Event Simulation for the LHC - High Energy Physics Group ...

Event Simulation for the 

Large Hadron Collider 

Bryan Webber 

Cavendish Laboratory 

University of Cambridge 

Event Simulation for the LHC 1 

IFT Colloquium, UAM, 04/04/13

Event Simulation for the 


• The Standard Model 

• Lepton-hadron and hadron-hadron collisions 

• Event generation, matching and merging 

• The Higgs boson 

• Beyond the Standard Model 

• Conclusions and prospects 



The Standard Model 

Matter 

fermions 

Gauge 

bosons 

Scalar 

boson 

Electroweak 

SU(2)xU(1) 

QCD 

SU(3) 



Lepton-Hadron 

Collisions 



Deep Inelastic Scattering 

1fm↔ 0.2GeV 

e 

M p c 2 ≈ 1GeV 

u 

u 

~10 -15 m 

= 1 fm 

d 




e 

u 

u 

d 




e 

u 

u 

u 

u 

d 




e 

u 

u 

u 

u 

d 



Quark and Gluon 

(Parton) Distributions 

xf 

1 

0.8 

0.6 

0.4 

0.2 

xS 

H1 and ZEUS HERA I+II PDF Fit 

xd v 

xg 

xu v 

HERAPDF1.5 NNLO (prel.) 

exp. uncert. 

model uncert. 

2 

= 2 GeV 

parametrization uncert. 

0 0.2 0.4 0.6 0.8 1 


IFT Colloquium, UAM, 04/04/13 

2 

Q 

Fraction of proton momentum 

x 

HERAPDF Structure Function Working Group March 2011 

Invariant 4-momentum 

transfer squared



xf 

1 

0.8 

0.6 

0.4 

0.2 

xS 


xd v 

xg 

xu v 


exp. uncert. 

2 

Q 

model uncert. 

2 

= 10 GeV 


0 0.2 0.4 0.6 0.8 1 


x 






xf 

1 

0.8 

0.6 

0.4 

0.2 

xS 


xd v 

xg 

xu v 


exp. uncert. 

model uncert. 

2 

Q 


2 

= 10000 GeV 

0 0.2 0.4 0.6 0.8 1 


x 





e 

u 

u 

d 




e 

u 

u 

d 




beam 

jet 

e 

 

p 

Hard scattering 

Gluon radiation 

Confinement 

quark jet 

Hadron formation 

 



HERA ep Collider 

• Located at DESY Hamburg 

• Electron-proton collisions at 318 GeV (Mpc 2 ~1 GeV) 

• Main experiments H1 and ZEUS 

• Closed June 2007 



ZEUS Detector 



ZEUS Event Display 

quark 

jet 

e 



eam 

jet 

e 

 

Theoretical Status 

Exact fixed-order 

perturbation theory 

Approximate all-order 

perturbation theory 

Semi-empirical 

local models only 

Hard scattering 


Confinement 

p 

quark jet 


 



Hadron-Hadron 

Collisions 



Tevatron Collider 

• Located at Fermilab near Chicago 

• Proton-antiproton collisions at 1.96 TeV 

• Main experiments CDF and D0 

• Closed September 2011 




• Located at CERN near Geneva 

• Proton-proton collisions at 7 TeV (2011), 8 TeV (2012) 

• Main experiments ATLAS and CMS 

• Design energy 14 TeV 



LHC Experiments 



A Toroidal LHC ApparatuS 

Muon Detectors Tile Calorimeter Liquid Argon Calorimeters 

22 m 

46 m 

Toroid Magnets Solenoid Magnet SCT Tracker Pixel Detector TRT Tracker 



ATLAS Muon Detector 

Man for scale 



ATLAS Calorimeters and Central Solenoid 

Man for scale 



ATLAS Event Display 

• Candidate for Higgs decay to e + e − µ + µ − 



Compact Muon Solenoid 

@A*),(8)*>?)/B2 

84*)(+ C4

CMS Event Display 

• Candidate for Higgs decay to e + e − µ + µ − 



LHC Collision 




Dijet production 



For small p t min and high energy inclusive parton—parton 

cross section is larger than total proton—proton cross 

section. 

Multiple Interactions 

! More than one parton—parton scatter per proton—proton 

• A Need feature a model of of hadron-hadron spatial distribution collisions, within protonnot 

present 

! Perturbation 

in lepton-lepton 

theory gives n-scatter 

or lepton-hadron: 

distributions 

✤ 

Multiple parton interactions in same collision 

• These give rise to extra hadron production 

✤ 

LHC Simulations 3 

Often called the underlying event 

Bryan Webber 

✤ 

Not to be confused with pile-up (multiple 

proton collisions in same bunches) 




quark jet 

beam 

jet 

p 

 

 

p 

beam 

jet 

quark jet 

Hard process 

Underlying event 


Confinement 




A high-mass dijet 

Mjj=4 TeV 

G. Dissertori : Experimental Summary 44 

33 

Event Simulation for the LHC IFT Colloquium, UAM, 04/04/13

QCD Factorization 

σ pp→X (E 2 pp) = 

1 

0 

dx 1 dx 2 f i (x 1 ,µ 2 ) f j (x 2 ,µ 2 )ˆσ ij→X (x 1 x 2 E 2 pp,µ 2 ) 

 

momentum 

fractions 

parton 

distributions 

at scale 

µ 2 

 

hard process 

cross section 

• Jet formation and underlying event take place over a 

much longer time scale, with unit probability 

• Hence they cannot affect the cross section 

• Scale dependences of parton distributions and hard 

process cross section are perturbatively calculable, 

and cancel order by order 



Dijet Mass Distribution 

[ATLAS-CONF-2012-110] 

