Higgs Measurements at Future e+e- Colliders. Maxim Perelstein, Cornell KITP New Accelerators for 21st Century mini program June

Transcription

1 Higgs Measurements at Future ee- Colliders Maxim Perelstein, Cornell KITP New Accelerators for 1st Century mini program June 6 016

2 Higgs: Highlights from LHC Run It exists! m=15 GeV / L 0 ) P ln(l - J CMS X ZZ WW 19.7 fb (8 TeV) 5.1 fb (7 TeV) 1 - Observed Expected 0 ± 1σ P J ± 1σ 0 ± σ P J ± σ 0 ± 3σ P J ± 3σ 1 m h h3 h b h6 h7 - h - h9 - h10 m h h3 h b h6 h7 qq gg production qq production It is a spin-0 object - h - h9 - h10 It couples to other particles with strength proportional to their mass (~10-0% level, some assumptions) Looks like the SM Higgs so far! Let s call it the Higgs. 1

3 Higgs: Big Questions Is the Higgs solely responsible for moderating the high-energy growth of scattering amplitudes of massive gauge bosons and fermions? (=does it give them their masses?) SM: Yes Is the Higgs an elementary (fundamentally novel, truly amazing) scalar? Or is it a composite ( like a pion, still pretty cool)? SM: Elementary If elementary, what (if anything) protects its mass against radiative corrections? ( hierarchy problem ) SM: Nothing Is the Higgs alone, or are there other scalar particles around? How did the Universe evolve from high-temperature, SU()xU(1) symmetric phase to the present broken-ew phase? ( EW phase transition ) SM: Smooth Cross-over SM: Alone

4 ! Mass Width Higgs: Observables* SM: no prediction SM: Coupling to W/Z SM: Coupling to Fermions SM: Coupling to photons, gluons SM: calculable one-loop effect Self-coupling SM: Couplings to exotic (non-sm) states Form-factors SM: none SM: none * Not all and not always are actually directly observable - more on this below 3

5 Observables/Questions Map Unitarizes? Elementary/ Composite? Mass Stabilization? Other Scalars? EW Phase Transition? 4

6 EXPERIMENTAL PROSPECTS

7 LHC Coupling Measurements LHC measures rates:! Couplings are extracted from a fit to rates:! statistical error ~ 0% small S/B - systematics pdf uncertainties ~few %! introduces model dependence No measurement of is available. Need to make assumptions. All LHC coupling determinations are model-dependent 5

8 ee- vs. Hadron Collider Smaller Event Samples ~100 M Higgses at LH-LHC (3 ab)! ~1 M Higgses at ee- facilities Much better S/B, clean environment LHC: Cross Section Oligarchy - the Strong dominate the Weak e.g. ee-: Cross Section Democracy No p.d.f. uncertainties Model-independent determination of total width ( couplings) is possible 6

9 Higgs Production in ee- ee- colliders in the GeV energy range are under discussion e e Z e e H Z W W - ν H ν e e Z Z e H e A possible physics program: Precise Higgstrahlung (Zh) Br ratio 50 GeV WW fusion 350 and 500 GeV Direct measurement of tth 500 (550?) GeV Some sensitivity to h^3 coupling at 500 GeV 7

10 Precision Higgsstrahlung Identify Zh events by reconstructing recoil mass No observation of the Higgs is needed unbiased, modelindependent measurement of cross section Directly infer coupling Infer total width: This method is somewhat limited statistically due to [Figure: Li et.al. (ILD Collaboration)] Measure SM final states, constrain non-sm width 8

11 W Fusion and Higgs Width SM Higgs width ~4 MeV too small for a direct measurement Indirect, but model-independent, determination of at ILC: 50 GeV: 500 GeV: Combine to infer 50 GeV: Extract (<% precision!) Infer couplings from Br measurements: 9

