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Opportunities and challenges of TLEP as a precision machine

Opportunities and challenges of TLEP as a precision machine for Electroweak Radiative Corrections. ‘Will redo te LEP program in a few minutes…. ’. EWRCs. relations to the well measured G F m Z a QED. at first order:. Dr = a /p ( m top /m Z ) 2 - a /4p log ( m h /m Z ) 2.

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Opportunities and challenges of TLEP as a precision machine

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  1. Opportunities and challenges of TLEP as a precisionmachine for Electroweak Radiative Corrections ‘Will redo te LEP program in a few minutes…. ’

  2. EWRCs relations to the well measured GF mZ aQED at first order: Dr = a /p (mtop/mZ)2 - a /4p log (mh/mZ)2 e3 = cos2qwa /9p log (mh/mZ)2 dnb=20/13 a /p (mtop/mZ)2 complete formulae at 2d order including strong corrections are available in fitting codes e.g. ZFITTER

  3. Electroweakprecision observables at e+e- collider comments : -- mostpowerfulrelationships : mZ vs Oi -- limitation fromuncertainty in QED (mZ) will affect maximallymZ vs sin2effW(all Z peakasymmetries) interpretation will affect mZ vs mW interpretation will *not* affect suchquantities as mZ vs lept and mZ vs Rb= b/ had -- great premium on mZ and Z from the line-shape scan -- b/ hadwillbeobtainedfromhighluminosityat the Z peak.

  4. LEP = 16 Million hadronic Z decays, 1.7 Million leptonicdecays, 1031 /cm2/s  3 Z events per second + 4 times that rate in Bhabhas = 15 events per second. 1036/cm2/s 1’500’000 events per second 1.5MHz …. 107 seconds  3 1012 Z decays. TeraZ CHALLENGE I design of detector and DAQ system to keephigh precision in cross-section measurement Small angle e+e- isnecessary for luminositydetermination as large angle e+e- isdominated by Z decaysthemselves

  5. Statisticalerrorswillreducenicely canwereducesystematicsalso? -- Energy calibration -- Luminositymeasurements -- Cross-section measurements

  6. energy resolution (resonant depolarization) +-200 keV! variations due to tides, trains, rain, etc.. mZ= 91187.5 +-2.1 MeV Energy calibration systematicswas 10 times that the measurementitselfbecause .. measurementwas not performedcontinuously. End of fills – systematicallyshifted 55% transverse polarizationwasachieved

  7. BeamPolarizationat TLEP-Z I do not considerhere the possibility of injectigpolarizedelectrons and positrons. A discouragingparameteragainstthisis the spin tune s = Ebeam[GeV]/0.4406486 =103.5 at the Z peak. Crossing all theseresonances in the accelerationwillkillpolarization for sure.  Build up polarization by Sokolov Ternoveffectathighenergy. where A is the limiting degree of polarization (92.4%) and  is the polarization time. The polarization time at the Z peakwas300 minutes in LEPI It willbe 300x(80/27) ~ 9’000 minutes or 150 hoursat TLEP-Z – ouch. wecan use wigglers and we must be patient.

  8. PolarizationWigglers as theyweredesigned for LEP I ( A.B and John Jowett, in Polarizationat LEP, CERN Yellow report 88-06) Asymmetric B- B+ B- 12 magnets in straight sections  65 m total 3 kW of SR locally per mA  4 MW extra power at the Z. 40 minutes polarization time. need to check manythingssuch as energyspreadetc…

  9. LEP3/TLEP parameters -1 soon at SuperKEKB: bx*=0.03 m, bY*=0.03 cm SuperKEKB:ey/ex=0.25%

  10. LEP2 was not beam-beam limited LEP3/TLEP parameters -2 LEP data for 94.5 - 101 GeV consistently suggest a beam-beam limit of ~0.115 (R.Assmann, K. C.)

  11. PolarizationWigglers as theyweredesigned for LEP I ( A.B and John Jowett, in Polarizationat LEP, CERN Yellow report 88-06) Asymmetric B- B+ B- 12 magnets in straight sections  65 m total 3 kW of SR locally per mA  4 MW extra power at the Z. 40 minutes polarizationtime at LEPI wouldbe 120 minutes need to check manythingssuch as energyspreadetc…

  12. Operation mode operation mode probablydifferent for the Z line shapemeasurement, for highintensitypeakmeasurements and for longitudinal polarizationmeasurements Proposed for line shapemeasurement itis important to keep a number of bunchestransversallypolarizedto perform the calibration continuously. Thesebunchesneed not becolliding. Thanks to synchrotron oscillations the averageenergy of collidingbeamscannotbedifferent to that of circulatingbeams (thiscanbechecked by beam position in dispersion zones) Spin matching techniques of LEP canbeused (low beta, solenoids, imperfections, etc..) hopefullyeasier if we have carefulthoughtahead of time. This shouldallow the systematicerror to bereducedbelow the 100 keV/beamlevel per measurement , withimprovementexpected as 1/sqrt(Nmeas) Keepsome fraction of the 2625 bunches not colliding and measurecontinuously. Can wekeep full luminositywhiledoingthis? (somereductionwould not kill us)

  13. Measuring sin2qWeff (mZ) sin2qWeff  ¼ (1- gV/gA) gV = gL + gR gA = gL - gR

  14. Longitudinal polarization Once polarizationis transverse itneeds to berotated in the direction of the beam to become longitudinal in the IP region and againthe same transverse in the next arcs  the art of spin rotators(there have been manyproposals, probably best are the Herarotators) For longitudinal polarizationexperimentsweneed to keep the beampolarized while in collisions. This is the main unknown. Top up mode shouldprovide stable operation whichis essential for the exquisiteorbit corrections, but willdilute the beampolarization as P = (1/P) / (1/P + 1/lumi) (or somethinglikethat). This is not solid science, but canbetested withtransersepolarizationbeforedeciding on the spin rotators. Wehadsomelimited MD experienceat LEP, whichshowedsomepolarization in collision but thiswasonly once. Weshoulddig-out thisresult. It maymeanthat the luminosityshouldremainat a few % of the maximal unpolarized luminosity. Still 1034/cm2/s willprovide 3.1010 detected Z decays per year.  towardssin2Weff = few 10-6 thisistwoordermanitudebetterthan the present 0.00016 Unlike the Z line shapere-measurementwhichcouldbe a few weeks of running thisis more likely to bea one yearaffair.

  15. Outlook I have begunto investigate the possibility of improving the EWRC sensitive observables at TLEP (aka EWPT) around the Z resonance. Not mWyet. -- Z peak observables canbemeasuredwithfantasticstatistics. b and hadron width, tau polarization, forwardbackwardasymmetries -- Beampolarizationiscritical for line shape and polarizedasymmetry. At TLEP, polarization time is 150 hours. Polarizationwigglers are necessary, also, polarimeters and spin rotators, etc… -- new measurements of the Z mass and widths (electronand neutrino) require line shape precision scan – unique to a circular machine. precisionaim: 0.1 MeV on mZ, Z -- Longitudinal polarizationrequiresdedicatedstudy to understandwhatpolarizationlevel canbemaintained in collision for a givenluminosity. Top-up injection should help a lot. This is a more important endeavour. (year) aimsin2Weff = few 10-6 . -- there are othersystematicerrorsrelated to luminositymeasurement and detectionuncertaintieswhichneed to beaddressed as well. -- suggest a workshop/working group for this.

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