DIJETS IN 8 TEV DATA 

[CMS PAS EXO-12-016] 

Events 

5 

10 

4 

10 

Data 

Fit 

!"#$@7#"&,&'$7A)67'8 9: ; 

3 

10 

 

s = 8 TeV 

L dt = 5.8 fb 

-1 

2 

10 

10 

1 

-1 

10 

ATLAS Preliminary 

Significance 

2 

0 

-2 

2000 3000 4000 

Reconstructed m jj 

2000 3000 4000 

Reconstructed m jj 

[GeV] 

• !"#$%&'()$'*+,"-'$".)/#/%"'+/'.0))-&12'(#11+/3'0#..'.4"%-$50 

• 5.8 fb-1 = 5.8 events per fb 

! "#$%&'()*#+),$--), ,, ).)/0123)4#5)678,)+7&((#7)$'%)8+9#7):8'-+7$&'+- 

• 1 fb =10-15 barn (1 barn = 10 -28 m 2 ~ nuclear size) 

• No sign of deviation from Standard Model (yet) 

! ;$:8'$")?+ 



Monte Carlo 

Event Generation 



Monte Carlo Event Generation 

• Aim is to produce simulated (particle-level) datasets like 

those from real collider events 

✤ i.e. lists of particle identities, momenta, ... 

✤ 

simulate quantum effects by (pseudo)random numbers 

• Essential for: 

✤ 

✤ 

✤ 

✤ 

Designing new experiments and data analyses 

Correcting for detector and selection effects 

Testing the SM and measuring its parameters 

Estimating new signals and their backgrounds 



LHC Event Generation 

p 

p 

Hard process 

Underlying event 

Parton showers 

Confinement 

Hadronization 

Hadron decays 



Parton Shower Approximation 

• Keep only most singular parts of QCD matrix elements: 

• Collinear dσ n+1 ≈ α 

S 

dξ i dφ i 

P ii (z i ,φ i ) dz i 

2π 

ξ 

• Soft dσ n+1 ≈ α i 

i 2π dσ n 

 

S 

p i · p j 

(−T i · T j ) 

2π 

p i · kp j · k ωdωdξ dφ i 

i 

2π dσ n 

= α S 

2π 

≈ 

α S 

2π 

i,j 

 

i,j 

(−T i · T j ) ξ ij 

ξ i ξ j 

dω 

ω dξ i 

 

(−T i · T j )Θ(ξ ij − ξ i ) dω ω 

i,j 

j 

dφ i 

2π dσ n 

dξ i 

ξ i 

dσ n 

ξ i =1− cos θ i 

θ ij >θ i 

i 

θ i 

ω =(1− z i )E i 

z i E i 

Angular-ordered parton shower 



Cluster Hadronization Model 

• In parton shower, relative transverse momenta 

evolve from a high scale Q towards lower values 

• At a scale near LQCD~200 MeV, perturbation 

theory breaks down and hadrons are formed 

Preconfinement 

• Before that, at scales Q0 

approximation: gluon = colour—anticolour 

~ few 

pair. 

x LQCD, there is 

universal preconfinement of colour 

colour structure 

• 

of Decay parton of preconfined shower: colour-singlet clusters provides pairs a basis 

up close in phase for space hadronization models 

spectrum of colour-singlet pairs asymptotically 









• Before that, at scales Q0 ~ few x LQCD, there is 

r approximation: gluon = colour—anticolour pair. 



• 
















• 
















• 






Colour Preconfinement 

• Mass distribution of preconfined clusters is universal 



Monte Carlo Event Generators 

• Traditionally (imprecise) general-purpose tools 

• Much recent work to make them more precise 



MC Event Generators 

HERWIG 

http://projects.hepforge.org/herwig/ 

Angular-ordered parton shower, cluster hadronization 

v6 Fortran; Herwig++ 

PYTHIA 

http://www.thep.lu.se/∼torbjorn/Pythia.html 

Dipole-type parton shower, string hadronization 

v6 Fortran; v8 C++ 

SHERPA 

http://projects.hepforge.org/sherpa/ 

Dipole-type parton shower, cluster hadronization 

C++ 

“General-purpose event generators for LHC physics”, 

A Buckley et al., arXiv:1101.2599, Phys. Rept. 504(2011)145 



Parton Shower Monte Carlo 

• Hard subprocess: 

q¯q → Z 0 /W ± 

http://mcplots.cern.ch/ 

• Leading-order (LO) normalization need next-to-LO (NLO) 

• Worse for high pT and/or extra jets need multijet merging 



Improving Event Simulation 

Hard subprocess 

e.g. 

qq → Z 0 qq 




NLO Hard subprocess 

(virtual correction) 





(real emission) 





+Parton showering 

= Double counting?? 




Multijet 





Multijet 


+Parton showering 

= Double counting?? 



Matching & Merging 

• Two rather different objectives: 

• Matching parton showers to NLO matrix elements, without 

double counting 

✤ 

✤ 

MC@NLO 

POWHEG 

Frixione, BW, 2002 

Nason, 2004 

• Merging parton showers with LO n-jet matrix elements, 

minimizing jet resolution dependence 

✤ 

✤ 

✤ 

CKKW 

Dipole 

MLM merging 

Catani, Krauss, Kühn, BW, 2001 

Lönnblad, 2001 

Mangano, 2002 



MC@NLO matching 

S Frixione & BW, JHEP 06(2002)029 

• Compute parton shower contributions (real and 

virtual) at NLO 

✤ 

Generator-dependent 

• Subtract these from exact NLO 

✤ 

Cancels divergences of exact NLO! 

