Gavin Salam* Rudolf Peierls Centre for Theoretical Physics and All

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

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 Limited by PDFs, QCD corrections nj 3 VH nj 5 H bb nj 5 s-chan ! n n 6 H ⌧⌧ j 4 j ! Z 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 ! 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 W Z t¯t t VV H WV V t¯tWt¯tZ t¯tH t¯t Vjj WW W Zjj EWK Excl. Z WW 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

Papers commonly cited by ATLAS and CMS (since 2017) 1 as of 2019-02-13, excluding self-citations; all papers > 0.2 alg. GEANT4 jet t ≡ them (red papers QCD) physics Anti-k 0.8 cite (A.Read) new Manual Box PDFs MG5aMCatNLO for that

(2007) 8.1 2016 FastJet tests (2004) technique MC POWHEG papers 0.6 NNPDF30 (T.Junk) Pythia 6.4 (2010) CL(s) Physics POWHEG 8.2 CMS Likelihood PDFs POWHEG PDFs

& PDFs Pythia 1.1 PDFs technique Pythia MC Particle single-top CT10 0.4 of (2001) Sherpa ATLAS CL(s) NNPDF23 top++ CTEQ6 of MSTW2008 PDF4LHC-RunII InspireHEP Herwig++ Review POWHEG FxFx EvtGen from data

0.2 on fraction based Salam GP by

0 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 generation 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". From Ref. [2].

2 2.2.1.1 Gluon fusion In this section we document cross section predictions for a standard model Higgs boson produced through gluon fusion in 27 TeV pp collisions. To derive predictions we include contributions based on perturbative computations of scattering cross sections as studied in Ref. [47]. We include perturbative QCD corrections through next-to-next-to-next-to-leading order (N3LO), electroweak (EW) and approximated mixed QCD-electroweak corrections as well as effects of finite quark masses. The only modification with respect to YR4 [45] is that we now include the exact N3LO heavy top effective theory cross section of Ref. [48] instead of its previous approximation. The result of this modification is only a small change in the central values and uncertainties. To derive theoretical uncertainties we follow the prescriptions outlined in Ref. [47]. We use the following inputs:

ECM 27 TeV mt(mt) 162.7 GeV m (m )4.18 GeV b b (5) mc(3 GeV)0.986 GeV ↵S(mZ )0.118 PDF PDF4LHC15_nnlo_100 [49]

All quark masses are treated in the MS scheme. To derive numerical predictions we use the program iHixs [50]. Sources of uncertainty for the inclusive Higgs boson production cross section have been assessed gluonrecently fusion in refs. Higgs [47, 51, 52 theory, 45]. Several uncertainties sources of theoretical uncertainties were identiﬁed.

12 LHC

% 8 (PDF+s) 100 ×

6 (1/mt) total / i (t,b,c) (EW) 4 (PDF-TH) 2 (scale) 0 0 20 40 60 80 100 Collider Energy / TeV Fig. 1: The ﬁgure shows the linear sum of the different sources of relative uncertainties as a function of the collider energy. Each coloured band represents the size of one particular source of uncertainty as described in the text. The component (PDF + ↵S) corresponds to the uncertainties due to our imprecise knowledge of the strong coupling constant and of parton distribution functions combined in quadrature. 13

– Missing higher-order effects of QCD corrections beyond N3LO ((scale)). – Missing higher-order effects of electroweak and mixed QCD-electroweak corrections at and beyond (↵ ↵) ((EW)). O S – Effects due to ﬁnite quark masses neglected in QCD corrections beyond NLO ((t,b,c) and (1/mt)).

17 QCD theory anticipated / needed for full exploitation of HL-LHC

(1) Fixed-order / resummed calculations ➤ Core processes at high accuracy (2→1 and 2→2): 1%, N3LO ➤ Splitting functions at N3LO (also needed for potential ep machines) ➤ Complex processes at few percent accuracy

➤ Accuracy at high pT

➤ Technical requirements for NLO multi-particle precision ➤ Multi-variate analyses / observables: performance and uncertainties ➤ Non-perturbative eﬀects ➤ Resummation (incl. SCET) ➤ Accurate predictions for BSM eﬀects

