a circular e + e - collider to study h(125)?

Particle Flow : From Past to Future

A circular e+e- collider to study H(125)?Outline Introduction : A new era has just startedStrategic questionsWhy is precision needed ?The Boson and the LHCThe party line : International Linear e+e- Collider (ILC)An advantageous alternative : Circular e+e- Colliders (LEP3, TLEP)What ? Where ? Why ? How ? When ? How Much ?The LEP3 and TLEP Physics programme TeraZ, MegaW, Higgs Factory, Top FactoryLEP3 and TLEP as a Higgs Factory with the CMS detectorConclusions30 Oct 2012PH Seminar1Patrick Janot2/8/131Bibliography[1] CMS, Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC, Phys.Lett. B716 (2012) 30-61[2] ATLAS, Observation of a New Particle in the Search for the SM Higgs Boson with the ATLAS Detector at the LHC, ibid 1-29[3] P. Janot and G. Ganis, The HZHA Generator in Physics at LEP2, CERN Report 96/01 (Vol.2) 309[4] S. Dittmaier et al., Handbook of LHC Higgs cross sections: inclusive observables, CERN-2011-002 (Vol.1) 76 [5] R.S. Gupta, H. Rzehak, J.D. Wells, How well do we need to measure Higgs boson couplings?, arXiv:1206.3560 (2012)[6] H. Baer et al., Physics at the International Linear Collider, in preparation, see http://lcsim.org/papers/DBDPhysics.pdf[7] ATLAS, Physics at a High-Luminosity LHC with ATLAS, ATL-PHYS-PUB-2012-004 (2012), ESPP Contribution #174[8] CMS, CMS at the High-Energy Frontier, ESPP Contribution #177 [9] M.L. Mangano et al., Higgs cross sections in pp collisions at very high energy, ESPP Contribution #176[10] J.E. Brau et al., The physics case for an e+e- linear collider, ESPP Contribution #69[11] R.W. Assmann, LEP Operation and Performance with Electron-Positron Collisions at 209 GeV, Chamonix 2001.[12] A. Blondel, F. Zimmermann, A High Luminosity e+e- Collider in the LHC tunnel to study the Higgs Boson,arXiv:1112.2518 (2011)[13] M. Koratzinos , talk given at the 2nd LEP3 day (Oct. 2012)[14] P. Azzi et al., Prospective studies for LEP3 with the CMS detector, arXiv 1208.1662 (2012)[15] A. Butterworth, talk given at the 2nd LEP3 day (Oct. 2012)[16] M. Zanetti, talk given at the 2nd LEP3 day (Oct. 2012)[17] H. Stoeck et al., ILD Letter of Intent, arXiv:1006.3396 (2010)[18] M. Silari, talk given at the 2nd LEP3 day (Oct. 2012)[19] J. Osbore and C. Waiijer, Pre-Feasability Assessment for an 80 km Tunnel Project at CERN, ESPP Contribution #165[20] A. Blondel et al., High luminosity e+e- circular colliders for precise Higgs and other measurements, ESPP Contribution #173[21] J. Wenniger, talk given at the 2nd LEP3 day (Oct. 2012)[22] U. Wienands, talk given at the 2nd LEP3 day (Oct. 2012)[23] A. Blondel, A scheme to measure the polarization at the Z pole at LEP Phys.Lett. B202 (1988) 145, Erratum-ibid. 208 (1988) 531[24] M. Klute et al., Measuring Higgs Couplings from LHC Data, arXiv:1205.2699 (2012) [25] W. Lohmann et al., LCWS/ILC2007

30 Oct 2012PH Seminar2Patrick JanotIntroduction (1)Reminder : A new state was discovered by CMS and ATLAS

\

Decaying in ZZ and gg, with Higgs-like properties, and mH ~ 125.5 0.5 GeV/c230 Oct 2012PH Seminar3

CMSCMS

CMS

[1,2]Patrick JanotIntroduction (2)This discovery strongly influences the strategy for future collider projectsWe are now entering the precision measurement eraNeed to characterize the new stateMeasurement of Higgs branching ratios and related couplingsMeasurement of the Higgs coupling to the top quarkHiggs quantum numbers determination Higgs mass precision measurementHiggs boson self couplingsTotal Higgs decay widthNeed to determine the (tree-level) structure of the theoryInvisible Higgs decays, Exotic Higgs decaysParameterization of deviations from SM through higher-order operatorsNeed to evaluate (new physics) loop-induced effects Interpretation of the H gg and H gg branching fractionsPrecision electroweak measurementsPrecision mass measurements (W, Z, top, ) LHC discoveries at 13 TeV (2015-2022) will lead to an even broader horizonWill strongly influence the strategy for future collider projects as well

30 Oct 2012PH Seminar4Patrick JanotStrategic QuestionsQuestion #1What is the precision needed for all these measurements about H(125) ?

Question #2Can the LHC measure H(125) with enough precision and answer enough questions?Or do we need a complementary machine ?

Question #3If one needs a complementary machine, what is it ?m+m- collider ? Yet too hypothetical, too far in future not addressed todaygg collider ? Too limited a physics programme not addressed todaye+e- collider ? Well established linear collider projects exist (ILC, CLIC)If e+e-, linear or circular ?

