Precision EW measurements at Future accelerators

Transcription

1 Precision EW measurements at Future accelerators Will redo te LEP program in a few minutes. 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 1

2 : top mass predicted (LEP, mostly Z mass&width)03/94 top quark discovered (Tevatron) 06/95 t HooU and Veltman get Nobel Prize 10/98 (c) Sfyrla

3 Higgs boson mass cornered (LEP H, M Z etc +Tevatron m t, M W ) Higgs Boson discovered (LHC) Englert and Higgs get Nobel Prize (c) Sfyrla

4 Is it the end?

5 Is it the end? Certainly not! -- Dark mader -- Baryon Asymmetry in Universe -- Neutrino masses are experimental proofs that there is more to understand. We must con2nue our quest HOW?

6 1. ELECTROWEAK PRECISION TESTS (EWPT) Due to the non-abelian Gauge theory, Electroweak observables offer sensi2vity to electroweakly coupled new par2cles if they are nearby in Energy scale or -- if they violate symmetries of the Standard Model (in which case, no «decoupling») Higgs boson and top-bomom mass splinng cons2ture such symmetry viola2ons 2. TESTS OF ELECTROWEAK SYMMETRY BREAKING (EWSB) Is the H(125) a Higgs boson? à couplings propor2onal to mass? if not could be more complicated EWSB e.g. more Higgses à Higgs supposed to cancel WW scamering anomalies at TeV scale does this work? 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 6

7 Alain Blondel WIN 05 June 2005 EWRCs relations to the well measured G F m Z α QED at first order: Δρ = α /π (m top /m Z ) 2 - α /4π log (m h /m Z ) 2 ε 3 = cos 2 θ w α /9π log (m h /m Z ) 2 δ νb =20/13 α /π (m top /m Z ) 2 complete formulae at 2d order including strong corrections are available in fitting codes e.g. ZFITTER, GFITTER

8 The main players Inputs: G F = (6) 10 5 /GeV 2 from muon life lme M Z = ± GeV Z line shape α = 1/ (44) electron g EW observables sensi2ve to new physics: M W = ± LEP, Tevatron sin 2 θ eff = W ± WA Z pole asymmetries Nuisance paramenters: α (M Z ) =1/ (14) hadronic correc2ons to running alpha α S (M Z ) =0.1187(7) strong coupling constant m top = ± 0.76 GeV from LHC+Tevatron combinalon m H = ATLAS ± 0.37 (stat) ± 0.18 (syst) GeV ± CMS ± 0.26 (stat) ± 0.14 (syst) GeV 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 8

9 FUTURE ACCELERATORS 1. High Luminosity LHC (3000 h 14 TeV) à 2035 An essenlally approved program 2. ILC as GigaZ, MegaW, Higgs and top factory A very mature study of a new technique 3. Circular e+e- Z,W,H,top factories A «young» study of a very mature technique TeV hadron collider $$$$$$$$$$$ 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 9

10 SNOWMASS report References: LEP Z peak paper arxiv:hep-ex/ Phys.Rept. 427: ,2006 LEP2 Electroweak paper arxiv: [hep-ex] Phys. Rep. Gfider Group arxiv: v2 The Electroweak Fit of the Standard Model auer the Discovery of a New Boson at the LHC J. Erler and P. Langacker ELECTROWEAK MODEL AND CONSTRAINTS ON NEW PHYSICS PDG dec 2011 «and references therein» Alain Blondel Precision EW measurements 15 July 2015 at future accelerators 10

11 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 11

12 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 12

13 NB (AB): lme scale (2030++) is typical of any new CERN or with CERN contribulon; no real funding unll HL-LHC upgrade is complete. 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 13

14 hmp://cern.ch/fcc and hmp://cern.ch/fcc-ee first 15 July 2015 NB (AB): lme scale for FCC-ee similar to CLIC (2030++) Alain Blondel Precision EW measurements at future accelerators 14

15 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 15

16 Goal performance of e+ e- colliders FCC-ee as Z factory: Z (possibly with crab-waist) possible upgrade complementarity ww NB: ideas for lumi upgrades: -- ILC arxiv: (not in TDR). Upgrade at 250GeV by reconfiguralon auer 500 GeV running; under discussion) -- FCC-ee (crab waist) 16

17 At the end of LEP: Phys.Rept.427: ,2006 N ν = ± σ :^)!! This is determined from the Z line shape scan and dominated by the measurement of the hadronic cross-sec2on at the Z peak maximum è The dominant systema2c error is the theore2cal uncertainty on the Bhabha cross-sec2on (0.06%) which represents an error of ± on N ν Improving on N ν by more than a factor 2 would require a large effort to improve on the Bhabha cross-section calculation!