14 QCD theory anticipated / needed for full exploitation of HL-LHC

(2) General purpose Monte Carlo event-generator tools ➤ Perturbative improvements for Matching and Merging (e.g. generalisation of approaches for parton shower + NNLO merging,) ➤ Understanding & exploiting relation between parton-shower algorithms and resummation ➤ Phenomenological Models (hadronisation, underlying event, also connects with HI physics, neutrino programmes, low energy QCD, various “beyond colliders” experiments, cosmic-ray physics)

15 projected improvements in PDFs & strong coupling

➤ plot illustrates use of pseudodata Projected invariant tt mass data gluon PDF with projected tt data

with HL-LHC stats to obtain 3 Lumi error = 1.5 % 10 1.3 Q = 100 GeV

estimates of expected PDF 102 original g/g

uncertainties at HL-LHC [fb/GeV] 10 1.2 tt 1

➤ /dm PDF extractions will need to move to −1 σ 10 PDF4LHC15

d 1.1 PDF4LHC15+ HL-LHC m N3LO once available 10−2 tt HL-LHC pseudo-data, F = 0.2 10−3 3 ➤ mtt [GeV] strong coupling remains contentious 1.4 10 1 1.3 ➤ tensions between diﬀerent groups’ Ratio 1.2 0.9 extractions (PDFs, event shapes, 1.1 1 PDF4LHC15 and to a lesser extent lattice QCD) 0.9 0.8 PDF4LHC15 + HLLHC tt 0.8 ➤ F = 0.2 what ultimate accuracy on 10-15 0.7 0.6 year timescale? 3 0.7 10 10−5 10−4 10−3 10−2 10−1 mtt [GeV] x 16

Figure 3.5. Left: As in Fig. 3.2, now for the mtt¯ distribution in top quark pair production. Right: As in Fig. 3.3, now for the gluon PDF after including the HL–LHC tt¯ pseudo–data in the ﬁt.

Correlations between inclusive jet production (η<0.5) and the gluon PDF Correlations between direct photon production (η<0.6) and the gluon PDF

ρ 1 ρ 1 0.8 0.8

0.6 0.6 0.4 0.4

0.2 0.2 0 0

−0.2 −0.2

−0.4 −0.4 −0.6 −0.6

−0.8 PDF4LHC15 + HLLHC p −0.8 PDF4LHC15 + HLLHC Eγ T T −1 −1 10−5 10−4 10−3 10−2 10−1 10−5 10−4 10−3 10−2 10−1 x x Figure 3.6. As in Fig. 3.1, now for the correlation coecient between the gluon PDF and the central rapidity bin of the inclusive jet (left) and direct photon (right) pseudo–data.

in the forward rapidity region, relevant for LHCb. In Fig. 3.9 we show the correlation coecient between the strange PDF and the lepton rapidity distributions in W +charm production pseudo– data both for the central and the forward rapidity regions. We can see that indeed there is a large correlation between the strange PDF and the W +charm production pseudo–data in a broad range of x values. For the case of central production, we find ⇢ 0.9 in the range of 10 3 x 0.1, while for forward production the correlation coecient ⇢ peaks at a somewhat   smaller value, and covers a broader range in x, with in particular a coverage of the small and large–x regions that is complementary to the central production pseudo–data. The comparison between the HL–LHC pseudo–data and the corresponding theoretical predictions for W +charm production both in the central and forward regions are collected in Fig. 3.10. In the central region, we see a clear reduction of the PDF uncertainties after including the pseudo–data into the fit, by around a factor two. This reduction of uncertainty is approximately constant as a function of the lepton rapidity. At forward rapidities instead, we find that before adding the pseudo–data the PDF uncertainties grow very fast with rapidity, reaching up to 30% for ⌘ 4.5, while after including it they are markedly reduced and become l ' more or less constant with rapidity as in the central region. Taking into account the correlation coecients shown in Fig. 3.9, these results indicates that W +charm production in the forward region provides valuable constraints on the large–x strangeness, which is currently a↵ected by large uncertainties. This PDF uncertainty reduction on strangeness upon the addition of the W +charm pseudo–

15 to maximally exploit proposed future colliders (ee, eh, hh)