12 ILC Proposal Item C.M. Energy Length Parameters GeV GeV 31 km Luminosity 1.8 x10 34 cm - s Repetition Beam Pulse Period Beam Current Beam size (y) at FF SRF Cavity G. Q 0 5 Hz 0.73 ms 5.8 ma (in pulse) 5.9 nm 31.5 MV/m Q 0 = 1x10 10 few GeV pre-accelerator source e- Polarization 80% e Polarization 30% ILC Accelerator Concept KeV ILD SiD Geant4-based FullSym, incl. beam effects damping ring few GeV bunch compressor Nano-beam Technology few GeV GeV main linac collimation SRF Technology final focus IP extraction & dump - Electron and Positron Sources (e-, e) : - Damping Ring (DR): - Ring to ML beam transport (RTML : - Main Linac (ML SCRF Technology - Beam Delivery System (BDS - 0 years of R&D, key technologies demonstrated - Technical Design Report (TDR) A. Yamamoto, completed in volumes, incl. Physics, Accelerator, Detectors (arxiv) 10 1

13 ILC Operating Scenarios ILC Parameters Joint Working Group T. Barklow, J. Brau, K. Fujii, J. Gao, J. List, N. Walker, K. Yokoya arxiv: Integrated Luminosities [fb] integrated luminosities [fb] ILC, Scenario H-0 ECM = 50 GeV ECM = 350 GeV ECM = 500 GeV Luminosity Upgrade years coupling precision [%] ILC Scenario H-0 model-independent with hadronic recoil years HZZ HWW Hbb Hcc Hgg Hττ Hγγ Htt Γ H Hµµ p s R L dt Lpeak Ramp T T tot Comment [GeV] [fb 1 ] [fb 1 /a] [a] [a] TDR nominal at 5 Hz TDR nominal at 5 Hz operation at 10 Hz Luminosity upgrade TDR lumi-up at 5 Hz lumi-up operation at 10 Hz Figure 7: Time evolution of precision on various couplings of the Higgs boson in the scenar G-0 and H-0. integrated luminosity with sgn(p(e ),P(e )) = p s (-,) (,-) (-,-) (,) [fb 1 ] [fb 1 ] [fb 1 ] [fb 1 ] 50 GeV GeV GeV Table 3: Integrated luminosities per beam helicity configuration resulting from the fractions in ~600K Higgs at 50 GeV, 1M Higgs at 500 GeV 11 4

14 Higgs Couplings - ILC 10% 9% 8% 7% 6% 5% Projected Higgs coupling precision (7-parameter fit) HL-LHC 14 TeV, 3000 fb (CMS, Ref. arxiv: ) HL-LHC 14 TeV, 3000 fb (CMS-, Ref. arxiv: ) ILC 500 GeV, 500 fb 350 GeV, 00 fb 50 GeV, 500 fb ILC 500 GeV, 4000 fb 350 GeV, 00 fb 50 GeV, 000 fb ILC HL-LHC 3000 fb combination % 10 ILC 500 GeV, 500 fb 350 GeV, 00 fb 50 GeV, 500 fb 9% 8% 7% 6% 5% Projected precision of Higgs coupling and width (model-independent fit) ILC 500 GeV, 4000 fb 350 GeV, 00 fb 50 GeV, 000 fb ILC HL-LHC 3000 fb combination 18% 0% if GeV 4% 4% 3% 3% % % 1% 1% 0% κ Z κ W κ b κ g κ γ κ τ, µ κ c, t 0% κ Z κ W κ b κ g κ γ κ τ κ c κ t κ µ Γtot Γ (CL95%) invis Constrained 7-parameter Fit (for comparison w/lhc) Model-Independent Fit (only possible at ee-) Higgs Portal invisible or exotic decays RED - initial ILC running, 8 years ORANGE - full ILC running, 0 years BLUE - use HL-LHC measurement of from LCC Physics WG,

