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Importance of Beam Parameters for e+e- Colliders - Beam Polarization, Luminosity Measurement, Transverse Beam Energy Cal

This article discusses the significance of beam parameters, such as luminosity measurement, longitudinal and transverse beam polarization, and beam energy calibration, for e+e- colliders. It also explores the potential for direct discovery of exotic particles and the importance of achieving high precision measurements.

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Importance of Beam Parameters for e+e- Colliders - Beam Polarization, Luminosity Measurement, Transverse Beam Energy Cal

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  1. “on the importance of beams parameters for e+e- colliders Luminosity Luminosity measurement longitudinal beam polarization • transverse beam energy calibration, beam energy profile/spread” Alain Blondel Physics at the FCCs

  2. FCC-eeLuminosity Z WW HZ tt LEPx105! Event statistics : ECMerrors: Z peakEcm : 91 GeV 5 1012 e+e- Z WW thresholdEcm : 161 GeV 108 e+e- WW ZH thresholdEcm : 240 GeV 106 e+e- ZH tt thresholdEcm : 350 GeV 106 e+e- tt LEP x 105 LEP x 2.103 Never done Never done 100 keV 300 keV 1 MeV 2MeV

  3. High luminostiy drives the direct discoverypotential: exotic Higgs decays, dark sectors, hidden photons, new Higgs bosons, Axions Right-Handed neutrinos Alain Blondel Physics at the FCCs

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  8. BeamPolarizationcanprovide main ingredient to PhysicsMeasurements Transverse beampolarizationprovidesbeamenergy calibration by resonantdepolarization  lowlevel of polarizationisrequired (~10% issufficient)  at Z & W pair thresholdcomesnaturally  at Z use of asymmetricwigglers at beginning of fillssincepolarization time isotherwisevery long.  couldbeusedalso at ee H(126) (depending on exact mH !)  use ‘single’ non-collidingbunches and calibratecontinuously duringphysicsfills to avoid issues encountered at LEP  thisis possible with e+ and e- Compton polarimeter(commercial laser)  shouldcalibrate at energiescorresponding to half-integer spin tune must becomplemented by analysis of «averageE_beam» to E_CM relationship For beamenergieshigherthan ~90 GeVcanuse ee  Z  or ee  WW events to calibrateECMat 2-4 MeV level: matches requirements for mH and mtopmeasts Aim: Z mass & width to ~100 keV (stat: 10 keV) W mass &width to ~500 keV (stat : 300 keV) Alain Blondel Physics at the FCCs

  9. BeamPolarization and Energy calibration We have concludedthat first priorityis to achieve transverse polarization in a waythatallowscontinuousbeam calibration by resonantdepolarization (energymeasurementevery ~10 minutes on ‘monitoring’ single bunches) - This is a unique feature of circulare+e- colliders - baseline running schemedefinedwith monitoring bunches, wigglers, polarimeter - the question of the residualsystematicerrorrequiresfurtherstudies of the relationshipbetween spin tune, beamenergy at IRs, and center-of-mass energy  targetis O(100keV) at Z and W pair thresholdenergies (averaged over data taking) ‘Do wewant longitudinal polarization’?  lowerpriority at Z, W, top: no information thatwecannotobtainotherwise fromunpolarized AFBasymmetriesor final state polarization (top, tau) + toomuchloss of luminosity in present running scheme to providegain in precision.

  10. All exceeds the theoreticalprecisionfrom(mZ) (310-5) or the comparisonwithmW (500keV) But thisprecision on sin2leptWcanonlybeexploited at FCC-ee!

