1. Impact of electromagnetic deflection due to beam-beam effect on Bhabha scattering C. Rimbault, LAL Orsay Krakow, February 12-13 2006

2. Impact of electromagnetic deflection due to beam-beam effect on Bhabha scattering C. Rimbault, LAL Orsay 1.Motivation 2.Generation in GUINEA-PIG 3.Study of beam-beam effects on Bhabha scattering 4.Comparison for different beam parameter sets 5.Mean questions

3. Bhabha scattering & electromagnetic deflections Bhabhas are used to measure the luminosity: L int = N Bhabha /  Bhabha Bhabha cross section : Beam-Beam effect  Energy radiation + EM deflections  modification of the angular distribution ?  modification of the theoretical cross section ?  Would it be possible to estimate L with  L/L < 10 -4 ? e+e+ e-e- e+e+ e-e-  e+e+ e-e- e+e+ e-e-  ++...

4. Bhabha scattering & electromagnetic deflections 10 6 Bhabhas produced with BHLUMI, √s=500 GeV, 25≤  ≤90 mrad * Lorentz boost in lab frame because of beamstrahlung emission GUINEA-PIG EM deflection treatment (same as for the e + e - pairs) for the analyse : 30≤  ≤75 mrad, cut on energy: 0.8 E i * Nominal set * (see A. Stahl LC-DET-2005-004) QUESTION: Which method to introduce bhabha in GUINEA-PIG : external or internal Bhabhas production ?

5. Beam-beam effect on the Bhabha scattering modification of initial state Beamstrahlung  modification of e + e - 4momenta Differential cross section 500 GeV 480 GeV 460 GeV *

6. Beam-beam effect on the Bhabha scattering modification of initial state Beamstrahlung  modification of e + e - 4momenta Cross section calculated in GP  th = 3.889 nbarn “defocusing” effect

7. Bhabha scattering & electromagnetic deflections Modification of final state e-e- e+e+ e+e+ e-e- Deflection of Bhabhas due to the field of the opposite beam.  focusing of ~0.04 mrad  diff Vs  0

8. Bhabha scattering & electromagnetic deflections Modification of final state    (mrad)    (mrad)    before deflection    after deflection N Bh bef. def. = 35986 N Bh added by def. = 4 N Bh suppressed by def. = 132 Difference between theoretical and “real” nb of Bhabhas : -0.36%  “Bhabha suppression effect”

9. Beam parameters for 500 GeV TESLANominalLow QLarge YLow PHigh Lumi N2 10 10 1 10 10 2 10 10 Nbunches per train2820 5640282013302820  x [nm] 554655495 452  y [nm] 5.05.73.58.13.83.5  z [  m] 300 150500200150  x [mrad] 1.0 E-5 1.2 E-51.0 E-5  y [mrad] 3.0 E-84.0 E-83.0 E-88.0 E-83.5 E-83.0 E-8  x [mm] 15.021.012.010.0  y [mm] 0.4 0.20.40.2 P_Beamstrahlung [10 5 W] 3.352.482.052.673.067.90 Luminosity [ 10 34 cm -2 s -1 ] 2.92.0 2.14.9

10. Bhabha scattering & electromagnetic deflections Impact of beam parameter sets 30-75 NominalLow QLarge YLow PHigh Lumi (N th -N real ) /N th (%)0.360.350.310.660.80 “/nominal1.000.970.861.832.22 d  (mrad) 0.0380.0290.0280.0590.073 P_Beamstrahl [10 5 W]2.482.052.673.067.90 “/nominal1.000.821.071.233.18 HighLum LargeY Nominal

11. Relation with pair deflection a previous study Deflection limit of nominal case

12. Summary Impact of EM Deflection effect on Bhabha scattering > 10 × 10 -4 Beamstrahlung + EM deflections : partial cancellation  Necessity to well know the impact of EM deflection  Need a tool : Which kind of tool do you want ? Need to found a correlated variable to evaluate the “Bhabha suppression effect”  Who ?