XLVI TH Rencontres de Moriond QCD and High Energy Interactions Theoretical Summary

1. XLVITHRencontres de MoriondQCD and High Energy InteractionsTheoretical Summary Lance Dixon (CERN & SLAC) La Thuile, 26 March 2011

2. Lots to Review! L. Dixon TheoreticalSummary We heard an amazing number of excellent talks on different theoretical ideas and approaches And, especially with the advent of the LHC, a flood of new data from the energy frontier, which heavily impacts many theories of new physics at the electroweak scale Can’t possibly cover everything Apologies in advance if I missed your favorite topic or talk, or if I distorted it

3. Some General Themes L. Dixon TheoreticalSummary Searching for new physics – new terms in the Lagrangian of Nature – in many different channels Searching for, or further exploring, new phenomena in QCD, e.g. QGP in heavy ion collisions, or diffraction in new kinematical regimes Improving the precision of theoretical predictions in systematic approximations like pQCD, SCET, other resummations Establishing new frameworks/models/pictures where no fully systematic approximation exists

4. New Physics the big picture But still lots to do in understanding “old physics” S. Todorova L. Dixon Theoretical Summary H. Murayama

5. Where is Higgs? • Been looking for him for decades • Know everything but Higgs mass • Search really heating up now, both • from last stages of Tevatron operation, • first stages of LHC M. Cooke LEP2 direct search Precision electroweak Look for now mostly in WW, ZZ, and bb (with associated W or Z) L. Dixon Theoretical Summary

6. SM Higgs at Tevatron • Expect 10-12 fb-1 total by September shutdown. • Could “fail to exclude” at 2s • Hard to get to 3s evidence in SM unless analysis • improvements are greater than projected M. Cooke L. Dixon Theoretical Summary

7. SM Higgs at Tevatron (cont.) • Low mass region more difficult, at ~ 1.5-2 x SM now, with 5.9 fb-1, even with many channels, improved acceptances, hadronict’s, MVAs, … M. Cooke not yet updated for new channels • High mass region also difficult, many channels, but most sensitive is • Now CDF/D0 each can exclude a range of masses gg H  WW  lnln R. Lysak L. Dixon Theoretical Summary

8. SM Higgs at Tevatron (cont.) New high mass combination of CDF and D0 J. Hays L. Dixon Theoretical Summary

9. But Wait! • Theoretical uncertainties leave (high mass) • Higgs in a “half dead, half alive state” - A. Djouadi L. Dixon Theoretical Summary

10. Which uncertainties? Biggest ones: 1) gg H haslarge higher order corrections A. Djouadi However, partial N3LO results and NNLL resummationssuggest(to me) that final cross section will not dip to lowest value in k=3 range. • 2) gg H strongly dependent on g(x) • for x~0.1. Different pdf sets give quite • different cross sections: • MSTW, CTEQ, NNPDF have Tevatron jet data, •  g(x) larger • - ABKM09, HERAPDF do not, g(x) smaller. L. Dixon TheoreticalSummary

11. But Wait! V. Radescu • Brand new NNLO fit to HERA data: HERAPDF1.5 • Gives large x gluon much closer to MSTW! • NNLO Higgs cross section • not yet shown, but clearly it • will rise a lot closer to that • using MSTW. High Mass L. Dixon Theoretical Summary

12. How to improve sH uncertainty? • Very large logs due to soft-gluons. To go beyond • NNLO, can resum“eikonal logs”: • NNLL Catani,deFlorian, Grazzini, Nason • also Ahrens et al., arXiv:1008.3162 • Maybe go to next-to-eikonal approximation before long. C. White H • Would still want at least one N3LO hard term: a3d(x) L. Dixon Theoretical Summary

13. Improve uncertainties from cuts T. Becher L. Dixon Theoretical Summary Effect of jet vetos. Need to resum large logs here, ~ ln(mH/qT), from soft and collinear ISR. Done at Tevatron (as I understand it) by reweighting MC to an NNLL resummation of Higgs qT spectrum (HQT, Bozzi et al.; and/or RESBOS). SCET recently applied to resum another variable, “beam thrust”. Reweight to this, check consistency…Berger et al. Subtle “collinear anomaly” in SCET applied to Drell-Yan qT resummation (where there is a ton of data). Stay tuned for final predictions.

