From the Discovery of the Higgs Boson to the Search for Dark Matter -New results from the LHC-

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1 From the Discovery of the Higgs Boson to the Search for Dark Matter -New results from the LHC- Karl Jakobs Physikalisches Institut Universität Freiburg / Germany

2 LHC and Data Taking, First look at the data at highest energies The profile of the Higgs Boson - What do we know today about the Higgs boson? Announcement: 4 th July 2012 Search for Physics Beyond the Standard Model (Focus on Dark Matter) Future: where do we go from here

3 The Standard Model of Particle Physics γ m W 80.4 GeV m Z 91.2 GeV (i) Constituents of matter: quarks and leptons (spin-½ fermions) (ii) Four fundamental forces: described by quantum field theories (except gravitation) à massless spin-1 gauge bosons (iii) The Higgs field: à scalar field, spin-0 Higgs boson

4 The Brout-Englert-Higgs Mechanism F. Englert and R. Brout. Phys. Rev. Lett. 13 (1964) 321; P.W. Higgs, Phys. Lett. 12 (1964) 132, Phys. Rev. Lett. 13 (1964) 508; G.S. Guralnik, C.R. Hagen, and T.W.B. Kibble. Phys. Rev. Lett. 13 (1964) 585.

5 The Brout-Englert-Higgs Mechanism Complex scalar (spin 0) field φ with potential: V (φ) = µ 2 (φ *φ) + λ(φ * φ) 2 For λ > 0, µ 2 < 0: Spontaneous Symmetry Breaking Omnipresent Higgs field: vacuum expectation value v 246 GeV Higgs Boson (mass not predicted, except m H < ~1000 GeV) Particles acquire mass through couplings to the Higgs field

6 The Brout-Englert-Higgs Mechanism Complex scalar (spin 0) field φ with potential: V (φ) = µ 2 (φ *φ) + λ(φ * φ) 2 For λ > 0, µ 2 < 0: Spontaneous Symmetry Breaking Couplings proportional to mass Higgs boson decays preferentially into the heaviest accessible particles

7 The Open Questions

8 Key questions of particle physics 1. Mass What is the origin of mass? A Higgs particle seems to exist! What is its profile? Is it the Standard Model Higgs boson? Dark energy Gas Dark matter Stars 2. Unification - Can the interactions be unified? - Are there new types of matter, e.g. supersymmetric particles? Are they responsible for the Dark Matter in the universe? 3. Flavour - Why are there three generations of particles? - What is the origin of the matter-antimatter asymmetry (Origin of CP violation)

9 The Large Hadron Collider ] Delivered Luminosity [fb ATLAS Online Luminosity 2011 pp s = 7 TeV 2012 pp s = 8 TeV 2015 pp s = 13 TeV 2016 pp s = 13 TeV 7/16 calibration Data taking at the LHC (pp): 2011: s = 7 TeV L = 5 fb : s = 8 TeV L = 25 fb -1 0 Jan Apr Jul Oct Month in Year 2015: s = 13 TeV L = 4 fb : L = 39 fb -1

10 Data taking at the LHC Until end of 2012: > Proton-proton collisions ~ collisions recorded Z à µµ decays registered Data taking extremely successful (beyond all expectations) Accelerator: beam intensity so high, that during one bunch crossing more than 20 proton-proton interactions take place Experiments: - High efficiency for recording the collision data: ~93.5% - Functioning detector channel >99%

11 Z à µ + µ - with 20 reconstructed pp vertices

12 High p T jet events at the LHC Event display that shows the highest-mass central dijet event collected during 2010, where the two leading jets have an invariant mass of 3.1 TeV. The two leading jets have (p T, y) of (1.3 TeV, -0.68) and (1.2 TeV, 0.64), respectively. The missing E T in the event is 46 GeV. From ATLAS-CONF

13 Double differential jet production cross sections, as a function of p T and rapidity y (full 2015 data set, s = 13 TeV) Leading order some NLO contributions Also at the highest energies explored so far, the data are well described by NLO perturbative QCD calculations (NLOJet++)

14 In addition to QCD test: Sensitivity to New Physics Di-jet mass spectrum provides large sensitivity to new physics e.g. resonances decaying into qq, excited quarks q*,. Search for resonant structures in the di-jet invariant mass spectrum No evidence for resonant structures: à Excited quarks with masses m q* < 5.6 TeV can be excluded (95% C.L.) (For comparison: pre-lhc m q* limit was at 0.87 TeV, from the Tevatron)

