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Stefan E. M üller Laboratori Nazionali di Frascati

Evaluation of a m pp between 0.35 and 0.95 GeV 2 with data from the KLOE detector. Stefan E. M üller Laboratori Nazionali di Frascati. (f or the KLOE collaboration). 2007 Europhysics Conference on High Energy Physics Manchester, 19-25 July 2007. Dispersion integral :. .

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Stefan E. M üller Laboratori Nazionali di Frascati

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  1. Evaluation of ampp between 0.35 and 0.95 GeV2 with data from the KLOE detector Stefan E. Müller Laboratori Nazionali di Frascati (for the KLOE collaboration) 2007 Europhysics Conference on High Energy Physics Manchester, 19-25 July 2007

  2. Dispersion integral:  ahadr can be expressed in terms of (e+e- hadrons) by the use of a dispersion integral: • Ecut is the threshold energy above which pQCD is applicable • s is the c.m.-energy squared of the hadronic system • K(s) is a monotonous function that goes with 1/s, • enhancing low energy contributionsofhadr(s)

  3. (e+e-+-) with ISR: Mhadr ds(e+ e- hadrons +g) dMhadr =s(e+ e- hadrons) H(Mhadr) Particle factories have the opportunity to measure the cross section s(e+ e- hadrons) as a function of the hadronic c.m. energy M hadr by using the radiative return: This method is a complementary approach to the standard energy scan. Neglecting FSR effects: Requires precise calculations of the radiator H  EVA + PHOKHARA MC Generator (S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999) (H. Czyż, A. Grzelińska, J.H. Kühn, G. Rodrigo, Eur. Phys. J. C 27, 2003)

  4. DANE: A -Factory e+e--collider with =m1.0195 GeV Integrated Luminosity Peak Luminosity Lpeak= 1.4 • 1032cm-2s-1 Total KLOE int. Luminosity: L dt ~ 2500 pb1 (2001 - 05) DEAR, This talk is based on 240pb-1 from 2002 data! • 2006: • Energy scan with 4 points around m-peak • 225pb-1 at = 1000 MeV

  5. KLOE Detector Driftchamber sp/p = 0.4% (for 900 tracks) sxy 150mm, sz 2 mm Excellent momentum resolution

  6. KLOE Detector sE/E = 5.7% /E(GeV) sT= 54 ps /E(GeV)  50 ps (Bunch length contribution subtracted from constant term) Excellent timing resolution Electromagnetic Calorimeter

  7. Event Selection   Pion tracks at large angles 50o< p <130o a) Photons at small angles < 15oor > 165o   No photon detection!  • High statistics for ISR photons • Very small contribution from FSR • Reduced background contamination  

  8. Event Selection     Pion tracks at large angles 50o< p <130o a) Photons at small angles < 15oor > 165o  No photon detection! • High statistics for ISR photons • Very small contribution from FSR • Reduced background contamination   b) Photons at large angles 50o<  < 130o   • Photon is observed in the detector! • Threshold region accessible • Increased contribution from FSR • Contribution from • f0(980)

  9. Event selection MTrk (MeV) 220 200 p+p-p0 180 p+p-g(g) signal region 160 140 120 m+m-g(g)region (+ e+e-g(g) 100 80 0.4 1.0 0.5 0.6 0.7 0.8 0.9 0.3 Mpp2(GeV2) • Experimental challenge: Fight • background from •  • ee ee(g) • ee (), • separated by means of kinematical • cuts in trackmass MTrk • (defined by 4-momentum conservation • under the hypothesis of 2 tracks with • equal mass and one photon) and Missing Mass Mmiss (defined by 4-momentum conservation under the hypothesis of e+e-+-x To further clean the samples from radiative Bhabha events, a particle ID estimator for each charged track based on Calorimeter Information and Time-of-Flight is used.

  10. Published result with 2001 data Published KLOE Result: Improvements/updates with respect to 2001: Phys. Lett. B606 (2005) 12 s (e+e- p+p- ) nb 30% cosmic veto inefficiency recovered in 2002 by introducing additional software trigger level KLOE 2001 Data 140pb-1 Improved offline-event filter reduces its systematic uncertainty to <0.1% New generator BABAYAGA@NLO - theoretical error of Bhabha reference cross section goes from 0.5% to 0.1% - Bhabha cross section value is lowered by 0.7% Trigger efficiency correction had to be updated due to a doublecounting of efficiencies. Mpp2 (GeV2) app(0.35-0.95 GeV2) = (388.7  0.8stat4.9syst) · 10-10

  11. Trigger 2001 update Impact of update on trigger correction on 2001 cross section: KLOE 2001 TRG updated KLOE 2001 published KLOE 2001 TRG updated KLOE 2001 published Changes published value on app by 0.4%

  12. Small angle analysis 2002 Preliminary!!! Statistics: 242pb-1 of 2002-data 3.4 Million Events qMiss<150 or qMiss>1650  r-w Interference M2(GeV2) M2(GeV2)

