1 / 16

MEASUREMENT of e + e - HADRONIC CROSS SECTION with RADIATIVE RETURN at KLOE

MEASUREMENT of e + e - HADRONIC CROSS SECTION with RADIATIVE RETURN at KLOE. Barva Maura - Università Roma Tre On behalf of the KLOE Collaboration LNF Spring School - May 2004. Summary. Motivation of s hadr s hadr with radiative return Results on s ( e + e -  p + p - ) at small angle

fritz-gaines
Download Presentation

MEASUREMENT of e + e - HADRONIC CROSS SECTION with RADIATIVE RETURN at KLOE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MEASUREMENT of e+e- HADRONIC CROSS SECTION with RADIATIVE RETURN at KLOE Barva Maura - Università Roma Tre On behalf of the KLOE Collaboration LNF Spring School - May 2004

  2. Summary • Motivation of shadr • shadr with radiative return • Results on s(e+e-p+p-) at small angle • Conclusions and outlook L.N.F. Spring School - May 2004

  3. g* m+ m+ q g* g* q Why the measurement of the cross section is important? THE ANOMALOUS MAGNETIC MOMENT OF THE MUON Magnetic moment for pointlike fermion Dirac because there are quantum correction (Dirac prediction) Hadronic vacuum polarization amSM = amQED + amhad +amEW L.N.F. Spring School - May 2004

  4. Status of am: Theorical vs Experimental value Last result from BNL: 01/04 E821 t-data from ALEPH, OPAL, CLEO e+e- dominated by CMD-2 |am(e+ e-) –am( data)|: 2.7 s -Deviation |am(t) –am( data)|: 1.4 s - Deviation A NEW MEASUREMENT IS VERY IMPORTANT! L.N.F. Spring School May 2004

  5. Hadronic contribution to am • The error on am(theo) is dominated by the error on amhad • This quantity is not evaluable in pQCD, but it can be calculatedby DISPERSION INTEGRAL: The factors 1/s inthe dispersion relation makes the low energy region particularly relevant. The e+e-p+p- channel accounts for ~70% of the contribution both toamhad Input: a) Hadronic electron-positron cross section data b) Hadronic t- decays, which can be used with the help of the CVC-theorem and an isospin rotation (plus isospin breaking corrections) L.N.F. Spring School - May 2004

  6. Complementary approach: Take events with Initial State Radiation (ISR) r s’ “Radiative Return” to r-resonance: e+ e- r + g  p+ p- + g How to perform this measurement? traditional way : measuring cross section by varying e beams energy energy scan BUT DAFNE is a f - factory and therefore runs at fixed c.m.s.-energy: s = mf= 1.019 MeV L.N.F. Spring School - May 2004

  7. s(had) through radiative return The s(e+e-  p+p-g) is a function of the 2-Pion invariant mass s’=Mpp.To extracts(e+e-  p+p-) with the ISR we • Need to know the RADIATOR FUNCTION H(s) H(s) is evaluable From MC Phokhara • Have to get rid of “pure” FSR: which causes events with Mg* = s to be assigned to lower s´ values • Have to properly include radiative corrections (including simultaneously emission of ISR and FSR) L.N.F. Spring School - May 2004

  8. Ebeams 510 MeV • 2 separate rings for e+e- to minimize beam-beam interaction • two interaction region: KLOE-DEAR/FINUDA • crossing angle: 12.5 mrad (px(f) 13 MeV) DAFNE Parameters Design 120+120 N of bunches 120 Lifetime (mins) 40 Bunch current (mA) 4.41030 Lbunch (cm-2s-1) Lpeak (cm-2s-1) 5.31032 • DAFNE performance: • 2000 run: 25pb-1, 7.5 x107f decay first published results • 2001 run: 190pb-1, 5.7 x108f decay • 2002 run: 300pb-1, 9.0 x108f decay Anlysis in progress DAFNE: the Double Annular F-factory for Nice Experiments L.N.F. Spring School - May 2004

