Precision QCD Physics Input to European Strategy Update Gavin Salam* Rudolf Peierls Centre for Theoretical Physics and All Souls College University of Oxford Snowmass Energy-Frontier Workshop — Open Questions and New Ideas 21 July 2020, EF01-04 parallel session * on leave from CERN TH department and from CNRS (LPTHE) 1 European Particle Physics Strategy Update (EPPSU), 2018 – 2020 ➤ http://europeanstrategyupdate.web.cern.ch/welcome ➤ Major preparatory work on approved and proposed future colliders, e.g. ➤ Report on the Physics at the HL-LHC, and Perspectives for the HE-LHC ➤ FCC physics and design reports ➤ Submitted input: https://indico.cern.ch/event/765096/contributions/ (10pp/doc) ➤ Open Symposium (May 2019), including strong interactions session & summary ➤ Physics briefing book: arXiv:1910.11775 (strong interactions: section 4) ➤ January 2020: final closed meeting of European Strategy Group ➤ Final strategy document published June 2020 2 3 two broad roles for QCD QCD in service of broad particle QCD as a physics goals colliders fascinating subject (Higgs, EW, in its own right DM/BSM, etc.) 4 from Thomas Gehrmann’s EPPSU talk Where do we stand? • QCD at high energies: weak coupling and asymptotic freedom • Perturbative QCD as quantitative framework • Dynamics of quarks and gluons • Jet observables were early test of QCD • Factorization separates weak from strong coupling effects • Quantitative predictions • Multi-loop calculations for inclusive quantities • Higher orders (NLO, NNLO, …), resummation and parton shower simulation • Strong coupling dynamics parametrized in parton distributions, hadronization Thomas Gehrmann ESPP Update Open Symposium Granada 5 from Thomas Gehrmann’s EPPSU talk Where do we stand? • Precision tests of the Standard Model Standard Model Production Cross Section Measurements Status: March 2019 total (2x) 11 10 inelastic ATLAS Preliminary [pb] Theory • Measurements of masses and couplings ps TeV σ Run 1,2 = 5,7,8,13 6 incl 10 LHC pp ps =5TeV 1 Data 0.025 fb− dijets • 105 Interplay of calculations and pT > 25 GeV LHC pp ps =7TeV 4 1 10 nj 0 Data 4.5 4.9 fb− measurements ≥ − LHC pp ps =8TeV 3 nj 1 10 ≥ nj 0 pT > 125 GeV ≥ 1 total Data 20.2 20.3 fb− pT > 100 GeV n 2 WW j ≥ − t-chan • ≳ 2 WW Accuracy on most cross sections 5% nj 1 nj 1 10 ≥ ≥ WZ WW nj 3 LHC pp ps = 13 TeV ≥ Wt WZ total ZZ WZ n 2 nj 2 j ≥ ≥ 1 Data 3.2 79.8 fb− 1 nj 4 ZZ ZZ ggF 10 ≥ H WW − • nj 3 nj 4 ! W γ Limited by PDFs, QCD corrections ≥ nj 3 ≥ VH ≥ nj 5 H bb nj 5 s-chan ! ≥ ≥ n n 6 H ⌧⌧ j 4 j ! Zγ 1 ≥ ≥ tZj nj 6 ≥ Wjj n 5 nj 7 j ≥ ≥ VBF H WW • Perturbative QCD as analysis tool 1 ! n 8 10− j ≥ n 6 j ≥ H γγ ! Zjj n 7 2 j ≥ 10− nj 7 ≥ H ZZ 4` • Jet substructure techniques ! ! W ±W ± 10 3 • Data-driven background predictions − WZ pp Jets γ W Z t¯t t VV γγ H WV Vγ t¯tWt¯tZ t¯tH t¯tγ γγγ Vjj WW Wγγ Zγjj EWK Excl. Zγγ WWγ VVjj tot. tot. tot. tot. tot. tot. EWK Thomas Gehrmann ESPP Update Open Symposium Granada 6 from Thomas Gehrmann’s EPPSU talk Where do we stand? • QCD at strong coupling: diverse research program • Hadron physics, low-energy dynamics, heavy ions • Precision spectroscopy of light hadrons ⟷ lattice QCD at high precision • Determination of hadron properties CODATA-2014 µp 2013 • Proton radius 5.6 s • Form factors µp 2010 H spectroscopy • Nucleon structure e-p scatt 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.9 1706.00696 proton charge radius [fm] • Demands and drives new quantitative approaches • Understanding non-perturbative dynamics of QCD Thomas Gehrmann ESPP Update Open Symposium Granada 7 from Thomas Gehrmann’s EPPSU talk Where do we stand? • Crucial interplay between QCD at strong and at weak coupling • Non-perturbative effects on precision collider observables • Parton distributions • Intrinsic transverse momentum • Soft underlying event and hadronization • Hadronic input to SM tests and BSM searches • Form factors in flavor physics • Hadronic cross sections in neutrino and astroparticle physics 0811.4622 • Hadronic effects in QED precision observables: α(MZ), (g-2)μ Thomas Gehrmann ESPP Update Open Symposium Granada 8 from Thomas Gehrmann’s EPPSU talk Where do we stand? • Feed-in and feed-back between strong and weak coupling QCD • Example: photon content of the proton (photon PDF) • Important ingredient to EW corrections of collider processes • Required for precision predictions at highest energies • Previously ad-hoc models with large uncertainty • LUXqed • relate to elastic and inelastic form factors • Exploit low-energy data • Combine with perturbative QCD evolution • Different