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

•  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? •  Search for Physics Beyond the Standard Model (Focus on Dark Matter)

•  Future: where do we go from here

Announcement: 4th July 2012

The Standard Model of Particle Physics

(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

γ

mW ≈ 80.4 GeV mZ ≈ 91.2 GeV

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.

The Brout-Englert-Higgs Mechanism

For λ > 0, µ2 < 0: “Spontaneous Symmetry Breaking”

Complex scalar (spin 0) field φ with potential:

→ Omnipresent Higgs field: vacuum expectation value v ≈ 246 GeV → Higgs Boson (mass not predicted, except mH < ~1000 GeV) → Particles acquire mass through couplings to the Higgs field

V (φ) = µ2(φ *φ) + λ(φ *φ)2

The Brout-Englert-Higgs Mechanism

For λ > 0, µ2 < 0: “Spontaneous Symmetry Breaking”

Complex scalar (spin 0) field φ with potential:

V (φ) = µ2(φ *φ) + λ(φ *φ)2

•  Couplings proportional to mass

•  Higgs boson decays preferentially into the heaviest accessible particles

The Open Questions

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?

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)

Dark matter Dark energy

Stars

Gas

The Large Hadron Collider

Month in YearJan Apr Jul Oct

]-1

Del

iver

ed L

umin

osity

[fb

05

101520253035404550

ATLAS Online Luminosity = 7 TeVs2011 pp = 8 TeVs2012 pp = 13 TeVs2015 pp = 13 TeVs2016 pp

7/16 calibration

Data taking at the LHC (pp): 2011: √s = 7 TeV L = 5 fb-1 2012: √s = 8 TeV L = 25 fb-1 2015: √s = 13 TeV L = 4 fb-1 2016: L = 39 fb-1

Data taking at the LHC

•  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%

Until end of 2012: > 1015 Proton-proton collisions ~ 1010 collisions recorded 25 �106 Z à µµ decays registered

Z à µ+ µ- with 20 reconstructed pp vertices

High pT 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 (pT, y) of (1.3 TeV, -0.68) and (1.2 TeV, 0.64), respectively. The missing ET in the event is 46 GeV. From ATLAS-CONF-2011-047.

Double differential jet production cross sections, as a function of pT and rapidity y (full 2015 data set, √s = 13 TeV)

Also at the highest energies explored so far, the data are well described by NLO perturbative QCD calculations (NLOJet++)

Leading order

…some NLO contributions

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 mq* < 5.6 TeV can be excluded (95% C.L.)

(For comparison: pre-LHC mq* limit was at 0.87 TeV, from the Tevatron)

Standard Model processes at the LHC

pp

total (x2)

inelastic

JetsR=0.4

nj ≥ 10.1< pT < 2 TeV

nj ≥ 20.3<mjj < 5 TeV

γ

fid.

pT > 25 GeV

pT > 100 GeV

W

fid.

nj ≥ 0

nj ≥ 1

nj ≥ 2

nj ≥ 3

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

Z

fid.

nj ≥ 0

nj ≥ 1

nj ≥ 2

nj ≥ 3

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

nj ≥ 0

nj ≥ 1

nj ≥ 2

nj ≥ 3

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

t̄tfid.

total

nj ≥ 4nj ≥ 5

nj ≥ 6

nj ≥ 7

nj ≥ 8

t

tot.

s-chan

t-chan

Wt

VVtot.

ZZ

WZ

WW

ZZ

WZ

WW

ZZ

WZ

WW

γγ

fid.

H

fid.

H→γγ

VBFH→WW

ggFH→WW

H→ZZ→4ℓ

H→ττ

total

Vγ

fid.

Zγ

Zγ

Wγ

t̄tWtot.

t̄tZtot.

t̄tγ

fid.

ZjjEWK

fid.

WWExcl.

tot.

Zγγ

fid.

Wγγ

fid.

VVjjEWKfid.