17 5. Numerically dominant effects due multi-photon emission constitute another key problem; their+ - complexity will be often comparable to that of the electroweak loop calculations. The future emethodologye colliders of joint treatment of electroweak and QCD loop corrections with the photonic corrections is essentially at hand (AB from the LHC?). In practice, however, construction ➤ 3-loopof and new partial Monte Carlo 4-loop programs, calculations which can of handle Zff vertex efficiently for the Tera-Z above problems,for EW pseudo-observables will need special efforts [6]. ➤ precision for decays, e.g. in Higgs physics and top-quark physics The elementary techniques for higher order perturbative SM corrections are basically under- ➤ newstood, generations but their use in of practical MC programs calculations for at theQED level and of computer EW eff programsects, understanding will be highly non- two-photon physicstrivial and will require considerable effort. The understanding of all sources of possible theoretical uncertainties will be fundamental for success of the FCC-ee data analysis.

4 5 2,l 6 Z [MeV] Rl [10 ] Rb [10 ] sineff ✓ [10 ] Present EWPO theoretical uncertainties EXP-2018 2.3 250 66 160 TH-2018 0.4 60 10 45 EWPO theoretical uncertainties when FCC-ee will start EXP-FCC-ee 0.1 10 2 6 6 ÷ TH-FCC-ee 0.07 7 3 7

Table 1: Comparison for selected precision observables of present experimental measurements (EXP-2018), current theory errors (TH-2018), FCC-ee precision goals at the end of the Tera-Z run (EXP-FCC-ee) and rough estimates of the theory errors assuming that electroweak 3-loop corrections and the dominant 4-loop EW-QCD corrections are available at the start of FCC-ee (TH-FCC-ee). Based on discussion in [2]. 18

Table 1 shows the current experimental and theoretical errors (EXP-2018, TH-2018) for some basic Z-physics EWPOs, and the prospective measurement errors at FCC-ee (EXP-FCC-ee) to- gether with the corresponding estimate for theoretical uncertainties after the leading 3/4-loop results become available (TH-FCC-ee). The entry TH-2018 takes into account recent completion of the 2-loop electroweak calculations [7, 8], so the error estimate comes solely from an estimate of magnitudes of missing 3-loop and 4-loop EW and mixed EW-QCD corrections. The estimated TH-FCC-ee error stems from remaining 4-loop and higher effects. These are rather difﬁcult to estimate presently, however, a rough conservative upper bound on them has been provided in [2]. They are denoted in Tab. 1 as TH-FCC-ee. As we can see, the uncertainties of the TH-FCC-ee scenario are comparable to the corresponding EXP-FCC-ee experimental errors and will not limit the FCC-ee physics goals. An illustration of complexity of future perturbative calculations is provided in Table 2, where the numbers of distinct topologies of diagrams to be calculated and the numbers of diagrams and various categories at the 1-, 2- and 3-loop order are shown for the most complicated Z b¯b decay. ! According to Ref. [2], the calculation of fermionic 3-loop corrections, which will be the largest part of them, are within reach, already with present methods and tools. Another important issue in electroweak ﬁts are uncertainties from the existing (often experi-

5 future pp colliders FCC Physics Opportunities

➤ combination of higher energies and jet rate luminosities will continue to push potential @ 100 TeV pp for precision

➤ need for precision will extend to high 10k events (1% stat.prec) transverse momenta → requires improved for jets with pT > 15 TeV treatment of EW corrections, including mixed QCD-EW eﬀects

➤ very high-multiplicity ﬁnal states, possibly involvingFigure 5.4: multiple High-pT jet scales rates (left) → needs and luminosity evolution of the minimum pT thresholds leading to 1 and 10% statistical uncertainties (right). understanding of regions of validity of perturbation theory, interplay with parton showers, etc., including for EW objects

1 Figure 5.5: Left plot: combined statistical and 1% systematic uncertainties, at 30 ab , vs pT threshold; these are compared to the rate change induced by the presence of 4 or 8 TeV gluinos in the running of ↵S. Right plot: the gluino mass that can be probed with a 3 deviation from the SM jet rate (solid line), and the pT scale at which the corresponding deviation is detected.