  11. Longitudinal polarization: reduction of polarization due to continuous injection The collidingbuncheswillloseintensitycontinuouslydue to collisions. In FCC-eewith 4 IPs, L= 28 1034/cm2/s beamlifetimeis 213 minutes In FCC-eewith 2 IPs, L= 1.4 1036/cm2/s beam life time is 55minutes Luminosityscalesinversely to beam life time. The injected e+ and e- are not polarized asymptoticpolarizationisreduced. Assume herethat machine has been wellcorrected and beams (no collisions, no injection) canbepolarized to nearly maximum. (ElianaGianfelice in Rome talk) (polarization time is 26h)

  12. We have simulated the simultaneouseffect of -- naturalpolarization -- beamconsumption by e+e- interactions -- replenishmentwithunpolarizedbeams assumingoptimisticallya maximal 90% asymptoticpolarization Running at full luminosity P_max=0.03! P_eff=0.03 Running at 10% Lumi P_max=0.24, P_eff=0.21 Running at 1% Lumi P_max=0.66, P_eff=0.5

  13.  ALRscales as 1/(P2L) Optimum around a reduction of luminosity by a factor 18. This isstill a luminosity of ~1035 per IP… and the effective polarizationis 30%. This isequivalent to a 100% polarizationexptwithluminosityreduced by 180.

  14. FCC-ee beam polarization and Energy Calibration EPOL group: K OideCERN/KEK, S. Aumon, P. Janot , D. El Kechen, T. Lefevre, A. Milanese, T. Tydecks, J. Wenninger, F. Zimmermann, CERN W. Hillert, D Barber DESY, D. Sagan, CornellG. Wilkinson, Oxford E Gianfelice-Wendt, FERMILABA Blondel, M Koratzinos, GENEVA P. Azzurri (Pisa)M Hildreth, Notre-Dame USAI Koop , N Muchnoi, A Bogomyagkov, S. Nikitin, D. Shatilov BINP; NOVOSIBIRSK

  15. Somereferences (not a complete set!): B. Montague, Phys.Rept. 113 (1984) 1-96; Polarization at LEP, CERN Yellow Report 88-02; Beam Polarization in e+e- , AB, CERN-PPE-93-125 Adv.Ser.Direct.High Energy Phys. 14 (1995) 277-324; L. Arnaudon et al., Accurate Determination of the LEP Beam Energy by resonant depolarization, Z. Phys. C 66, 45-62 (1995). Spin Dynamics in LEP http://dx.doi.org/10.1063/1.1384062 Precision EW Meastson the Z Phys.Rept.427:257-454,2006 arXiv:0509008v3 D.P. Barber and G. Ripken``Handbook of Accelerator Physics and Engineering” World Scientific (2006), (2013)D.P. Barber and G. Ripken, Radiative Polarization, Computer Algorithms and Spin Matching in Electron Storage Rings arXiv:physics/9907034 for FCC-ee: First look at the physics case of TLEP arXiv:1308.6176, JHEP 1401 (2014) 164DOI: 10.1007/JHEP01(2014)164 M. Koratzinos FCC-ee: Energy calibration IPAC'15 arXiv:1506.00933 E. Gianfelice-Wendt: Investigation of beam self-polarization in the FCC-eearXiv:1705.03003 October EPOL workshop: https://indico.cern.ch/event/669194/

  16. Requirementsfromphysics • Center-of-mass energydeterminationwithprecision of  100 keVaround the Z peak • Center-of-mass energydeterminationwithprecision of  300 keVat W pair threshold • 3. For the Z peak-cross-section and width, requireenergy spread uncertainty E/E =0.2% • NB: at 2.3 1036/cm2/s/IP : full LEP statistics106  2.107qqin 6 minutes in eachexpt • -- use resonantdepolarization as main measuringmethod • -- use pilot bunches to calibrateduringphysics data taking: 100 calibrations per day10-6rel. each • -- long lifetime at Z requires the use of wigglers at beginning of fills • takedata at points where self polarizationisexpected • s =ECM = x 0.8812972 GeV • Giventhe Z and W widths of 2 GeV, thisiseasy to accommodatewithlittleloss of statistics. • the Higgss-channel 125.09+-0.2 corresponds to vs = 141.94+-022 (need to shift beam energies) Alain Blondel Physics at the FCCs