14. ? Where is SUSY? • Been looking for her for decades • Know nothing (theoretically) about any masses (no upper • bounds, anyway, except for lightest Higgs) • Search really heating up now, from first stages of LHC, • but also Tevatron, progress in flavor physics too L. Dixon Theoretical Summary

15. “Generic” SUSY Cascade Searches at LHC • Already surpassed Tevatron in many cases! N. Barlow M. Chiorboli • Will discover or really constrain overall mass scale over next two years L. Dixon Theoretical Summary

16. Many more specialized SUSY Searches • Just one example: top squarkmight be much lighter than • other quarks, because of running effects, large tL-tR splitting): ~ ~ Tevatron, Ph. Gris L. Dixon Theoretical Summary

17. SUSY Higgs • Relatively simple sector: only depends on ~ masses of heavy Higgses, H, A, H± • Light Higgs h has mass < MZ cosb + radiative corrections • LEP2 lower bound  want tanbsomewhat large • Unification suggests very large tanb ~ mt/mb ~ 40 • If MA small, coupling of h to b,s,d,t,m,e all enhanced by tanb • However, if MA large – decoupling limit – effect shuts off ~ tanb L. Dixon Theoretical Summary

18. Direct SUSY Higgs Search Cross section tan2β enhanced Tevatron, St. Denis (roughly, due to SUSY radiative corrections!) watch this space? L. Dixon Theoretical Summary

19. SUSY in Flavor • Muon g-2 anomaly likes large tanβ • Rare B decays can also get huge enhancements • However, both also depend on masses, • flavor mixings of other superpartners Bs,d m+m- M.-O. Bettler, R. Fleischer L. Dixon Theoretical Summary

20. Bs m+m- (cont.) • Exciting because LHCb has already reached • ~ Tevatron sensitivity: M.-O. Bettler • Will cover much of remaining distance to SM in next year or two L. Dixon Theoretical Summary

21. Theory input for Bs m+m- R. Fleischer Predict using “U spin” s  d L. Dixon Theoretical Summary

22. U spin for CP Asymmetries too R. Fleischer Enough information to solve for g At LHCb L. Dixon Theoretical Summary

23. Other New Physics Theories • 4th generation • New W’s or Z’s • Vector-like quarks • Axial-like gluons • Universal (Flat) Extra Dimensions (UED) • Warped Extra Dimensions (RS) • String Excitations • Black Holes (only the safe kind?) Taylor Strogolas Harel Thompson Cho Brandt • Many searched for in di-lepton, di-photon, or di-jets • Particle masses excluded up to around 1 TeV • Other searches often harder, more model specific L. Dixon Theoretical Summary

24. Strings at the LHC? T. Taylor Possibly, if there are also large extra dimensions, and string mass scale M is also very low. gg g*  gg qg  q*  qg … BIGdi-jet bump from So big that L. Dixon Theoretical Summary

25. pQCD for colliders If you don’t know exactly what to look for, need to understand all major SM processes. • Every process shown • also occurs with one more jet • at ~ 1/5 the rate • Very important to understand not only Standard Model production of X but also of • X + n jets • where • X = W, Z, tt, WW, H, … • n = 1,2,3,… LHC @ 7 TeV _ • New physics • Higgs physics L. Dixon Theoretical Summary

