1. The road to the ElectroWeak Symmetry Breaking 18 th January 2012 Seminar at Johns Hopkins University S.Bolognesi (Johns Hopkins University)

2. Outline  Status: CMS results in a nutshell, focusing on high mass H->VV  move to larger mass (>600 GeV beyond SM)  improve sensitivity to smaller xsec -> Vector Boson Fusion  The final arbiter: VV scattering 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 2  The Higgs boson and the ElectroWeak Symmetry Breaking (EWSB) control of V+jets background jet merging signal characterization (angular analysis)  What’s next ? control of VV background

3. Why we need the Higgs The Higgs boson provides 1) an EXPLICATION of the W,Z mass (ie EWSB) 2) a DESCRIPTION of the fermions masses  1 is really fundamental to make the SM “working” (next slides) … even if not less arbitrary!  2 is just another way of formulating the same question: why the fermions have those particular masses? why the fermions have those particular Higgs couplings? (SM works well without 2: just the fermio-phobic Higgs) 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 3

4. EWSB and the W, Z mass Gauge invariance SU(2) U(1) EM complex scalar doublet of SU(2) scalar potential ( >0,  <0) with minimum (= empty state) at SU(2) 3 Goldstone bosons  i 1 physical scalar field (v = empty expectation value) generic Gauge Gauge unitario 4 Gauge fields combined into known vector bosons: W,Z with mass, photon massless 1 physical scalar field -> Higgs 4 Gauge fields W i ,B  U(1) or × 01/18/2012 seminar 4

5. V V Higgs and unitarity in VBF VBF is the smoking gun of the EWSB ! Same behavior for all VV amplitudes (s channel only) (t channel only) (t and u channels) canale Scanale T QGC V V V VV -> VV Vector Boson Fusion (VBF) W,Z mass (-> longitudinal degrees of freedom) arise from the Higgs mechanism: without Higgs, W + L W - L ->W + L W - L would break unitarity V 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 5

6. VBF and VV scattering  VV scattering spectrum  (VV->VV) vs M(VV)  Whatever we will see or not see at low mass (<2×m W ), the EWSB mechanism must be probed in the VV final state  search for possible resonances in VBF  measurement of VV scattering spectrum is the fundamental probe to test nature of Higgs boson or to find alternative EWSB mechanism  SB <1TeV SB sector weakly coupled SB sector strongly coupled eg, strongly interacting light Higgs SM No-Higgs  SB >1TeV Unitarity violation other scenarios possible: 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 6

7. Higgs production and decay 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 7

8. CMS results  WW→lnqq, ZZ→llqq limited by huge V+jets background, taken from simu/data with large theoretical/statistical error  ZZ→llnn:  WW→lnln at high mass limited by signal << WW background (  not effective) >400 GeV limited by Z+jets tail at high MET: not large but not well known (controlled with  +jets → statistical error+met uncertainty) 200-400 GeV limited by non-Z background (top, W+jets, WW)  ZZ→4l limited by statistics (only ZZ background: small and well known) drives the UL for mH>300-400 drives the UL for mH 200-300

9. Future improvements ?  Combination of >5 different channels (ele, mu, btag, …) Robust!  Very optimized analyses, some space for further improvement. With higher lumi: use shape analyses (where not yet done) extract background (norm and shape) from data with lower uncertainty extract signal with multidimensional fit (now only mZZ fit) 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 9

10. What’s next ? higher mass lower xsec 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 10

11. 1 TeV masses: not anymore “the” Higgs → General search for X→VV→4f: → importance of semileptonic final states xsec larger than Higgs: at high mass still very low number of events per fb -1 RS Graviton vs SM Higgs: exotic models (eg, Technicolor, ExtraDimension, …) first, repeat “Higgs” search for different spin, width resonance CMS AN-2010-35: Angular Analysis of Resonances pp → X → ZZ 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 11

12. Available results: ZZ low statistics MET control V+jetsZZ→4lZZ→llnn  CDF search for G→ZZ: same features discussed for high mass Higgs @ LHC ZZ→lljj: large V+jets arXiv:1111.3432v1