Question #4What can a circular e+e- collider do for us ?30 Oct 2012PH Seminar5Patrick JanotQuestion #1 : Precision Needed (1)CouplingsMany channels are open most couplings can be measured from decaysLarge theoretical uncertainties (2 - 6%, mostly QCD) needs improvements

Are the effects of new physics measurable ?30 Oct 2012PH Seminar6DecayBR [%]Unc. [%]bb57.93.6.46.cc2.812.0.0226.WW21.64.gg8.210.ZZ2.64.0.275.Z0.169.H [MeV]4.04.mH = 125 GeV

[3,4]Patrick JanotQuestion # 1 : Precision Needed (2)Couplings (contd)Typical tree-level coupling modifications from SUSYPseudo-scalar A very hard to find at the LHC for moderate tanb and mA > 200 GeV

Large effect on Hbb and Htt couplingTo be measured a priori as precisely as possibleEssentially decoupled from Electroweak Precision Measurements

Typical coupling modifications from composite Higgs modelsAll couplings reduce together according to the compositeness scale f

To be measured a priori as precisely as possibleEventually visible in Electroweak (High) Precision Measurements

30 Oct 2012PH Seminar7

[5,6]Patrick JanotQuestion #1 : Precision Needed (3)Couplings (contd)Typical loop-induced effects from top partners (e.g., stops)Light top partners are needed to solve hierarchy problem

To be measured a priori as precisely as possible

Per-cent-level measurements sensitive to new physics at the TeV scaleMulti-TeV new physics needs sub-percent precisionSome models / parameters give effects of the order of 5%Underlying new physics affect differently each of the couplings Precise measurement of all couplings gives a clue of the nature of new PhysicsVery precise electroweak measurements would complete the understanding

MassdBRHff/dmH ~ -2% / GeV ; dBRHVV/dmH ~ +6% ; and dsHZ/dmH ~ -3% @ 125 GeV.A mass measurement to 50 MeV is enough for all practical purposes


[3,6]Patrick JanotQuestion # 2 : The boson @ LHC (1)The LHC is a Higgs Factory Total cross section at 8 TeV : 22 pb 1M Higgs already produced15 Higgs bosons / minute

Five different production modesMany couplings testable

Do we really need another machine?

Fundamental measurements: *BR for all channels XX H YYProduction : gg H, VBF, WH, ZH, ttH - Only the first two seen so far Decay : gg, ZZ, WW, , bb, - Only the first three seen so far(XX)*BR(YY) = (XX) * (YY) / tot(H) Cannot extract couplings without assumptions on the total widthEither measure ratios of couplings, or make assumptions.


Patrick JanotQuestion # 2 : The boson @ LHC (2)CMS projections assuming no exotic decays and reduced set of couplingsAlso assumed stable trigger/detector/analysis performanceIrrespective of pileup conditions

Approved program (300 fb-1 @ 13 TeV)10-15% on fermionic couplings5-6% on bosonic couplings5-10% on couplings through loops

HL-LHC (3000 fb-1 @ 13 TeV) Constant systematic uncertainties Moderate improvement (30%)5-10% precision on couplingsScaling systematic uncertaintiesFactor 2-3 improvement2-4% precision on couplingsMight not be sensitive to new physicsAt scales beyond ~500 GeV


[7]Patrick JanotQuestion # 2 : The boson @ LHC (3)ATLAS projections for partial width ratiosInsensitive to most systematic uncertaintiesWhile keeping some sensitivity to new physics

Approved program (300 fb-1 @ 13 TeV)20-30% on most coupling ratios10% on gHWW/gHZZ5% on gHgg/gHZZ

HL-LHC (3000 fb-1 @ 13 TeV) Improvement by a factor 2-3 for most ratiosExcept gHWW/gHZZMight not be sensitive to new physicsAt scales beyond ~500 GeV

Note : any precise measurement of one of the couplingswould lead mechanically to the determination of the others


[8]Patrick Janot

Difficult couplings : Htt and HHHPreliminary analysis from ATLAS for ttHIn the ttgg final stateSelection with one leptonMeasure signal strength with 20% precision Potential for Htt coupling : ~ 10%With the 3000 fb-1 of HL-LHCFirst look at the double Higgs production from ATLASIn the bbgg and the bbWW final states : will be tough !Potential for the HHH coupling : ~ 30% (CMS + ATLAS, HL-LHC)Larger potential of HE-LHC Cross sections for ttH and HH increase by large factors (7-10) at 33-40 TeVSubstantial increase of the scale for new physics searches, too

Is HL-LHC the LHC upgrade we want ?

Question # 2 : The boson @ LHC (4)30 Oct 2012PH Seminar12

[7,8,9]Patrick JanotQuestion #3 : Another machine ? So do we need another, complementary, machine ?Mass and Spin will be determined at LHC with adequate accuracy quite soonBut accuracy on couplings is limited to ~5% Far from the sub-per-cent level required, substantially model dependent

It seems we would need it But what would be this other machine ?Must measure couplings to the per cent, in a model-independent waym+m- collider ? The longest-term project (if at all feasible)Very good prospects for total Higgs width direct measurement to a few %Ideal for additional, heavier, Higgs bosons (if any)gg collider ? Probably the worst physics prospectsLarge gg backgrounds into fermion and boson pairs; Untagged Higgs.e+e- collider ? Physics prospects are good and solid projects exist Todays focus.Linear Colliders studied / conceived / designed for two decades30 Oct 2012PH Seminar13Patrick JanotQuestion #3 : A linear e+e- collider ? (1)Higgs Physics at a linear e+e- colliderAt the HZ threshold (s = 250 GeV, 5 years)Tagged Higgs, largest cross sectionIndividual branching ratios to a few %Invisible and exotic decaysPossibly total Higgs decay width

At the top threshold (s = 350 GeV, 5 years)Measure top quark mass with high precision (Input to EWRC)

At s = 500 GeV, > 10 years running (ILC) Measure Htt coupling to 15% with e+e- ttHMeasure HHH coupling to 50% with e+e- ZHH