motivation to address similar questions 1607.04266 Thomas Gehrmann ESPP Update Open Symposium Granada 9 to maximally exploit HL-LHC 10 QCD theory is workhorse of LHC experiments them 1 cite that 0.8 papers GEANT4 0.6 & CMS ATLAS0.4 of Anti-kt jet alg. fraction 0.2 MG5aMCatNLO 0 FastJet Manual POWHEG Box NNPDF30 PDFs Pythia 8.1 CL(s) technique (A.Read) POWHEG (2007) Likelihood tests for new physics Papers POWHEG (2004) Pythia 6.4 MC commonly Pythia 8.2 CT10 PDFs cited as of Sherpa 1.1 2019-02-13,by ATLAS CL(s) technique (T.Junk) (red papers NNPDF23 PDFs excluding and top++ self-citations;CMS CTEQ6 PDFs (since MSTW2008 PDFs ≡ all papers PDF4LHC-RunII QCD) 2017) > Herwig++ MC 0.2 Review of Particle Physics 2016 POWHEG single-top (2010) FxFx EvtGen (2001) InspireHEP from data on based Salam GP by Plot 11 These coupling measurements assume the absence of sizable s = 14 TeV, 3000 fb-1 per experiment additional contributions to GH . As recently suggested, the patterns Total Needof quantum for precision interference between @ backgroundHL-LHC and Higgs-mediated ATLAS and CMS Statistical HL-LHC Projection production of photon pairs or four leptons are sensitive to GH . Experimental ➤ Measuringillustrated the off-shellin the four-fermion case of Higgs final states, physics and assuming Theory Uncertainty [%] the Higgs couplings to gluons and ZZ evolve off-shell as in the 2% 4% Tot Stat Exp Th κγ 1.8 0.8 1.0 1.3 ➤ SM,theory the HL-LHC uncertainty will extract (PDFGH with + a 20% strong precision at 68% CL. Furthermore, combining all Higgs channels, and with the sole κW 1.7 0.8 0.7 1.3 assumptioncoupling that + the missing couplings tohigher vector bosons orders) are not larger than κ 1.5 0.7 0.6 1.2 the SM ones (k 1), will constrain G with a 5% precision at Z dominatesV in 7/9 channelsH 95% CL. Invisible Higgs boson decays will be searched for at κg 2.5 0.9 0.8 2.1 HL-LHC in all production channels, VBF being the most sensitive. ➤ κ 3.4 0.9 1.1 3.1 Thethis combination is with of the ATLAS assumption and CMS Higgs of boson coupling mea- t surementsreduction will set by an x2 upper in limit today’s on the Higgs theory invisible branching κb 3.7 1.3 1.3 3.2 ratio of 2.5%, at the 95% CL. The precision reach in the mea- κτ 1.9 0.9 0.8 1.5 surementsuncertainties of ratios will be at the percent level, with particularly κ 4.3 3.8 1.0 1.7 interesting measurements of kg /kZ, which serves as a probe of µ ➤ newdepending physics entering on channel, the H gg loop,it can can be measured the with an ! κZγ 9.8 7.2 1.7 6.4 uncertainty of 1.4%, and kt /kg, which serves as probe of new 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 physicsuncertainties entering the forgg theH loop, signal with a or precision the of 3.4%. ! Expected uncertainty backgroundA summary of that the limits dominates. obtained on first and second gen- eration quarks from a variety of observables is given in Fig. 2 Figure 1. Projected uncertainties on ki, combining (left). It includes: (i) HL-LHC projections for exclusive decays of ATLAS and CMS: total (grey box), statistical (blue), the Higgs into quarkonia; (ii) constraints from fits to differential experimental (green) and theory (red). From Ref. [2]. cross sections of kinematic observables (in particular pT); (iii) 12 constraints on the total width GH relying on different assumptions (the examples given in the Fig. 2 (left) correspond to a projected limit of 200 MeV on the total width from the mass shift from the interference in the diphoton channel between signal and continuous background and the constraint at 68% CL on the total width from off-shell couplings measurements of 20%); (iv) a global fit of Higgs production cross sections (yielding the constraint of 5% on the width mentioned herein); and (v) the direct search for Higgs decays to cc using inclusive charm tagging techniques. Assuming SM couplings, the latter is expected to lead to the most stringent upper limit of kc / 2. A combination of ATLAS, CMS and LHCb results would further improve this constraint to kc / 1. The Run 2 experience in searches for Higgs pair production led to a reappraisal of the HL-LHC sensitivity, including several channels, some of which were not considered in previous projections: 2b2g, 2b2t, 4b, 2bWW, 2bZZ. Assuming the SM Higgs Figure 2. Left: Summary of the projected HL-LHC limits on the quark Yukawa couplings. Right: Summary of constraints on the SMEFT operators considered. The shaded bounds arise from a global fit of all operators, those assuming the existence of a single operator are labeled as "exclusive".