• Generate modified no-emission (LO+virtual) and 

real-emission hard process configurations 

✤ 

Some may have negative weight 

• Pass these through parton shower etc. 

✤ 

Only shower-generated terms beyond NLO 



POWHEG matching 

P Nason, JHEP 11(2004)040 

• POsitive Weight Hardest Emission Generator 

• 

Use exact real-emission matrix element to generate 

hardest (highest relative pT) emission configurations 

✤ 

✤ 

✤ 

No-emission probability implicitly modified 

(Almost) eliminates negative weights 

Some uncontrolled terms generated beyond NLO 

• Pass configurations through parton shower etc 



Z 0 at Tevatron 

http://mcplots.cern.ch/ 

• Absolute normalization: 

LO too low 

• POWHEG agrees with 

rate and distribution 



pp → γγ at Tevatron Run II 

gg at Tevatron 

dσ/dp γγ 

⊥ /dM γγ [pb/GeV 2 ] 

10 −2 (a) 50 GeV< M γγ

W asymmetry at LHC 

n II, pp → W → l ¯ν at LHC 7 TeV 

φ ∗ η 

Aµ 

MC/data 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

1.4 

1.2 

1 

0.8 

0.6 

Muon charge asymmetry in W decays 

ATLAS data 

Herwig++ LO 

Herwig++ Powheg 

0 0.5 1 1.5 2 

A µ = N(µ+ ) − N(µ − ) 

N(µ + )+N(µ − ) 

|η µ | 

Lepton charge asymmetry 

-0.2 

-0.3 

0 0.5 1 1.5 2 2.5 3 3.5 4 



0.3 

0.2 

0.1 

0 

-0.1 

pl 

T 

s=7 TeV 

> 20 GeV 

η µ = log tan(θ µ /2) 

-1 

ATLAS (extrapolated data, W → lν) 35 pb 

-1 

CMS (W→ µν) 36 pb 

-1 

LHCb (W→ µν) 36 pb 

MSTW08 prediction (MC@NLO, 90% C.L.) 

CTEQ66 prediction (MC@NLO, 90% C.L.) 

HERA1.0 prediction (MC@NLO, 90% C.L.) 

(a) 

ATLAS+CMS+LHCb 

Preliminary 

Figure 2: The lepton charge asymmetry from W-boson decays in bins of absolute pseudorapidity f 

• 

three different experiments ATLAS, CMS and LHCb. The asymmetry results of the LHCb and 

Asymmetry probes parton distributions 

Collaborations are obtained from the muon channel only and have been communicated within the 

@ higher orders 5/21 

Electroweak Working Group by representatives of the respective collaborations. 

u ¯d → W + → µ + ν 4 Acknowledgments 

µ vs dū → W − → µ −¯ν µ 

⏐η ⏐ 

ATLAS-CONF-1211-129 

We wish to thank the LHC Electroweak Working Group, in particular M. Mangano, T. Shears, R 

Nulty, M. Pioppi, P. Tan and G. H. de Monchenault for fruitful discussions on the definition of a com 

fiducial phase space and for the communication of the LHCb and CMS results.

Entries / 10 GeV 


700 

300 

600 

200 

500 

100 

Data 2011 

400 

MC@NLO 

0 

20 40 60 80 100 120 140 160 180 200 

300 

200 

100 

! 

Top quark at LHC 

600 

ATLAS 

ATLAS 

500 

-1 

-1 

L dt = 2.05 fb 

! 

L dt = 2.05 fb 

5 

400 

Data 2011 

Data 2011 

ATLAS 

L dt = 2.05 fb 

-1 

1 The distribution of (a) lepton p T and (b) b-tagged jet p T for the selected events compared to the MC@NLO simulation 

events. 0The 0 

20 

data 

40 

is 

60 

shown 

80 

as 

100 

closed 

120 

(black) 

140 160 

circles 

180 

with 

200 

the statistical uncertainty. 

40 60 80 

The 

100 

MC@NLO 

120 140 

prediction 

160 180 

is normalised 

e data and is shown as a solid (red) line. The overflow events at high p T are added into the final bin of each histogram. 

Lepton p [GeV] 

b-tagged jet p [GeV] 

Events / 20 GeV 

(a) 

T 


600 300 

500 200 

400 100 

3000 

200 

100 

! 

ATLAS 

L dt = 2.05 fb 

Data 2011 

MC@NLO 

40 60 80 100 120 140 160 180 

300 

-1 

1 The distribution of (a) lepton p T and (b) b-tagged jet p T for the selected events compared to the L dt MC@NLO = 2.05 fb 

-1 

500 

simulation 

events. The data is shown as closed ! 

L (black) dt = 2.05 circles fb with the statistical uncertainty. The MC@NLO prediction is normalised 

250 

e data and is shown as a solid (red) line. The overflow events at high p T are added into the final bin of each histogram. 

400 

200 

Data 2011 

350 

MC@NLO 

600 300 

150 

ATLAS 

300 

ATLAS 

-1 

-1 

500 

! 

L dt = 2.05 fb 

200 

100 ! 

L dt = 2.05 fb 

Data 2011 

250 

50 

400 100 

MC@NLO 

200 

Data 2011 

MC@NLO 

0 

3000 

150 50 100 150 200 250 300 

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 


700 

600 

500 

400 

350 

100 

50 

(a) 

! 