  13. Luminosity: At KLOE, Luminosity is measured using „Large angle Bhabha“ events (55o<qe<125o) KLOE is its own Luminosity Monitor! The luminosity is given by the number of Bhabha events divided for an effective cross section obtained by folding the theory with the detector simulation. • Generator used for Bhabha cross section: • BABAYAGA (Pavia group): • seff = (428.00.3stat) nb • C. M. Calame et al., Nucl. Phys. B758 (2006) 227 New version of generator gives 0.7% decrease in cross section compared to previous version Quoted accuracy: 0.1%

  14. Radiative corrections Fp=1 s (ppg) with Fp=1 [nb] H(s) Radiator-Function H(s) (ISR): • ISR-Process calculated at NLO-level • PHOKHARAgenerator (Czyż, Kühn et.al) • Precision: 0.5% Radiative Corrections: i) Bare Cross Section divide by Vacuum Polarisation  from F. Jegerlehner: http://www-com.physik.hu-berlin.de/~fjeger/ ii) FSR - Corrections Cross section spp must be incl. for FSR FSR corrections have to be taken into account in the efficiency eval. (small angle acceptance, MTrk) and in the passage M2 Net effect of FSR is ca. 0.8%: FSR contr. (sQED)

  15. Small angle result from 2002 data: Preliminary!!! Systematic errors on ampp: STotal= 1.1%

  16. Comparison 2001-2002: (updated)

  17. Evaluating amppwith small angle Dispersion integralfor2p-channel in energy interval 0.35 <Mpp2<0.95 GeV2 2001 published result (Phys. Lett. B606 (2005) 12): app(0.35-0.95GeV2) = (388.7  0.8stat4.9syst) · 10-10 Applying update for trigger eff. and change in Bhabha-cross section used for luminosity evaluation: app(0.35-0.95GeV2) = (384.4  0.8stat4.9syst) · 10-10 2002 preliminary: app(0.35-0.95GeV2) = (386.3  0.6stat3.9syst) · 10-10

  18. Large angle analysis: p g f, r p g f p p f g f0 r p p  small!  important! Preliminary!!! • important cross check with small angle analysis • threshold region is accessible • photon is detected (4-momentum constraints) • lower signal statistics • FSR not negligible anymore • large   p+p-p0background • irreducible bkg. from f decays 240 pb-1 2002 Data Nr. of events / 0.01 GeV2 Mpp2 [GeV2] Threshold region non-trivial due to irreducible FSR-effects, to be estimated from MC using phenomenological models (interference effects unknown) & & f0 FSR rp

  19. Large angle analysis (cont‘d): p+ g p- W Apply dedicated selection cuts: Preliminary!!! • Exploit kinematic closure of the event •  Cut on angle btw. ISR-photon and missing momentum • Kinematic fit inp+p-p0hypothesis using 4-momentum andp0-mass as constraints • FSR contribution added back to • cross section (estimated from PHOKHARA • generator) 2002 Data L = 240 pb-1 LA stat.+syst. error Error on LA dominated by syst. uncertainty on f0 contr. • Reducible background fromp+p-p0 • andµ+µ-g well simulated by MC Mpp2 [GeV2] • Model dependence of irreducible background from f f0g p+p-g is the dominating uncertainty. Estimated • using different models for f0-decay and input from dedicated KLOE f f0g analyses (with f0decaying to charged • and neutral pions).

  20. Comparison SA-LA 2002: Preliminary!!!  (sLA-sSA)/sSA  Range of comparison LA stat.+syst. error Range of comparison app between 0.5 - 0.85 GeV2: Small angle: app(0.50-0.85GeV2) = (255.4  0.4stat  2.5syst) · 10-10 Large angle: app(0.50-0.85GeV2) = (252.5  0.6stat  5.1syst) · 10-10 (60% of systematical error due to f0-uncertainty)

  21. ampp Summary: Summary of the small angle results: Preliminary!!! Jegerlehner (hep-ph/0703125): Using new KLOE result would increase difference from 3.2s to 3.4s

  22. ampp Summary: Comparison withamppfrom CMD2 and SND in the range 0.630-0.958 GeV : Phys. Lett. B648 (2007) 28 Preliminary!!!

  23. Conclusions: • We have obtained app in the range between 0.35 - 0.95 GeV2 using cross section data obtained via the radiative return with photon emission at small angles. • The preliminary result from 2002 data agrees with the updated result from the published KLOE analysis based on 2001 data • Data from an independent and complementary KLOE measurement (Large angle analysis) of the 2p-cross section has been used to obtain app in the range between 0.5 - 0.85 GeV2 • All three KLOE results are in good agreement KLOE results also agree with recent results on app from the CMD2 and SND experiments at VEPP-2M in Novosibirsk

  24. Outlook: • Refine the small angle analysis by unfolding for detector resolution, evaluating further possible backgrounds, etc. • Continue evaluation of resonance contributions in the large angle analysis • Measure the pion form factor via bin-by-bin ratios of pions over muons (Normalization to muons instead of absolute normalization with Bhabhas) • Obtain pion form factor from data taken at = 1000 MeV (outside the f resonance) • suppression of background from f-decays • determination of f0-parameters

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