W ±W ±

WZ

σ[p

b]

10−3

10−2

10−1

1

101

102

103

104

105

106

1011 Theory

LHC pp√s = 7 TeV

Data 4.5 − 4.9 fb−1

LHC pp√s = 8 TeV

Data 20.3 fb−1

LHC pp√s = 13 TeV

Data 0.08 − 14.8 fb−1

Standard Model Production Cross Section Measurements Status: August 2016

ATLAS Preliminary

Run 1,2√s = 7, 8, 13 TeV

Summary of important Standard Model cross sections

Status of Higgs Boson measurements

Expected number of decays in data: ~ 950 H à γγ mH = 125 GeV ~ 60 H à ZZ à 4 ℓ ~ 9000 H à WW à ℓν ℓν

Higgs Boson Production Gluon fusion Vector boson fusion WH/ZH associated production tt associated production

*) LHC Higgs cross-section working group Large theory effort

VBF

Meanwhile the NNNLO = N3LO calculation for the gluon-fusion process exists; B. Anastasiou et al. (2015) à LHC = Long and Hard Calculations

Higgs Boson Decays

[GeV]HM100 200 300 400 500 1000

Higg

s BR

+ T

otal

Unc

ert

-310

-210

-110

1

LHC

HIG

GS

XS W

G 2

011

bb

cc

ttgg

Z

WW

ZZ

*) LHC Higgs cross-section working group

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) - 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 (mH = 125.5 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)

*)

Result of the Searches for H à γγ

•  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

Phys. Rev. D90 (2014) 112015 EPJ C74 (2014) 3076

[GeV]m110 120 130 140 150 160

wei

ghts

- fit

ted

bkg

-8-6-4-202468

wei

ghts

/ G

eV

0

20

40

60

80

100

120

140

160

180

200

DataCombined fit:

Signal+backgroundBackgroundSignal

= 7 TeVs -1 Ldt = 4.5 fb

= 8 TeVs -1 Ldt = 20.3 fb

s/b weighted sum

Mass measurement categories

ATLAS

Result of the Searches for H à γγ Phys. Rev. D90 (2014) 112015 EPJ C74 (2014) 3076

[GeV]m110 120 130 140 150 160

wei

ghts

- fit

ted

bkg

-8-6-4-202468

wei

ghts

/ G

eV

0

20

40

60

80

100

120

140

160

180

200

DataCombined fit:

Signal+backgroundBackgroundSignal

= 7 TeVs -1 Ldt = 4.5 fb

= 8 TeVs -1 Ldt = 20.3 fb

s/b weighted sum

Mass measurement categories

ATLAS

Measured signal strengths: µ = σobs / σSM ATLAS: µ = 1.17 ± 0.27 CMS: µ = 1.14 ± 0.26

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: - Two high pT 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

products

Vector Boson Fusion qqH

φφ ηη

η

q

H à γγ VBF candidate event

ET(γ1) = 80.1 GeV, η = 1.01 ET(γ2) = 36.2 GeV, η = 0.17 mγγ = 126.9 GeV ET(jet1) = 121.6 GeV, η = -2.90 ET(jet2) = 82.8 GeV, η = 2.72 mjj = 1.67 TeV

H à γγ VBF candidate event

ET(γ1) = 80.1 GeV, η = 1.01 ET(γ2) = 36.2 GeV, η = 0.17 mγγ = 126.9 GeV ET(jet1) = 121.6 GeV, η = -2.90 ET(jet2) = 82.8 GeV, η = 2.72 mjj = 1.67 TeV

Phys. Rev. D90 (2014) 112015

H à ZZ à e+e- µ+ µ- candidate event

Reconstructed mass spectra from 4ℓ decays

Significance in each experiment > 6σ

Phys. Rev. D91 (2014) 012006

[GeV]l4m80 90 100 110 120 130 140 150 160 170

Eve

nts

/ 2.5

GeV

0

5

10

15

20

25

30

35 Data

= 1.51)µ = 125 GeV H

Signal (m

Background ZZ*

tBackground Z+jets, t

Systematic uncertainty

l 4 ZZ* H -1Ldt = 4.5 fb = 7 TeV s

-1Ldt = 20.3 fb = 8 TeV s

ATLAS

Measured signal strengths: ATLAS: µ = 1.44 CMS: µ = 0.93

Phys. Rev. D89 (2014) 092007

+0.29 - 0.23

+0.40 - 0.33

H à WW* à ℓν ℓν signal

0

200

400

600

800

50 100 150 200 250 300

0

50

100

150

0

stat ± Obssyst ± Bkg

HiggsWWMisidVVTopDY

Bkg - Obssyst ± Bkg

Higgs

(b) Background-subtracted

[GeV]Tm

Even

ts /

10 G

eV

µµee/+µe, 1jn(a)