MC@NLO 

Lepton p 

T 

Leading additional jet p 

T 

(a) 

ATLAS 

[GeV] 

[GeV] 

ATLAS, arXiv:1203.5015 

dN / d|y| 

2 Distribution of (a) leading additional jet p T and (b) leading additional jet rapidity in the selected events compared 

e MC@NLO 0 simulation of t¯t events. The data is shown as closed 0 (black) circles with the statistical uncertainty. The 

NLO prediction is normalised to the data and is shown as a solid (red) line. In the p T distribution, the overflow events 

igh p T are added into the final bin of the histogram. In the rapidity distribution, variable bin sizes are used such that the 


dN / d|y| 

600 

200 

100 

(b) 

(b) 

Data 2011 

(b) 

MC@NLO 

MC@NLO 

• Top pair production 

• ATLAS at LHC (7 TeV) 

• Rapidity 

• Both decays leptonic: 

S Frixione, P Nason, BW, JHEP 08(2003)007 

Event Simulation 

50 100 

for 

150the LHC 

200 250 300 

0 0.2 0.4 0.6 0.8 1 1.260 

1.4 1.6 1.8 2 


-1 

b-tagged jet p 

T 

! 

T 

ATLAS 

[GeV] 

Leading additional jet |y| 

y = 1 E + 

2 log pL 

E + p L 

t¯t → b¯bl + l − ν¯ν

Multijet Merging 

• Objective: merge LO n-jet matrix elements * 

with parton showers such that: 

Qcut 

✤ 

✤ 

✤ 

Multijet rates for jet resolution > Qcut are 

correct to LO (up to Nmax) 

Shower generates jet structure below Qcut 

(and jets above Nmax) 

Leading (and next) Qcut dependence cancels 

q 

E 

* ALPGEN or MadGraph, n

!(W + " n-jets) 

!(W) 

!(W + " n-jets) 

!(W + " (n-1)-jets) 

-1 

10 

-2 

10 

-3 

10 

0.2 

0.1 

0 

CMS, JHEP01(2012)010 

data 

energy scale 

unfolding 

MadGraph Z2 

MadGraph D6T 

Pythia Z2 

W+jets at LHC 

10 Results 

{ 

merged 

(PS only) 

-1 

36 pb 

jet 

E T 

at 

s 

W $ e# 

= 7 TeV 

> 30 GeV 

CMS 

1 2 3 4 

inclusive jet multiplicity, n 

s σ(W+ ≥ n jets)/σ(W) (top) and σ(W+ ≥ n jets)/σ(W+ ≥ (n − 1) jets) 

tron channel compared with the expectations from two MADGRAPH tunes 

with error bars correspond to the data. The uncertainties due to the energy 

procedure are shown as yellow and hatched bands, respectively. The error 

tal uncertainty. 



jets) [pb] 

"(W + !N jet 

Theory/Data 

10 

10 

10 

4 

3 

2 

10 

1 

1 

0 

% 

Ldt=36 pb 

-1 

anti-k T 

jets, R=0.4 

jet 

jet 

p >30 GeV, |y |

LHC Cross Section Summary 

The Standard Model in one slide 

• 

Tuesday, March 26, 2013 

Surprisingly good agreement 

Natural SUSY with ATLAS - 26th March 2013 - CERN 

• No sign of non-Standard-Model phenomena (yet) 



But all is not perfect ... 

• Dijet flavours versus jet pT 

16 

ATLAS, arXiv:1210.0441 

BB fraction [%] 

1.1 

1 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

Data stat. uncert. only 

Pythia 6.423 

Herwig++ 2.4.2 

Powheg + Pythia 6.423 

Total error 

ATLAS 

Data 2010, 

-1 

s= 7 TeV, ! 

Ldt=39 pb 

50 100 200 300 

BC fraction [%] 

2 

1.8 

1.6 

1.4 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 

! 


Pythia 6.423 



Total error 

ATLAS 

Data 2010, 

Ldt=39 pb 

-1 

s= 7 TeV 

50 100 200 300 

CC fraction [%] 

4.5 

4 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 


Pythia 6.423 



Total error 

ATLAS 

Data 2010, 

-1 

s= 7 TeV, ! 

Ldt=39 pb 

50 100 200 300 

Jet p 

T 

[GeV] 

Jet p 

T 

[GeV] 

Jet p 

T 

[GeV] 

(a) 

(b) 

(c) 

BU fraction [%] 

9 

8 

7 

6 

5 

4 

3 


Pythia 6.423 



Total error 

ATLAS 

Data 2010, 

-1 

s= 7 TeV, ! 

Ldt=39 pb 

50 100 200 300 

[GeV] 

• Interesting 

(d) 

excess of 

(e) 

(single) b quark 

(f) 

jets 

Fig. 10 The unfolded dijet flavour fractions for each leading jet p T bin (black points) with PYTHIA 6.423 (squares), Herwig++ 2.4.2 (circles) and 

POWHEG+PYTHIA 6.423 (filled triangles) predictions overlaid. The error bars on the data points show statistical uncertainties only, whereas the 

Jet p 

T 

full uncertainties appear as shaded bands. 

CU fraction [%] 

18 

16 

14 

12 

10 

8 


Pythia 6.423 



Total error 

ATLAS 

Data 2010, 

-1 

s= 7 TeV, ! 

Ldt=39 pb 

50 100 200 300 



Jet p 

T 

[GeV] 

UU fraction [%] 

94 

92 

90 

88 

86 

84 

82 

80 

78 

76 

74 

72 


Pythia 6.423 



Total error 

ATLAS 

Data 2010, 

-1 

s= 7 TeV, ! 

