Precision EW measurements at Future accelerators

Alain Blondel Precision EW measurements at future accelerators

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Precision EW measurements at Future accelerators

‘Will redo te LEP program in a few minutes…. ’

15 July 2015

1994-1999: 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

1997-2013 Higgs boson mass cornered (LEP H, MZ etc +Tevatron mt , MW)

Higgs Boson discovered (LHC) Englert and Higgs get Nobel Prize

(c) Sfyrla

Is it the end?

Is it the end?

Certainly not! -- Dark matter -- Baryon Asymmetry in Universe -- Neutrino masses

are experimental proofs that there is moreto understand. We must continue our quest HOW?

Alain Blondel Precision EW measurements at future accelerators

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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?

Alain Blondel WIN 05 June 2005

relations to the well measured GF mZ aQED

Dr = a /p (mtop/mZ)2

- a /4p log (mh/mZ)2

at first order:

e3 = cos2qw a /9p log (mh/mZ)2

dnb =20/13 a /p (mtop/mZ)2

complete formulae at 2d orderincluding strong corrections are available in fitting codes

e.g. ZFITTER , GFITTER

EWRCs

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The main playersInputs: GF = 1.1663787(6) × 10−5 /GeV2 from muon life time 6 10-7

MZ = 91.1876 ± 0.0021 GeV Z line shape 2 10-5

α = 1/137.035999074(44) electron g-2 3 10-10

EW observables sensitive to new physics:MW = 80.385 ± 0.015 LEP, Tevatron 2 10-4

sin2qWeff = 0.23153 ± 0.00016 WA Z pole asymmetries 7 10-4

Nuisance paramenters: a (MZ) =1/127.944(14) hadronic corrections 1.1 10-4

to running alpha aS (MZ) =0.1187(7) strong coupling constant 7 10-3

mtop = 173.34 ± 0.76 GeV from LHC+Tevatron 4 10-3

combination mH = ATLAS 125.36 ± 0.37 (stat) ± 0.18 (syst) GeV 125.17 ± 0.25 2 10-3 CMS 125.03 ± 0.26 (stat) ± 0.14 (syst) GeV

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FUTURE ACCELERATORS

1. High Luminosity LHC (3000 fb-1 @ 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

4. 100 TeV hadron collider $$$$$$$$$$$

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SNOWMASS report

References: LEP Z peak paper arXiv:hep-ex/0509008 Phys.Rept.427:257-454,2006LEP2 Electroweak paper arXiv:1302.3415 [hep-ex] Phys. Rep. Gfitter Group arXiv:1209.2716v2 The Electroweak Fit of the Standard Model after the Discovery of a New Boson at the LHCJ. Erler and P. Langacker ELECTROWEAK MODEL AND CONSTRAINTS ON NEW PHYSICS PDG dec 2011 «and references therein»

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NB (AB): time scale (2030++) is typical of any new machine @ CERN or with CERN contribution; no real funding until HL-LHC upgrade is complete.

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

http://cern.ch/fcc and http://cern.ch/fcc-ee

first

Alain Blondel Precision EW measurements at future accelerators

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Goal performance of e+ e- colliders

complementarity

NB: ideas for lumi upgrades: -- ILC arxiv:1308.3726 (not in TDR). Upgrade at 250GeV by reconfiguration after 500 GeV running; under discussion) -- FCC-ee (crab waist)

FCC-ee as Z factory: 1012 Z (possibly 1013 with crab-waist)

ww

possibleupgrade

Nn = 2.984 0.008

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 theoreticaluncertainty on the Bhabha cross-section (0.06%)which represents an error of 0.0046 on Nn

Improving on Nn 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.427:257-454,2006

given the very high luminosity, the following measurement can be performed

Neutrino counting at TLEP

Beam polarization and E-calibration @ TLEP

Precise meast of Ebeam by resonant depolarization ~100 keV each time the meast is made

At LEP transverse polarization was achieved routinely at Z peak.instrumental in 10-3 measurement of the Z width in 1993 led to prediction of top quark mass (179+- 20 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 E2/r 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. DmZ ~0.1 MeV, DZ ~0.1 MeV, DmW ~ 0.5 MeV

350 GeV: the top mass• Advantage of a very low level of beamstrahlung• Could potentially reach 10 MeV uncertainty (stat) on mtop

From Frank Simon, presented at 7th TLEP-FCC-ee workshop, CERN, June 2014

A Sample of Essential Quantities:

X Physics Present precision

TLEP statSyst Precision TLEP key Challenge

MZMeV/c2

Input 91187.5 2.1

Z Line shape scan

0.005 MeV<0.1 MeV

E_cal QED corrections

ZMeV/c2

Dr (T)(no Da!)

