1. Measurement of the DA  NE Luminosity with the KLOE Experiment Federico Nguyen Università Roma TRE – INFN Roma III February 10 th 2005 EURIDICE Midterm Collaboration Meeting

2. Federico Nguyen 10-02-2005 Outline  Motivations: the error on    Selection criteria of large angle Bhabha events  Comparisons among MC codes  Main systematics of the experimental analysis  Conclusions: how can we improve?

3. Federico Nguyen 10-02-2005 DA  NE and KLOE Electromagnetic Calorimeter Pb / Scintillating Fibres Endcap + Barrel = 98% (4  ) DA  NE, e + e  collider at  s ~ 1.019 GeV ~ M  Drift Chamber 4 m , 3.3 m length 90% He, 10% i-C 4 H 10 Superconducting Coil B=0.52 T

4. Federico Nguyen 10-02-2005 Resolutions in KLOE  E /E = 5.4%/  E(GeV)   p /p = 0.4% (  45°)  r  = 150  m,  z = 2 mm  vtx ~ 3 mm e  e   e  e   e  e   e  e   EMC features: Drift Chamber features:  t = 56ps /  E(GeV)  133ps

5. Federico Nguyen 10-02-2005 Selection of large angle Bhabha   angle btw the 2 most energetic clusters nr. of events e  e   e  e  e  e   the luminosity is given by Bhabha events divided for a  evaluated folding theory (QED rad. corrs.) with the detector simulation  2 clusters with:  eV  eV  55 o    125 o   |  1  2  180 o |  9 o 2 tracks with:   7.5 cm, |z|  15 cm  p  400 MeV  opposite curvature

6. Federico Nguyen 10-02-2005 The MC code BABAYAGA  BABAYAGA:  each e ± can emit up to 4 photons  multiphoton emission parameterized by structure functions D(x,Q 2 ), folding the Born cross section     evolution equations are solved by the numerical method Parton Shower   the accuracy is evaluated comparing with the exact O(  ) evaluation, the authors quote 0.5% within our cuts  Pavia group has worked at an improved version C. M. Carloni Calame et al., Nucl. Phys., B584, 459, 2000

7. Federico Nguyen 10-02-2005 The MC code BHWIDE  BHWIDE:  up to 100  ’s per event  complete O(  ) corrections  exact phase space integration  collinear and infrared logarithms accounted for to all orders  claimed precision is   % according to the LEP2 requirements B B contains the infrared divergence due to virtual corrections S (k,m   S (k,m   contains the infrared divergence due to bremsstrahlung corrections W. Placzek et al., hep-ph/9903381, 1999 S. Jadach et al., Phys. Lett., B390, 298, 1997

8. Federico Nguyen 10-02-2005 BHWIDE vs. BABAYAGA we compared the 2 MC codes applying our kinematic cuts  eV 55 o  125 o  eV 55 o  125 o   |  1  2  180 o |  9 o we tested the differential cross sections in acollinearity, , and lost energy, v  1  M ee 2 /s, no significant difference has been found in the shapes

9. Federico Nguyen 10-02-2005 Comparisons of cross sections (460.8  0.1 stat ) nb BHAGENF(460.8  0.1 stat ) nb (459.4  0.1 stat ) nb BABAYAGA (459.4  0.1 stat ) nb (456.2  0.1 stat ) nb BHWIDE(456.2  0.1 stat ) nb (455.3  0.1 stat ) nb MCGPJ(455.3  0.1 stat ) nb 0.7 % 0.1 % 0.3 % comparing the MC codes in treating virtual (  exchange and vacuum polarization are “switched off”), soft and hard  corrections, the cross sections for our kinematic cuts are:  BHAGENF features:  complete O(  ) corrections  corrections due to e + e  → e + e    authors quote O(0.5%) accuracy E. Drago and G. Venanzoni, Report INFN-AE-97-48, 1997 F. Berends and R. Kleiss, Nucl. Phys., B228, 537, 1983   Monte Carlo Generator with Photon Jets:  use of structure functions  complete O(  ) corrections  authors quote O(0.2%) accuracy A. Arbuzov et al., Report Budker INP-2004-70, 2004 A. Arbuzov et al., JHEP 9710:001, 1997

10. Federico Nguyen 10-02-2005 Momentum and  comparisons we checked that the MC code folded with the detector simulation reproduces the kinematic variables, especially at the borders dn/dp [(0.5 MeV) -1 ] + Data - Babayaga (MC) - Bhagenf (MC)  MC data perfect agreement in the acollinearity distributions very good agreement near p ~ 400 MeV p  400 MeV  

11. Federico Nguyen 10-02-2005 Polar angle systematics global agreement is very good but the cut occurs in a steep region of the distributions  estimate of border mismatches after normalizing MC to make it coincide with data in the region    , we estimate as a systematic error:   MC data

12. Federico Nguyen 10-02-2005 Background estimate (I) A0 A1 events/3 MeV DATA MC other than Bhabha, there are events with m trk ~ 137 MeV, e  e      around m trk ~ [100,170] MeV t he exponential is subtracted from data m trk : 4-mom. conserv. under the hypothesis of 2 equal mass tracks and a 

13. Federico Nguyen 10-02-2005 a second method consists in discr. e  at least one track identified as  an average of background content of 0.55% and a systematic error of 0.10% are estimated Background estimate (II) E (first plane) (MeV) E (last plane) (MeV) E (first plane) (MeV) E (last plane) (MeV) pions deposit ~ 40 MeV in each plane electrons deposit mostly in the first plane and negligible amount in the rest  eeee

14. Federico Nguyen 10-02-2005 Dependence on sqrt(s) since the cross section is evaluated at the nominal value of s 1/2  = 1019.5 MeV, we corrected for DA  NE variations of s 1/2 in time  L/L =  is parameterized as a function of s 1/2, from Monte Carlo:

15. Federico Nguyen 10-02-2005 List of systematics  (theory)   (experiment) =  (total error)  due to  s   putting all together: BHAGENF:  eff = ( 430.7 ± 0.3 stat ) nb BABAYAGA:  eff = ( 431.0 ± 0.3 stat ) nb both groups of authors claim 0.5% summing in quadrature 

16. Federico Nguyen 10-02-2005  the measurement of the luminosity is performed using large angle Bhabha events, detected in KLOE in 2001  the major source of uncertainty is from theory  we are going to use the improved version of BABAYAGA, and also BHWIDE and MCGPJ to pin down the 0.5% factor  what about implementing recent 2 loop evaluations?  from the experimental side we are going to analyse the 2002 data, and we are going to look at the process e + e  →  as an independent luminometer reaction, which is the precision of radiative corrections in this channel? Conclusions and perspectives A. A. Penin, hep-ph/0501120 R. Bonciani et al., hep-ph/0411321 M. Czakon et al., hep-ph/0412164

17. Federico Nguyen 10-02-2005 Loss of cosmic events at the trigger level, events are rejected because they have characteristics similar to cosmic rays (amount of energy released at the outer planes of the EMC) genuine cosmic event Bhabha event rejected because taken as cosmic a fraction of 0.41% large angle Bhabha events are lost because of this