Ldt=39 pb 

50 100 200 300 

Jet p 

T 

[GeV]

The Higgs Boson 



Higgs Boson 

Opening ceremony, Paralympic Games, London, August 2012 



Higgs Boson 

`The Hunt for the Higgs’, BBC TV, January 2012 



The Standard Model 

PARADOX! 

g g H g g 



Higgs Production 

t t 

H 



Higgs Production 

t 

H 

t 



Higgs Decay 

g 

H 

t 

t 

g 



Higgs Decay 

g 

H 

W + 

W 

g 



Higgs Production & Decay 

g 

t 

H 

t 

t 

t 

g 




g 

t 

H 

W + 

t 

W 

g 



Higgs Production by 

Vector Boson Fusion 

W + 

H 

W − 



Higgs Production by 

Vector Boson Fusion 

W + 

H 

W − 

• Forward jets 

• Few central jets 

• Central jet veto 

increases S/B 







is 

d 

s, 

ta 

e 

i- 

s 

- 

d 

e 

- 

e 

- 

s- 

d 

g 

e 

- 

- 

). 

g 


Events - Bkg 

weights / 2 GeV 

$ 

$ weights - Bkg 

3500 ATLAS 

3000 

2500 

2000 

1500 

1000 

500 

200 

100 

0 

-100 

-200 

100 

80 

60 

40 

20 

8 

4 

0 

-4 

-8 

ATLAS, Phys.Lett. B716(2012)1 

-1 

s=7 TeV, # Ldt=4.8fb 

-1 

s=8 TeV, # Ldt=5.9fb 

(a) 

Data 

Sig+Bkg Fit (m =126.5 GeV) 

H 

Bkg (4th order polynomial) 

H 

100 110 120 130 140 150 160 

(b) 

100 110 120 130 140 150 160 

(c) 

100 110 120 130 140 150 160 

(d) 

!" 

Data S/B Weighted 

Sig+Bkg Fit (m =126.5 GeV) 

H 

Bkg (4th order polynomial) 

100 110 120 130 140 150 160 

(() (*) (+) (,) (-) 

' γγ !"#$%& 

- 

m ! [GeV] 

eEvent Simulation for the LHC 78 


./".01&!2$3456$7!89$:6;!/!( 

.01!?36 

1!?36!@A'BA:$:6 

±(σ 

±* σ 

89$:6;!/!(

tical leptons is taken into account [53, 55, 56]. 

Higgs Signal and 

Table 1: Event generators used to model the signal and background 

Background 

processes. “PYTHIA” indicates that 

Simulation 

PYTHIA6 and PYTHIA8 are 

used for simulations of √ s = 7TeV and √ s = 8TeV data, respectively. 

Process 

ggF, VBF 

WH, ZH, t¯tH 

W+jets, Z/γ ∗ +jets 

tt, tW, tb 

tqb 

q¯q → WW 

gg → WW 

q¯q → ZZ 

gg → ZZ 

WZ 

Wγ+jets 

Wγ ∗ [65] 

q¯q/gg → γγ 

Generator 

POWHEG [57, 58]+PYTHIA 

PYTHIA 

ALPGEN [59]+HERWIG 

MC@NLO [60]+HERWIG 

AcerMC [61]+PYTHIA 

MC@NLO+HERWIG 

gg2WW [62]+HERWIG 

POWHEG [63]+PYTHIA 

gg2ZZ [64]+HERWIG 

MadGraph+PYTHIA, HERWIG 

ALPGEN+HERWIG 

MadGraph+PYTHIA 

SHERPA 

The event generators used to model signal and backplied 

to accou 

simulation (e 

are used to c 

cation efficien 

4. H → ZZ ( 

The search 

decay H → 

vides good s 

600 GeV), la 

lution of the 

for Higgs bo 

isolated lepto 

tons with the 

expected cros 

√ 

cess H → ZZ 

s = 7TeVa 

The large 

(Z (∗) /γ ∗ )(Z (∗) 

ZZ (∗) . For lo 

ground contr 

ATLAS, Phys.Lett.B716(2012)1 

where charge 




Standard Model predictions for MH = 126 GeV: 

σ pp→H (7 TeV) = 17.5pb, σ pp→H (8 TeV) = 22.3pb 

Prob(H → γγ)=0.23 % 

σ pp→H→γγ (7 TeV) = 39 fb , σ pp→H→γγ (8 TeV) = 50 fb 

80+110 events after selection cuts and detector efficiencies 

Both ATLAS and CMS saw some excess 



Ratios to Standard Model 

• ;#7/'*,0#%'##K#F:A#L#B:A# 

# 

• ;''*.%-&#1#3)..)-##G)7#1 

./1'*7/./-0'8#3).+10%5%,%0 

• ().+10%5%,%02#>%04#!"#KF#> 

)5'/79/6#./1'*7/./-0#%'#E 

#$%&'(()*+,-+.+/'-/%)'-0)*+,-'()*1&%-,12 

• 

!"#!$%&'() 

No sign (yet) of significant deviations from Standard Model 

! 34*%&$%05))6789))%:;%/1%05)"7

*)+%,,-)./-01(- 

%"&'$&()*%)*+,(-.'/"*$0 

',(/"?-@A-)(BB'-$C#=(=CD3-CD-EF)G82.-H3I ('-B?"J(#B 

55)&6'$$(7,)89:'/(:) 

:/2-" 1+/2-3456 

%-$OC##3%'-C?3-$"#'('D3#D-J(DO-DO3-@AN--J(DO(#-&#$3?DC(#D(3'-1'DCD('D($C%%M-="F(#CD3=6 

#)/*)9-(&",()2(',8-(2($/)*%)9-*9(-/"(,0 

" D',,0) F ) G-829/K-± L/9-1'DCD/6-± L/2-1'M'D/6 

• !%.+,/'0#1-1,2'%'#%'#0)#3).+*0/#04/#3).5%-/6#'%&-1,#'07/-&04#8#51'/6#)-# 

1,,#191%,15,/#%-+*0':## 

ATLAS Higgs Update 

• ;-#%-# 

04%'#01,?@# 

Higgs mass 

 

