Stefano Di Falco & Achim Denig Universität Karlsruhe The new pp g(g) Montecarlo and Report on the luminosity measurement KLOE Workshop Conca Specchiulla, June 10 th - 12 th, 2002

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, ppg selection for small g angle Trigger FILFO/par=5 PPGTAG (tracks, vertex, M TRACK,…) Pion fiducial volume: 40 o < q p < 140 o New!! Photon fiducial volume: 0 o < q g < 15 o New!! E >10 MeV (in fact cut on E S ) Likelihood M TRACK DATA…MC

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, s HADR and Montecarlo generators The hadronic cross section measurements needs MC help in more steps: acceptance: is determined using the p angular distribution and q g correlations between selection efficiencies (mainly FILFO) M TRACK cut: cuts on the tail due to the radiation of one or more ISR g Furthermore: Final state radiation and ISR-FSR interference: needs to be know only with rough approximation in the small angle analysis Radiation Function: used to extract the pion form factor F p from the M pp 2 Luminosity determination (BABAYAGA)

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, ppg Montecarlo generators ISRFSRmeme precision EVA* (J.Kühn et al.) a + coll.ra d. pointlike p 0~2% PHOKHARA* o (J.Kühn et al.) a2a2 NO 0 ~0.5% AFRODITE* (F.Jegerlehner et al.) a (+ a 2 ?) pointlike p + F p 0 ? KKMC (e + e ff+n g ) (S.Jadach et al.) CEEX NO0(<0.2%) * Interfaced with Geanfi o Modified to impose cuts on the pp system instead of the g s

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Comparison Eva-Phokhara: q g EVA doesnt give the correct cross section for q g < 0.1 o : Q g min = 0 o now available! Higher s, lower background, no smearing problems !

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Comparison Eva-Phokhara: Q 2 EVA was generating too many events at small angle, nonetheless the Q 2 spectrum shape was correct:

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Comparison Eva-Phokhara: q g smearing Nonetheless the cut q g >5 o was causing troubles especially at large Q 2 because of the resolution on q g : +10% -10% The discrepancy was due to the EVA, with PHOKHARA its no more present: EVA PHOKHARA +10% -10%

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Comparison Eva-Phokhara: s TOT ISR in EVA doesnt include the vacuum polarization and O(a 2 ) terms The global effect on s for large q g is ~2% (flat in Q 2 )

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Contamination from FSR ISR radiation (PHOKHARA) s TOT = 14.3 nb FSR radiation (EVA) s TOT = 0.03 nb (~0.2%) FSR ISR+FSR M 2 % ISR photons are mostly emitted collinear to the e + e - beams (small angle) while the FSR ones prefer the pion direction. At leading order = and then the cut: 165 o suppresses FSR when 40 o < p < 140 o (also p + p - p 0 background is suppressed)

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Summary & Outlook on ppg generators A new Montecarlo, PHOKHARA, with O(a 2 ) ISR, is available and has been adapted to our experimental cuts and interfaced with Geanfi. It allows to lower to 0 the lower cut on the missing momentum (q g ) resolving the smearing problems and decreasing the impact of FSR and p + p - p 0 background The work to include FSR in Phokhara is going on. Results are waited also from Afrodite (Berlin-Cracow group) and KKMC (work not yet started) to evaluate the systematics as discrepancies of the different theoretical calculations. A realistic multiphoton generator including FSR will be very important to perform the measurement at large angle needed to cover the low M pp 2 region.

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Luminosity counters Data Trigger EmC Reconstruction FILFO LAB ( >45°) Golden Bhabha ( > 25° including ) Trigger Luminosity ( Bhabhas on Barrel ) DC Reconstruction GGL: > 45°) DC - Events Selection: 2 Tracks from I.P. with opp. charge First Hits > 50 cm separated 400 MeV < E + - < 600 MeV VLAB > 55°) B and Energy calibrated NO YES EMC - Events Selection: 300 MeV < E + - < 800 MeV, | T CL1 - T CL2 | 50, cos( Acoll. (3d) ) < Effective s (nb) ~ 800 ~5700 ~ 119 ~ 800 ~ 425

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, VLAB systematics The luminosity is given as usual by: L = N / EFF where EFF is the theoretical cross section evaluated from MC including the efficiencies for the selection cuts MC-Data difference in: 1) Acceptance 2) Efficiency 3) Background contamination Variations in time due to Running Conditions: s, p, L-R asymmetries not const., Beam position not const. EmC - Calibration (DC?) Machine Background Monitoring Tool Has been studied in the past: MC and Data distributions agree very well <1% level The systematics of the measurement are given by :

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Acceptance (checks) TOTAL CROSS SECTION (CORNER REGION EFFECT? ): = % % q e (degrees) Relative difference

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Efficiencies Cluster Inefficiency: P miss > 20 MeV | miss - 90 o | < 35 o | T cl | < 10 ns | R cl | > 10 cm additional N cl = 0 Tracking Inefficiency: N cl =2 N tr =1 To be refined ! Data-MC: better than 1% Monitoring… % %

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Background LAB - Sample VLAB - Sample LAB - SampleVLAB - Sample Removed by E +- > 400 MeV Cut After Likelihood Before Likelihood 0.3 % backgr.

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Effect of run conditions: s Suppose D s = +1 MeV Two effects: Change in Bhabha cross section: % L / L Change of the efficiency (95.65%) for 2 tracks with E + - >400 MeV % L / L L / L % Radiative Tail well described by Theory BABAYAGA GEANFI Data

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Effect of run conditions: beam position Effect of a shift Dz=–1 cm of the interaction point on the cut on Polar Angle of Clusters Corresponds to a left - right asymmetry = 1% Variations in single bins reach ~2% but compensate each other… VLAB (only barrel) % L / L

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, GGLLAB Additional infos on machine background Mean value of not associated hits Mean of Nclu Mean of E TOT -E 1 -E 2 Accidental rate inside +50 < T< +70 ns ( T0= )

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Cross check VLAB – gg and GBHA VLAB - GGL VLAB - GBH 2002 data Runs > 85nb nb-1: VLAB = 0.5% GGL = 1.0% GBH = 0.1% = 0.3 % RMS = 1.0 % = -2.8 % RMS = 0.6 %

S. Di Falco & A. Denig – Conca Specchiulla, June 10 th -12 th, Summary & Outlook (luminosity) Error on Luminosity enters in our - cross section measurement as absolute normalization Precision required: <= 1% ?! VLAB sample is more stable and reliable than the previous LAB Systematic error: - theoretical error estimated 0.5% - no evidence for experimental effects larger than 1% - agreement gg - VLAB ~0.3% (similar theoretical uncertainties) In the latest version VLAB selection includes the monitoring of many variables useful to determine the quality of the run (and eventually discard the bad ones) Works in progress: description of hard Bremsstrahlung, …. Cross check of Lumi-Bhabha-measurement by looking at - data