15 includes the International Linear Collider (ILC) [7] and the Compact Linear Collider (CLIC) [8] while the latter is represented by the FCC-ee and CEPC (Fig. 3). CEPC and FCC-ee Proposals agrams at electron 40 years including the recent experimental confirmation of the existence of its last 0verGeV. Left: ing piece, the Higgs boson fundamental questions remain open (such as the small Higgs ess Luminosity [1034 cm-s] n mass compared to the Planck scale, dark matter, matter-antimatter asymmetry, neuo masses,...) which may likely not be fully answered through the study of proton-proton sions at the Large Hadron Collider (LHC). Notwithstanding their lower center-of-mass gies, high-energy e e colliders feature several advantages in new physics studies comd to hadronic machines, such as direct model-independent searches of new particles pling to Z*/γ* with masses up to m s/, and clean experimental environment with al and final states very precisely known theoretically, (i.e. well understood backgrounds out blind spots of p-p searches). Combined with high-luminosities, an e e collider thus provide access to studies with δx precision at the permille level, allowing indirect traints to be set on new physics up to very-high energy scales ΛNP (1 TeV)/ δx. s exist to build future circular (FCC-ee 1), CEPC ) ) and/or linear (ILC 3), CLIC 4) ) colliders (Fig. 1). The advantages of circular machines are (i) their much higher lu Z : cm s - 36 W W : cm-s 10 Fig. 3. Example layouts of FCC-ee project (Left) and CEPC project (Right). The FCC-ee will be located at the CERN site while the FCC-ee (Baseline, IPs) FCC-ee (Target, 4 IPs)yet fixed. An example layout near the location of the CEPC is not ILC city of Qinhuangdao is demonstrated in the right plot. The two ILC (Lumi Upgrade) CLIC plot have 50 km and 100 circumferences. circles in the right Proposals in earlier stages than ILC, but technology is well established (e.g. LEP) CEPC ( IPs) 35 HZ : cm-s The FCC-ee and CEPC will be operated at several Circular colliders can provide 10 centre-of-mass energies, of which s = GeV luminosity, but drops sharply is suitable for the Higgshigh boson precision plings 1can directly measurements. Dedicated runs atw/energy the Z pole and the of the 0SM or the 1000 WW production threshold are equally important, as s [GeV] w physics models they provide excellent electroweak precision Multiple IPs/detectors constant from theas a function re 1: Target luminosities of center-of-mass energy for future circular measurements. Data at the Z pole also provide detector 13 C-ee, CEPC) and linear (ILC, CLIC) e e colliders under consideration. the deviation is calibration to reduce the detector systematic eration process at 34 - tt : cm s HZ : cm-s 500 GeV : cm-s tt : cm-s Dashed lines : Possible energy and luminosity upgrades