# HCP Symposium, • High Nov resolution 2012 mass • C7/9%)*'#7/'*,0#%-#D*,2#+1+/78#*'%-&# 

measurements 

T. Adye, Moriond, 

from 

March 2013 

H and (*) l EBFF#1-1,2'/'#)G##1-6#558#D*,2# 

spectra 

1-1,2'/'#G)7#8#HI,/+0)-8#1-6#JJ8# 

&19/##K#F:H#L#B:A## 

# 

• M/>#7/'*,0#%'##K#F:A#L#B:A# 

# 

• ;''*.%-&#1#3)..)-##G)7#1,,# 

./1'*7/./-0'8#3).+10%5%,%02#%'#ANO:# 

• ().+10%5%,%02#>%04#!"#KF#>%04# 

• Combine and 4l mass )5'/79/6#./1'*7/./-0#%'#EAO:# 

measurements 

 

• Signal strengths, and 4l , allowed to 

vary independently 

!"#!$%&'()%*+,*%,-*. 

Don’t assume SM couplings 

0.13 (stat) 0.14 (sys) 

! " # $%&'& ( )'%* +,-, * ' ' * +.+ GeV 

• Use profile likeliho 

 

# * / 0 

/ 0 

m AB# 

H confidence inte 

• CMS plot corresponds to partial 8 TeV lumin 

nuisance paramet 

(4.8 fb -1 + 20.7 fb -1 ) 

• Be careful when comparing numbers in the ta 

experimental syst 

• Previous measurement, Dec 

• 

2012: 

My “combination” between ATLAS and CMS 

• Asymptotically, -2 



in the ratio of their masses, up to simple factors reflecting the parti 

really so? 

To Be Confirmed 

The mass of 125 GeV makes the Standard Model Higgs boson exce 

to find. 

• 

However, once we 

Spin and parity 0 + have found the particle, 

: correlations in VV * this special m 

decays 

advantage. At this mass, the Standard Model Higgs boson has a la 

decay• channels Production with substantial mechanisms: branching gg, VBF, fractions WH,ZH, available ttH for stud 

Gianotti put it in her July 4 lecture: “Thank you, Nature.” 

• Self-coupling (HH production): difficult at LHC 

• Total width 4.2 MeV: impossible? 

Mele reviewed the phenomenology of the Standard Model Higgs bos 

of 126. GeV, referring to it properties as “the new set of Standard Mod 

rameters” [23,24]. The predicted width of the boson is 4.2 MeV. The m 

fractions are: 

• Decay fractions: 

bb 56% τ + τ − 6.2% γγ 0.23% 

WW ∗ 23% ZZ ∗ 2.9% γZ 0.16% 

gg 8.5% cc 2.8% µ + µ − 0.02% 

For all of these modes except cc, there is a strategy to observe the deca 



Achievable Precision? 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: Capabilities of LHC for model-independent measurements of Higgs boson couplings. 

The plot shows 1 σ confidence intervals for LHC at 14 TeV with 300 fb −1 . No error 

is estimated for g(hcc). The marked horizontal band represents a 5% deviation from the 

Standard Model prediction for the coupling. 

M Peskin, arXiv:1207.2516 



Achievable Precision? 

 

 

 

 

 

 

 

 

Figure 2: Comparison of the capabilities of LHC and ILC for model-independent measurements 

of Higgs boson couplings. The plot shows (from left to right in each set of error 

bars) 1 σ confidence intervals for LHC at 14 TeV with 300 fb −1 , for ILC at 250 GeV and 

250 fb −1 (‘ILC1’), for the full ILC program up to 500 GeV with 500 fb −1 (‘ILC’), and for a 

program with 1000 fb −1 for an upgraded ILC at 1 TeV (‘ILCTeV’). The marked horizontal 

band represents a 5% deviation from the Standard Model prediction for the coupling. 

M Peskin, arXiv:1207.2516 



Status of the Standard Model 

• It is a respectable (renormalizable) quantum field theory 

• All predicted relationships between measurable 

quantities are calculable (in principle) 

• Calculations need a short-distance (high-energy) cutoff, 

but are not sensitive to its scale or nature, as long as it 

respects SM symmetries 

• So a finite high-energy theory (ultraviolet completion) is 

implicitly assumed 

• So far, predicted relationships are in satisfactory 

agreement with experiment (I believe) 



Consistency of SM 

• MW, mt predicted from MH 

• Pulls on observables 



Beyond the 

Standard Model? 



Why BSM? 

• The Standard Model is incomplete 

✤ 

No Dark Matter or Dark Energy (95% of Universe) 

✤ 

✤ 

✤ 

No neutrino masses 

Not enough matter-antimatter asymmetry 

 

No unification of fundamental forces 

• New phenomena at TeV 

scale could solve these 

1 

 

60 

50 

40 

30 

20 

✤ 

Leading ideas: Supersymmetry and Extra Dimensions 

1 

1 

 

1 

2 

SM 

MSSM 

10 1 

3 

1 am (10 −18 m) 

0 

2 4 6 8 10 12 14 16 18 



log 10 

(E/GeV) 

 

 

 

Our world 

Our directions 

Extra directions

Christopher Young 

Christopher You 

Searching for new signals 

0-lepton m eff Analysis: Results 

0-lepton High Multiplicity Analy 


4 

10 

3 

10 

2 

10 

10 

-1 

! 