perturbative calculations and in the knowledge of the PDFs. For measurements sensitive to the shape of the distribution (e.g. the running of ↵S or the search of shape anomalies due to higher-dimension operators), the absolute luminosity determination does not contribute to the systematics. The jet energy resolution will only lead to a predictable smearing of the pT spectrum. Furthermore, the energy resolution itself will be very small, limited in the multi-TeV region by the 2.6% constant term, as reported in Volume 3, Section 7.5.2. The stochastic contribution, even in presence of 1000 pile-up events, scales in the region ⌘ < 1.3 like 104%/ p /GeV, and drops below the % level for p >10 TeV. The leading | | T T experimental systematics will most likely be associated with the determination of the⇠ absolute jet-energy p scale (JES). A great deal of experience is being accumulated at the LHC on the JES calibration [143,144], combining, among others, test-beam data, hardware monitoring via sources, and data-driven balancing + techniques. The latter rely on events such as Z[ e e]+jet, g+jet or multijets. The precise measure- ! ment of EM energy deposit of photons and electrons allows the calibration of the jet energy, up to energy levels where there is sufﬁcient statistics. At larger energies, leading jets are calibrated against recoil sys- 1 tems composed of two or more softer jets. In their ﬁnal calibration of approximately 20 fb of 8 TeV data from run 1, CMS [144] achieved a JES uncertainty for central jets of about 0.3% in the 200-300 GeV 1 range. ATLAS [143], using 3.2 fb of 13 TeV data, determined a more conservative uncertainty of less than 1% for central jets with pT in the range 100-500 GeV. A naive rescaling of the statistics based on the

54 PREPRINT submitted to Eur. Phys. J. C PDFs:PDFs: StillStill workwork toto dodo forfor FCC...FCC...

■ Still large PDF uncertainties in pp at 100 TeV in key (x,Q2) regions:

NEW PHYSICS High-x

g uncert. from David PRECISION PHYSICS d’Enterria’s EPPSU talk Mid-x LOW-X gg PHYSICS

Low-x ■ FCC-ep required to reach O(1%) uncertainty for s(W,Z,H) at FCC-pp g uncert.

Strong Interactions, EPPS Update, May'19 18/27 David d'Enterria (CERN) 20 The ep Physics at the Energy Frontier and unfold hadron sub-structure for LHC and FCC-hh unambiguously New ep colliders RPV SUSY, LQ beyond HERA c.m.s. Substructure ? Extensions of both 2 H HH x and Q ranges are crucial for pp Large x experiments and High Higgs Gluon & HEP theory Precision Boson valence developments; from Uta QCD & quarks EW (t, W, Z) Klein’s HERA established Physics the validity of EPPSU talk pQCD down to x > 10-4 (DGLAP) High Density due to a very high

momentum transfer squared 2 - Matter lever arm in Q : Saturation?

four New form of - high luminosity gluonic matter? colliders with high c.m.s. small x for UHE energy of Neutrinos & FCC-hh 1.3 3.5 TeV

Bjorken 21 High-precisionHigh-precision gluongluon && quarkquark jetjet studiesstudies (FCC-ee)(FCC-ee)

■ Exploit FCC-ee H(gg) as a ”pure gluon” factory: H→gg (BR~8% accurately known) provides O(100.000) extra-clean digluon events.

■ Multiple handles to study gluon radiation & g-jet properties: ➧Gluon vs. quark via H→gg vs. Z→qq from David (Profit from excellent g,b separation) d’Enterria’s ➧ Gluon vs. quark via Z→bbg vs. Z→qq(g) (g in one hemisphere recoiling EPPSU talk against 2-b-jets in the other). + - ➧ Vary Ejet range via ISR: e e →Z*,g*→jj(g) ➧ Vary jet radius: small-R down to calo resolution LH angularities

■ Multiple high-precision analyses at hand: – BSM: Improve q/g/Q discrimination tools [G.Soyez et al.] – pQCD: Check NnLO antenna functions. High-precision QCD coupling. – non-pQCD: Gluon fragmentation: Octet neutralization? (zero-charge gluon jet with rap gaps). Colour reconnection? Glueballs ? Leading h's,baryons?

Strong Interactions, EPPS Update, May'19 21/27 David d'Enterria (CERN) 22 Highly-boostedHighly-boosted jets,jets, multijetsmultijets (FCC-pp)(FCC-pp)

■ Proton-proton collisions at 100 TeV provide unique conditions to

produce & study highly-boosted objects: top, W, Z, H, RBSM(jj),...