16 GGS PHYSICS AT THE CEPC Percentage level precisions can be achieved for the branching ratio measurements of H! bb, cc, gg, W W, ZZ. Higgs Measurements: CEPC mprove the measurement of. These are the most useful inputs from the LHC to e with CEPC. Similar studies with Estimated the ILC can be found in Refs. [40,measurements 56, 57]. Table 3.9 precisions of Higgs boson at the CEPC. All numbers refer to relative precisions except fit forfor mhseveral and BR(H! inv), for which are mh and 95% CL upper limit are quoted 10-parameter fit and the 7-parameter integrated luminosities n Tables 3.1 and 3.11,respectively. respectively. In addition, the combinations with expectaith theoretical uncertainties included) from HL-LHC from Ref. [58] are shown in MHwill operate at 14 (ZH) ( H) BR(H! bb ) H TeV center-of-mass e tables. It is assumed that the HL-LHC and accumulate an integrated luminosity of 3000 fb 1..8% 5.9 MeV 0.51%.8% Z Precision of Higgs coupling measurement (Contrained Fit) 1 Decay mode LHC 300/3000 fb H! bb CEPC 50 GeV at 5 ab H! cc b c wi/wo HL-LHC 0.8%.% g b H! H! WW 1.% 1.5% 1.3% 1.6% H! ZZ 4.3%10-4.3% H! 9.0% 9.0% H! µµ H! inv 17% 17% 0.8% 10-3 Constrained 7-parameter Fit (for comparison w/lhc) h 0.57% CEPC 50 GeV at 5 ab wi/wo HL-LHC.3% 1.7% Z inv ILC GeV at fb wi/wo HL-LHC 1.6% 0.1 W µ BR H! gg g c Precision of Higgs coupling measurement (Model-IndependentFit) Relative Error Relative Error (ZH) BR1 W b c g W Z Br(inv) Model-Independent Fit (comparison with ILC w/o lumi upgrade) 18 The 7 parameter fit result, and comparison with the HL-LHC. The projections for CEPC Figurebased 3.19 on Top: Comparison between LHC, HL-LHC and several benchmark luminosities of t All the are BR a simple ev with 5 ab 1 integrated luminosity shown. measurements The CEPC resultsare without combination withcounting method. The best achievbottom: The (e 10ofparameter 1 fit result and comparison with the ILC. The CEPC at 50 GeV wi input are shown with dashedable edges. The LHC projections for anis integrated fb ZH) precision at the CEPC 0.8%luminosity for e 300! BR(H! bb ). In this mea- 1 integrated luminosity and the ILC GeV at fb are shown. The CEPC and IL n with dashed edges. surement, the precision is limited by the statistical uncertainties. Systematic uncertainties [from CEPC pre-cdr postedwith athl-lhc ] edges. without combination input are shown with dashed from the efficiency/acceptance of the detector, the luminosity and the beam energy deexpected to bebeyond small.thethe integrated CEPC Higgs properties termination measurementsare mark a giant step HL-LHC. First luminosity can be measured with 1.1M Higgs at 50 GeV, no higher-energy running n contrast to the LHC, aa lepton collider Higgslevel, factoryasisachieved capable ofatmeasuring precision of 0.1% LEP [43].theThe center-of-mass energy will be 3.4. Higgs width and coupling strengths the Higgs Aresulting comparison with Self-coupling the HLknown toofbetter than boson. 110 MeV, in negligible uncertainties on the recoil mass meayears, IPs, L=*10e34 cm-sec only possible with model-dependent such comparison is within surements. assumptions. One The Higgs self-coupling, (hhh), is a critical parameter governing the dynamics 14 mework of a 7-parameter The fit, ascepc shownresults in Fig.are The details of combination statistically consistent with the ILC and the FCC-ee studies [8, troweak symmetry breaking. It does not enter the CEPC phenomenology direct L-LHC with several benchmark CEPC luminosities is shown in Table Even

17 Higgs Measurements: FCC-ee s(gev): 90 (Z) 15 (eeh) 160 (WW) 40 (HZ) 350 (tt) 350 (VV H) L /IP (cm s 1 ) L int (ab 1 /yr/ip) Events/year (4 IPs) Years needed (4 IPs) Table 1: Target luminosities, events/year, and years needed to complete the W, Z, H and top programs at FCC-ee. [L =10 35 cm s 1 corresponds to L int =1ab 1 /yr for 1 yr = 10 7 s]. Observable 40 GeV GeV g HZZ 0.16% 0.15% g HWW 0.85% 0.19% g Hbb 0.88% 0.4% g Hcc 1.0% 0.71% g Hgg 1.1% 0.80% g Hττ 0.94% 0.54% g Hµµ 6.4% 6.% g Hγγ 1.7% 1.5% Γ tot.4% 1.% BR inv 0.5% 0.% BR exo 0.48% 0.45% Figure 3: Distribution of recoil mass against Z ll (top) and Z qq (bottom) in the e e HZ process with H bb (top) and H ττ (bottom). Table 3: Expected model-independent uncertainties on Higgs couplings, total width, and branching ratios into invisible and exotic particles (invisible or not) 1). [from d Enterria, arxiv: ] 15

18 Higgs Self-Coupling Precision [%] ILC, P(e) = 30% Higgs Self-Coupling G-0 I-0 Snow H-0 40 ILC: Direct measurement at 500 GeV TeV precision years Precision (%) HL-LHC (3ab ) CEPC1 (1ab ) CEPC3 (3ab ) CEPC5 (5ab ) CEPC10 (10ab ) SPPC (3ab ) HL-LHC CEPC1 CEPC3 CEPC5 CEPC10 SPPC CEPC: indirect determination from (see McCullough 13) 16