  17. Simulations of polarizationlevelwith SITROS orbit and emittance corrections needed for the FCC-eeluminosity are sufficient to ensureusefullevels of polarization@Z &WW E. Gianfelice at the W at the Z Excellent level of polarization at the Z (evenwithwigglers) and sufficient at the W. Alain Blondel Physics at the FCCs

  18. scan proposed for FCC-ee E(peak)= 91.2 GeV spin tune = 103.5 E(-4) = 87.9 GeV spin tune = 99.5 `-4’ E(+4) = 93.8 GeV spin tune = 107.5 `+4’ E(+5) = 94.7 GeV spin tune = 108.5 `+5’ 2/3 at peak 1/3 off peak. P. Janot Alain Blondel Physics at the FCCs

  19. These are the beamenergies for the W thresholdmeasurement P. Azzurri

  20. A limitation: Touschekeffect Oide-sanpointed out that the ‘pilot bunches’ wouldloseparticles due to Touschekeffect Indeedthey have suchsmallemittance that the bunch population reduces fast if itislargerthat 4 1010 at the Z.  limit pilot bunchintensity to that value thisisless of an issue at the W Tobias Tydeckshas calculated the effect and writtenit up in the CDR! Alain Blondel Physics at the FCCs

  21. Hardware requirements: wigglers Given the long polarization time at Z, wigglerswillbenecessary. An agreement wasreached on a set of 8 wigglerunits per beam Polarizationwigglers 8 units per beam, as specified by ElianaGianfelice B+=0.7 T L+ = 43cm L-/L+ = B+/B- = 6 at Eb= 45.6 GeV and B+= 0.67 T => P=10% in 1.8H Eb = 60 MeV Ecrit=902 keV placede.g. in dispersion-free straight section H and/or F Alain Blondel Physics at the FCCs

  22. First single pole magnetic concept, keeps some of the ideas of the LEP design, in particular the “floating” poles narrower (200 mm) lateral poles central main coils beam mass ≈ 4 tons side trim coils wider (300 mm) central pole A. Milanese

  23. Hardware requirements: polarimeters e’ 2 Polarimeters, one for eachbeam Backscattered Compton  +e   + e532 nm (2.33 eV) laser; detection ofphotonand electron. Change upon flip of laser circularpolarization beamPolarization0.01 per second End point of recoilelectron beamenergy monitoring  4 MeV per second e laser  install photon-electron IP on inner ring in points H and F (Oide) Alain Blondel Physics at the FCCs Munchnoy

  24. Depolarization This is not-so trivial in FCC-ee! 16700 bunchescirculate time-between-bunches = 19ns, depolarize one-and-only-one of them. Kicker must have fast (<9ns) rise. • The LHC TF system works essentially on a bunch by bunch basis for 25ns. They would provide a transverse kick of up to ~20 mrad at the Z peak with ~10 MHz bandwidth. This is 10x more than what we may need- • a priori OK ! Alain Blondel Physics at the FCCs

  25. LEP long sweepworkswell at the Z. Severaldepolarizationsneeded:eliminateQsside band and 0.5 ambiguity Lesswell at the W: the Qsside bands are much more excitedbecause of energy spread, neediterationswith smaller and smallersweeps– work in progress. seeI. Kooppresentation.  Fourier analysis shows the side band situation at W. FCC-W spectrometer1/s First attempt at ‘LEP’ multiple sweep technique  Alain Blondel Physics at the FCCs