At s = 1-3 TeV (CLIC, ~ 5 years)Measure HHH coupling to 40% with e+e- HHnn (fast simulation)


[6,10]250 fb-1350 fb-1 1 ab-1 2 ab-1Patrick JanotQuestion #3 : A linear e+e- collider ? (2)New Physics programme at a linear e+e- collider ?Could be fantastic yet no clue of the scale of new Physics from the LHCMight emerge from 2012 data, or from the 13 TeV run from 2015 onwardsYet no argument to go for 500 GeV, 1TeV, or 3 TeV

The sole guaranteed physics consists of Higgs precision measurementsThe really unique physics programme shows up at the ZH thresholdMight argue that higher energies give access to the ttH and HHH couplings But they can be measured with similar/better precision at the HL/HE-LHC

Top physics at the threshold is a nice additionTo measure the top mass precisely (input to EWRC)To put precise constraints on asTo look for rare top decays (new physics)

Ultra-precise electroweak measurements at the Z pole and the WW threshold A must for the understanding of the EWSB mechanism and hints a new physics30 Oct 2012PH Seminar15Patrick JanotQuestion #3 : A linear e+e- collider ? (3)The physics case not driven by the fact that the collider is linearAdvantages for Linear CollidersStudied for 30 years and an example even exist (SLC)SLC took 10 years to reach 30% of its design luminosityPolarization of e- beam is easy electrons polarized at the source.Nice to have, but not really critical for Higgs study

Issues for Linear CollidersKnown to be very expensiveTo be revised at the end of 2012; current estimate ~10 G$.Luminosity is difficult to get nm beam size; each collision needs a new beam;Power hungry up to 300 MW, even at low energyBeam disruption by beamstrahlung effectBackgrounds (photons, e+e- pairs); Beam energy smearing; Only one interaction point

30 Oct 2012PH Seminar16Patrick JanotQuestion #4 : A circular e+e- collider ?Closest example : LEP2 Was in the LHC tunnelReached a centre-of-mass energy of 209 GeVNeed only 15 GeV more per beamPeak luminosity was 1032 cm-2s-1b*y = 5 cm ; sy = 3.5 mm Integrated luminosity : 1 fb-1/detectorNeeds a factor 100 more Note : LEP2 was not at the beam-beam limitRF Frequency was 352 MHzsz = 1.6 cm Luminosity lifetime was ~ 3 hoursDominated by Bhabha scattering, e+e- e+e- Beam power was 20 MWFour interaction points, four detectors

How can we extrapolate to get the missing GeV and fb-1 ?LEP3 would be the answer


[11,12]Patrick JanotThe LEP3 option : Where ?Obviously in the LHC tunnel, tooLEP2 parameters were not that far from what we wantThe cost would be minimized, by re-usingThe tunnel Save 1 G$The cooling infrastructure Save 1 G$Two multi-purpose detectors (CMS/ATLAS) Save 1 G$Also saves significant amount of time for constructionIntegration in the tunnel : less difficult than LHeC (no concurrent operation needed)30 Oct 2012PH Seminar18

[13]Patrick JanotThe LEP3 option : Where ?Obviously in the LHC tunnel, tooLEP2 parameters were not that far from what we wantThe cost would be minimized, by re-usingThe tunnel Save 1 G$The cooling infrastructure Save 1 G$Two multi-purpose detectors (CMS/ATLAS) Save 1 G$Also saves significant amount of time for constructionIntegration in the tunnel : less difficult than LHeC (no concurrent operation needed)30 Oct 2012PH Seminar19

LEP3Can also be made much simpler !

After the 13 TeV programme(with or without HL-LHC run, choice depends on physics in 2022) Before the 33 TeV programme(Should HE-LHC be chosen as our LHC upgrade, cannot start before 2035 to have magnets ready)[13]Patrick JanotThe LEP3 option : Energy ?Energy chosen to maximize the HZ cross section / physics potentialMaximum is at 260 GeV : 212 fbOnly 6% smaller at 240 GeV : 200 fbBut reduces SR energy losses by 40%Also reduces operation costBest for Physics ~ 23711 Getting the energy at small costSR energy losses : 6-7 GeV / turnLC : 120 GeV lost at each collision Would need only 300-350 ILC-type cavities Gradient : 20 MV/m, Frequency 1.3 GHzPresent parameters foresee 580 ILC-type cavitiesTo increase the momentum acceptance Needed for beamstrahlung, see laterTotal length : 818 meters (LEP2 : 864 m) RF power during operation : 50 MW/beamIssue : Power handling of the RF couplersNeeds R&D or use SPL cavities (700 MHz)


LEP2LEP3

[14,15][28]Patrick JanotThe LEP3 option : Luminosity ?Getting a factor 100 in luminosity wrt LEP2 ?Needs more focusing : Reduce b*y from 5 cm to 1 mm and b*x from 1.5 cm to 2 mm The LHeC optics can be applied and does the job ! Beam sizes at IP : sx = 71 mm ; sy = 0.32 mm, still quite relaxed.Needs in turn shorter bunchesILC cavities : The RF frequency increases from 352 MHz to 1.3 GHzReduces bunch length from 1.6 cm to 0.23 cmExpected luminosity : 1.07 1034 cm-2 s-1 at 240 GeV (i.e., 100 fb-1 / year / IP)Bhabha scattering burns the beams : lifetime ~ o(15) minutesRequires continuous top-up injection (with a B-factory-like design) (Requires 6 GV more RF as well, for the accelerator ring)