Resolving small angular dijet sep. ∆R ≈ 2M(jj)/pT(j). ■ Jet substructure: key to separate dijets from QCD & (un)coloured resonance decays, e.g.

R10-TeV Æ tt,qq,gg,WW from David d’Enterria’s ■ Diffs. in MC generators for EPPSU talk quark vs. gluon jets (& jet radius).

■ Also unique multijet (N>>10) BSM, QCD studies

[FCC-pp, arXiv:1607.01831] Strong Interactions, EPPS Update, May'19 22/27 David d'Enterria (CERN) 23 resources & the next generation

24 incoming / early-stage researchers and subsequent career development

➤ early-stage researchers need recognition for a variety of types of contribution (e.g. including the technical work that simply “makes things work” but that comes neither with glory nor even necessarily papers) ➤ how do we ensure recognition for early-stage researchers working within the medium-sized teams (O(10) researchers) that are increasingly common? ➤ specialisation v. broad training ➤ successful projects need skills that span interface with maths (incl. computer algebra), interface with computing, machine-learning, and a range of physics/ pheno applications → individuals specialise ➤ at same time we need to ensure future generation can combine speciﬁc expertise with broad physics ability within the ﬁeld

25 issues of long-term support

➤ funding for projects that last longer than typical funding cycles ➤ support for codes: ➤ state-of-the-art physics codes often developed in small groups, but subsequent long-term maintenance & user-support of successful codes often requires substantial dedicated expert time, which can be a substantial burden ➤ the “glue” codes (e.g. LHAPDF, HepMC): may not be seen as physics by funding agencies, but support (people/resources) & evolution essential for long-term smooth operation of the field ➤ “mechanisms need to be developed to share the effort between event generator projects and their user communities” [Id114] (& we need to ensure that conditions are attractive for those who do this well, e.g. in terms of career recognition) ➤ computing aspects ➤ adapting codes to new architectures ➤ availability of state-of-the-art hardware (e.g. hundreds of GPUs, very high-memory machines) ➤ many university groups can’t afford to keep up with disparate landscape of hardware. How best to share nationally and internationally? 26 Summary

27 QCD theory summary

➤ Advances in QCD theory are essential to exploit HL-LHC and future colliders (and already built into some projections!) ➤ They will involve a wide range of topics, spanning calculations of amplitudes to Monte Carlo event generations, including phenomenological work to connect with data ➤ Theory advances can bring light also on many topics of intrinsic interest in QCD, including proton structure, exotic hadrons, connections with “theorists’s theories” like N=4 SUSY ➤ Continued support of QCD theory is essential for success of European collider programme, and community needs to keep in mind ➤ recognition of contributions of early-stage researchers as teams grow larger ➤ funding structure for increasingly long-term theory projects ➤ positions and career development for individuals who provide essential “support” roles (maintenance of widely used tools, interfacing with & support for users, …) ➤ computing (access to hardware and expertise) 28 backup

29 2.2.1.1 Gluon fusion In this section we document cross section predictions for a standard model Higgs boson produced through gluon fusion in 27 TeV pp collisions. To derive predictions we include contributions based on perturbative computations of scattering cross sections as studied in Ref. [47]. We include perturbative QCD corrections through next-to-next-to-next-to-leading order (N3LO), electroweak (EW) and approximated mixed QCD-electroweak corrections as well as effects of finite quark masses. The only modification with respect to YR4 [45] is that we now include the exact N3LO heavy top effective theory cross section of Ref. [48] instead of its previous approximation. The result of this modification is only a small change in the central values and uncertainties. To derive theoretical uncertainties we follow the prescriptions outlined in Ref. [47]. We use the following inputs:

ECM 27 TeV mt(mt) 162.7 GeV m (m )4.18 GeV b b (5) mc(3 GeV)0.986 GeV ↵S(mZ )0.118 PDF PDF4LHC15_nnlo_100 [49]

% 8 (PDF+s) 100 ×

17 Theoretical path for QCD physics: main inputs

Id100 Precision calculations for high-energy collider processes

Id101 Theory Requirements and Possibilities for [ee colliders]

Id114 MC event generators for HEP physics event simulation

Id163 Quantum Chromodynamics: Theory