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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

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: top mass predicted (LEP, mostly Z mass&width) 03/94 top quark discovered (Tevatron) 06/95 t’Hooft and Veltman get Nobel Prize 10/98 (c) Sfyrla

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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

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Is it the end?

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Certainly not! -- Dark matter -- Baryon Asymmetry in Universe -- Neutrino masses are experimental proofs that there is more to understand. We must continue our quest HOW?

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15 July 2015 Alain Blondel Precision EW measurements at future accelerators 6 Due to the non-abelian Gauge theory, Electroweak observables offer sensitivity to electroweakly coupled new particles 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-bottom mass splitting constiture such symmetry violations 1. ELECTROWEAK PRECISION TESTS (EWPT) 2. TESTS OF ELECTROWEAK SYMMETRY BREAKING (EWSB) Is the H(125) a Higgs boson? couplings proportional to mass? if not could be more complicated EWSB e.g. more Higgses Higgs supposed to cancel WW scattering anomalies at TeV scale does this work?

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Alain Blondel WIN 05 June 2005 relations to the well measured G F m Z QED = m top /m Z ) 2 - log m h /m Z ) 2 at first order: = cos 2 w log m h /m Z ) 2 b =20/13 m top /m Z ) 2 complete formulae at 2d order including strong corrections are available in fitting codes e.g. ZFITTER, GFITTER EWRCs

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

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15 July 2015 Alain Blondel Precision EW measurements at future accelerators 9 FUTURE ACCELERATORS 1. High Luminosity LHC (3000 fb 14 TeV) 2035 An essentially 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 $$$$$$$$$$$

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15 July 2015 Alain Blondel Precision EW measurements at future accelerators 10 SNOWMASS report References: LEP Z peak paper arXiv:hep-ex/ Phys.Rept.427: ,2006arXiv:hep-ex/ LEP2 Electroweak paper arXiv: [hep-ex] Phys. Rep. Gfitter Group arXiv: v2 The Electroweak Fit of the Standard Model after 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»

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

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

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

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15 July 2015 Alain Blondel Precision EW measurements at future accelerators 14 NB (AB): time scale for FCC-ee similar to CLIC (2030++) and first

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

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

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

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

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Beam polarization and TLEP Precise meast of E beam by resonant depolarization ~100 keV each time the meast is made At LEP transverse polarization was achieved routinely at Z peak. instrumental in measurement of the Z width in 1993 led to prediction of top quark mass ( GeV) in March 1994 Polarization in collisions was observed (40% at BBTS = 0.04) At LEP beam energy spread destroyed polarization above 60 GeV E E 2 / At TLEP transverse polarization 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 continuously no interpolation errors due to tides, ground motion or trains etc… << 100 keV beam energy calibration around Z peak and W pair threshold. m Z ~0.1 MeV, Z ~0.1 MeV, m W ~ 0.5 MeV

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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

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A Sample of Essential Quantities: X Physics Present precision TLEP stat Syst Precision TLEP keyChallenge M Z MeV/c2 Input 2.1 Z Line shape scan MeV < 0.1 MeV E_calQED corrections Z MeV/c2 (T) (no !) 2.3 Z Line shape scan MeV < 0.1 MeV E_calQED corrections RlRl s, b Z Peak StatisticsQED corrections N Unitarity of PMNS, sterile ’s Z Peak Z+ (161 GeV) >lumi meast Statistics QED corrections to Bhabha scat. RbRb bb Z Peak Statistics, small IP Hemisphere correlations A LR , 3, (T, S ) Z peak, polarized bunch scheme Design experiment M W MeV/c2 , 3, 2, (T, S, U) ± 15 Threshold (161 GeV) 0.3 MeV <1 MeV E_cal & Statistics QED corections m top MeV/c2 Input ± 900 Threshold scan 10 MeVE_cal & Statistics Theory limit at 100 MeV?

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Theoretical limitations R. Kogler, Moriond EW 2013 Experimental errors at FCC-ee will be times smaller than the present errors. BUT can be typically times smaller than present level of theory errors Will require significant theoretical effort and additional measurements! FCC-ee ? SM predictions (using other input) ? ? Alain Blondel Precision EW measurements at future accelerators 22

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

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b Full HL-LHC Z W H t

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Light Higgs is produced by “Higgstrahlung” process close to threshold Production xsection has a maximum of ~200 fb TLEP: /cm 2 /s 400’000 HZ events per year (2 million Higgses in 5 years) e+e+ e-e- Z* Z H For a Higgs of 125GeV, a centre of mass energy of 240GeV is sufficient kinematical constraint near threshold for high precision in mass, width, selection purity Z – tagging by missing mass Higgs Production Mechanism in e+ e- collisions

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e+e+ e-e- Z* Z H Z – tagging by missing mass ILC total rate g HZZ 2 ZZZ final state g HZZ 4 / H measure total width H empty recoil = invisible width ‘funny recoil’ = exotic Higgs decay easy control below theshold

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the 8B$ ILC

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

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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 relative Higgs couplings including ttH (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 normalization at the ZH thr, -- top mass with <100 MeV precision. -- W mass at threshold and sin 2 W eff Circular collider can improve Z mass and width (<0.1 MeV) and m W (beam energy calibration) and generally provide higher statistics invisible widths of Higgs and Z bosons. another order of magnitude HHH coupling will remain above 10% level until the 100 TeV collider. WW scattering is best done at hadron colliders More theoretical work and dedicated measurements will be required to match improving experimental errors! Outlook 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 32

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Status of Tevatron W mass 33 PRD 89 (2014) PRL 108 (2012) 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 sensitive 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 2012 world average: 15 MeV

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Prospects for Tevatron W mass Largest single uncertainties 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 motivated to further confront indirect precision (11 MeV) 34 projected arxiv:

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Prospects for LHC W mass The LHC has excellent detectors and semi-infinite statistics 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 better PDFs. Momentum scale Recoil model/MET 35 Phys.Rev.D83: ,2011 arxiv:

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

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

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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 prod. Challenge will be to reduce systematics by measuring related processes. i f observed prod (g Hi ) 2 (g Hf ) 2 extract couplings to anything you can see or produce from H if i=f as in WZ with H ZZ absoulte normalization

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

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Similarly Would be sensitive to a doublet of new fermions where Left and Right have different masses etc… (neutrinos are already included) Note that often EW radiative corrections do not decouple with mass => a very powerful tool of investigation = m top /m Z ) 2 - log m h /m Z ) 2 = cos 2 w log m h /m Z ) 2 b =20/13 m top /m Z ) 2 15 July 2015 Alain Blondel Precision EW measurements at future accelerators 40

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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 times the luminosity of LEP, ILC, CLIC CERN is launching a 5 years international 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. Back to the future

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

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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. ttH 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. estimates (30% each exp) 10-20% at 3 TeV (CLIC) percent-level precision needs 100 TeV pp machine For the study of H(126) alone, and given the existence of HL-LHC, an e+e- collider with energy above 350 GeV is not compelling w.r.t. one working in the 240 GeV – 350 geV energy range. The stronger motivation for a high energy e+e- collider will exist if new particle found (or inferrred) at LHC, for which e+e- collisions would bring substantial new information Higgs Physics with e e colliders above 350 GeV?

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