[12]Patrick JanotThe LEP3 option : Beamstrahlung ? (1)Luminosity at LEP3 obtained with 45 kHz repetition rate Hence the relaxed beam parameters : vertical beam size = 320 nmTo be compared with ILC : 5 nm ; or CLIC : 1 nmA lot of good consequencesReliable operation of the machineNegligible beamstrahlung effects for physics~100% of the collisions within 1% of the nominal beam energy (cf. 88% for ILC)Beam energy spread ~0.1% (cf. ~2% for ISR)Beam energy spectrum perfectly knownNegligible PU rate from gg interactionsPU probability ~0.3%cf. 4 events / pulse in CLICcf. 2-3 events / bunch in ILCNegligible backgrounds from beam disruptionNo specific requests for the detectorTracker, forward detectors, No specific requests for background simulation


ILD TPC at 500 GeV[16,17]Patrick JanotThe LEP3 option : Beamstrahlung ? (2)Luminosity at LEP3 obtained with 45 kHz repetition rate (contd)Small beamstrahlung losses are cumulative

For each collision0.01% of the electrons have DE/E>1%10-6 of the electrons have DE/E>2%10-10 of the electrons have DE/E>4%

Hence, beam lifetime decreasing exponentially with energy acceptance Unacceptable losses with a 1% energy acceptance Beam lost in less than 1 secondLarge losses with a 2% energy acceptanceAbout 1% of the beam lost every second, beam lost within in a minuteNegligible losses with a 4% energy acceptanceRequires more RF voltage to keep these energy tails in(hence the 580 cavities for a very comfortable margin)Needs to study compatibility with the low-b optics30 Oct 2012PH Seminar23

[16]Patrick JanotThe LEP3 option : Other goodiesCollider rings have historically delivered According to design, and often exceeding itSee most recent examples : LEP1, LEP2, PEP2, KEKBDesign LEP3 parameters give 1.1 x 1034 cm-2s-1 at 240 GeVIt is a factor 2 larger than the ILC at the same energyNot counting the beamstrahlung effects in ILCThe current parameters can be (and will be) optimized No showstopper has yet been identified

Number of detectorsLEP3 can accommodate four interaction points (as was LEP2)Four detectors = four times the integrated luminosityAll Higgs branching fraction measurements will be statistically limitedSystematic cross checksFour collaborations = four times the number of people involvedImportant sociological argumentCan accommodate two linear-collider-type detectors in addition to CMS & ATLAS20 years of detector R&D and collaboration building can be capitalized


Patrick JanotThe LEP3 option : CostCould build LEP3 for a canonical 1 billion $Obtained from the known price of RF cavities, klystrons, and magnetsThe rest of the infrastructure and two detectors exist already

A factor ~10 smaller than a linear collider, roughly

Price of the Higgs boson ? Expect 100,000 Higgs bosons / detector over a period of 5 years at LEP3Basic investment in the two-detector configuration : ~ 5 k$ / Higgs bosonBasic investment in the four-detector configuration : ~ 5 k$ / Higgs bosonTwo addl detectors cost ~ 1 B$, but twice more Higgs bosons to analyse

Expect 50,000 Higgs bosons over a period of 5 years at ILC250Basic investment in the ILC configuration : ~200 k$ / Higgs bosonEach Higgs boson is 40 times more expensive than at LEP3

30 Oct 2012PH Seminar25Patrick JanotThe LEP3 option : CostCould build LEP3 for a canonical 1 billion $Obtained from the known price of RF cavities, klystrons, and magnetsThe rest of the infrastructure and two detectors exist already

A factor ~10 smaller than a linear collider, roughly

Price of the Higgs boson ? Expect 100,000 Higgs bosons / detector over a period of 5 years at LEP3Basic investment in the two-detector configuration : ~ 5 k$ / Higgs bosonBasic investment in the four-detector configuration : ~ 5 k$ / Higgs bosonTwo addl detectors cost ~ 1 B$, but twice more Higgs bosons to analyse

Expect 50,000 Higgs bosons over a period of 5 years at ILC250Basic investment in the ILC configuration : ~200 k$ / Higgs bosonEach Higgs boson is 40 times more expensive than at LEP3

30 Oct 2012PH Seminar26Disclaimer : numbers in this slide can be off by a factor 2But encouraging enough to justify a design study Patrick JanotThe LEP3 option : When ?Possible timescale for LEP3Conceptual design report at the end of 2014Need to study a few issues, of which : Power dissipation in RF CouplersProtection against synchrotron radiationIntegration of the accelerator ring with detectorsIf the case is still present, decision to go ahead taken during LS2 (2017)Depends on LHC physics outcomes (50-100 fb-1 at 13 TeV)Technical design report in 2019-2020If the case is still present, installation can start at LS3 (2022)Depends on LHC physics outcomes (300 fb-1 at 13 TeV)LEP took 18 months to installPhysics could start around 2024, for 10 years Fits well with the possibility of HE-LHCHigh-field magnets could be ready by 2032-2035Cohabitation with HL-LHC is suboptimal, more difficult, but feasibleWould mean alternate periods for HL-LHC and LEP3 Could also do without HL-LHC : Depends on LHC physics outcomes 30 Oct 2012PH Seminar27[13,15,18]Patrick JanotA long-term vision for CERN : TLEP (1)A 80-km tunnel around Geneva avoiding Jura, Saleve, and VuacheCould host a 350 GeV e+e- collider (called TLEP) as a first step Feasible by 2025 - 2030 ? Needs a long-term decision for CERN. 30 Oct 2012PH Seminar28