15 Standard Model processes at the LHC Standard Model Production Cross Section Measurements Status: August 2016 σ [pb] total (x2) ATLAS Preliminary inelastic Theory n j < p T < 2 TeV n j < m jj < 5 TeV p T > 25 GeV p T > 100 GeV n j 0 n j 0 n j 1 n j 0 n j 2n j 1 n j 1 n j 3n j 2 n j 2 n n j 4 j 3 n j 3 n j 4 n j 5 n j 4 n j 5 n j 6 n n j j 5 6 n j 7 n n j 7 j 6 n j 7 total n j 4 n j 5 n j 6 n j 7 n j 8 Run 1,2 t-chan Wt s-chan s = 7, 8, 13 TeV WW WW WW WZ ZZ WZ ZZ WZ ZZ total ggf H WW H ττ VBF H WW H γγ H ZZ 4l Zγ W γ Zγ LHC pp s =7TeV Data fb 1 LHC pp s =8TeV Data 20.3 fb 1 LHC pp s = 13 TeV Data fb W ± W ± WZ pp Jets R=0.4 γ fid. W fid. Z fid. t t fid. t tot. VV tot. γγ fid. H fid. Vγ fid. t twt tz t tγ tot. tot. fid. Zjj EWK fid. WW Excl. tot. Zγγ Wγγ VVjj EWK fid. fid. fid.

16 Summary of important Standard Model cross sections

17 Status of Higgs Boson measurements Expected number of decays in data: ~ 950 H à γγ m H = 125 GeV ~ 60 H à ZZ à 4 l ~ 9000 H à WW à lν lν

18 Higgs Boson Production Gluon fusion Vector boson fusion VBF WH/ZH associated production * ) LHC Higgs cross-section working group Large theory effort tt associated production Meanwhile the NNNLO = N 3 LO calculation for the gluon-fusion process exists; B. Anastasiou et al. (2015) à LHC = Long and Hard Calculations

19 Higgs Boson Decays Higgs BR + Total Uncert cc bb gg WW ZZ tt * ) LHC HIGGS XS WG 2011 Useful decays at a hadron collider: - Final states with leptons via WW and ZZ decays - γγ final states (despite small branching ratio) ττ final states (more difficult) Z [GeV] 1000 M H - In addition: H à bb decays via associated lepton signatures (Higgs should be produced in association with a vector boson or top quarks) SM predictions (m H = GeV): BR (Hà WW) = 22.3% BR (H à bb) = 56.9% BR (H à ZZ ) = 2.8% BR (H à ττ ) = 6.2% BR (H à γγ) = 0.24% BR (H ൵) = 0.022% à at 125 GeV: only ~11% of decays not observable (gg, cc) * ) LHC Higgs cross-section working group

20 Result of the Searches for H à γγ weights / GeV Ldt = 4.5 fb -1 Ldt = 20.3 fb Phys. Rev. D90 (2014) EPJ C74 (2014) 3076 s= 7 TeV s= 8 TeV s/b weighted sum Mass measurement categories ATLAS Data Combined fit: Signal+background Background Signal weights - fitted bkg [GeV] m Background interpolation in the region of the excess (obtained from sidebands) High signal significance in both experiments: ATLAS: 5.2σ (4.6σ expected) CMS: 5.7σ (5.2σ expected) Establishes the discovery in this channel alone

21 Result of the Searches for H à γγ weights / GeV Ldt = 4.5 fb -1 Ldt = 20.3 fb Phys. Rev. D90 (2014) EPJ C74 (2014) 3076 s= 7 TeV s= 8 TeV s/b weighted sum Mass measurement categories ATLAS Data Combined fit: Signal+background Background Signal weights - fitted bkg [GeV] m Measured signal strengths: µ = σ obs / σ SM ATLAS: µ = 1.17 ± 0.27 CMS: µ = 1.14 ± 0.26

22 Vector Boson Fusion qqh Motivation: Increase discovery potential at low mass Improve and extend measurement of Higgs boson parameters (couplings to W and Z bosons, and fermions in the decays, e.g. τ leptons) Distinctive Signature of: q - Two high p T forward jets (tag jets) Large invariant mass, large η separation - Little jet activity in the central region (no colour flow) central jet Veto Tag jets Higgs decay φ η η products