19 Higgs Formfactors Form-factors may be induced e.g. by compositeness e /Z /Z Z O WW = g H W a µ W a,µ O BB = g 0 H B µ B µ O WB = gg 0 H a HW a µ B µ O H = 1 (@ µ H ) O T = 1 (H $ D µ H) O (3)` L =(ih a $ D µ H)( L L µ a L L ) O (3)` LL =( L L µ a L L )( L L µ a L L ) O`L =(ih $ D µ H)( L L µ L L ) O e R =(ih $ D µ H)(ē R µ e R ) [Craig, Farina, McCullough, MP, 14] [see also Beneke, Boito, Wang, 14; Craig, Gu, Liu, Wang 15] e h / =0.5% / =0.1% PEW LHC O WW 5.1/ / O BB 1.0/0.64./ O WB.1/ / O H.5/ / O T.0/ / O (3)` L 8.6/5.4 19/ O (3)` LL 5.3/3.4 1/ O`L 10.1/6.4 3/ OR e 8.7/5.5 19/ ~CEPC ~ TLEP 95% c.l. /5-sigma sensitivity one operator at a time 17

20 ! Prospects Summary Mass Width SM: no prediction SM: ~0.01% ~-3% Coupling to W/Z SM: ~ % Coupling to Fermions SM: Coupling to photons, gluons SM: calculable one-loop effect ~1-3% [3rd genc] ~10% [mu] ~1% Self-coupling SM: ~30% Couplings to exotic (non-sm) states Form-factors SM: none SM: none ~0.5% in 18

21 THEORETICAL! IMPLICATIONS

22 Higgs: Big Questions Is the Higgs solely responsible for moderating the high-energy growth of scattering amplitudes of massive gauge bosons and fermions? (=does it give them their masses?) SM: Yes Is the Higgs an elementary (fundamentally novel, truly amazing) scalar? Or is it a composite ( like a pion, still pretty cool)? SM: Elementary If elementary, what (if anything) protects its mass against radiative corrections? ( hierarchy problem ) SM: Nothing Is the Higgs alone, or are there other scalar particles around? How did the Universe evolve from high-temperature, SU()xU(1) symmetric phase to the present broken-ew phase? ( EW phase transition ) SM: Smooth Cross-over SM: Alone 19

23 Higgs and Unitarity In the SM without the Higgs, amplitude grows with energy, eventually predict Prob>1- nonsense!!! M E In the SM with the Higgs, the problem is fixed - theory can be valid up to arbitrarily high scale (until Planck)!! M E 0! If the HVV coupling is not exactly SM, cancellation is spoiled, the theory predicts its own demise : e.g. 0.5% (0.5%) precision probes 0

24 Models with Higgs as a bound state of new QCD are well motivated: no (big) hierarchy problem! So far, Higgs looks elementary between Higgs Compositness some hierarchy is required and compositeness scale Most models (e.g. Little Higgs) incorporate this hierarchy by assuming that the Higgs is a pseudo-ngb corresponding to a broken global symmetry of the new strong dynamics sector PNGB : e.g. Suppression of Higgs couplings: 0.5% (0.5%) precision on hvv will test Similar scales probed by form factor measurements 1

25 ! Higgs Naturalness X If Higgs is elementary, mass stabilization may be achieved by top partners (TPs) Higgs-TP coupling is fixed: 6y t = X i g i ( 1) F i c i But nothing else is: TP may have spin 0 ( stop ), 1/, even 1; may or cancellation may not argument be colored, electrically charged, COLORED top partners (SUSY, Little H): LO shifts in COLORLESS top partners (Twin H): NLO shift in t h h t, FT~1 % interpretation requires an independent top Yukawa ILC-500! [Carmi, Falkowski, Kuflik, Volansky, 1; Farina, MP, Rey-Le Lorier, 13] No sensitivity at the LHC! [Craig, Englert, McCullough, 13] 1 FT~5%

