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Debora Leone IEKP – Universität Karlsruhe

DPG Tagung M ünchen, 24.03.2006. Debora Leone IEKP – Universität Karlsruhe. Study of the reaction e + e -  p + p - at KLOE. Introduction Result on the small photon angle analysis (Phys. Lett. B606, 12 (2005)) Large photon angle analysis (in progress) Conclusion. g*. B field.

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Debora Leone IEKP – Universität Karlsruhe

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  1. DPG Tagung München, 24.03.2006 Debora Leone IEKP – Universität Karlsruhe Study of the reaction e+e-p+p- at KLOE • Introduction • Result on the small photon angle analysis (Phys. Lett. B606, 12 (2005)) • Large photon angle analysis (in progress) • Conclusion

  2. g* B field · q m m + + · · g* * g q Hadronic contribution to (g-2)m Magnetic momentum: with amSM = amQED + amhad + amEW Due to quantum corrections: amhadincludes contributions not evaluable in pQCD, but it can be provided by s(e+ e- hadrons) by means of dispersion relation: K(s) is a steady function that goes with 1/s, enhancing low energy contributions of shadr(s) In energy range <1 GeV, e+e-  p+p-contributes to more than 60% to amhad

  3. Mhadr ds(e+ e- hadrons + g) dM2hadrons =s(e+ e- hadrons) H(M2hadr ) s(e+e- p+p-) with Radiative Return DAFNE is designed for a fixed center-of-mass energy: s = mf = 1.02 GeV We can measure s(e+e-p+p-) as a function of the hadronic c.m. energy M2hadr (S.Binner, J.H. Kühn, K. Melnikov, Phys.Lett. B459,1999) Precise knowledge of ISR – process: Radiator function MC generator: Phokhara (H. Czyz, A. Grzelinska, J.H. Kühn, G. Rodrigo, hep-ph/0308312) “Radiative Return” to (w) resonance e+e-  (w)   +- This method is a complementary approach to the energy scan.

  4. PRO & CONTRA • high statistics for ISR • low relative FSR contribution • suppressed   p+p-p0background • threshold region not covered • no kinematic closure of event (%) MC:FSR /(ISR + FSR) Mpp2 (GeV2) Small photon polar angle analysis SELECTION • Pion tracks:50o< p<130o • Photons: g <15o or g>165o No photon tagging: KLOE result (140 pb-1 of 2001) Phys. Lett. B606 (2005) 12

  5. |Fp(s)|2 CMD-2 KLOE 45 40 35 30 1.3% Error 25 0.9% Error 20 s (GeV2) Mpp2 (GeV2) 15 10 5 0 0.4 0.5 0.6 0.7 0.8 0.9 ampp·1010 365 370 375 380 385 KLOE result compared with CMD-2 • s(e+e-p+p-) result • statistical error: negligible • experimental systematic uncertainty: 0.9% • theoretical systematic uncertainty: 0.9% • Total systematic error: 1.3% • Pion Form Factor comparison • with result from CMD-2 experiment: • KLOE and CMD-2 in fair agreement • Dispersion integral evaluation • KLOE:(375.6  0.8stat  4.9syst+theo) 10-10 • CMD-2: (378.6  2.7stat  2.3syst+theo) 10-10 • KLOE and CMD-2 in good agreement

  6. DEHZ‘03 DEHZ’03 [e+e- based] New DEHZ’03 [t based] Experiment E821 am-11 659 000 ∙ 10-10 am- 11 659 000 ∙ 10-10 140 150 160 170 180 190 200 210 am- 11 659 000 ∙ 10-10 Muon anomaly comparison Theory - Experiment KLOE and CMD-2 results used to evaluate the hadronic contribution and therefore the muon anomaly Standard model prediction: • KLOE measurement • Phys. Lett. B606 (2005) 12 • New 4th order QED calculation • (Kinoshita, Nio) • Phys. Rev. D70 (2004) 113001 • New ‘Light-by-light’ calculation • (Melnikov, Vainshtein) • Phys. Rev. D70 (2004) 113006 CMD-2 and KLOE averaged in hadronic contribution DEHZ’04 [e+e-] Theory (SM) - Experiment amexp - amtheo = ( 25.2 ± 9.2 ) ·10-10 2.7 standard deviations difference

