Beijing, Feb 3 rd, % e+ Poalarization 1 Physics with an initial positron polarisation of ≈30% Sabine Riemann (DESY)

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 2 Outline Low positron polarization Physics Case ? Utilization of P e+ ≈ 30%  fast or slow helicity reversal  requirements Summary and outlook

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 3 Physics case Refer to previous talks given by Gudi and others: e+ polarization  improves accuracy of SM measurements  increases sensitivity to physics beyond SM  decisively to find out what the underlying physics is With e+ polarization processes can be enhanced or suppressed; clean initial states with known helicities

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 4 Advantage: e+ Polarization No doubts: 60% e+ polarization are needed What about ~30% for the beginning?

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 5 Utilization of P=~30% Better physics? see next slides remember: first LC studies were done also with a (60%, 40%) option !! 30%  test of facilities during the first years of operation

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 6 Baseline Machine Physics between 200 GeV and 500 GeV Luminosity: Running year zero for commissioning Year 1-4: L int = 500 fb -1 : 1. year 10%  L int ≈ 50 fb year 30%  L int ≈ 150 fb Year 60%  L int ≈ 300 fb year 100%  L int ≈ 500 fb -1  expected statistics: few 10 4 ee  HZ at 350 GeV (mH≈120 GeV) 10 5 ee  tt at 350 GeV 5·10 5 (1·10 5 ) ee  qq (  ) at 500 GeV 10 6 ee  WW at 500 GeV  statistical cross section uncertainties at per-mille level !!  e+ polarization will help (beginning of LC studies: L int ~ 50 fb -1 )

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 7 P eff Increase of effective polarization: P e- / P e For comparison: old LC studies: (60%,40%)  P eff =0.8

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 8  P eff Decrease of error on  P eff (error propagation) 30%: Improvement by factor 2 (1.5)

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 9 Enhancement /suppression of initial state polarization Example: suppression factors for WW production Complicated mixture of , Z exchange Large LR asymmetry depending on production angle P e- P e

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 10 Transverse polarization does NOT work with e- polarization only sensitivity to new physics (CP violation, graviton) Rizzo M H =1.5 TeV, E=500 GeV, L=500 fb -1

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 11 (90%, 0%)  (80%, 30%) ? same size of –Suppression of undesired hel. states for some processes –effective polarization (~0.9) BUT:  P eff (90%; 0%) = 2…1.4 ·  P eff (80%; 30%) (uncor…correlated) Is (90%,30%) an alternative to (80%, 60%) ? No - due to less significant physics goals

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 12 Physics goal

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 13 Physics goal

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 14 e+ helicity reversal e- trains e+ trains % spent to ‘wrong’ helicity pairing  gain due to xs enhancement for J=1 processes by e+ pol is lost improvement of  P eff remains – if systematic errors are small enough asymmetries can be measured, systematic effects are largely cancelled out If the e+ helicity will be switched quite frequently this scheme corresponds to a ‘slow’ Blondel scheme with luminosity ratio 1/1/1/1 for  ++ /  +- /  -+ /  -- Can use annihilation data for polarization measurement (see POWER report and work done by K. Moenig)

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 15 Helicity reversal: Blondel Scheme Perform 4 independent measurements (s-channel vector exch.) Can determine P e+ and P e- simultaneously (A LR ≠0) need polarimeters at IP for measuring polarization differences  P e-,  P e+ between + and – states   P

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 16 Helicity reversal: Blondel Scheme this technique measures directly lumi-wted polarizations any depolarization effect properly taken into account (?) Polarization differences have to be measured with high accuracy Estimated accuracy needed for the first 4 years:  dP/P ≤0.3% (0.5%) Long-term intensity stability  correction and additional syst. error

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 17 Helicity reversal Frequency of e+ reversal: + and – helicity with equal ratio  No reversal during the first year(s) is not an option at all! often enough to avoid unknown systematic (time dependent) uncertainties Tolerances: Intensity asymmetry: desired 0.1% (?) at the beginning 1% is more realistic polarization asymmetry: <1%  desired (at least for the ~60% e+ pol): train-by-train Low reversal frequencies (days): each measurement is done separately  large luminosity/intensity corrections  Need accurate measured lumi and intensities etc.  Further studies are needed …

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 18 Remarks Need to understand relative detector efficiency for ‘+ -’ and ‘- +’ modes at level of few 10 -3, later Need to measure polarization difference, P e+ (-) - P e+ (+) at level of <10 -2 later To reach the high accuracy will be difficult unless can measure these modes simultaneously, ie. can switch positron polarization randomly train-to-train Note: even if positrons are nominally unpolarized, need to verify this!  Positron polarimeter at the IP is needed anyway.

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 19 Layout of positron damping ring system showing the parallel spin rotation beam lines for randomly selecting positron polarization direction. A pair of kicker magnets is turned on between pulse-trains to deflect the beam to the spin rotation solenoids with negative B- field. space for spin rotators must be foreseen K. Moffeit et al., SLAC-TN

Beijing, Feb 3 rd S. Riemann, 30% e+ Polarization 20 Summary & Conclusion 30% is benefit for physics we could have a polarized machine from the beginning! Allows test of operation with both beams polarized  should be used for physics – otherwise it has to be destroyed (see also slides from L. Malysheva / I. Bailey) Utilization of low e+ polarization needs - Positron polarization measurement - Spin rotation frequency? Desired: train-by-train proposed scheme exists: spin rotators before (LTR) and after the DR (RTL) are needed (see SLAC-TN , EUROTeV-Report ) other solutions for helicity reversal? no reversal is worse than no polarization! Further design & simulation work has to be done and should include the ~30% option (depolarisation, polarimeter, spin-flip-frquency etc.)