26 Stops: Direct (LHC) vs. Indirect (ILC) (ee-) CB 3.% % % CB Difficult region: compressed spectra 1% m Difficult region ( blind spot ): stop1 and stop loops cancel Complementarity: both likely needed for robust test of stops up to 1 TeV 3

27 Friends and Relations Other scalar fields at the weak scale appear in many models, with different gauge quantum numbers and/or Yukawas The 15 GeV mass eigenstate may contain admixture of these fields, leading to coupling shifts away from the SM Example 1: Higgs Doublets in the MSSM!! 3 V m 4 =sin( ) =1O Z sin 4 4 [ V ] SM m 4 A 3 t m =1O Z cos 4 cos. [ t ] SM b [ b ] SM =1O m A 3 m Z sin 4 cos. m A, Example : Singlet to decoupling is fastest in the case of the coupli 4

28 Higgs Mixing: Implications ILC GeV Higgs is difficult to accommodate in the Minimal SUSY Model (MSSM) Popular solution: Introduce an extra singlet scalar field (NMSSM, or -SUSY) Size of non-sm components in the 15 Higgs is inversely correlated with fine-tuning Precision Higgs program will definitively test this proposal D HDoublet FractionL S HSinglet FractionL Figure 9. Projected 95% c.l. sensitivity of future and prop singlet and non-sm doublet admixture in the 15 GeV Higg Higgs coupling measurements will improve dramatically center-of-mass energy will collect large samples of Higg addition, electron-positron colliders with energies su c Higgs boson have been proposed, such as the ILC [16] o er a prospect of very precise determination of many section, we explore potential implications of such measu [Farina, MP, Shakya 13] 1 D HDoublet FractionL

29 Electroweak Phase Transition At high T, Higgs acquires positive plasma mass^, EW symmetry is restored EW symmetry first broken ~nanosecond after the Big Bang If 1st order phase transition, baryon-antibaryon asymmetry may have been generated in this PT ( EW baryogenesis ) Dynamics described by effective potential:! V T (h) = i g i ( 1) F i T π dkk log[1 ( 1) F i exp( β k Mi )] Higgs-dependent Mass Crossover in the SM; 1st order requires new states at the weak scale with significant Higgs couplings (but not necessarily coupled to any other SM states) Precision Higgs program is crucial for looking for such states! 6

30 EWPT and Higgs Cubic 1st order EWPT requires O(1) changes to the finite-t effective potential Generically physics inducing such changes also induces O(1) change to T=0 effective potential (through loops or mixing) Higgs self-coupling is the first experimental handle on this shape Ξ vs Λ 3 Ξ vs Λ Ξ 1.5 Ξ Λ % deviations from the SM are typical in models with 1st order EWPT Λ 3 [Noble, MP, 07] [Kanemura et.al., 05] 7

31 EWPT and Other Couplings Higgs cubic is the most direct probe of EWPT, but is difficult to measure If new states are colored/charged, they shift If new states mix with the H, see Friends/Relations In any case, new states induce one-loop shift in LH stau model >4% shift in colorless top partners) 300 h=1, f~h1,l ê, hgg h=, Singlet, hzz (just like Singlet model >0.5% shift in mf HGeVL k mf HGeVL k [Katz, MP, 14] [Curtin, Meade, Yu 14] 8

32 Implications Summary Is the Higgs solely responsible for moderating the high-energy growth of scattering amplitudes of massive gauge bosons and fermions? (=does it give them their masses?) Is the Higgs an elementary (fundamentally novel, truly amazing) scalar? Or is it a composite ( like a pion, still pretty cool)? If elementary, what (if anything) protects its mass against radiative corrections? ( hierarchy problem ) Is the Higgs alone, or are there other scalar particles around? How did the Universe evolve from high-temperature, SU()xU(1) symmetric phase to the present broken-ew phase? ( EW phase transition ) 1st order EWPT region covered in most models 9