F! comparison with other results F! F! other / F! KLOE ( 1 M!! (GeV ) M!! (GeV ) only statistical errors are shown better agreement on the - peak band: KLOE error, and data points: other experiments 14

15 Fit to the pion form factor F " (s) = & BW GS # (s) 1+ $ s M BW (s) ) ( % + +, BW GS #' (s) ' % * 1+, this fit F! Preliminary statistical error only M!! (GeV ). /dof = 79.3/54 15

16 Fit in the --/ region: momentum scale check F " (s) = & BW GS # (s) 1+ $ s M BW (s) ) ( % + +, BW GS #' (s) ' % * 1+, this fit F! Preliminary statistical error only M!! (GeV ) / mass where expected: momentum scale is OK 16

17 Conclusions We have obtained the contribution to a µ!! in the range between GeV using cross section data obtained via the ISR events with photon emission at small angles. The result from new data agrees with the updated result from the published KLOE analysis, we are working to combine results KLOE results also agree with recent results on a µ!! from the CMD and SND experiments at VEPP-M in Novosibirsk The new F! shows better agreement with Novosibirsk spectra 17

18 Outlook Independent analysis is in progress using detected photons emitted at large angle (progress in scalar meson modelling) We are also measuring the pion form factor using the ratio of!!% over µµ% yields (instead of absolute normalization) Finally we are measuring pion form factor from data taken at $s= M ' - 0 MeV (1 GeV) 18

19 SPARES 19

20 Comparison data 0

21 KLOE: performances for the!!% analysis see talk of A. Passeri Electromagnetic Calorimeter Pb / Scintillating Fibres Endcap + Barrel = 98% (4!) Drift Chamber 4 m 0, 3.3 m length 90% He, 10% i-c 4 H 10 " E /E = 5.4%/$E(GeV) e + e - # e + e - both detectors provide the trigger " p /p = 0.4% (& > 45 ) " M!! ~ 1 MeV 1