L dt = 4.7 fb 

Data 2011 ( s = 7 TeV) 

SM Total 

tt and single top 

Z+jets 

W+jets 

Diboson 

multijet 

SM+SU(500,570,0,10) 

SM+SU(2500,270,0,10) 


SRA 

1/2 

Number of Entries events / 100 / 2 GeV 

6 

10 10 

5 

10 

10 

4 

10 

3 

10 10 

2 

4 

3 

2 

10 

10 

10 

! 

L dt ~ 4.7 fb 

-1 


Data -1 

L dt = 

2011 

! 

4.7 fb 

( s 

Data 2011 ( s = 7 TeV) 

= 7 TeV) 

Background prediction 

SM Multi-jets Total (inc. tt# qq) 

tt Alpgen and single tt# top ql,ll 

Z+jets Alpgen W# (e,µ,%)$ 

W+jets Alpgen Z# $ 

Diboson Alpgen Z# % 

multijet SUSY m 0 =2960, m 1/2 =240 

SM+SU(500,570,0,10) 

SM+SU(2500,270,0,10) 

" 7 jets p 

T 

> 55 GeV 


SRA’ 

1/2 

Number of events / 2 GeV 

6 

10 

5 

10 

4 

10 

3 

10 

10 

2 

10 

A 

1 

11 

1 

DATA / SM 

10 

2.50 500 1000 1500 2000 2500 3000 2.5 0 0 2 500 4 1000 6 1500 8 10 2000 12 250014 3000 16 

1.5 2 

1.5 

0.5 1 

1.5 2 

1 

1 0.5 

0 

0 0 

0 500 1000 1500 2000 2500 3000 0 500 1000 1500 2000 2500 3000 

m eff 

(incl.) [GeV] 

miss 

1/2 

m eff / (incl.) [GeV [GeV] 

] 

DATA / SM 

DATA / Prediction 

-1 

2 20 

E T 

H T 

10 

DATA / Prediction 

-1 

1.5 

1 

0.5 

0 

0 

• “SUSY” = Constrained Minimal 

Supersymmetric Standard Model 

14 / 48 

• Huge parameter space still to explore 



A 7-Jet Event 

Christopher Young 

0-lepton High Multiplicity Analysis: Re 



ATLAS SUSY Search 

ATLAS SUSY Searches* - 95% CL Lower Limits (Status: March 26, 2013) 

Inclusive searches 

3rd gen. 

gluino 

mediated 

3rd gen. squarks 

direct production 

EW 

direct 

RPV Long-lived 

particles 

MSUGRA/CMSSM : 0 lep + j's + E T ,miss 

MSUGRA/CMSSM : 1 lep + j's + E T ,miss 

Pheno model : 0 lep + j's + E T ,miss 

Pheno model : 0 lep + j's + E T ,miss 

± 

± 

Gluino med. 

% 

! ( 

~ 

g"qq 

% 

! ) : 1 lep + j's + E 

~ 

T ,miss 

GMSB ( l 

GMSB NLSP) ( 

% 

# NLSP) : 2 lep : (OS) 1-2 # 

+ + j's j's + + E 

E T ,miss 

T ,miss 

GGM (bino NLSP) : & & + E 

T ,miss 

GGM (wino NLSP) : & + lep + E 

T ,miss 

GGM (higgsino-bino NLSP) : & + b + E 

T ,miss 

GGM (higgsino NLSP) : Z + jets + E T ,miss 

Gravitino LSP : 'monojet' + E T ,miss 

0 

g~ "bb! % : 0 lep + 3 b-j's + E 

0 

g~ "tt! % 

1 

T ,miss 

: 2 SS-lep + (0-3b-)j's + E 

1 0 

g~ "tt! % 

T ,miss 

: 0 lep + multi-j's + E 

1 0 

g~ "tt! % 

T ,miss 

0 

b 

~ ~ ~ ± 

b 

~ 1 

"t! % 1 

"b! % 

: 0 lep + 3 b-j's + E 

~ ~ ~ 1 

T ,miss 

bb, 

: 0 lep + 2-b-jets + E 

1 

T ,miss 

bb, 

: 2 

± 

t"b! 

~ ~ 

% SS-lep + (0-3b-)j's + E 

~ 1 

T ,miss 

tt 

(light), : 

± 

t"b! 

~ % 1/2 lep (+ b-jet) + E 

1 

T ,miss 

tt 

(medium), : 1 lep 

± 

0 

~ ~ 0 

tt 

(heavy), 

~ t"t! % t"t! % 

t"b! % + b-jet + E 

1 ~ 

T ,miss 

tt 

(medium), : 2 lep + E 

,miss 

~ ~ 

1 

T 

tt 

(heavy), : 1 lep + b-jet + E 

1 

T ,miss 

: 0 lep + 6(2b-)jets + E 

1 

T ,miss 

tt 

(natural GMSB) : Z("ll) + b-jet + E 

~ ~ ~ ~ 

T ,miss 

t 2 

t 2 

, t 2 

" t 1 

+Z : Z("ll) + 1 lep 

~ ~ ~ 0 

+ %- 

+ ~ 

!% ! , ! " l$(l$ 

% +% 

% l l l"l! % 

+ b-jet + E 

T ,miss 

L L 

, 

% : 2 lep + E 

1 

T ,miss 

) 

- % + % 

± % ! 

0 ~ ~ 

l l L 

l($ % $) : 3 lep + E 

% ±% 0 L 

l($ % ! , ! 