23 H à γγ VBF candidate event E T (γ 1 ) = 80.1 GeV, η = 1.01 E T (γ 2 ) = 36.2 GeV, η = 0.17 m γγ = GeV E T (jet 1 ) = GeV, η = E T (jet 2 ) = 82.8 GeV, η = 2.72 m jj = 1.67 TeV

24 H à γγ VBF candidate event Phys. Rev. D90 (2014) E T (γ 1 ) = 80.1 GeV, η = 1.01 E T (γ 2 ) = 36.2 GeV, η = 0.17 m γγ = GeV E T (jet 1 ) = GeV, η = E T (jet 2 ) = 82.8 GeV, η = 2.72 m jj = 1.67 TeV

25 H à ZZ à e + e - µ + µ - candidate event

26 Reconstructed mass spectra from 4l decays Phys. Rev. D91 (2014) Phys. Rev. D89 (2014) Events / 2.5 GeV Data 35 ATLAS H ZZ* 4l s = 7 TeV s = 8 TeV -1 Ldt = 4.5 fb -1 Ldt = 20.3 fb Signal (m = 125 GeV µ = 1.51) H Background ZZ* Background Z+jets, tt Systematic uncertainty m 4l [GeV] Measured signal strengths: ATLAS: µ = 1.44 CMS: µ = Significance in each experiment > 6σ

27 Phys. Rev. D92 (2015) Events / 10 GeV Events / 10 GeV (b) Background-subtracted Obs - Bkg Bkg± syst Higgs H à WW* à lν lν signal ATLAS HWW* -1 s =8TeV, 20.3fb -1 s =7TeV, 4.5fb (a) n j 1, e µ+ee/ µµ Obs± stat Bkg± syst Higgs WW Misid VV Top DY Events / 10 GeV data H WW W+jets WZ+ZZ+VVV top DY+jets WW JHEP 01 (2014) 096 CMS 4.9 fb (7 TeV) fb (8 TeV) m ll Measured signal strengths: -1-1 m H = 125 GeV eµ 0-jet [GeV] 0 ATLAS: µ = m T [GeV] CMS: µ = Very significant excesses visible in the transverse mass (ATLAS: 6.1σ) and m ll distributions (CMS: 4.5σ)

28 H à WW* à lν lν signal Phys. Rev. D92 (2015) µ VBF ATLAS HWW*ll -1 s=7tev,4.5fb s=8 TeV,20.3fb -1 Obs(1.0,1.3) Obs±1 Obs±2 Obs±3 Exp SM (1,1) Exp SM ± 1,2, µ ggf Measured signal strengths: ATLAS Gluon fusion (ggf): µ = VBF: µ =

29 Couplings to quarks and leptons? Search for H à ττ and H à bb decays

30 Couplings to quarks and leptons? Search for H à ττ and H à bb decays; Challenging signatures due to jets (bb decays) or significant fraction of hadronic tau decays Vector boson fusion mode essential for H à ττ decays Associated production WH, ZH modes have to be used for H à bb decays Exploitation of multivariate analyses Z Events / 10 GeV µ had + e had VBF ATLAS Preliminary -1 L dt = 20.3 fb s = 8 TeV Signal Region Data H(125) Z Others Fake Uncert MMC m [GeV]

31 Evidence for H à ττ decays JHEP 05 (2014) 104 JHEP 04 (2015) 117 ln(1+s/b) w. Events / 10 GeV ATLAS H VBF+Boosted -1 s = 7 TeV, 4.5 fb s = 8 TeV, 20.3 fb -1 Data H(125) (µ=1.4) Z Others Fakes Uncert. Weighted (Data-Bkg.) H(125) (µ=1.4) H(110) (µ=1.6) H(150) (µ=6.2) [GeV] m MMC m ττ distribution, events weighted by ln (1+S/B) Measured signal strengths: ATLAS: µ = 1.43 (4.5σ) CMS: µ = 0.78 ± 0.27 (3.2σ) One of the most important LHC results in 2014 / 2015

