1. Top-quark physics ─ Theory Status ─ Peter Uwer ICHEP 2014, Valencia, 7.7.2014 GK1504

2. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 2 Content  Tremendous progress in the theoretical description of top- quark physics  Possible, due to many synergies in recent developments  Per cent level accuracy for inclusive quantities  (10%) level accuracy for exclusive processes even for “large” multiplicities  Many recent results publicly available for the analysis in form of Computer code  Top-quark physics ideal laboratory for precise tests of the Standard Model and New Physics searches Heaviest elementary fermion discovered so far  strong coupling to the Higgs, very sensitive to electro weak symmetry breaking

3. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 3 Steps towards precision Fixed-order Perturbative Corrections (NLO,NNLO) Beyond fixed order 1/ , ln(  ) LL,NLL,NNLL Predictions for observable final state Top-decay… Matching with Parton-shower à la MC@NLO and Powheg INPUT m t,  s, V tq, PDFs, Precise theoretical predictions NNLO predictions for top- quark pair and single top- quark production Top-quark mass measurements Combined fit mt,as,gPDF tt+2Jets Matched and merged @ NLO Towards distributions in NNLO Unified description of tt and tW production Cannot cover everything since time is to short Focus on new directions / developments illustrated through specific examples Apologies to all those, who's work is not mentioned

4. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 4 Inclusive top-quark pair production in NNLO Recent progress: NNLO / NNLL QCD predictions Top-quark pair production in Born approximation: Very active field, see also related work: [Czakon,Mitov,Fiedler ‘12, ‘13] [Bonciani, Ferroglia,Gehrmann,Manteuffel,Studerus ’11,Abelof, Gehrmann-de Ridder, ‘12] Bonciani, Ferroglia,Gehrmann,Manteuffel,Studerus ’13] Abelof,Gehrmann-de Ridder, Maierhöfer,Pozzorini ’14,… (Distributions: work in progress)

5. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 5 Inclusive top-quark pair production in NNLO [Hathor 2.1, Top++ 2.0] Residual scale (in)dependence restricted scale variation to avoid large ratios  NLO  NNLO shifts cross section by 13pb (5.4%)  Significant reduction of scale dependence [Czakon,Mitov,Fiedler ‘12, ‘13]

6. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 6 Inclusive top-quark pair production in NNLO [Hathor 2.1, Top++ 2.0]  NNLO  NNLL shifts cross section by 6.7pb (2.7%)  NNLL resummation further stabilizes residual scale dep. Residual scale (in)dependence restricted scale variation to avoid large ratios [Czakon,Mitov,Fiedler ‘12, ‘13]

7. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 7 Inclusive top-quark pair production in NNLO Scale (in)dependence using the MS mass m(m) Use mass renormalized in minimal subtraction (“running mass”, MS mass) Mass is just another parameter, can be renormalized/defined using different schemes

8. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 8 Inclusive top-quark pair production in NNLO Scale (in)dependence using the MS mass For differential distributions using the MS mass in NLO see [Dowling,Moch ‘13] Scale variation: Scale (in)dependence further improved! 0.512 [Czakon,Mitov,Fiedler ‘12, ‘13 +Hathor 2.1]

9. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 9 Steps towards distributions in NNLO accuracy [Guzzi, Lipka, Moch ‘14] Construct ansatz for one-particle inclusive distributions based on soft gluon resummation +…

10. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 10 Steps towards distributions in NNLO accuracy [Guzzi, Lipka, Moch ‘14]  Scale dependence is reduced  Agreement with data is improved  How well is inclusive cross section reproduced ?  Impact of damping factors ? (normalized!)

11. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 11 Top-quark pair production in association with jets  Higher order corrections typically large for high multiplicities  NLO required  Average momentum scale decreases with increasing jet mult. Soft and coll. emission important  parton shower Different phase space regions require different theoretical treatment

12. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 12 Matching and Merging LO NLO Remove double counting through matching à la MC@NLO, Powheg Merging: Use appropriate Description in specific phase space region Combine LO/NLO & PS Mad5_aMC@NLO, MEPS@NLO [Frederix, Frixione 12 Höche,Krauss,Schönherr,Siegert 13, Gehrmann,Höche,Krauss,Schönherr,Siegert 13, Alwall,Frederix,Frixione,Hirschi,Maltoni,Mattelaer, Shao,Stelzer,Torrielli,Zaro 14]  Unified description Fixed order Parton shower

13. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 13 Top-quark pair production in association with jets [Höche,Krauss,Maierhöfer,Pozzorini,Schönherr,Siegert ‘14]  much improved uncertainties, unified description Progress possible due to very advanced one-loop technology and high degree of automation Matching and merging: de facto standard for future predictions ?

14. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 14 Single top-quark production Born processes for single top-quark production: t-channel s-channel Wt production NLO corrections for the t-channel: + … Cancel in interference with Born due to color Interesting: V_tb, b-pdf, source of polarized top-quarks,…

15. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 15 Single top-quark production in NLO [Hathor-2.1]  Small NLO corrections  Scale uncertainties very small  PDF uncertainties small However:  Sizeable cancellations in t-channel NLO corrections  Box diagrams don’t contribute Size of the NLO corrections accidentally small ? scale var. up and down PDF uncert.

16. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 16 Single top-quark production: Steps towards NNLO ++…+ +… (neglected)  “Factorizable” NNLO corrections under control  Fully differential  What about double-box contributions? [Brucherseifer,Caola, Melnikov ‘14] NNLO Results for top-quark production: (  may affect distributions…)

17. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 17 Disentangling tW and tt production tW production in NLO ─ real corrections [Frixione,Laenen, Motylinski, Webber, White 08] In NLO tW and tt production interfere For an overview of different strategies see Recent progress: Study in the 4-flavour scheme keeping top- quark / W-boson off-shell effects and a finite b-quark mass [Cascioli,Kallweit,Maierhöfer,Pozzorini 14, Frederix 14] (  gauge invariance, realistic cuts…)

18. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 18 Disentangling tW and tt production Technically very challenging, possible only due to recent progress in one-loop calculations + automation Full calculation  allows gauge invariant separation in - narrow width limit  on-shell top-quark pair prod. - finite remainder  off shell contr., single-top, ….  includes all interference terms Corrections to inclusive cross sections well behaved

19. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 19 Disentangling tW and tt production Complete cross section Finite width contribution b-jet multiplicity Finite b-quark mass allows full phase coverage Interesting to see how this will affect realistic analysis

20. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 20 Top-quark mass measurements  Measurements based on established methods start to reach intrinsic limitations due to […my view.] -Ambiguity MC mass  Pole mass -Sometimes used leading order analysis -Intrinsic uncertainties of the pole mass (and the fact that the measurements are getting incredible precise…)  Very active field, new techniques and improved known methods under investigation  New methods follow the same theme: Fit top mass through measurement of theoretically well defined observable (holds also for distributions)

21. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 21 New methods ─ m t from tt+1-jet [Fuster et al 13] High sensitivity Insensitiv to PDFs Pert. theory reliable Small impact of non-pert. modelling Small experimental uncertainties Requirements for sub percent level accuracy Further improvements to the already very precise measurements very challenging. Use complementary methods with comparable uncertainties to cross check measurements (M lb, ttj, lepton-spectra, endpoint analysis)

22. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 22 Constraining non-perturbative input of the SM Top-quark pair production sensitive to gluon distribution  Use top-quark pair production to constrain the gluon luminosity [Czakon, Mangano, Mitov, Rojo 13] x = 0.06…0.5 X-Range:

23. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 23 Determining the gluon PDF, m t and  s in a global fit [Alekhin, Blümlein,Moch 14] Only a handful data points for inclusive cross section used so far, no distributions included, more to come  Incl. of tt data leads to consistent results ABM11   ABM12  Top-quark mass determination: (correlations taken into account by the fit) As usual: Be careful that we don’t absorb New Physics into the PDFs

24. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 24 Conclusion / Summary  Tremendous progress in the theoretical description of top- quark physics  Possible, due to many synergies in recent developments  Per cent level accuracy for inclusive quantities  (10%) level accuracy for exclusive processes even for “large” multiplicities  Many recent results publicly available for the analysis in form of Computer code The time of “predicted discoveries” might be over for a while, remember method successfully applied over hundreds of years: Turn every stone and look below Top-quark physics is a very big one, many things may hide below

25. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 25

26. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 26 Precision physics with tops ─ Future directions Further test top-quark physics at the quantum level transversal polarisation, specific spin correlations in tt Nice example: Top-quark charge asymmetry t  SM predictions typically small, any significant deviation may point to new physics Alternative observables: ( m w -m t -m h, vacuum stability are of the same type…) virt. corr. to tt real corr. to tt @ NLO

27. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 27 Inclusive top-quark pair production in NNLO [Top++ 2.0, Hathor 2.1] Residual scale dependence restricted scale variation to avoid large ratios [Top++ 2.0]

28. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 28 Top-quark pair production ─ theory status Incl. cross section NLO Incl. cross section NNLO 1989 [Dawson, Ellis, Nason ’89, Beenakker et al ’89,91] [Bernreuther, Brandenburg, Si, PU ’04 [Czakon,Mitov 08] Spin dependent cross section NLO 2004 [Bonciani, Catani, Mangano,Nason ‘98, Kidonakis, Laenen, Moch, Vogt 01] NLL resummation 19982008 Analytic results NLO Steps towards NNLL [Moch, PU 08] Bound state effects [Kiyo,Kuhn,Moch,Steinhauser,PU 08 Hagiwara, Sumion, Yokoya 08] Full NNLL resummation 2010 [Czakon,Fiedler,Mitov 13] 2013 Combined NNLL and 1/  [Ahrens, Beneke,Czakon, Ferroglia, Mitov, Schwinn…] Impressive theoretical progress in last 25 years Similar for single top-quark production Many more results on differential distributions, add. jets, combination with parton shower, top decay… Th. uncertainty below ~5% Further progress will require substantial effort from theory Some milestones

29. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 29 What is currently done in experiment ATLAS-CDF-CMS-D0 combination: [arXiv 1403.4427] “The systematic uncertainty related to the specific MC choice is found to be marginal with respect to the possible intrinsic difference between the top-quark mass implemented in any MC and the pole mass definition” From different studies: My feeling: Large effects unlikely

30. Peter Uwer (HU Berlin) | Top-quark physics – Theory status ─ | ICHEP14 Valencia, 07.07.2014 | 30 Testing the SM with top-quarks ─ examples [Degrassi, Di Vita, Elias-Miro,Spinosa,Giudici ’12, Alekhin, Djouadi, Moch ’12] Vacuum stability Consistency of the SM  Precise theoretical predictions required