The Higgs Boson Discovery and the Road Ahead

James Wells CERN & UM Paris July 1, 2013 The Higgs Boson Discovery and the Road Ahead HISTORICAL SLIDE – 2 YEARS OLD
Should we believe in the Higgs boson? The Higgs boson is a speculaLve parLcle explanaLon for elementary parLcle masses. Cons: 1.  One parLcle carries all burdens of mass generaLon? 2.  Fundamental scalar not known in nature. 3.  Hasn’t been found yet. 4.  Too simplisLc -­‐-­‐ dynamics for vev not built in. 5.  Idea not stable to quantum correcLons. Pros: SLll consistent with experimental facts! 2 Higgs boson unstable to QM A quantum loop is quadraLcally divergent. Higgs mass, connected to Higgs vev, is unstable to the highest mass scales in the theory. Confusing: MPl is 1,000,000,000,000,000,000 Lmes more massive than hydrogen, whereas the Higgs boson is only 130 Lmes more massive than hydrogen. 3 Cures of the Naturalness Problem, and the ResulLng Higgs boson Entourage 1.  Disallow all scalars in the theory (Technicolor). 2.  Symmetry cancels quadraLc divergences (supersymmetry) 3.  Disallow higher mass scales (extra dimensions). 4 OLD SLIDE – 2 YEARS OLD
New Physics Ideas and Higgs boson viability Trying to fix and understand Higgs physics leads to new ideas that have states that look very similar to the Standard Model Higgs boson. Precision Electroweak Data almost demands this to be true. What does the future hold for the Higgs boson? DISCOVERY!! 5 New York Times mass = 125 – 126 GeV 6 What does "almost 'The' Standard Model Higgs boson" mean? The boson has the same, measured mass of 126 GeV. However, its producLon rates are slightly different, and its probabiliLes of decaying into various other parLcles are slightly different. . . . The deviaLons from these e's may be only a few percent or less. Will take many years to be sensiLve to that, and perhaps even requires another collider (e+e-­‐). 7 What for the Future? Manifestly obvious that we should study carefully every Higgs boson property accessible. This will happen at the LHC and its possible upgrades This is also the quesLon being asked of the linear collider Not a totally easy quesLon to answer. With S. Gupta and H. Rzehak we have been looking at this. Higgs boson mass Conjecture: There is no value added from bemer-­‐than-­‐LHC measurements Implica2on: Any discussion about how this or that e+e-­‐ opLon etc. helps obtain a bemer Higgs mass determinaLon is of limited value. I would be happy to be proved wrong, but let me explain why I say this through two important examples: Fate of the Universe & Supersymmetry tests (no Lme for susy example). 9 LHC Measurement of Higgs Mass It is claimed by CMS and ATLAS [1] that a measurement of the Higgs mass to bemer than 0.1% accuracy is possible with 30 q-­‐1 at 14 TeV. For 126 GeV Higgs mass that means bemer than 150 MeV mass determinaLon. Why would we want it bemer? [1] See, e.g., Fig 10.37 of CMS TDR vol II (2007). See also Fig. 19-­‐45 of ATLAS TDR. 10 Fate of the Universe λ λ = MH2 / 2v2 MZ MPl Q Higgs mass lower than some criLcal value and potenLal is unstable, and the universe can phase transiLon to another vacuum. 11 Fate of universe (cont.) EquaLon for the criLcal mass needed for stability is Espinosa et al. The 3 GeV uncertainty is from unknown higher effects. The uncertainty on criLcal MH from a 300 MeV uncertainty in Mtop, is already 600 MeV, which well above LHC uncertainLes for MH. No more measurements of the Higgs mass are going to help this quesLon. 12 Supersymmetry tests By definiLon we can state that the lightest Higgs boson of SUSY has a mass of tanβ is the raLo of vevs of the two Higgs doublets and ΔS2 contains all the SUSY masses and mixings etc. At leading order 13 Supersymmetry tests (cont.) Let us consider the impossible: (1) tanβ is measured perfectly, (2) ΔS2 is measured to bemer than 0.5%, (3) mtop is measured to bemer than 100 MeV. What uncertainty does that give to the Higgs mass predicLon? Answer: 140 MeV. (1σ deviaLons range for mtop and ΔS2) Measuring the Higgs boson mass to bemer than this is not useful. 14 Higgs boson couplings Enough on the Higgs boson mass. What about its couplings? How well do we need to know the couplings? One approach: Who knows?!!! UnsaLsfactory. Let's first decide on some criteria to answer the quesLon. 