[19]Pre-feasibility assessment (2012)Patrick JanotA long-term vision for CERN : TLEP (2)Three main physics argumentsReaches s = 350 GeV (top threshold) with L = 6.1033 cm-2s-1, same RF as LEP3Top mass, as, rare top decays, WW H, With the available beam power, can accommodate more bunches at s = 240 GeVReaches 5.1034 cm-2s-1 at the ZH threshold (conservative)With 2 or 4 detectors, up to 40 x more Higgs bosons than the ILC at 240 GeVIs extendableAs a second step, tunnel can accommodate a VHE-LHCs = (80km/27km) (20T/8T) 14 TeV = 100 TeV

Cost ? (from extrapolations)Tunnel and Collider would be the largest contributors : say 2.5 - 3.5G$ + 2 G$Detectors would be next : say 1 or 2G$ for two or four detectorsStill less expensive than a linear collider : 5 to 7 G$Individual Higgs cost over a five-year period : ~ 2.5 to 3.5 k$ / Higgs bosonEach Higgs boson is, again, 50-80 times less expensive than at a linear colliderIf you had 10 billion $, where would you put them ? ILC ? TLEP + VHE-LHC ? Probably imprudent to decide now30 Oct 2012PH Seminar29LEP tunnel: 0.7 G$9km LHeC: 0.25 G$< 2 x LEP3~RF, magnetsPatrick JanotMachine Parameter Summary30 Oct 2012PH Seminar30

Parameters not yet optimized[20]Patrick JanotThe LEP3 Physics Programme (1)LEP3 as a Higgs Factory, s = 240 GeV : Five yearsWith an instantaneous luminosity of 1034 cm-2s-1500 fb-1 / experiment, i.e., 100,000 Higgs events in each detector

With Z e+e- or m+m- , measure sHZ Count events independently of the Higgs boson decayThen measure sHZ BR(H XX)With exclusive final state selection, including invisible and exotic decaysObtain model independent measurements of HXX couplingsSee CMS study for the achievable precision


e+e-Z*ZHPatrick JanotThe LEP3 Physics Programme (1)LEP3 as a Higgs factory, s = 240 GeV : Five years (contd)Backgrounds are manageable, rates are small as at LEP2, very basic trigger suffice

Large Bhabha scattering cross section (above 5o off the beam axis)Allow the integrated luminosity to be measured to better than 0.1%No systematic from beam energy spectrum (no beamstrahlung)

Can also measure other Higgs properties (no difference wrt linear collider)Mass Spin from HZ threshold scan CP from angular distributions

Precise measurement of the e+e- HZ cross sectionIntegrated lumi measured with Bhabha scattering to better than 0.1%(cross section indicated for at least one electron above 5o off the beam axis)30 Oct 2012PH Seminar32

Patrick JanotThe LEP3 Physics Programme (2)LEP3 as a Higgs factory, s = 240 GeV : Five years (contd)Direct measurement of the W mass with e+e- W+W- qqqq, lnqqWith ~8 million WW events in 500 fb-1, and extrapolating from LEP2 figuresStatistical uncertainty on mW ~ 1 MeV/c2 / experiment

Requires a precise beam energy measurement, from the knowledge of mZWith ~650,000 ZZ events (of which 400,000 without Z nn)Statistical uncertainty on Ebeam ~ 5 MeV / experimentWith 1 million Z(g) events (with Z e+e-, m+m-) [radiative returns]Statistical uncertainty on Ebeam ~ 3 MeV / experimentMay be improved with the use of Z hadrons ?

Combined expected accuracy on mWWith 4 experiments Can reach a combined precision on mW of ~1 MeV/c2 Today, LEP + Tevatron reached a precision of 15 MeV/c2Will be difficult to improve at the LHC beyond 10 MeV/c230 Oct 2012PH Seminar33Patrick JanotThe LEP3 Physics Programme (3)LEP3 as a TeraZ factory, s ~ mZ : One yearWith the available RF power, can keep 50 times more current at s ~ mZDistributed in 200 x 200 bunchesIdentical bunches as at 240 GeV : same beamstrahlung, same pileup, But instantaneous luminosity of 5 x 1035 cm-2s-1250 times larger than the linear collider GigaZ optionIntegrated luminosity three orders of magnitude larger 5 ab-1 / experiment, and four detectors Total of o(1012 Z) : LEP3 is a TeraZ factory Can repeat the LEP1 programme every 10 minutesContinuous detector calibration cancel all experimental uncertaintiesInteresting observation : Event rateZ decays + Bhabha events (1o) + gg collisions add up to a rate of 25 kHzCMS high-level trigger currently collects events at a rate of 1kHz A factor 25 to find ?Luckily, CMS events at LHC are big and slow to processEspecially with 30-40 PU eventsTypically 20 times bigger/slower than a LEP3 Z hadronic decay 30 Oct 2012PH Seminar34Patrick JanotThe LEP3 Physics Programme (4)LEP3 as a TeraZ factory, s ~ mZ : One year (contd)Repeat all LEP1 / SLD measurements with 25 to 100 times better precision

L : Requires Luminosity measurement (dedicated luminometers)E : Requires beam Energy measurement (resonant depolarization)P : Could require beam Polarization (towards ALR measurement)30 Oct 2012PH Seminar35

Nn = 2.984 0.008 DELPHIL3OPALNn = 2Nn = 3Nn = 4

Patrick JanotThe LEP3 Physics Programme (5)Digression : Luminosity measurementDedicated luminometers from 1 to 5 degrees of the beam axisPlaced in front of the focusing quadrupolesNo specific study done for LEP3 yetNegligible beamstrahlung is a great advantageNeed theoretical developments to understand se+e- to better than 5 x 10-5

Digression : Polarization and polarization measurementLEP1 : reached 60% polarization with a single beam at 45 GeVPolarization was lost in collision because of design flawsShould be possible to maintain it with some care in the designSpin-rotator for LEP3 may re-use HERA, SuperB or LHeC experience

Polarization in situ measurement, together with ALRScheme with alternate polarized and unpolarized bunches exists

Not critical for the LEP3 programme at the Z poleCan be arranged as a separate programme for the ALR measurement30 Oct 2012PH Seminar36[22][23][21]Patrick JanotThe LEP3 Physics Programme (6)Digression : Beam energy measurementUltra-precise resonant depolarization method, unique to a ringPrecision limited to 2 MeV at LEP1 by the extrapolation to collision conditionsAt LEP3, can use one of the 200 bunches to make this measurementNo extrapolation needed !