13. Available results: W+2jets CDF “bump” ATLAS & D0 xchecks S.Bolognesi (Johns Hopkins University) 13

14. Control of V+jets  Improving theoretical tools (Blackhat, Madgraph, …)  Control region (eg, Z→jj sidebands) has very low stat for M(lljj)~1 TeV rely on them to extrapolate at higher energy/multiplicity test them where we have statistics 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 14

15.  QCD measurement (jet p T >20-30 GeV): → syst. dominated by jet scale, PileUp removal V+jets  Data unfolded for detector effects → compared to NLO (“hadron level”) ATLAS: 01/18/2012 seminar 15

16. V+jets at Tevatron At low p T, low multiplicity: but results limited by systematics interesting discrepancy data-NLO observed → new variables D0 novel measurement: angular correlations have much lower systematics 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 16

17. High mass: what’s new ?  Can we simply keep the same Higgs analysis strategy? Not at very high masses!  New experimental issues at very high mass (1 TeV and above) X → boosted VV → jet merging (and nearby leptons)  Unknown signal and very small background → no point in pushed optimization! Keep model independent approach as much as possible  How to disentangle the various models? peak → mass and width, xsec and BR spin! → angular analysis 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 17

18. >1 TeV M(ZZ)→4f : jet merging (1)  Jet merging:  R 0.8 (CA) → M X >600 GeV  R 0.5 (Akt) → M X >900 GeV approx Handles to distinguish wrt to jets from QCD (eg, X→ZZ→2l2j VS Z+jets):  jet mass ttbar → WW→ln (jj) CMS EXO-11-006 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 18

19.  jet radiation: soft/collinear singularity in QCDno singularity, just decay! Jet merging (2) by David Krohn (Harvard)JHU seminar: Path-Integral Jets www.pha.jhu.edu/groups/particle-theory/seminars/talks/F11/talk.khron.pdf Handles to distinguish wrt to jets from QCD (eg, X→ZZ→2l2j VS Z+jets): 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 19

20. Jet pruning  Remove all parts of the jet which are soft and wide angle Boosted objects mass reconstruction improved  QCD jets mass substantially decreased -> lower backgrounds Typically used for boosted top or boosted H→bb … arXiv:0912.0033v1 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 20

21. Example in X→ZZ→2l2j First look at Z boosted (no numbers yet) … M G 1500 GeV RS Graviton CA 0.8 preliminary, A.Bonato, R.Covarelli X->ZZ->2l2q signal Z+jets before jet pruning after jet pruning before jet pruning after jet pruning 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 21

22. Angular analysis (1)  X→ZZ→4f decay kinematic fully defined by 5 angles signal (M X 250):MC from Johns Hopkins 0+, 0- 1+, 1- 2+m, 2+L, 2- X→ZZ Z decays 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 22

23.  Can be clearly used to disentangle different signals… but what about background?  Already used in H→ZZ→2l2q: cut on likelihood Z+jets from MC: no correlations,  To optimize further (multidimensional fit), need full theoretical description of background:  qq → ZZ:  gg also available → can be used to disentangle qq-gg!! signal: ideal × uncorr. accept (background from jj sidebands) Angular analysis (2) CMS PAS -11- 017 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 23

24. What’s next ? higher mass lower xsec 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 24

25. Improve sensitivity  Improve theoretical control of signal: → NNLO&NNLL effects, precise mass shape prediction, signal-background interference (back-up) background: → control of ZZ, WW ewk continuum  Factor 5 in luminosity wrt to present results  WHY? Models with lower xsec  HOW? Ex of (light) composite higgs: (studied in the Higgs Xsec WG and documented in 2 Yellow Report) First LHC to Terascale Workshop (Sept 2011): LCH at LHC by J.R. Espinoza 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 25