26. pQCD for hadron colliders L. Dixon Theoretical Summary Great advancement of last 5 years: Monte Carlo programs that matchleading order QCD exact matrix elements to parton showers (LO ME+PS) – ALPGEN, MadGraph, SHERPA. Describe event “shapes” pretty well But, we need to do better, especially with normalizations. For this we need NLO QCD. Even better would be NLO QCD matched to a parton shower (NLOPS). Even better than that, merging samples with different numbers of jets, as in LO ME+PS but at NLO  MENLOPS

27. (Approximate) MENLOPS L. Dixon Theoretical Summary Merging samples with different numbers of jets at NLO = MENLOPS Can get very close with a recipe combining available NLOPS (POWHEG) and LO ME+PS tools, at least for Drell-Yan (W,Z) and also top-quark pair production K. Hamilton

28. New NLO methods and results L. Dixon Theoretical Summary Unitarity-based method applied to one-loop 6-point amplitudes entering pp  W+W+ + 2 jets T. Melia Same sign dilepton background Preparation for full pp  WW + 2 jets, QCD background to WW electroweak scattering Unitarityrecycles trees into loops Greatly improved theory uncertainty 

29. New NLO methods (cont.) L. Dixon Theoretical Summary All NLO calculations need one-loop amplitudes, but they also need to integrate tree cross sections with one extra partonover a singular phase space region. Catani-Seymour dipole subtraction method for dsAis standard, but requires lots of different terms – may be computationally limiting step. Method proposed by Nagy-Soper recently implemented. T. Robens Promising for more complex processes if integrals of subtraction terms dsA can be tabulated numerically.

30. Approximate (N)NLO method L. Dixon Theoretical Summary LoopSim– method to approximate higher order corrections –like an approximate Sudakov factor S. Sapeta Works best when leading-order (LO) QCD is anomalously small – i.e. when there are “giant K factors”, as in Z + 1 jet production at LHC

31. Top is here O. Brandt Z. Ye Parameter in PYTHIA M. Cristinziani • Yukawa coupling is parameter in • Lagrangian(related to MS mass) • Given this exceptional precision, • theorists need to do a better job • of relating the two masses • (via pole mass, presumably) ___ Z. Ye Helps, but now only sensitive at 5 GeV level L. Dixon Theoretical Summary Based on

32. Top mostly looks normal so far S. Amerio M. Cristinziani J. Gruschke L. Dixon Theoretical Summary

33. Except for maybe AFB O. Brandt _ L. Dixon TheoreticalSummary In SM, AFB = 0 at O(as2). MC is O(as3), first order in which AFB ≠ 0 Would like O(as4), to be sure no large corrections. People working on it, in conjunction with s(t t) at NNLO. What about measuring AFB with an extra jet? Known at second order already [Dittmaier, Uwer, Weinzierl]

34. New physics for AFB? Bai, Hewett, Kaplan, Rizzo, 1101.5203 L. Dixon Theoretical Summary • s-channel heavy color-octet, Lorentz vector state • Candidates: top-color, technicolor, universal and warped extra dimensions, chiral color, axi-gluons, …  dijet and Mtt bumps • t-channel: flavor-changing interactions • same sign tops, especially at LHC

35. QCD in extreme or nonperturbative environments A. Tang A. Koshelkin L. Dixon Theoretical Summary Self-consistent nonperturbative solution to coupled gluon-quark quasi-classical equations: currents generated by fermions and gauge field exactly compensate each other Proposed application to heavy ion collisions as alternative to Glasma model [McLerran ,Venugopalan]

36. Extreme QCD (cont.) B. Zakharov L. Dixon Theoretical Summary Study jet quenching via (quasi)perturbative approach, Bethe-Heitler gluon radiation + collisional losses off scattering centers in quark-gluon plasma, Technically challenging calculation. At the end, very sensitive to non-perturbative distance scales r ~ 1/Q, reflected in dependence on as freezing point used

