Electr Elec troweak eak pr precisio ision me measureme ments - PowerPoint PPT Presentation

CERN 4-5 March 2019 500-1-001 - Main Auditorium 0 E 3 n : d 3 s 1 5 , 9 M 1 0 a 2 r 2 r a 0 M 1 9 4 , 1 s t 8 r : a 3 t OVERVIEW OF THE 0 S FCC CONCEPTUAL DESIGN REPORT h / 9 t t p 4 3 s : 9 / 8 / i 7 n / d t i c e n o v . c e r h / e n . c Electr Elec troweak eak pr precisio ision me measureme ments at at F FCC- CC-ee ee Roberto Tenchini INFN Pisa

30 years from the start of LEP (1989) and 36 years since the discovery of Z and W bosons (1983) Direct measurement of W mass Gfitter group, Nov 2014 400 Higgs mass [GeV] compared to SM tree level calculation Measurements Results of the EW fit 350 LHC 90% CL, PDG 68% CL, LEPEWWG 300 68% CL, Gfitter 68% CL, Gfitter (incl. direct searches) 250 200 150 100 50 0 1995 2000 2005 2010 2015 Year Precise Z mass measurement at LEP Sensitivity to EW loops Sensitivity of loops to new particles

FCC-ee operation model assumed for the CDR • Integrated luminosity goals for Z and W physics LEP (4 IPs) • 150 ab - 1 around the Z pole (~ 25 ab - 1 at 88 and 94 GeV, 100 ab - 1 at 91 GeV) 0.6 fb -1 2.4 fb -1 • 12 ab - 1 around the WW threshold (161 GeV with ±few GeV scan) working point luminosity/IP total luminosity (2 IPs)/ yr physics goal run time [10 34 cm -2 s -1 ] [years] Z first 2 years 100 26 ab -1 /year 150 ab -1 4 Z later 200 48 ab -1 /year W 25 6 ab -1 /year 12 ab -1 2 These are H 7.0 1.7 ab -1 /year 5 ab -1 3 important, top (350 GeV) 0.8 0.2 ab -1 /year 0.2 ab -1 1 too, for WW top later (365 GeV) 1.4 0.34 ab -1 /year 1.5 ab -1 4 physics !

EW Physics observables at FCC-ee OkuWW (10 8 WW) TeraZ (5 X 10 12 Z) From data collected in a lineshape energy scan: From data collected around and above the WW threshold: • Z mass (key for jump in precision for ewk fits) • W mass (key for jump in precision for ewk fits) • Z width (jump in sensitivity to ewk rad corr) • W width (first precise direct meas) • R l = hadronic/leptonic width (α s (m 2 Z ), lepton • R W = Γ had / Γ lept (α s (m 2 Z )) couplings, precise universality test ) • Γ e , Γ µ , Γ τ (precise universality test ) • peak cross section (invisible width, N ν ) • Triple and Quartic Gauge couplings (jump in • A FB ( µµ ) (sin 2 θ eff , α QED (m Z 2 ), lepton couplings) precision, especially for charged couplings) • Tau polarization (sin 2 θ eff , lepton couplings, α QED (m Z 2 )) • R b , R c, A FB (bb), A FB (cc) (quark couplings)

Determination of Z mass and width • uncertainty on m Z (≈ 100 KeV) is dominated by the correlated uncertainty on the centre-of-mass energy at the two off peak points at FCC-ee continuous E CM calibration (resonant depolarization) gives ∆ E CM ≈ 10 KeV (stat) + 100 KeV (syst) • the off peak point-to-point anti-correlated uncertainty has a similar impact (≈ 100 KeV) on Γ Z • Requirements on the detector are not crucial for these two measurements, but should not be forgotten either: control of acceptance over √ (s) is important. The exact choice of the off peak energies for m Z , Γ Z is not very crucial at FCC-ee (differently from LEP) because of the high statistics. Instead the exact choice is crucial for α QED (m Z 2 ) which is driving the choice of √s - ≈ 88 GeV and √s + ≈ 94 GeV (slide 19).

FCC-ee Beam Polarization and Energy Calibration (I) 1. Priority from Physics : Δ E/E ~O(10 -6 ) around Z pole and WW threshold à Z,W mass&width 2. Exploit natural transverse beam polarization present at Z and W (E.Gianfelice, S.Aumon) 2.1 This is a unique capability of e+e- circular colliders 2.2 Sufficient level is obtained if machine alignment is good enough for luminosity 2.2 Resonant depolarization has intrinsic stat. precision of <~10 -6 on spin tune (I.Koop) 2.3 Required hardware (polarimeter, wigglers depolarizer) is defined & integrated (K.Oide) 2.4 Running mode with 1% non-colliding bunches and wigglers defined (Koratzinos) FCC-ee simulation of resonant depolarization I. Koop, Novosibirsk LEP 6 Alain Blondel Physics at the FCCs 04/03/19 260 seconds sweep of depolarizer frequency