Ultimate precision better than 0.1 MeVMeasure GZ to better than 0.1 MeV (limited to 2 MeV @ LEP1: tides; TGV, rain; + extrapolation)


0123Bx-Bxe-pBdipolePrecision 210-6 DEbeam 0.1 MeV !1993n ~ B ~ EPatrick JanotThe LEP3 Physics Programme (7)LEP3 as a MegaW factory, s ~ 2mW : One yearReminder : What was achieved at LEP2

With 1035 cm-2s-1, i.e., 1 ab-1 in a year (105 times larger data sample)DmW reduced to 0.7 MeV per experiment (stat. only)Grand combination with 240 GeV leads to a precision of 300 keV on mWResonant depolarization might not be operational at Ebeam ~ 80 GeVAlternatively, use 2x107 Z(g) events for a similar precision on 30 Oct 2012PH Seminar38

mW = (80.40 0.22) GeV/c2(10pb-1/expt)Patrick Janot

The LEP3 Physics Programme (8)Opens a whole new book in EWSB precision measurements:

March 2012 (Moriond) After LHC + LEP3 (conservative) 1 MeV for mW, factor 25 at the Z pole (+500 MeV for mtop) 30 Oct 2012PH Seminar39

LEP excluded

++++mWZ poleNew Physics

?Patrick JanotThe LEP3 Physics Programme (9)Will pave the way towards future facilities at the energy frontierAll electroweak measurements become sensitive to weakly interacting new physicsEach observable depends on S,T,U in a different wayFor example : 30 Oct 2012PH Seminar40

Patrick JanotThe TLEP Physics ProgrammeSame as LEP3, with less synchrotron radiation, plusFive to ten times more luminosity at s = 240 GeVCan do in a couple years what a linear collider would do in 40 years.

Two to five times more luminosity at s = mZ or 2mWUltimate precision for all electroweak observables

Top physics at s = 350 GeV Measure the top mass to 50 MeVAnd more Higgs measurementsMore statistics for HZ WW fusion opens up for gHWW30 Oct 2012PH Seminar41

10 fb-1/pointDmtop=100 MeV[6]Patrick JanotPrecision Measurements with CMS ? (1)The CMS detector exists and runs in pp collisionsData can be used to check the predictions of the simulation30 Oct 2012PH Seminar42

Patrick JanotPrecision Measurements with CMS ? (2)Longitudinal view

Next challenge : Accelerator beam pass-through !Or more creative solution ? 30 Oct 2012PH Seminar43

TrackerECALHCALMuonsHCALCoil (4T)

LEP3 needs focusing quadrupoles at 4mVery small CLIC prototypes existand would fit ! Patrick JanotPrecision Measurements with CMS ? (3)An octant in the transverse view

Large magnetic field, efficient tracking / muon Id, fine ECAL granularity, simple designWell suited for particle-flow reconstructionAlthough not initially designed for that (unlike LC detectors)30 Oct 2012PH Seminar44

gh0ehmPatrick JanotPrecision Measurements with CMS ? (4)A global event description : 30 Oct 2012PH Seminar45

Patrick JanotPrecision Measurements with CMS ? (5) Comparison with a typical LC detector

c tagging or gluon tagging not yet attempted in CMS

CMS typically 2-10 times worse than LC typical detectorNot a real surprise : it was not optimized for e+e- collisionsLets see the impact on Higgs precision measurements (CMS vs LC detector)30 Oct 2012PH Seminar46ObjectCMSLCJets50%/E+4%25-30%/EMissing energy50%E

25%E

Muon momentum2%0.2%Electron momentum2%0.2%b tagging30%50%Patrick JanotHiggs Precision Measurements with CMSGeneral comment about the analysesAll results given in the next slides are realistic, but also very conservativeFull CMS detector simulation is used throughout500 fb-1 were simulated/reconstructed for signal and backgroundsSimulation of the 5 years of LEP3 could be done within a weekNo optimization of the reconstruction was attempted, e.g., Tracking could have been made more efficient for the simple LEP3 eventsb tagging could have included soft-lepton tagsUpgraded pixel detector could have been used in the simulationJet algorithms could have been optimizedThe exact same analysis tools as for the recent CMS Higgs search were usedVery basic selection algorithms were developedMostly because analysis started in June and had to finish July 31st No multivariate analysis was attemptedNo constrained fits were used only simple jet energy rescaling so farIn the grand combination with four detectors, all detectors are assumed to be CMSWhile at least two would obviously be LC-type detectorsNot all Higgs decay channels have yet been addressed30 Oct 2012PH Seminar47Patrick JanotHiggs Precision Measurements with CMSGeneral comment about the analysesAll results given in the next slides are realistic, but also very conservativeFull CMS detector simulation is used throughout500 fb-1 were simulated/reconstructed for signal and backgroundsSimulation of the 5 years of LEP3 could be done within a weekNo optimization of the reconstruction was attempted, e.g., Tracking could have been made more efficient for the simple LEP3 eventsb tagging could have included soft-lepton tagsUpgraded pixel detector could have been used in the simulationJet algorithms could have been optimizedThe exact same analysis tools as for the recent CMS Higgs search were usedVery basic selection algorithms were developedMostly because analysis started in June and had to finish July 31st No multivariate analysis was attemptedNo constrained fits were used only simple jet energy rescaling so farIn the grand combination with four detectors, all detectors are assumed to be CMSWhile at least two would obviously be LC-type detectorsNot all Higgs decay channels have yet been addressed30 Oct 2012PH Seminar48Examples that follow to be taken as illustration onlyRoom for very substantial improvementsSee [14] for more details Patrick JanotMeasurement of the e+e-ZH cross sectionModel-independent measurement with Z e+e-, m+m-Two oppositely-charged same-flavour leptons With possible Bremsstrahlung photons, invariant mass within 5 GeV of the Z massReject radiative events (ISR) with pT , pZ , acoplanarity cuts (+ photon veto)Display the mass recoiling to the two leptons, and fit (Crystal Ball + pol3)3.1% precision on sHZ If the invisible decay width can be excluded, request the recoil to be visible2.6% precision on sHZ