15 How well do we need to measure the Higgs boson coupling? Criterion: What are the largest coupling deviaLons away from the SM Higgs couplings that are possible if no other state directly related to EWSB (another Higgs, or “rho meson”) is directly accessible at the LHC. We looked at three important examples: -­‐ Supersymmetry -­‐ Singlet Higgs mixed in with the SM Higgs -­‐ Composite Higgs 16 ParentheLc Thoughts on ImplicaLons for SUSY First, I am slightly more encouraged about Supersymmetry than I was a year ago…. Why? A) Limits on superpartners from the old 114 GeV Higgs mass limit was generically more worrisome than any limits LHC at 7 TeV could provide. B) A light-­‐ish SM-­‐like Higgs boson (less than about 140 GeV) is always what I expected. And it had not shown up yet. But now we have a Higgs boson, and it looks SM-­‐like. Worry A has not changed at all, and worry B has gone away for SUSY. CorrecLons to Higgs Couplings in MSSM Two leading correcLons are a) mixing of would-­‐be SM Higgs with heavy Higgs Not mass eigenstate "HSM" x "Hheavy" mixing angle is ~ mZ2 / mA2 b) Finite b quark mass correcLons, disrupLng Yukawa – Mass relaLon bL SUSY bR 18 Summary of Higgs CorrecLons for SUSY If no extra heavy Higgses are found at LHC at 14 TeV with 300 q-­‐1 of integrated luminosity, the maximum deviaLons of the light Higgs from the SM couplings are hZZ, hWW < 1 %, hm = 3 %, hbb = 100 %, hγγ derived from these If we also include that no superpartners are found then it becomes hZZ, hWW < 1 %, hm = 3 %, hbb = 10 %, hγγ derived from these 21 de
diso a
nts
ow
SUMMARY hV V
ht̄t
hb̄b
Mixed-in Singlet
6%
6%
6%
Composite Higgs
8% tens of % tens of %
Minimal Supersymmetry < 1%
3%
10%a , 100%b
LHC 14 TeV, 3 ab 1
8%
10%
15%
TABLE I: Summary of the physics-based targets for Higgs
boson couplings to vector bosons, top quarks, and bottom
quarks. The target is based on scenarios where no other exotic
electroweak symmetry breaking state (e.g., new Higgs bosons
or ⇢ particle) is found at the LHC except one: the ⇠ 125 GeV
SM-like Higgs boson. For the hb̄b values of supersymmetry,
superscript a refers to the case of high tan > 20 and no
superpartners are found at the LHC, and superscript b refers
to all other cases, with the maximum 100% value reached for
the special case of tan ' 5. The last row reports anticipated
1 LHC sensitivities at 14 TeV with 3 ab 1 of accumulated
luminosity [5].
Details in Gupta, Rzehak, JW, arXiv:1206.3560. 22 Implica2ons of Oddi2es in Higgs Sector But what if the Higgs boson is not pure SM? What if it … Is composite, or Mixes with singlet(s) Part of mulL-­‐doublet theory 23 Extra condensing Higgs boson – singlet under SM Higgs Masses and Mixings 24 Two Paths to LHC Discovery Within this framework, we studied two ways to find Higgs boson at the LHC: 1)  Narrow Trans-­‐TeV Higgs boson signal 2)  Heavy Higgs to light Higgs decays Bowen, Cui, JW 25 Narrow Trans-­‐TeV Higgs Boson When the mixing is small, the heavy Higgs has smaller cross-­‐secLon (bad), but more narrow (good). InvesLgate Point C example 26 Two Signals 1) 27 H-­‐>WW-­‐>jjlν
Techniques: Atlas & CMS TDRs and Iordanidis, Zeppenfeld, ‘97 Between 1.0 & 1.3 TeV 13 signal events in 100 q-­‐1 vs. 7.7 bkgd H-­‐>WW (solid) WWjj (dashed) mjj (domed) 28 Difference from SUSY heavy Higgs boson SUSY heavy Higgs has qualitaLvely different behavior: Haber et al. ‘01 Heavy Higgs decays mostly into tops or bomoms (or susy partners) depending on tanβ. 29 H decays to lighter Higgses We can also have a heavier Higgs boson decaying into two lighter ones in this scenario. Both Higgses suppressed with respect to SM Higgs. Standard Higgs search channels are reduced by 50% -­‐-­‐ takes even longer to find…. Search through H-­‐>hh decays. 30 Heavy to Light Higgs rate Considered discovery mode (Richter-­‐Was et al.): 30 q-­‐1 bkgd esLmates Bowen, Cui, JW 31 Conclusions Higgs boson discovery extraordinary, even if expected. Conjecture: LHC will measure the Higgs boson mass as well as we will ever want it. My expectaLon is that Higgs observable deviaLons from the SM will be small (less than 10%) and may need future e+e-­‐ to see it. Extra Higgs bosons are generic and may be found a~er many years of LHC running.