18 Neutrino coun2ng at TLEP given the very high luminosity, the following measurement can be performed

19 Beam polarizalon and TLEP Precise meast of E beam by resonant depolarizalon ~100 kev each +me the meast is made At LEP transverse polarizalon was achieved roulnely at Z peak. instrumental in 10-3 measurement of the Z width in 1993 led to predic+on of top quark mass ( GeV) in March 1994 Polarizalon in collisions was observed (40% at BBTS = 0.04) At LEP beam energy spread destroyed polarizalon above 60 GeV σ E E 2 / ρ è At TLEP transverse polariza+on up to at least 80 GeV to go to higher energies requires spin rotators and siberian snake TLEP: use single bunches to measure the beam energy conlnuously no interpola+on errors due to +des, ground mo+on or trains etc << 100 kev beam energy calibralon around Z peak and W pair threshold. Δm Z ~0.1 MeV, ΔΓ Z ~0.1 MeV, Δm W ~ 0.5 MeV

20 350 GeV: the top mass Advantage of a very low level of beamstrahlung Could potentially reach 10 MeV uncertainty (stat) on m top From Frank Simon, presented at 7 th TLEP-FCC-ee workshop, CERN, June 2014

21 X M Z MeV/c2 Physics Present precision Input ±2.1 A Sample of Essenlal Quanlles: Z Line shape scan TLEP stat Syst Precision MeV <±0.1 MeV TLEP key E_cal Challenge QED correclons Γ Z MeV/c2 Δρ (T) (no Δα!) ±2.3 Z Line shape scan MeV <±0.1 MeV E_cal QED correclons R l α s, δ b ± N ν Unitarity of PMNS, sterile ν s ±0.008 R b δ b ± A LR M W MeV/c2 m top MeV/c2 Δρ, ε 3, Δα (T, S ) Δρ, ε 3, ε 2, Δα (T, S, U) ± ± 15 Input ± 900 Z Peak ± Z Peak Z+γ(161 GeV) ± Z Peak ± Z peak, polarized Threshold (161 GeV) Threshold scan Stalslcs ->lumi meast Stalslcs Stalslcs, small IP ± bunch scheme 0.3 MeV <1 MeV E_cal & Stalslcs 10 MeV E_cal & Stalslcs QED correclons QED correc2ons to Bhabha scat. Hemisphere correlalons Design experiment QED coreclons Theory limit at 100 MeV?

22 Theore2cal limita2ons R. Kogler, Moriond EW 2013 FCC-ee SM prediclons (using other input) ? ? ? ? Experimental errors at FCC-ee will be mes smaller than the present errors. BUT can be typically mes smaller than present level of theory errors Alain Blondel Precision EW measurements Will require significant theore2cal effort and addi2onal measurements! at future accelerators 22

23 The Higgs 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 23

24 Full HL-LHC W Z H t b τ µ

25 Higgs Produc2on Mechanism in e+ e- collisions Light Higgs is produced by Higgstrahlung process close to threshold Produclon xseclon has a maximum of ~200 ƒ TLEP: /cm 2 /s è HZ events per year (2 million Higgses in 5 years) Z tagging by missing mass e - H Z* e + Z For a Higgs of 125GeV, a centre of mass energy of 240GeV is sufficient è kinemalcal constraint near threshold for high precision in mass, width, seleclon purity

26 ILC Z tagging by missing mass total rate g HZZ 2 ZZZ final state g HZZ4 / Γ H è measure total width Γ H empty recoil = invisible width funny recoil = exolc Higgs decay easy control below theshold e - H Z* e + Z

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28 the 8B$ ILC

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31 This will remain the reserved domain of the hadron colliders with HL-LHC and FCC-hh! 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 31

32 Outlook Future colliders will improve the precision on Electroweak Precision Tests by one to two orders of magnitude, providing inclusive probe of the existence new, weakly coupled, physics. HL LHC will contribute to map the relalve Higgs couplings including dh (4%) and HHH (30%/exp?) Further improvements can be expected (Tevatron, LHC) for m W (5 MeV?) and m top (500 MeV?) e+e- colliders provide -- invisible Higgs width and absolute coupling normalizalon at the ZH thr, -- top mass with <10 MeV precision. -- W mass at threshold and sin 2 θ W eff Circular collider can improve Z mass and width (<0.1 MeV) and m W (beam energy calibralon) and generally provide higher stalslcs è invisible widths of Higgs and Z bosons. à another order of magnitude HHH coupling will remain above 10% level unll the 100 TeV collider. WW scadering is best done at hadron colliders More theore2cal work and dedicated measurements will be required to match improving experimental errors! 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 32