Patrick JanotMeasurement of the e+e-ZH cross sectionModel-independent measurement with Z e+e-, m+m-Two oppositely-charged same-flavour leptons With possible Bremsstrahlung photons, invariant mass within 5 GeV of the Z massReject radiative events (ISR) with pT , pZ , acoplanarity cuts (+ photon veto)Display the mass recoiling to the two leptons, and fit (Crystal Ball + pol3)3.1% precision on sHZ If the invisible decay width can be excluded, request the recoil to be visible2.6% precision on sHZ


Comparison with ILC studies3% precisionPatrick JanotMeasurement of sHZ x BR(Hinvisible) Same approach as beforeWith the requirement that the event consists of only the two leptons (+Brem)Display the mass recoiling against the two leptons (with BRinvis = 100%)Complete the analysis with Z -> b bbarForce the events to form two jets, and apply very pure b tagging criterionInvariant mass with 15 GeV of the Z massSame cuts on pT, pZ, acoplanarity, as in the dilepton caseWith BRinvis = 100%, measure sHZ to 2.2%Can exclude BRinvis values all the way down to 1.5% if not signal is observedIn that case, measure sHZ to 2.7% (with the visible final state)30 Oct 2012PH Seminar51

Patrick JanotMeasurement of sHZ x BR(Hbb) Leptonic final state : Z e+e-, m+m-Exact same selection as for the sHZ measurementForce the rest of the event to form two jets, and apply a tight b taggingPrecision of 3.1% on sHZ x BR(Hbb) Missing energy final state : Z nnExact same selection as for invisible Higgs with Z bbSubstitute missing mass for visible mass, and display the rescaled visible massPrecision of 1.8% on sHZ x BR(Hbb)


Patrick JanotMeasurement of sHZ x BR(Hbb) The four-jet channel : Z qqForce the event to form four jets, all identified as hadronic jets (particle multiplicty)No significant missing energy : visible mass > 180 GeVFour jet energies rescaled to satisfy E,p conservation (directions unchanged)Distance to ZZ and WW hypotheses in excess of 10 GeVOne pair compatible with a Z, the other (the Higgs) with mass larger than 100 GeVIf several such combinations exist, take that with the largest b tag for the H pairDisplay mH = m12 + m34 91.2 GeV

Background shape taken from simulationFit to a 3rd order polynomialSignal fit to a double Gaussian Precision of 1.5% on sHZ x BR(Hbb)

Combined precision : 1.0%Hot news : 5C and 6C improve this by ~20%Not displayed / not used here


Patrick JanotMeasurement of sHZ x BR(Ht+t-) Analysis similar to the bb decaySubstitute tau tagging for b tagging Addressed only the hadronic and leptonic Z decaysNo mass determination in the missing energy channel

Combined precision of 4.3% on sHZ x BR(Htt)


Patrick JanotMeasurement of sHZ x BR(HW+W-) Many Z and WW decay channels analysedLeptonic decaysSelect the lepton pairs as for the HZ cross section measurementRequest the recoiling to consist ofEither four hadronic jets (WW 4q)With anti-b-tagging cut (rejects H bb)Or an additional lepton, missing pT > 15 GeV, and at least one jet (WW lnqq)

Background from other Higgs decay channels significantTake if from the SM for the time being. Will do a global fit eventually.30 Oct 2012PH Seminar55

11.9%11.7%Patrick JanotMeasurement of sHZ x BR(HW+W-) Many decay channels analysed (contd)Hadronic Z decays, fully leptonic WW decays (WW lnln)Two leptons, opposite charge, opposite flavour, mass between 10 and 70 GeV/c2Same lepton flavours also studied, but statistically less interestingMissing transverse momentum > 25 GeV/cRecoiling system with Nch>10 and compatible with the Z mass (25 GeV/c2)Invisible Z decays, fully hadronic WW decays (WW 4q)Request four jets, no electron, no muon, no tau, anti-b-tagging cutMissing mass > 75 GeV/c2, missing momentum > 30 GeV/c, direction > 25 degrees30 Oct 2012PH Seminar56

9.7%12.8%Patrick JanotMeasurement of sHZ x BR(HW+W-) Combined precision on sHZ x BR(HW+W-)Can potentially improve with a study of the fully hadronic final state (6 jets)Being worked onThe four individual channels give a precision of 11.9%, 11.7%, 12.8% and 9.7%Combines to a precision on sHZ x BR(HW+W-) of 5.6%

Toward a measurement of sHZ x BR(Hcc, gg)The above assumes the SM (or the measured values) for the other signal channelsSmall and dominated by bb in llqqln and in 2qlnlnLarger, 50% bb and 50% gg+cc in ll4q and in 2n4qThe llqq final state (two jets, anti-b-tag) is instead enriched in gg and cc (no WW)Could simultaneously fit gg and cc together with WWTake bb and ZZ from the measurements Under study as we speakWould benefit from the upgraded pixel detectorWould benefit from dedicated c and gluon tagging algorithmsWe know that it is possible from ILC studies.