2495.2 2.3

Z Line shape scan

0.008 MeV<0.1 MeV

E_cal QED corrections

Rlas , db 20.767

0.025Z Peak 0.0001

0.002 - 0.0002

Statistics QED corrections

NnUnitarity of PMNS, sterile n’s

2.984 0.008

Z Peak

Z+(161 GeV)

0.000080.004 0.001

->lumi meast

Statistics

QED corrections to Bhabha scat.

Rbdb 0.21629

0.00066Z Peak 0.000003

0.000020 - 60

Statistics, small IP

Hemisphere correlations

ALRDr, e3 ,Da(T, S )

0.15140.0022

Z peak, polarized

0.000015 4 bunch scheme

Design experiment

MWMeV/c2

Dr, e3 , e2, Da(T, S, U)

80385 ± 15

Threshold (161 GeV)

0.3 MeV<1 MeV

E_cal &Statistics

QED corections

mtopMeV/c2

Input 173200 ± 900

Threshold scan

10 MeV E_cal &Statistics

Theory limit at 100 MeV?

Alain Blondel Precision EW measurements at future accelerators

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Theoretical limitationsR. Kogler, Moriond EW 2013

Experimental errors at FCC-ee will be 20-100 times smaller than the present errors.

BUT can be typically 10 -30 times smaller than present level of theory errors Will require significant theoretical effort and additional measurements!

FCC-ee

0.0005 0.0001

0.0005?

0.0005?

0.0005 - 0.001

SM predictions (using other input)

0.000003 0.000001

0.000001?

0.000003?

0.000002

0.0000

0.000000

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The Higgs

b

Full HL-LHCZ

W

Ht

Light Higgs is produced by “Higgstrahlung” process close to thresholdProduction xsection has a maximum of ~200 fbTLEP: 2. 1035/cm2/s 400’000 HZ events per year (2 million Higgses in 5 years)

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

e+

e-

Z*

Z

H

Z – tagging by missing mass

ILC

total rate gHZZ2

ZZZ final state gHZZ4/ H

measure total width H

empty recoil = invisible width‘funny recoil’ = exotic Higgs decayeasy control below theshold

the 8B$ ILC

Alain Blondel Precision EW measurements at future accelerators

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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 twoorders 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 mW (5 MeV?) and mtop (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 sin2 qW

eff

Circular collider can improve Z mass and width (<0.1 MeV) and mW (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

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Status of Tevatron W massPRD 89 (2014) 072003PRL 108 (2012) 151803

• 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)

projectedarxiv:1310.6708

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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

Phys.Rev.D83:113008,2011

arxiv:1310.6708

Higgs factory performancesPrecision 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 measurements @HL-LHC precision 1-4% with 3000 fb-1

LC adds Inv + totalwidths at % level

NB without TLEP the SM line would have a 2.2 MeV width

in other words .... D(Dr)= 610-6 +several tests of same precision

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.

if observed prod (gHi )2(gHf)2 extract couplings to anything you can see or produce from H if i=f as in WZ with H ZZ absoulte normalization

Example (from Langacker, Erler PDG 2011)Dρ =e1=a(MZ) . T e3=4 sin2θW a(MZ) . S

From the EW fit Dρ = 0. 0004+0.0003−0.0004

-- 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 mt mb

Measurement implies

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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

Dr = a /p (mtop/mZ)2 - a /4p log (mh/mZ)2

e3 = cos2qw a /9p log (mh/mZ)2

dnb =20/13 a /p (mtop/mZ)2

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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 50-70 km ring, e+e- Higgs factory followed by HE pp.

Back to the future

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LHC 5 MeV

(0.1) 0.15 0.1

1.51.8

NB QED!@ Z pole amount for 0.3.MeV on mZ

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 240-250 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?