ILC Baseline Design: Physics with Polarized Positrons Sabine Riemann (DESY) 24 May 2007 Posipol, Orsay

S. Riemann: ILC Baseline Positron Polarization Outline Baseline Design  Low positron polarization Physics Case ? Utilization of Pe+ ≈ 30% helicity reversal requirements Summary and outlook 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Physics case Refer to previous talk(s) 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 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Baseline - Physics Physics between 200 GeV and 500 GeV Luminosity: Running year zero for commissioning Year 1-4: Lint = 500 fb-1: 1. year 10%  Lint ≈ 50 fb-1 2. year 30%  Lint ≈ 150 fb-1 3. Year 60%  Lint ≈ 300 fb-1 4. year 100%  Lint ≈ 500 fb-1  expected statistics: few 104 eeHZ at 350 GeV (mH≈120 GeV) 105 ee tt at 350 GeV 5·105 (1·105) ee  qq (mm) at 500 GeV 106 ee  WW at 500 GeV  statistical cross section uncertainties at per-mille level !!  e+ polarization will help (beginning of LC studies: Lint ~ 50 fb-1) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

ILC Baseline design: e+ Polarization ? RDR: helical undulator (60% e+ = update value) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

ILC Baseline design: e+ Polarization RDR: helical undulator  ~30% e+ polarization e+ spectrum with g collimator 3.4mrad photon beam: distance undulator center target ~ 500m 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

W. Gai Yield and Pol. The yield will drop from ~1.37 down to ~1.29 when length of drift increased up to 500m from 50m.

S. Riemann: ILC Baseline Positron Polarization Utilization of P=~30% 30% e+ polarization for physics? remember: first LC studies were done also with a (60%, 40%) option !! (60%; 40%)  Peff=0.81 (80%; 40%)  Peff=0.91 (80%; 30%)  Peff=0.88 30%  test of facilities during the first years of operation 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization D Peff Decrease of error on Peff=(Pe- + Pe+)/(1+Pe- Pe+) see also Gudi’s talk for the advantages 30%: Improvement by factor 2 (1.5) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

Draft RDR: Positron Source Linac to Damping Ring Beam Line: spin rotation line  need also spin flip for (+) AND (–) helicity of positrons If no polarization is needed  we have to destroy the 30%! (Few turns in DR without spin rotation before DR are not sufficient; see studies of L. Malysheva) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization e+ Helicity Reversal e+ helicity flip less frequent than e- helicity reversal e- trains - + - + - + - + - + - + e+ trains + + + + + + - - - - - - 50% spent to ‘wrong’ helicity pairing  gain due to xs enhancement for J=1 processes by e+ pol is lost improvement of DPeff remains for quite frequent reversal – and 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 s++ / s+- / s-+ / s-- Can use annihilation data for polarization measurement (see POWER report and work done by K. Moenig) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

Helicity reversal: Blondel Scheme Perform 4 independent measurements (s-channel vector exch.) Can determine Pe+ and Pe- simultaneously (ALR≠0) need polarimeters at IP for measuring polarization differences d|P+|±, d|P-|± between + and – states  DP (dP±) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Helicity reversal Blondel Scheme technique measures directly lumi-weighted polarizations depolarization effect properly taken into account Polarization differences have to be measured with high accuracy Disadvantage of Blondel Scheme with high energy data: new physics in s-channel Estimated accuracy needed for the first 4 years:  dPeff/Peff ≤0.3% (0.5%) Long-term intensity stability  correction and additional syst. error 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Helicity reversal Frequency of e+ helicity reversal: + and – helicity with equal ratio  No reversal during the first year(s) is not an option at all! (…E166…) No reversal  Advantage of reduced error DALR on Peff is lost!! Low reversal frequencies (days): each measurement is done separately  large luminosity/intensity corrections  Need accurate measured lumi and intensities etc. 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Helicity reversal Tolerances: Intensity asymmetry: desired O(‰) (?) at the beginning 1% is more realistic polarization asymmetry: <1% Need to understand relative detector efficiency for ‘+ -’ and ‘- +’ modes at level of few 10-3, later 10-4 Need to measure polarization difference, |Pe+|+ - |Pe+|- at level of <10-2 later 10-3 ( polarimeter @ IP) To reach the high accuracy will be difficult unless we can measure the (+) and (-) modes simultaneously, i.e. to switch positron polarization randomly train-to-train Note: even if positrons are nominally unpolarized, we have tor verify this  desired (at least for the ~60% e+ polarization): train-by-train 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization space for spin rotators must be foreseen K. Moffeit et al., SLAC-TN-05-045 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. 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization (90%, 0%)  (80%, 30%) ? similar size of effective polarization, Peff ~0.9 BUT: D Peff (90%; 0%) = 2…1.4 ·D Peff (80%; 30%) (uncor…correlated) Suppression of undesired helicity states for some processes with (80%, 30%) Is (90%,30%) an alternative to (80%, 60%) ? No - due to less significant physics goals (no transverse polarization  see Gudi’s talk) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization

S. Riemann: ILC Baseline Positron Polarization Summary & Conclusion We will have a polarized machine from the beginning! Already 30% e+ polarization is benefit for physics Low P(e+) allows test of operation with both beams polarized Utilization of low e+ polarization needs - Positron polarization measurement - Spin rotation - Spin flip • frequency? Desired: train-by-train • proposed scheme exists: spin rotators before (LTR) and after the DR (RTL) are needed (see SLAC-TN-05-045, EUROTeV-Report-2005-024-1) • other solutions for helicity reversal? • no reversal is perhaps worse than no polarization! Further design & simulation work has to be done and should include the ~30% option (depolarisation, polarimeter, spin-flip-frequency etc.) 24 May 2007 Posipol, Orsay S. Riemann: ILC Baseline Positron Polarization