32 Results on the search for H à bb decays Phys. Rev. D89 (2014) JHEP 1501 (2015) 069 Weighted events after subtraction / 20.0 GeV ATLAS -1 s = 8 TeV Ldt = 20.3 fb lep., 2+3 jets, 2 tags Weighted by Higgs S/B Data 2012 VH(bb) (µ=1.0) Diboson Uncertainty m bb [GeV] Reconstructed m bb signals (after subtraction of major, non-resonant backgrounds) Reference signal from WZ, and ZZ with Z à bb seen Positive, but non-conclusive Higgs boson signal contribution observed Signal strengths: ATLAS: µ = 0.50 ± 0.36 CMS: µ = 1.0 ± 0.5

33 Profile of the New Particle Is it the Standard Model Higgs Boson? Mass ( input parameter ) Spin, J CP quantum number Production rates Couplings to bosons and fermions

34 Higgs boson mass The two high resolution channels H à ZZ*à 4l and H à γγ are best suited (reconstructed mass peak, good mass resolution) Good control of the lepton and photon energy scales, calibration via Z à ll and J/ψ and ϒ signals, improved understanding of lepton and photon reconstruction Phys. Rev. D90 (2014) Scale Electrons, < J/ e e + - Z e e Calibration uncertainty ATLAS -1 s=8 TeV, Ldt =20.3 fb E T [GeV] Impressive accuracy reached: %

35 Individual and combined results: Higgs boson mass (cont.) -First ATLAS and CMS combination of Higgs boson results- PRL 114 (2015) ATLAS and CMS Run 1 Total Stat. Syst. LHC Total Stat. Syst. ATLAS H ± 0.51 ( ± 0.43 ± 0.27) GeV CMS H ± 0.34 ( ± 0.31 ± 0.15) GeV ATLAS HZZ 4l ± 0.52 ( ± 0.52 ± 0.04) GeV CMS HZZ 4l ± 0.45 ( ± 0.42 ± 0.17) GeV ATLAS +CMS ± 0.29 ( ± 0.25 ± 0.14) GeV ATLAS +CMS 4l ± 0.40 ( ± 0.37 ± 0.15) GeV ATLAS +CMS +4l ± 0.24 ( ± 0.21 ± 0.11) GeV m H [GeV] ATLAS + CMS: m H = ± 0.21 (stat) ± 0.11 (syst) GeV Precision of 0.2% - Statistical uncertainty still dominant - Major systematic uncertainties: Lepton and photon energy scales and resolutions - Theoretical uncertainties small

36 Spin and CP Standard Model Higgs boson: J P = 0 + à strategy is to falsify other hypotheses (0 -, 1 -, 1 +, 2 -, 2 + ) Angular distributions of final state particles show sensitivity to spin In particular: H à ZZ* à 4l decays (in addition: H à WW* à lν lν) Spin-2 data Spin-0 Data strongly favour the spin-0 hypothesis of the Standard Model Many alternatives can be excluded with confidence levels > 99%)

37 Result on different J CP hypothesis tests Eur. Phys. J C75 (2015) 476 In both experiments: data are consistent with J P = 0 + hypothesis, many alternative models are excluded with high significance

38 Couplings to bosons and fermions

39 Signal strengths for various production and decay modes Combined ATLAS + CMS results arxiv: Rates for all production and decay modes consistent with the Standard Model expectations

40 Higgs boson couplings Production and decay involve several couplings for experts Production: Decays: e.g H à γγ (best example) (Decay widths depends on W and top coupling, destructive interference) Benchmarks defined by LHC cross section working group (leading-order tree-levelframework): - Narrow width approximation: à rates for given channels can be decomposed as: i, f = initial, final state Γ f, Γ H = partial, total width - Modifications to coupling strength are considered (coupling scale factors κ), tensor structure of Lagrangian assumed as in Standard Model

41 Results on fit for boson and fermion coupling scale factor JHEP 08 (2016) 045 Assume only one scale factor for fermion and vector couplings: κ V = κ W = κ Z κ F = κ t = κ b = κ τ (top sensitivity via production loop) Excellent agreement with the Standard Model predictions found

42 ATLAS and CMS summary on coupling results JHEP 08 (2016) 045 λ = Yukawa coupling for fermions g/2v = couplings for W/Z bosons The consistency of the couplings of the observed boson with those predicted for the Standard Model Higgs boson is tested in various ways, and no significant deviations are found.