Even

ts /

10 G

eVATLAS

-1fb 20.3 TeV, =8 s-1fb 4.5 TeV, =7 s

WW*H

•  Very significant excesses visible in the “transverse mass” (ATLAS: 6.1σ) and mℓℓ distributions (CMS: 4.5σ)

Measured signal strengths: ATLAS: µ = 1.09 CMS: µ = 0.72

[GeV]llm0 100 200 300

Even

ts /

10 G

eV

0

500

1000

data WW→ H

W+jets

WZ+ZZ+VVV

top DY+jets

WW

= 125 GeVHm 0-jetµe

CMS (8 TeV)-1 (7 TeV) + 19.4 fb-14.9 fb

JHEP 01 (2014) 096

+0.20 - 0.18

+0.23 - 0.21

Phys. Rev. D92 (2015) 012006

H à WW* à ℓν ℓν signal

Phys. Rev. D92 (2015) 012006

ggFµ

0 1 2 3 4

VBF

µ

0

1

2

33

2

1

ATLASll WW*H

-1fb 20.3 TeV, 8 = s-1fb 4.5 TeV, 7 = s

1.3) (1.0, Obs 1 ± Obs 2 ± Obs 3 ± Obs

1) (1, SM Exp 3 2, 1, ± SM Exp

Measured signal strengths: ATLAS Gluon fusion (ggF): µ = 1.02 VBF: µ = 1.27

+0.53 - 0.45

+0.29 - 0.26

Couplings to quarks and leptons ?

Search for H à ττ and H à bb decays

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

[GeV]MMCm0 50 100 150 200 250

Even

ts /

10 G

eV0

50100150200250300350400450

Data (125)H

ZOthersFake Uncert.

VBFhade + hadµ ATLAS Preliminary

= 8 TeVs Signal Region-1 L dt = 20.3 fb

Z

Evidence for H à ττ decays

Measured signal strengths: ATLAS: µ = 1.43 (4.5σ) CMS: µ = 0.78 ± 0.27 (3.2σ)

mττ distribution, events weighted by ln (1+S/B)

One of the most important LHC results in 2014 / 2015

ln(1

+S/B

) w. E

vent

s / 1

0 G

eV

0

20

40

60

80

[GeV]MMCm50 100 150 200W

eigh

ted

(Dat

a-Bk

g.)

0

10

20=1.4)µ((125) H=1.6)µ((110) H=6.2)µ((150) H

Data=1.4)µ((125) H

ZOthersFakesUncert.

ATLAS VBF+Boosted H

-1, 4.5 fb = 7 TeVs-1, 20.3 fb = 8 TeVs

JHEP 04 (2015) 117 JHEP 05 (2014) 104

+0.43 - 0.37

[GeV]bb

m

50 100 150 200 250

Weig

hte

d e

vents

after

subtr

action / 2

0.0

GeV

0

2

4

6

8

10Data 2012

=1.0)µVH(bb) (DibosonUncertainty

ATLAS

-1

Ldt = 20.3 fb∫ = 8 TeV s

0+1+2 lep., 2+3 jets, 2 tags

Weighted by Higgs S/B

Results on the search for H à bb decays

Signal strengths: ATLAS: µ = 0.50 ± 0.36 CMS: µ = 1.0 ± 0.5

•  Reference signal from WZ, and ZZ with Z à bb seen •  Positive, but non-conclusive Higgs boson signal contribution observed

Reconstructed mbb signals (after subtraction of major, non-resonant backgrounds)

JHEP 1501 (2015) 069 Phys. Rev. D89 (2014) 012003

Profile of the New Particle Is it the Standard Model Higgs Boson?