  9. The KLOE detector:KLOng Experiment Electromagnetic calorimeter  lead/scintillating fibers (1 mm ), 15 X0  4880 PMT’s  98% solid angle coverage Drift chamber (4 m   3.75 m, CF frame)  Gas mixture: 90% He + 10% C4H10  12582 stereo–stereo sense wires  almost squared cells • Beam pipe : (spherical, 10 cm , 0.5 mm thick) • Instrumented permanent magnet quadrupoles (32 PMT’s) L.N.F. Spring School - May 2004

  10. Measurement of sppg– Analysis scheme Pion tracks at large angles from a vertex close to IP Photons at small angles to enhance ISR: dsISR/dW  1/sin2q • relative contribution of “pure” FSR below the % level over entire Mppspectrum • reduce background • Lose events with Mpp< 600 MeV LARGE ANGLE ANALYSIS (see after…) L.N.F. Spring School - May 2004

  11. MTRK (MeV) p+p-p0 p+p-gg tail signal region mp m+m-g + e+e-g mm mr2 Summary of syst. errors and background Acceptance 0.3% Trigger 0.3% FILFO 0.6% Tracking 0.3% Vertex 0.3% Likelihood 0.1% Track mass 0.2% Backg. Subsraction 0.5% Unfolding 0.3% Total exp 1.0% Luminosity 0.6% Vacuum Polarization 0.2% FSR 0.3% Radiator function 0.5% Total theory 0.9% 1.Rad. Bhabhas: Pion-Electron-Separation by means of a Particle-ID algorithm 2.f  p+ p- p0 e+e- m+ m- g: Kinematic Separation: “Trackmass“ L.N.F. Spring School - May 2004

  12. High Statistics! High Resolution! r-w interference obtained from PHOKHARA H(Mpp2) Mpp2 (GeV2) Analysis: s(e+e- p+p-g) Statistics: 141pb-1 of 2001-Data 1.5 Million Events L.N.F. Spring School - May 2004

  13. |Fp|2 - KLOE 40  CMD2 30 20 KLOE (376.5  0.8stat  5.1syst+theo) 10-10 (378.6  2.7stat  2.3syst+theo) 10-10 CMD2 10 0 0 0.5 0.7 0.9 Analysis: Pion Form Factor and amhad • We have evaluated the dispersions integrals for the 2-Pion-Channel in the energy range 0.35 <M2pp<0.95 GeV2 ampp = (389.2  0.8stat  3.9syst  3.5theo) 10-10 • Comparison with CMD-2 in energy range 0.37 <M2pp<0.93 GeV2 The results are in good agreement! L.N.F. Spring School - May 2004

  14. N(ppg) / MeV 103 102 Mpp (MeV) 10 300 400 500 600 700 800 900 (1) amhad prospect: Large Angle analysis • The energy region close to threshold, Mpp< 600 MeV, is excluded by our selection cuts • This region contributes ~20% to amhad • We use events at large photon angles to access lower • M2region.(Photon tagging • will be possible in this case) • Check FSR parametrization (by looking to charge asymmetry) • This analysis is going on... MeV L.N.F. Spring School - May 2004

  15. (2) amhad prospect: the direct measurement of • We are also studying a direct measurement of R • This method is independent from the luminosity estimate • We are working on obtaining particle ID combining calorimetric and kinematically variables 2002 DATA!!! ppg events mmg events Likelihood Mass Trk L.N.F. Spring School - May 2004

  16. Conclusion: • Summary: • We have presented the first precise measurement of hadronic cross section using radiative return at KLOE • Our result is in agreement with CMD2, therefore confirming the existing discrepancy bewteen SM and BNL result on (g-2)m • Ongoing activities • Large angle photon analysis: to study the low Mpp2 region and measure the asymmetry to check the FSR results • The direct measurement of R=(e+e-  +-g)/(e+e-  +-g) L.N.F. Spring School - May 2004

More Related