43 First Higgs boson results from Run 2 at s = 13 TeV

44 Physics Beyond the Standard Model

45 Hitoshi Murayama, IPMU Tokyo & Berkeley

46 Additional Higgs bosons / γγ resonances? Both ATLAS and CMS searched for resonances in di-photon events using 2015 data at s = 13 TeV Background determined by fitting the data with a smooth function, and independently from Monte Carlo simulation (normalized to data in the low mass region) Excesses with local significances of 3.6σ (ATLAS) and 2.6σ (CMS)

47 led to lot of excitement in the theory community

48 2016 data: excess at 750 GeV not confirmed data: - no clustering around 750 GeV, and 3.8 times more data - consistency with 2015 data at the 2.7σ level (ATLAS) It appears that the 2015 excess was a statistical fluctuation

49 Supersymmetry Important motivation: - Supersymmetry provides a candidate for dark matter - Unification of couplings of the three interactions seems possible - Quadratically divergent quantum corrections are cancelled Energy (GeV) χ LSP: lightest supersymmetric particle

50 Results on the Search for Supersymmetry Example: search for squark and gluino production; decays to jets and LSP à jets + large missing transverse energy Data are in agreement with predictions from background from Standard Model processes p p p q q g q q q q χ 0 1 χ 0 1 χ 0 1 1/2 Events / 4 GeV ATLAS Preliminary -1 L dt = 20.3 fb 10 jets, p 50 GeV M J T 340 GeV Data, s=8 TeV Background prediction Multi-jets (inc. tt qq) Sherpa tt ql,ll Single top MadGraph tt + V Sherpa W+b Sherpa W (e,µ,) Sherpa Z 0 [ ~ g, ]:[900,150] [GeV] 1 SUSY contribution would show up here p g q q χ miss E T / 1/2 H T [GeV ] E T miss / H T = missing transverse energy normalized to the square root of the total transverse energy (H T ) seen in the event

51 Results on the Search for Supersymmetry à Exclusion limits are set on masses of these particles p q q χ 0 1 p q χ 0 1 q p p g g q q q q χ 0 1 χ 0 1 m(gluino) > 1.8 TeV (95% CL) for the partners of the first two generations and light LSPs; (significant improvement from 1.4 TeV (Run 1)) however: - Mass limits depend on assumptions on m χ (LSP) - So far, simple decay scenarios investigated (not most general search) - Mass limits for third generation squarks are weaker

52 Results on dedicated searches for stop quarks Weaker mass limits for partners of the top quark (lower production rate, tt background) Dedicated searches, often with particular assumptions à significant improvements, however, parameter coverage not yet complete!

53 Is low-energy SUSY dead? Under attack from all sides, but not dead yet. Some of the simplest models are ruled out, however, interpretations rely on many simplifying assumptions. Plausible natural scenarios still not ruled out; Light stop and/or RPV scenarios have fewer constraints. There is no reason to give up hope of finding SUSY at the LHC.

54 Further searches for Dark Matter particles -using signatures with large missing energy- Example: mono-jet search, E T miss spectrum - Mono-jet - Mono-photon - Mono-W or mono-z - Mono Higgs (H à bb) - Mono-top Data are in good agreement with the expectations from Standard Model processes (applies to all mono-x searches)

55 Interpretation in terms of spin-independent DM scattering cross sections à link to direct Dark Matter detection experiments Model dependent (depends on mediator type (vector, axial-vector,.. ) and mass) [active, emerging field of common and unified interpretations] Example: vector-like mediators: LHC shows sensitivity at low masses of DM particles

56 The Future Operation at the increased energy of s = 13 TeV until end 2018 (Run 2) Upgraded detectors are needed to cope with the higher luminosity; Installation in Long Shutdowns ( ) and ( ) LHC long term running plans:

57 Major Physics Prospects Precise measurements of Higgs boson profile (rare, interesting decay modes, test of more exotic models, e.g. composite Higgs, Higgs self coupling, ) Extend the searches for New Physics in all possible directions, cover more complex scenarios, + look for the unexpected! ATL-PUB ATL-PUB

58 Conclusions With the operation of the LHC at high energies, particle physics has entered a new era Performance of the LHC and the experiments is superb A milestone discovery made in July Strong evidence that the new particle is the long-sought Higgs boson of the Standard Model; - We moved from the discovery to the measurement phase; - The Higgs boson might be portal to New Physics (precision required) So far no signals from New Physics, however, only a small fraction of the parameter space at reach at the LHC has been explored Exciting times ahead of us, with new, unexplored energy regime in reach