  26. Fromresonantdepolarization to Center-of-mass energy -- 1. from spin tune to beamenergy-- The spin tune may not be en exact measurement of the average of the beamenergy along the magnetictrajectory of particles. Additional spin rotations maybias the issue. Anton Bogomyagkovand ElianaGianfelicehave made manyestimates. synchrotron oscillations E/E -2 10-14 Energy dependent momentum compaction E/E 10-7 Solenoid compensation 2 10-11 Horizontal betatron oscillations E/E 2.5 10-7 Horizontal correctors*) E/E 2.5 10-7 Vertical betatron oscillations **) E/E 2.5 10-7 Uncertainty in chromaticity correction O(10-6 ) E/E 5 10-8 invariant mass shift due to beampotential 4 10-10 *) 2.5 10-6if horizontal orbit change by >0.8mm between calibration isunnoticed or if quadrupolestabilityworsethan 5 microns over that time. considerthat 0.2 mm orbitwillbenoticed **) 2.5 10-6for vertical excursion of 1mm. Consider orbit can be corrected better than 0.3 mm. Alain Blondel Physics at the FCCs

  27. Energy gains (RF) and energylosses (Arcs and Beamsstrahlung) At LEP the disposition of the RF units on eachside of the experiments had the effectthatanyasymmetry in the RF would change the energy of the beams at the IP, but not the averageenergy in the arcs. At FCC-ee, because the sequenceis RF – energyloss– IP – energyloss- RF sucherrors have littleeffect on the relationshipbetweenaverageenergy in the arcs and that at the IP. Theycaninduce a differencebetween e+ and e- (canbemeasured in expt!) Oide-san has shownthat one canindeed put all the RF in one straight section for Z and W running. Jorg Wenninger. Alain Blondel Physics at the FCCs

  28. Opposite sign dispersion at IP M. Koratzinos FCC-ee 45GeV Dima El Khechen note thatthisis an issue both for horizontal and vertical dispersion For FCC-ee at the Z we have: Dispersion of e+ and e- beams at the IP is 20um (uncorrelated average) –the difference in dispersion matters in this calculation –m’ply by SQRT(2), so . Sigma_y is 30nm Sigma_E is 0.132%*45000MeV=60MeV Delta_ECM is therefore 4MeV for a 10% offset Note that we cannot perform Vernier scans like at LEP, we can only displace the two beams by ~10%sigma_y Assume each Vernier scan accurate to 1% sigma_y, we need 100 vernier scans to get an ECM accuracy of 40keV – suggestion: vernier scan every hour It is likely that Van der Meer scans will be performed regularly at least once per hour or more. (100 per week)

  29. Beamstrahlung Beamstrahlungisemission of photons by (e.g. e+-) in the field of the other (e-+) In a linearcolliderlowenergytail of the collision energy distribution and a systematicbias. BUT In a circularcollideritinitiates a synchrotron oscillation! The particleenergy distribution remainssymmetric, but the energy spread isverymuchenlarged. Quantitatively the energyloss at the the IP in presence of beamstrahlungis0.62 MeV As DmitryShatilov points out thisenergylossiscompensated by the RF and the differencebetweencollidingbunches and non-collidingbuncheswillremainsmall the uncertaintyisassumed to belessthan a few percent of this (~ 20keV) D. Shatilov Alain Blondel Physics at the FCCs

  30. Without Beamstrahlung Gauss with E= E0 Lg10(/0) E/E0

  31. with Beamstrahlung E = 45.6 GeV E0/E = 0.00038, E/E = 0.00132, Black line: Gauss with E = 3.4 E0 Lg10(/0) E/E0 Energy acceptance: 1.3% = 34.2 E0

  32. E = 80 GeV E0 = 0.00066, E = 0.00153, Black line: Gauss with E = 2.3 E0 Lg10(/0) E/E0 Energy acceptance: 1.3% = 19.7 E0

  33. Determination of Energy spread At the Z peakwecollect 106  events every 5 minutes theirkinematicsisaffected by -- energy spread -- e+ vs e- energydifference. Patrick has shownthatindeedboth canbedeterminedwithextremely sufficientprecisionwith a few minutes up to a few hours. OK OK P. Janot Alain Blondel Physics at the FCCs