37. AdS/CFT • Not really QCD, but maybe it is “close enough” at strong coupling • Finite temperature • black hole present • (Hawking radiation) L. Dixon Theoretical Summary Another approach to understanding jet quenching, also the bulk properties of quark-gluon plasma. AdS/CFT maps a strongly-coupled 3+1 (conformal) gauge theory “holographically” to a semi-classical 4+1 gravitational theory in Anti-de Sitter space

38. AdS/CFT & bulk flow • Very strong coupling  very small viscosity: • h/s = 1/4pKovtun, Starinets, Son • Using this value in hydro codes gives second moment of azimuthal particle correlations, v2, consistent with observations first at RHIC, and now at LHC • M. Nicassio , ALICE Chen • Comparison with RHIC results •  30 % higher • Hydrodynamic model predictions with • viscous corrections in agreement • with observed increase |h|<0.8 0.2<pt<5GeV/c • Third moment, v3, recently • measured at RHIC, and in perfect agreement too! Chen L. Dixon Theoretical Summary

39. hot and dense medium parton AdS/CFT & jet quenching • Energy loss in strongly-coupled plasma is large – so large • it can’t be reliably computed for light quark – need heavy one • But that’s harder to measure, hasn’t been done (quite) yet, • though open charm has now been found in heavy ions  A. Mischke L. Dixon Theoretical Summary

40. g + c as energy loss probe F. Arleo Study, e.g. c b Preliminary computation using a perturbative energy loss framework L. Dixon Theoretical Summary

41. glueballs mesons baryons AdS/CFT for light hadron spectrum Closed strings Open strings on D8 D8-brane Meson & baryon masses, form factors, etc., agree surprisingly well with data, with only 2 free parameters D4 wrapped on D4-brane Nc strings are attached L. Dixon Theoretical Summary Can use a different model to put in quarksSugimoto

42. Nonperturbative QCD in B Physics q b T. Mannel L. Dixon Theoretical Summary Into the brown muck For mQ >> LQCD, a heavy quark is almost static within its meson, and its spin decouples Nowadays, want to go to high order in LQCD/mQ Have to classify all local operators at a given order

43. Nonperturbative QCD in B’s (cont.) T. Mannel • Relates matrix elements to better known • matrix elements of lower dimension operators. • Apply method to inclusive B  c l n decay width G   inclusive Also reviewed new lattice value L. Dixon Theoretical Summary

44. Nonperturbative QCD in B’s (cont.) G. Paz • CP asymmetry in B  sgonce thought to be • perturbative, precise SM test. • But now long-distance effects have been • estimated using SCET, found to be large exp vs. L. Dixon Theoretical Summary

45. From b to c _ _ L. Dixon TheoreticalSummary Life gets more difficult for theorists: LQCD/mcis not << 1. More model dependence, e.g. pole dominance model for the various topological amplitudes entering D decays C.-D. Lu Life (sometimes) gets easier for experimentalists: Particle yields can be much larger – consider for example the rich cornucopia of exotic c-c containing hadrons from 3872 to 4660 GeVD. Liventsev No analogs discovered yet in the b-b system

46. Want new particles? D. Liventsev L. Dixon Theoretical Summary

47. What are they? D. Liventsev Compute two-pion exchange (loop level) potential between baryons. Might be a bound state, but answer depends on cutoff in effective theory, so inconclusive d d or baryon-antibaryon?? C. Qiao L. Dixon Theoretical Summary

48. Soft & diffractive physics S. Todorova Proposed test for it: L. Dixon Theoretical Summary New implementation of a helical variation on the Lund string model

49. The underlying event at LHC C.-E. Wulz L. Dixon Theoretical Summary Harder than expected The “hard tail” of the underlying event is double parton scattering. Suggests that DPS should be visible at LHC soon, whether in bbjjE. Berger  gjjjas at TevatronN. Skachkov or maybe even Wjj or Zjj

50. Soft diffraction at LHC L. Dixon TheoreticalSummary MC strategy proposed to remedy this. K. Goulianos