33 Status of Tevatron W mass CDF and DØ have world s most precise measurements based on 20% and 50% of their data 1.1M and 1.7M Ws, resp. MT is the most sensilve single variable, lepton PT and MET used also Precision lepton response (0.01%) and recoil models (1%) built up from Z dileptons, Z mass reproduced to 6X LEP precision MW precision: CDF 19 MeV, DØ 23 MeV, LEP2 33 MeV PRL 108 (2012) PRD 89 (2014) world average: 15 MeV 33

34 Prospects for Tevatron W mass arxiv: projected Largest single uncertainles are stat. and PDF syst. 2X PDF improvement and incremental improvement elsewhere results in 9 MeV projected final Tevatron precision <10 MeV precision is well molvated to further confront indirect precision (11 MeV) 34

35 Prospects for LHC W mass Phys.Rev.D83: ,2011 The LHC has excellent detectors and semi-infinite stalslcs and thus has a good a priori prospect for a <10-MeV measurement Biggest three obstacles to surmount: PDFs: sea quarks play a much stronger role than the Tevatron. Need at least 2X bemer PDFs. Momentum scale Recoil model/met arxiv:

36 Higgs factory performances Precision on couplings, cross seclons, mass, width, Summary of the ICFA HF2012 workshop (FNAL, Nov. 2012) arxiv1302:3318 (as available at the +me) Coupling precision 1-4% with 3000 h -1 LC adds Inv + total widths at % level Circular Higgs Factory precision at few permil level.

37 NB without TLEP the SM line would have a 2.2 MeV width in other words... Δ(Δρ)= ± several tests of same precision

38 The LHC is a Higgs Factory! 1M Higgs already produced more than most other Higgs factory projects. 15 Higgs bosons / minute and more to come (gain factor 3 going to 13 TeV) Difficulties: several production mechanisms to disentangle and significant systematics in the production cross-sections σ prod. Challenge will be to reduce systemalcs by measuring related processes. σ iàf observed σ prod (g Hi ) 2 (g Hf ) 2 Γ H extract couplings to anything you can see or produce from if i=f as in WZ with Hà ZZ à absoulte normalizalon

39 From the EW fit Δρ = Example (from Langacker, Erler PDG 2011) Δρ =ε 1 =α(m Z ). T ε 3 =4 sin 2 θ W α(m Z ). S -- is consistent with 0 at 1σ (0= SM) -- is sensilve to non convenlonal Higgs bosons (e.g. in SU(2) triplet with funny v.e.v.s) -- is sensilve to Isospin violalon such as m t m b Measurement implies 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 39

40 Similarly Would be sensilve to a doublet of new fermions where LeU and Right have different masses etc (neutrinos are already included) Note that ozen EW radia2ve correc2ons do not decouple with mass => a very powerful tool of inves2ga2on Δρ = α /π (m top /m Z ) 2 - α /4π log (m h /m Z ) 2 ε 3 = cos 2 θ w α /9π log (m h /m Z ) 2 δ νb =20/13 α /π (m top /m Z ) 2 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 40

41 Back to the future 30 years later and with experience gained on LEP, LEP2 and the B factories we can propose a Z,W,H,t factory of many 2mes the luminosity of LEP, ILC, CLIC CERN is launching a 5 years interna2onal design study of Circular Colliders 100 TeV pp collider (FCC-hh) and high luminosity e+e- collider (FCC-ee) IHEP in China is studying CEPC a km ring, e+e- Higgs factory followed by HE pp.

42 NB Z pole amount for 0.3.MeV on m Z LHC à 5 MeV (0.1) July 2015 Alain Blondel Precision EW measurements at future accelerators 42

43 Higgs Physics with e + e - colliders above 350 GeV? 1. Similar precisions to the 250/350 GeV Higgs factory for W,Z,b,g,tau,charm, gamma and total width. Invisible width best done at GeV. 2. dh coupling possible with similar precision (2% full ILC) as HL-LHC (4%) 3. Higgs self coupling also very difficult precision ~20% at 1 TeV similar to HL-LHC prelim. eslmates (30% each exp) 10-20% at 3 TeV (CLIC) è percent-level precision needs 100 TeV pp machine è For the study of H(126) alone, and given the existence of HL-LHC, an e+ecollider with energy above 350 GeV is not compelling w.r.t. one working in the 240 GeV 350 gev energy range. è The stronger mo2va2on for a high energy e+e- collider will exist if new par2cle found (or inferrred) at LHC, for which e+e- collisions would bring substan@al new informa@on

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