26. Diboson production (WW,WZ,ZZ)  SM test: TGC fixed by ewk gauge structure → any deviation from SM in VV xsec is direct hint of NP in bosonic sector  Backgrounds for high mass Higgs→VV gg→ VV (LHC: few % of xsec with ~50% uncertainty) qqbar → VV WW,WZ,ZZ forbidden for ZZ + NLO qqbar + forbidden for ZW TGC LHC focused on leptonic final state, Tevatron looked at semileptonic but limited by systematics (V+jets) 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 26

27. VV: theoretical prediction qq→ZZ NLO + gg→ZZ  Uncertainty dominated by QCD part 01/18/2012 seminar 27 PDF+  s scale  WW in jet bins: uncertainty on  >=N) + modeling: MC@NLO vs ALPGEN qq

28. ZZ→4l: measurement  4l is 0.5% of ZZ xsec but very clean observed events: 8 expected events: 12.5±1.1 Dedicated EWK analysis with very low luminosity, Higgs results much beyond that 39% 16% 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 28

29. WW->lnln: measurement 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 29  Dedicated EWK results only with very low luminosity,  Higgs analysis much beyond that: stat. and syst. errors included 37%

30.  First search for a VBF resonance, feasible in 2012  Measurement of VV scattering spectrum with higher lumi (>50 fb -1 ) From VBF to VV scattering Tipical signature: forward-backward “spectator” jets with very high energy JHEP 0704 (2007) 052 VBF ggH + 2jets VBF ggH + 2jets 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 30

31. Higgs-like resonance in VBF  Today only WW→lnln. Expectations for next year: lumi > 10 fb-1  (vbf) ~ 0.1×  (gg) 0.5 effic. VBF cuts VBF yields in 2012 ~ 0.5 gg yields of 2011 summer results,  ZZ→4l will be still limited by statistics  WW→lnln will improve S/B (signal/10, WW*  s 2 )  semileptonic final states will have reasonable signal yields + much lower background than inclusive analysis eg, ZZ→lljj : signal yields for m H 300-500 ~ 15 – 5 events V+(N+1)jets/V+N jets ~ 0.15 → asking 2 jets reduces background to 2%! S/B may increase of a factor 2 (eff 0.5 ×  0.1 / 0.02)  RE-DO all the analyses in VBF mode (eg, fermiophobic) 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 31 with much less background: summer2011

32. VV scattering spectrum  In no Higgs case: BUT increasing of xsec at high VV is suppressed by → small difference btw SM and violation of unitarity (no Higgs) → with proper cut (eg  jets) can be enhanced -> selection of the longitudinal W SILH W ± W ± scattering PDF offshell bosons unpolarized bosons reducible background 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 32

33. Longitudinal polarization ud->udWW->udcs  mH 500 GeVnoHiggs (unitarity violation) WW tail (TT): neutrino WW tail (TT): lepton Higgs peak (LL): neutrino Higgs peak (LL): lepton Transverse distribution Longitudinal distribution  Angular analysis can boost LL-TT separation (new!): partonic study in the center of mass of W 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 33

34. VV scattering: interference effects 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 34... 2 signal irreducible background (  EW 6 ) qq->6f O(  EW 6 ) WW approximated without interference  Big interference effects considered only in Phantom JHEP 0603 (2006) 093 Accomando, Ballestrero, Bolognesi, Maina, Mariotti = WW signal with “a posteriori” cuts

35. Summary  experimental issue: control of V+jets (jet pruning)  several theoretical uncertainties on VV EWK continuum angular analysis  Ingredients along the EWSB road:  search for VBF resonance and measuring of VV scattering spectrum  search for generic resonance X->ZZ->4f  Main steps:  The first aim of the Higgs search is the understanding of the EWSB -> focus on H->VV final state 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 35

36. BACK-UP 18 th January 2012 Seminar at Johns Hopkins University S.Bolognesi (Johns Hopkins University) The road to the ElectroWeak Symmetry Breaking