30 Oct 2012PH Seminar57Patrick JanotMeasurement of sHZ x BR(Hgg) Quite rare a decay About 250 H -> gg events expected in 500 fb-1 Main background consist of double radiative returns to the Z mass e+e- nngg, eegg, mmgg, ttgg, and qqgg (both photons in the detector acceptance)Two photons with energy > 40 GeV, in the tracker acceptance, isolatedTake the pair for which the recoiling mass is closest to the Z massReject radiative eventsHiggs momentum direction more than 25 degrees away from the beam axisRapidity gap smaller than 2.0

Selection efficiency ~ 60%Precision of 14% on sHZ x BR(Hgg) Better diphoton mass resolution at hand(Energy regression used at CMS/LHC)


Patrick JanotMeasurement of sHZ x BR(Hm+m-) Even rarer a decay About 22 H -> m+m- events expected in 500 fb-1Definitely need the four detectors here : almost 90 events expected !Two oppositely charged muons (+ potential bremsstrahlung photons)Mass recoiling the muon pair with 15 Gev of the Z massReject WW -> mnmn by requesting two addl jets Also rejects Z -> nn (20% of HZ)Reject double radiative mm events by requesting no purely electromagnetic jetsAlso rejects Z -> ee (3.4% of HZ)Display the muon pair mass

A 4s excessPrecision of 28% on sHZ x BR(Hmm) Essential for a muon collider projectBetter dimuon mass resolution would helpBut already OK with CMS x 430 Oct 2012PH Seminar59

Patrick JanotSummary of LEP3/TLEP measurementsUnder the very conservative assumptions already stated :

Per-cent to sub-per-cent accuracy achieved on Hbb, Htt, HZZ, and HWW couplings(2) or (4) detectors assumed to be CMS.30 Oct 2012PH Seminar60

Patrick JanotSummary of LEP3/TLEP measurementsExtrapolation for TLEP with 5 x more luminosity and 2 ILC-type detectors

HZZ, HWW, Hbb, Htt, Hcc : few per-mil precision; 4 detectors would improve further.WW H still to be studied at 350 GeV; Not included here.30 Oct 2012PH Seminar61

Patrick JanotSummary of LEP3/TLEP measurementsComparison with ILC (Higgs Factory at s = 250 GeV) [10]

LEP3 : uncertainties typically smaller by a factor 2-3 than the ILCTLEP : uncertainties typically smaller by a factor 5 than the ILC 30 Oct 2012PH Seminar62

Patrick JanotSummary of LEP3/TLEP measurementsComparison with LHC and HL-LHC (CMS and SFitter projections) [8,23]

LEP3/TLEP exceed substantially LHC sensitivityEven in its highest luminosity version30 Oct 2012PH Seminar63

Patrick JanotConclusions (1)LEP3 is an exciting project for PhysicsHiggs physics better than the full 1 TeV ILC programmeWhen combined with HL-LHC or better, HE-LHC, for ttH and HHH couplingsUnique electroweak precision measurementsSensitive to weakly interacting new physics beyond the TeV scaleTogether with Higgs coupling measurements

LEP3 is a cost-effective projectIt is therefore an interesting opportunity for Europe, for CERN,And even for the LHC and ILC collaborations !Even if they dont fully realize it as we speak The money saved can be used for other exciting projects HE-LHC, VHE-LHC, CLIC @ 3 TeV

LEP3 is a popular project A lot of interest around the world30 Oct 2012PH Seminar64Patrick Janot

LEP3 2011SuperTristan 2012LEP3 on LI, 2012LEP3 in Texas, 2012FNAL site filler, 2012West Coast design, 2012Chinese Higgs Factory, 2012UNK Higgs Factory, 2012LEP3 (and circular Higgs Factory) is a popular project around the worldPatrick Janot65Conclusions (2)LEP3 might even be feasible, in little timeAlmost everything is off the shelf lots of synergies with other projectsBut it is not an easy machineFitting LEP3 in the LHC tunnel together with LHC is not easy, and sub-optimalNeed to weigh the relative merits of LEP3 + HE-LHC and of HL-LHC + HE-LHCAs an option for ATLAS and CMSThe choice really depends on the LHC findings in the next 5 years LEP3 operation could start around 2024-2025, for 10 yearsA number of accelerator issues still need to be worked outRF coupler, optics energy acceptance, 2nd ring integration, synchroton radiation,

TLEP is a superior machine (energy and luminosity)A tiny bit more expensive although not as much as ILCWith a much longer timescale requires a long-term vision for CERNExtendable towards a VHE-LHC

30 Oct 2012PH Seminar66Patrick JanotConclusions (3)Final concluding statements

If the LHC measurements are not sufficient to show the way towards new physics a lepton collider will be necessary

For this purpose, LEP3 and TLEP can provide an economical and robust solutionTo study the H(125) state with high precisionTo perform outstanding precision measurements of the Z, W, H (top)With higher statistics than a linear collider At more than one interaction point

Within our lifetimes

11 Oct 2012GGI Workshop : Higgs Focus Week67Patrick Janot

a circular e + e - collider to study h(125)?

Documents

e e linear collider

circular e e colliders

high luminosity e e

lep3 day

higgs factory

higgs couplings

precise higgs

higgs boson couplings