FCC-ee Beam Polarization and Energy Calibration (II) 3. From spin tune measurement to center-of-mass determination ν s = ​𝑕 −2 / 2 ​𝐹𝑐/𝑛𝑓 = ​𝐹𝑐/ 0.4406486(1) 3.1 Synchrotron Radiation energy loss (9 MeV @Z in 4 ‘arcs’) calculable to < permil accuracy 3.3 Beamstrahlung energy loss (0.62 MeV per beam at Z pole), compensated by RF (Shatilov) 3.4 RF asymmetries issue solved with RF at only one point for Z and W running 3.5 E b + vs E b asymmetries and energy spread can be measured/monitored in expt: - e+e- → µ + µ - longitudinal momentum shift and spread (P. Janot) Polarimeters: D. Shatilov: Monitor beam beam energy polarization, spectrum provide also without/with relative beam beamstrahlung energy monitoring 5. Additional errors from betatron motion in non-planar orbits estimate < 100keV Munchnoy 6. point to point errors monitored with e+ γ polar/spectrometer or µ + µ - pairs at ~keV precision è On track to match goal of 100 (300) keV errors on E CM at Z (WW) energies (pt-to-pt smaller) 7

Γ Z and beam energy spread 0.3 0.2 0.1 • The beam energy spread affects the 0 Δσ / σ (%) lineshape changing the cross section by − 0.1 − 0.2 − 0.3 Difference 0.4 − • The size of the energy spread (≈ 60 MeV) and its impact on 43 43.5 44 44.5 45 45.5 46 46.5 47 47.5 48 E b (GeV) Γ Z (≈4 MeV) is similar to LEP, but the approach to tackle the corresponding systematic uncertainty different because of FCC-ee beam crossing angle • At LEP it was controlled at 1% level by measuring the longitudinal size of the beam spot, at FCC-ee can be measured with similar precision from the scattering angles of µ + µ - events

Control of energy spread with µ + µ - • FCC-ee: Asymmetric optics with Patrick Janot beam crossing angle α of 30 mrad One million dimuon events • α is measured in e+e- à µ + µ - ( γ ) Events Spread (no BS) 5 Spread (BS) 10 = 0.1 mrad σ θ , φ BS=beamstrahlung With ISR Asymmetry = 0.1% ± 4 10 together with γ (ISR) energy, both distributions sensitive to energy spread. 3 10 • Energy spread measured at 0.1% with 10 6 muons (4 min at FCC-ee) − 3 × 10 2 10 5 4 3 2 1 0 1 2 3 4 5 − − − − − Longitudinal Boost, x γ • Current calculations of ISR emission spectrum sufficient • Detector requirement on muon angular resolution 0.1 mrad Can keep related systematic uncertainty on Γ Z at less than 30 keV

Measurement of luminosity, σ had and neutrino families • Realistic goal on theoretical uncertainty from higher order for low angle Bhabha is 0.01% (*), corresponding to a reduction of a factor 8 in uncertainty on number of light neutrino families, N ν (we are already at mid road ≈ 0.04% ) • Another goal is a point to point relative normalization of 5 10 -5 for Γ Z (*) Blondel, Jadach et al., arXiv:1812.01004 • To match this goal an accuracy on detector construction and boundaries of ≈ 2 µ m is required • clever acceptance algorithms, a la LEP, with independence on beam spot position should be extended to beam with crossing angle • Can potentially reach an uncertainty of 0.01% also with e+e- à γγ , statistically 1.4 ab -1 are required (theory uncertainty already at this level, requires control of large angle Bhabha) • Measurement of N ν with similar precision provided by Z γ , Z à νν events (above the Z)

FCC-ee strategy for neutral couplings and sin 2 θ eff • Muon forward backward asymmetry at pole, A FB µµ (m Z ) gives sin 2 θ eff with 5 10 -6 precision (at least) • uncertainty driven by knowledge on CM energy ( point to point energy errors ) • assumes muon-electron universality • Tau polarization can reach similar precision without universality assumption • tau pol measures A e and A τ , can input to A FB µµ =3/4 A e A µ µ to measure µµ separately electron, muon and tau couplings, (together with Γ e , Γ µ , Γ τ ) • Asymmetries A FB bb , A FB cc provide input to quark couplings together with Γ b , Γ c NOTE that LEP approach was different: all asymmetries were limited by statistics and primarily used to measure sin 2 θ eff

tau polarization plays a central role at FCC-ee A pol = σ F , R + σ B , R − σ F , L − σ B , L • Separate measurements of = − A f σ tot A e and A τ from A polFB = σ F , R − σ B , R − σ F , L + σ B , L 3 4 A e = − σ tot At FCC-ee • very high statistics: improved knowledge of tau parameters (e.g. branching fraction, tau decay modeling) with FCC-ee data • use best decay channels ( e.g. τ à ρν τ decay very clean), note that detector performance for photons / π 0 very relevant à measure sin 2 θ eff with 6.6 10 -6 precision

A FB bb : from LEP to FCC-ee LEP combination dominated by statistics, projection for FCC-ee considers conservative reduction of various uncertainty components 0.00002 Most of this depends on stat. Can be reduced with improved calculations and proper choices of analysis methods (e.g. measure the asymmetry as a function of jet parameters, etc.) Simple method to reduce QCD corrections for lepton analysis: raise cut un lepton momentum, Improved measurements also for as statistics is no longer the charm sector: A FB cc dominant

Precisions on coupling ratio factors, A f Relative precisions, but for sin 2 θ eff