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  36. Heavy Flavourtagging With the very clean background conditions of FCC-eeitis possible to design the experimentalbeam pipe with a radius of 1.2cm. This meansthat an impact parameter precision of 4m (for 10 GeV/c particles) canbeachieved. The IR dimensions : Z WW ZH tt tt+ are alsoverysmallso the b-taggingefficiencyshouldbesimilar to ILC – or perhapsbetter. The practical applications in measurements of Rb, AFBb tau lifetime, etc… remain to be explored. Alain Blondel Physics at the FCCs

  37. Conclusions FCC-ee design studyisplacing a high emphasis on the fundamentals of systematicerrors -- Maximize total luminosity -- luminositymeasurement -- beamenergy calibration with transverse beampolarization -- the need for longitudinal polarizationis not verycompelling, and itisdifficult to obtainit withoutlosing 1-2 orders of magnitude in luminosity Wecanconcludethat the energy calibration for Z and W will match the goals. It couldbebetterwith more work Wecanconlcudethatluminositywillbemeasured at 2 10-4 relative levelwithlow angle Bhabhascattering. Cross-calibration withee  mightimprove the absolutenormalization Alain Blondel Physics at the FCCs

  38. Alain Blondel Physics at the FCCs

  39. LEP Resonantdepolarization, 1991 variation of RF frequency to eliminatehalfinteger ambiguity

  40. Manyeffectsspoil the calibration if itisperformed outsidephysics time -- tidesand otherground motion -- RF cavity phases -- histeresiseffects and environmentaleffects (trains…etc) Alain Blondel Physics at the FCCs

  41. by 1999 wehad an excellent model of the energy variations… but wewere not measuring the Z mass and widthanymore – wewerehunting for the Higgsboson!

  42. PAC 1995 LEP: This wasonlytried 3 times! Best result: P = 40% , *y= 0.04 , one IP FCC-ee Assuming 2 IP and *y= 0.01  reduceluminosity, 1010 Z @ P~30%

  43. Longitudinal polarization at FCC-Z? Main interest: measure EW couplings at the Z peakmost of whichprovidemeasurements of sin2leptW= e2/g2 (mz) (-- not to beconfusedwith -- sin2W = 1- mw2/mz2 Usefulreferencesfrom the past: «polarization at LEP» CERN Yellow Report 88-02 PrecisionElectroweakMeasurementson the Z Resonance Phys.Rept.427:257-454,2006 http://arxiv.org/abs/hep-ex/0509008v3 GigaZ @ ILC by K. Moenig

  44. Longitudinal polarization: reduction of polarization due to continuous injection The collidingbuncheswillloseintensitycontinuouslydue to collisions. In FCC-eewith 4 IPs, L= 28 1034/cm2/s beamlifetimeis 213 minutes In FCC-eewith 2 IPs, L= 1.4 1036/cm2/s beam life time is 55minutes Luminosityscalesinversely to beam life time. The injected e+ and e- are not polarized asymptoticpolarizationisreduced. Assume herethat machine has been wellcorrected and beams (no collisions, no injection) canbepolarized to nearly maximum. (ElianaGianfelice in Rome talk) (polarization time is 26h)

  45. We have simulated the simultaneouseffect of -- naturalpolarization -- beamconsumption by e+e- interactions -- replenishmentwithunpolarizedbeams assumingoptimisticallya maximal 90% asymptoticpolarization Running at full luminosity P_max=0.03! P_eff=0.03 Running at 10% Lumi P_max=0.24, P_eff=0.21 Running at 1% Lumi P_max=0.66, P_eff=0.5

  46.  ALRscales as 1/(P2L) Optimum around a reduction of luminosity by a factor 18. This isstill a luminosity of ~1035 per IP… and the effective polarizationis 30%. This isequivalent to a 100% polarizationexptwithluminosityreduced by 180.

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