•  Mass (“input parameter”) •  Spin, JCP quantum number •  Production rates Couplings to bosons and fermions

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

[GeV]TE10 20 30 40 50 60 70 80 90 100

Sca

le

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02-e+ e J/

-e+ eZ Calibration uncertainty

|<0.60Electrons, |

ATLAS -1=20.3 fbtdL=8 TeV, s

Phys. Rev. D90 (2014) 052004

Impressive accuracy reached: 0.1 – 0.3%

Higgs boson mass (cont.) -First ATLAS and CMS combination of Higgs boson results-

[GeV]Hm123 124 125 126 127 128 129

Total Stat. Syst.CMS and ATLAS Run 1LHC Total Stat. Syst.

l+4 CMS+ATLAS 0.11) GeV± 0.21 ± 0.24 ( ±125.09

l 4CMS+ATLAS 0.15) GeV± 0.37 ± 0.40 ( ±125.15

CMS+ATLAS 0.14) GeV± 0.25 ± 0.29 ( ±125.07

l4ZZH CMS 0.17) GeV± 0.42 ± 0.45 ( ±125.59

l4ZZH ATLAS 0.04) GeV± 0.52 ± 0.52 ( ±124.51

H CMS 0.15) GeV± 0.31 ± 0.34 ( ±124.70

H ATLAS 0.27) GeV± 0.43 ± 0.51 ( ±126.02

PRL 114 (2015) 191803

ATLAS + CMS: mH = 125.09 ± 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

Individual and combined results:

Spin and CP •  Standard Model Higgs boson: JP = 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

Spin-0

data

•  Data strongly favour the spin-0 hypothesis of the Standard Model •  Many alternatives can be excluded

with confidence levels > 99%)

Result on different JCP hypothesis tests

Eur. Phys. J C75 (2015) 476

•  In both experiments: data are consistent with JP = 0+ hypothesis, many alternative models are excluded with high significance

Couplings to bosons and fermions

Signal strengths for various production and decay modes

Combined ATLAS + CMS results arXiv:1606.02266

Rates for all production and decay modes consistent with the Standard Model expectations

Higgs boson couplings

•  Production and decay involve several couplings 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: - Modifications to coupling strength are considered (coupling scale factors κ), tensor structure of Lagrangian assumed as in Standard Model

i, f = initial, final state Γf, ΓH = partial, total width

for experts

Results on fit for boson and fermion coupling scale factor

JHEP 08 (2016) 045

Excellent agreement with the Standard Model predictions found

Assume only one scale factor for fermion and vector couplings: κV = κW = κZ κF = κt = κb = κτ (top sensitivity via production loop)

λ = Yukawa coupling for fermions √g/2v = couplings for W/Z bosons

ATLAS and CMS summary on coupling results

“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.”

JHEP 08 (2016) 045

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

Physics Beyond the Standard Model

Hitoshi Murayama, IPMU Tokyo & Berkeley

Additional Higgs bosons / γγ resonances?

Excesses with local significances of 3.6σ (ATLAS) and 2.6σ (CMS)

•  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)

… led to lot of excitement in the theory community …

2016 data: excess at 750 GeV not confirmed 750

•  2016 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

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

χ

Energy (GeV)

LSP: lightest super- symmetric particle

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

q̃

q̃p

p

01

q

01

q

g̃

g̃p

p

01

q

q

01

q

q1/2

Even

ts /

4 G

eV

-210

-110

1

10

210

310

410

510

610 =8 TeVsData, Background prediction

qq)tMulti-jets (inc. t ql,ll tSherpa t

Single top + VtMadGraph t

Sherpa W+b),µ (e,Sherpa W

Sherpa Z]:[900,150] [GeV]

10,g~[

PreliminaryATLAS-1L dt = 20.3 fb

50 GeV T

10 jets, p 340 GeV JM

2

]1/2 [GeVTH/missTE

2 4 6 8 10 12 14 16

ET

miss / √HT = missing transverse energy normalized to the square root of the total transverse energy (HT) seen in the event

SUSY contribution would show up here

Results on the Search for Supersymmetry à Exclusion limits are set on masses of these particles

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 mχ (LSP) -  So far, simple decay scenarios investigated (not most general search) -  Mass limits for third generation squarks are weaker

q̃

q̃p

p

01

q

01

q

g̃

g̃p

p

01

q

q

01

q

q

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!

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.

Further searches for Dark Matter particles -using signatures with large missing energy-

- Mono-jet - Mono-photon - Mono-W or mono-Z - Mono Higgs (H à bb) - Mono-top

Example: mono-jet search, ETmiss spectrum

Data are in good agreement with the expectations from Standard Model processes (applies to all mono-X searches)

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

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 (2019-2020) and (2024-2026)

•  LHC long term running plans:

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-2013-014 ATL-PUB-2013-011

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 2012 - 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