  7. PRO & CONTRA • the threshold region is accessible • one photon is detected (4-momentum constraints) • lower signal statistics • large FSR contributions • irreducible background from f to p+p-g decays • large   p+p-p0background contamination 500< qp,g <1300 g p Large photon polar angle analysis - signal selection Pion tracks:50o < p< 130o Photons: at least one with 50o <g< 130o and Eg > 50 MeV tagged measurement 50o<qp<130o 50o<qg<130o p+p-gMC p+p-p0MC Mpp2 [GeV2]

  8. Mtrk [MeV] p+p-p0 –MC p+p-g – MC mp m+m-g - MC mm Mpp2 [GeV2] mr2 Reducible background rejection threesources: Radiative Bhabhas e+e- e+e- , muon pairs e+e- m+m-  and +-0 Particle ID Radiative Bhabhasare separated by means of a particle-ID (likelihood function): signature of EmC-Clusters and time of flight of particles TrackMass To reject m+m-gand (partially) p+p-p0 background a cut in the plane Mtrk vs. Mpp2 is applied. Mtrk is the kinematical variable obtained by solving under the assumption of  x+ x- 

  9. p+ g p- W p+p-gMC p+p-p0MC [o] 20 0 10 70 30 40 50 60 Reducible background rejection Two further dedicated cuts to p+p-p0 rejection Kinematic fit Kinematic fit under the p+p-p0background hypothesis Two tracks in 40 < p < 140 At least twophotons, one of them with Eg > 40 MeV and 40 < g< 140 4-momenta conservation Minv(gg) = m(p0) 2 Data p+p-g MC  Angle 2 Angle between the missing momentum and the detected photon momentum

  10. p g r p g p f p f g f0 r p p Irreducible background m+m-gand p+p-p0 background channels well under control… but FSR events as e+e-  ppgFSR ff0 g pp g f r p  pg p all of them with p+p-g final state, indistinguishable from the signal signature & & FSR rp f0 Three processes of the same family: their amplitudes interfere At low Mpp2,ISR and FSR are not the only contributions to the mass spectrum and to the charge asymmetry model dependence for the additional contributions More phenomenological input needed concerning the hadronic models.

  11. KLOE preliminary Mpp2 [GeV2] 2002 Data L = 240 pb-1 Mpp2 [GeV2] dN/dMpp2 spectrum • 50o<qp,g<130o, Eg>50MeV • Both the particles not identified as electrons • Cut on 2 • Cut on TrackMass vs. Mpp2 • Cut on  angle The spectrum extends down to the 2-pions threshold

  12. 90o MC Pion polar angle [o] Forward-backward asymmetry +- system: A(ISR)  C-odd A(FSR)  C-even  an asymmetry is expected in the variable: test of sQED via comparison data/MC f0 KK model f0 ‘no structure’ af=p f0 ‘no structure’ af=p/2 no f0 A(f0) C-even 20o<qp<160o 45o<qg<135o Issue: to distinguish the effect of the interference (described in our MC by sQED ) and the effect of f0(980). Czyż, Grzelińska, Kühn, Phys.Lett.B 611(116)2006 Mpp [GeV]

  13. Forward-backward asymmetry At large photon angles, the amount of FSR is large and the interference between the two terms gives a sizeable effect. KLOE has already published a first measurement of the forward-backward asymmetry, and proven the sensitivity of this quantity to the presence of scalar mesons. Phys.Lett.B634 (06), 148 Using the f0 amplitude from Kaon Loop model, good agreement data-MC* both around the f0 mass and at low masses. • data • MC: ISR+FSR • MC: ISR+FSR+f0(KL) Mpp (MeV) Mpp (MeV) * G. Pancheri, O. Shekhovtsova, G. Venanzoni,hep-ph/0506332 zoom

  14. Forward-backward asymmetry Conclusion KLOE has measured for the first time the hadronic cross section with radiative return method, proving the validity of it. The measurement of the hadronic cross section in a different angular region and with tagged photon is in an advanced state. • The threshold region requires more studies, due to the irreducible background • The analysis on the r-peak and at high Mpp2 is close to the conclusion •  important check for the already published KLOE result. • Selection cuts are fixed • Evaluation of efficiencies is almost finished • test of model scalar QED possible • study of scalar mesons

  15. Backup slide

  16. Drift chamber Track momentum resolution sp/p  0.4% (q > 45°) Vertex resolution sxy  150 mm, sz  2 mm 12582 sense wires 52140 wires in total The KLOE detector at the DAFNE F-factory Electromagnetic calorimeter Energy resolution sE/E = 5.7%/E(GeV) Time resolution sT = 54 ps/E(GeV)  50 ps Pb/Scint fibres 4880 PM Magnetic Field of 0.52 T

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