Progress on F  with the KLOE experiment (untagged) Federico Nguyen Università Roma TRE February 27 th 2006

Federico Nguyen Outline  Present situation  Selection criteria: the “small angle” analysis  Particle discrimination  Preliminary estimates of the background processes  Conclusions

Federico Nguyen Available KLOE data sets in 2001, the veto of cosmic events (hardware) caused nonnegligible inefficiency in  events and made the measurement of  events not feasible, from 2002 on, this effect is taken out

Federico Nguyen KLOE: performances for the  analysis Electromagnetic Calorimeter Pb / Scintillating Fibres Endcap + Barrel = 98% (4  ) Drift Chamber 4 m , 3.3 m length 90% He, 10% i-C 4 H 10 the whole structure is surrounded by a superconducting coil B=0.52 T the whole structure is surrounded by a superconducting coil B=0.52 T   p /p = 0.4% (  45°)  r  = 150  m,  z = 2 mm  vtx ~ 3 mm,  M  ~ 1 MeV e  e   e  e  e  e   e  e   E /E = 5.4%/  E(GeV)

Federico Nguyen Fiducial volume no photon tagging: high statistics for ISR (~   ) low relative FSR contribution suppressed        wrt the signal the threshold region is not covered high statistics for ISR (~   ) low relative FSR contribution suppressed        wrt the signal the threshold region is not covered     a) 1 and only 1 vertex ( |z|  7 cm ) connected to 2 tracks b) each track with 50 o <  track < 130 o c) small angle  (     )

Federico Nguyen Benefits of the selected region M  2 (GeV 2 ) [%] KLOE result (140 pb -1 of 2001) : Phys. Lett., B606 (2005) 12 KLOE result (140 pb -1 of 2001) : Phys. Lett., B606 (2005) 12 in the selected region LO-FSR, and       yields are small, from which the published result is based on:  FSR-LO /  QED   /  

Federico Nguyen Normalization to  events benefits from normalizing to  events, in the limit of neglecting FSR effects: ′ ′ ′ Luminosity: 0.5% theory  0.3% exp., Bhabha most of the theoretical systematic effects cancel out

Federico Nguyen Statistical error              M  2 = 0.01 GeV 2 L = 240 pb -1,  = 50% flat in s′, in both channels contrary to the luminosity normalization, statistics is an issue, however it is a good cross check of the region intriguing because of the difference with  data estimate performed with PHOKHARA-4 H. Czyż et al., Eur.Phys.J.C39 (2005) 411

Federico Nguyen Discrimination  vs. e: time and energy time of flight: for low p values     e ~ 1 electrons deposit mostly in the first plane and negligible amount in the rest pions deposit ~ 40 MeV in each plane  /e separation is performed using a particle ID function based on time and quantity and shape of the energy released in the calorimeter

Federico Nguyen Improvements wrt the published result m miss, defined by the 4-momentum conservation under the hypothesis of e + e      X improved selection enlarged m trk acceptance, from 90 MeV to 80 MeV only 1/1000 of events with m miss > 120 MeV more efficient reconstruction filter: from 95% to 98.5% m trk, defined by 4-momentum conservation under the hypothesis of 2 equal mass tracks and a 

Federico Nguyen Discrimination efficiencies for  and  1) the procedure is tested 2) the event is selected if at least one of the 2 tracks is not identified to be an electron it leads to a rejection power ~ 97% for e + e   e + e  events while keeping a selection efficiency  99.8% for e + e    +    +    events  Log L  /L e (per track) electrons muons or pions before particle ID after particle ID m trk (MeV)

Federico Nguyen Definition of  and  events (I)  MeV  m trk  and inside the area, are  m trk  MeV are  M  2  [0.37,0.42] GeV 2 m trk (MeV)  no man’s land            (MC) DATA

Federico Nguyen Definition of  and  events (II)      M  2  [0.57,0.62] GeV 2 M  2  [0.87,0.92] GeV 2 m trk (MeV) ee  high M   can be neglected to 1st order

Federico Nguyen Tracking efficiencies for  events evaluated from data samples of     and       events, and from a MC sample of      events, and compared the agreement is on the level of %, at maximum, preliminary

Federico Nguyen Background for the  selection background yields are estimated using MC distributions after the whole selection, normalized to the luminosity of the selected data sample for data and 2 background sources: MC  M 2 (GeV 2 ) d  vis /dM 2 (nb/GeV 2 ) preliminary data MC      

Federico Nguyen The “raw”  spectrum M 2 (GeV 2 ) d  /dM 2 (events/0.01 GeV 2 )  M  2 = 0.01 GeV 2, L = 242 pb -1 of data taken in 2002 a) pion with 50 o <  track < 130 o b) small angle  (     ) c) m trk > 130 MeV and inside the area (m trk vs M  ) d) at least 1 track not to be identified as an electron preliminary

Federico Nguyen Background for the  selection background yields are estimated using MC distributions after the whole selection, normalized to the luminosity of the selected data sample for data and 2 background sources: M 2 (GeV 2 ) d  vis /dM 2 (nb/GeV 2 ) MC  preliminary MC       data

Federico Nguyen The “raw”  spectrum  M  2 = 0.01 GeV 2, L = 242 pb -1 of data taken in 2002 d  /dM 2 (events/0.01 GeV 2 ) M 2 (GeV 2 ) a) muon with 50 o <  track < 130 o b) small angle  (     ) c) m trk < 115 MeV d) at least 1 track not to be identified as an electron preliminary

Federico Nguyen  the extraction of F , from both the absolute measurement of  events and from the ratio of  to  events, is in an advanced state,  these methods have different systematics,  we are finalizing the estimate of the corrections and of the systematic uncertainties,  good control of  /  /e discrimination,  even on the theory side some improvements are expected Conclusions and perspectives Results will come soon… Please, stay tuned

Federico Nguyen Comparison among available data sets  a   ( ) KLOE,    SND,    CMD-2 EPS (‘05),    CMD-2,    M  2 (GeV 2 )  /  KLOE - 1 CMD-2 (‘04) and KLOE high M  disagreement btw KLOE and CMD-2/SND around the  peak fair agreement btw CMD-2 (‘04) and KLOE difference at about 1  btw KLOE and SND due to the  peak and above interpolation of KLOE 60 data points from 0.35 to 0.95 GeV 2  a      4 pts   ndf  P    4 pts   SND: Achasov et al., hep-ex/