37. Sources First LHC to Terascale Workshop (Sept 2011): LCH at LHC by J.R. Espinoza CMS AN-2010-35: Angular Analysis of Resonances pp → X → ZZ by David Krohn (Harvard)JHU seminar: Path-Integral Jets www.pha.jhu.edu/groups/particle-theory/seminars/talks/F11/talk.khron.pdf Boson Boson scattering analysis by A.Ballestrero (INFN Torino) LHC To Terascale Physics WSS.Bolognesi (Johns Hopkins University) 37

38. Mass shape From Passarino talk at last LHC to Terascale WS  Present approx: xsec for on-shell Higgs production and decay in zero width approx acceptance from MC with ad-hoc BW distribution 10-30% uncertainty on xsec for mH 400–600 GeV Study with QFT-consistent Higgs propagator in the YR2

39. Higgs qT q T > mH NNLO q T << mH NNLL (resumming ln(mH 2 /q T 2 ))  HqT: Uncertainties: factor/renorm scale PDF large mt approximation non perturb. effects (smearing with NP form factor) LHC To Terascale Physics WSS.Bolognesi (Johns Hopkins University) 39

40. Reweight to HqT  Very small effect on acceptance in 4l: 1-2%  HqT used to reweight full event generators (POWHEG at NLO) mH 120 GeV mH 500 GeV H p T H y mH 120 GeVmH 500 GeV Powheg Powheg re- weighted to Hqt HNNLO (larger if jet veto!) LHC To Terascale Physics WSS.Bolognesi (Johns Hopkins University) 40 (to be redone before PS)

41. Signal: jet counting  Analysis in exclusive jet bins (ex, WW+0,1,2 jets) if background depends on Njets for VBF → theoretical uncert in jet bins to be combined with correlations  varying renormalization and factorization scales in the fixed- order predictions for each exclusive jet cross section σN (results as 100% correlated) different treatments of the uncontrolled higher- order O(α 3 s) terms i.e., different NNLO expansions  inclusive xsec (σ≥Njets), as source of perturbative uncertainties σN = σ≥N − σ≥N+1 with error propagation LHC To Terascale Physics WSS.Bolognesi (Johns Hopkins University) 41

42. Signal: jet veto  Resummation of jet-veto logarithms ( ln(p cut /mH) ), induced by jet cut parameter p cut direct exclusive prediction from inclusive to exclusive prediction LHC To Terascale Physics WSS.Bolognesi (Johns Hopkins University) 42 Presently doable only on beam thrust variable (~raw approx of p cut ) and used to reweight MC@NLO

43. Signal-background interference  Recent results for WW, but focused on low mass Effect on gg→H→WW at LO m T < mH ( arXiv:1107.5569v1 ) non-resonant diagrams can be large for m T > mH  Worth to investigate further at high mass? also shape effects! 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 43

44. ZZ: theoretical prediction Single resonant contribution qq→ZZ NLO + gg→ZZ  ZZ fully from MC, well under control Interference in the final state with identical leptons 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 44

45. ZZ: theoretical uncertainties PDF+  s scale qq gg qq gg 01/18/2012 seminar S.Bolognesi (Johns Hopkins University) 45

46. WW: theoretical uncertainties  WW taken from MC for large m H → gg+qq NLO available (MCFM)  WW from control region for m H <200 GeV (mll,  ll)  in jet bins using uncert on  >=N) + modeling: MC@NLO vs ALPGEN PDF+  s and scale uncertainty dominates 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 46

47. WW→l l measurement Background Cuts  Complex analysis (no mass peak→counting experiment, many backgrounds)  background estimate:  signal acceptance: leptonic efficiency jet-veto efficiency missing E T uncertainty theoretical (gg box, PDF) W+jets tight lepton quality top (b-)jet veto Drell-YanZ mass veto missing E T WZ, ZZ, W  2 leptons estimated from data → estimated from MC 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 47  Main systematics:

48. WW/WZ→l 2j at CDF  First observation: 5.4  (first evidence at D0 with 4.4  in 2008)  Much larger backgrounds, no resolution to distinguish W/Z→jj fit to Mjj (3.9 fb-1) + matrix element method: (2.7 fb-1) discriminant exploiting full kinematic information, based on calculations of differential xsec of signal and background QCD from data data-MC validation of input kinematic variables fit to shape of discriminant (NLO expected ) Sara Bolognesi (CERN)Physics in Collisions, August 2011 48

49. WZ/ZZ→l  2b at Tevatron WZ → l bb + ZZ → bb b-tag jets + missing E T (+ topological cuts)  Crucial for Higgs search (ZH→ bb). Very complex analysis! No leptons! → huge background: multijets QCD, V+jets (from data) very sophisticated techniques: b-tag probability with Boosted Decision Tree or Neural Network which exploits much info and different variables different channels combined (0,1,2 b-tag) CDF (2b-tags) D0: CDF: (expected 4.6 pb) (expected 5.1 pb) Sara Bolognesi (CERN)Physics in Collisions, August 2011 49

50.  ZZ→2l2 (5.9 fb-1) Shape analysis with fit to neural network ZZ at CDF  ZZ→4l (6 fb-1) excess of events at high M ZZ (eg Randall Sundrum Graviton) But xsec still compatible with SM No excess in other final states  ZZ→2l2j Control of Z+jets very challenging to measure ZZ xsec control of Z+jets is crucial Sara Bolognesi (CERN) 50

51. (NLO expected ) WZ→3l+ at LHC  Very clean, low background (NLO expected ) CMS: ATLAS: Sara Bolognesi (CERN)Physics in Collisions, August 2011 51

52. (NLO expected ) Recent WZ→3l+ at Tevatron  D0 with 4.1 fb-1  Possible only at hadron colliders (charged final state) statistics 2 times smaller than LHC, while xsec is 6 times smaller Shape analysis with fit to neural network (NLO expected )  CDF with 7.1 fb-1 Sara Bolognesi (CERN)Physics in Collisions, August 2011 52 observed events: 34 expected signal: 23.3±1.5 expected background: 6.0±0.6

53. V+jets: ratios  Very well known theoretically → any deviation is hint of NP  Use high statistics W sample to predict Z+jets background for NP CMS PAS EWK-10-011  Many systematics cancel out 01/18/2012 seminarS.Bolognesi (Johns Hopkins University) 53

54. Z+b jets b-tagging with Secondary Vertex requirement or more sophisticated (eg Neural Network in D0) b-tag eff. measured separately from data b-tag purity extracted from data (eg SV mass fit)  PDF of b quarks fixed flavor scheme b only from gluon splitting variable flavor scheme gluon splitting integrated into the PDF  Benchmark for MSSM Higgs:  bbbar (large theoretical uncertainty on xsec) Background to ZH(H→bbar), NP search with lept+b-jets  b-jets analysis: (expected to coincide at NLO) measurement of Z+b / Z+jets to cancel other (non-btag) systematics Sara Bolognesi (CERN) 54

55. Z+b results (corrected for geometrical acceptance)  CDF (7.86 fb-1)  D0 (4.2 fb-1) NLO (m Z 2 ) 0.0192 +/- 0.0022  CMS (fixed flavor) (variable flavor) Similar results for muons No statistical power yet to disentangle fixed VS variable flavor scheme variable schema fixed schema 0.9 data/MC b-tag eff. b-tag eff. corrected results: Sara Bolognesi (CERN)Physics in Collisions, August 2011 17 TO BE UPDATED soon with 1fb -1 → much better precision!

56. W+c  Dominated by sg→Wc dg→Wc Cabibbo suppressed W+b even more suppressed LHC: W+c ~ 10% W+jets (W+b negligible) → Wcbar (Wc) measures the sbar (s) PDF MC predictions fit lifetime-tagging  CMS (unexpected! just a first go):  Tevatron: W+c ~ 5% W+jets semileptonic charm decay + opposite charge W and c CDF (4.3 fb -1 ): (NLO calculation ) Sara Bolognesi (CERN)Physics in Collisions, August 2011 20