$), l$ % "#$(#$ + E 

~ 

% : 2 lep + E 

1 1 1 

T ,miss 

) : 2 # 

1 1 1 

T ,miss 

!% ! " l L 

$ 

1 2 

( )% 0 ( )% 0 

T ,miss 

! ! " W * ! Z * ! : 3 lep + E 

% ± 1 2 

1 1 

T ,miss 

% ± 

Direct ! pair prod. (AMSB) : long-lived ! 

1 

Stable 

~ 

g, R-hadrons : low % 

', '& 

1 

GMSB, % ! 0 "& G ~ GMSB, stable # : low ' 

: non-pointing photons 

% 0 

1 

! " qqµ (RPV) : µ 

LFV : pp"$ % + heavy 

LFV : pp"$ % #+X, 

#+X, $ % $ % displaced vertex 

1 

#"e+µ resonance 

#"e(µ)+# resonance 

Bilinear RPV CMSSM : 1 lep + 7 j's + E T ,miss 

% 

! 

+% % % % 

- + 0 0 

! , ! "W! 

, ! "ee$ 

% +% % 

µ ,eµ$ : 4 lep + E 

1 1 -1 

0 1 1 

e 

T ,miss 

! ! , ..., ! "##$ : 3 lep + 1 # + E 

,miss 

~ e 

,e#$ 

1 1 1 

# 

T 

~ ~ 

g " qqq : 3-jet resonance pair 

g~ " tt, t"bs : 2 SS-lep + (0-3b-)j's + E 

T ,miss 

Scalar gluon : 2-jet resonance pair 

WIMP interaction (D5, Dirac !) : 'monojet' + E 

T ,miss 

-1 

L=5.8 fb , 8 TeV [ATLAS-CONF-2012-109] 

-1 


-1 


-1 


-1 

L=4.7 fb , 7 TeV [1208.4688] 

-1 

L=4.7 fb , 7 TeV [1208.4688] 

-1 

L=20.7 fb , 8 TeV [1210.1314] 

-1 

L=4.8 fb , 7 TeV [1209.0753] 

-1 


-1 

L=4.8 fb , 7 TeV [1211.1167] 

-1 


-1 


-1 


-1 


-1 


-1 


-1 


-1 


-1 

L=4.7 fb , 7 TeV [1208.4305, 1209.2102] 

-1 


-1 


-1 


-1 


-1 


-1 


-1 

L=4.7 fb , 7 TeV [1208.2884] 

-1 

L=4.7 fb , 7 TeV [1208.2884] 

-1 


-1 


-1 


-1 

L=4.7 fb , 7 TeV [1210.2852] 

-1 

L=4.7 fb , 7 TeV [1211.1597] 

-1 

L=4.7 fb , 7 TeV [1211.1597] 

-1 


-1 

L=4.4 fb , 7 TeV [1210.7451] 

-1 

L=4.6 fb , 7 TeV [1212.1272] 

-1 

L=4.6 fb , 7 TeV [1212.1272] 

-1 


-1 


-1 


-1 

L=4.6 fb , 7 TeV [1210.4813] 

-1 


-1 

L=4.6 fb , 7 TeV [1210.4826] 

-1 


167 GeV 

85-195 GeV 

~ ~ 

1.50 TeV q = g mass 

~ ~ 

1.24 TeV q = g mass 

~ 

g mass 

~ 

% 0 

1.18 TeV 

(m( q) < 2 TeV, light ! ) ATLAS 

1 

~ 

q mass 

~ 

% 0 

1.38 TeV 

(m( g) < 2 TeV, light ! ) 

Preliminary 

1 

~ 

0 

± 

0 

900 GeV g mass (m( 

% 

! ) < 200 GeV, m( 

% 

! ) = 

1 

(m( 

% 

! )+m( 

~ 

g)) 

1 

~ 

2 

1.24 TeV g mass (tan" < 15) 

~ 

1.40 TeV g mass (tan" > 18) 

~ 

g mass 

% 0 

1.07 TeV 

(m(! 

) > 50 GeV) 

1 

-1 

~ 

619 GeV g mass ) Ldt = (4.4 - 20.7) fb 

~ 

g mass 

% 0 

900 GeV 

~ 

g mass (m(H ~ (m(! 

) > 220 GeV) 

1 

s = 7, 8 TeV 

690 GeV 

) > 200 

1/2 

-4 

F scale (m(G ~ GeV) 

645 GeV 

) > 10 eV) 

~ 

0 

1.24 TeV g mass (m( 

% 

! ) < 200 GeV) 

1 

~ 

g mass 

% 0 

900 GeV 

(any m( ! )) 

8 TeV, all 2012 data 

1 

~ 

g mass 

% 0 

1.00 TeV 

(m(! 

) < 300 GeV) 

1 

~ 

g mass 

% 0 

8 TeV, partial 2012 data 

1.15 TeV 

(m(! 

) < 200 GeV) 

~ 

1 

0 

620 GeV 

~ 

b mass (m( 

% 

! ) < 120 GeV) 

7 TeV, all 2011 data 

1 

~ 

b mass 

% ± % 0 

430 GeV 

(m(! 

) = 2 m( ! )) 

1 

1 

0 

t mass (m( 

% 

! ) = 55 GeV) 

1 ~ 

t mass 

% 0 

% ± 

160-410 GeV 

(m(! 

) = 0 GeV, m( ! ) = 150 GeV) 

~ 

1 

1 

0 

~ ± 

160-440 GeV t mass (m( 

% 

! ) = 0 GeV, m( t)-m( 

% 

! ) = 10 GeV) 

~ 

1 

1 

t 

~ 

mass 

% 0 

200-610 GeV 

(m(! 

) = 0) 

1 

~ 

t mass 

% 0 

320-660 GeV 

(m(! 

) = 0) 

1 

0 

t mass 

% 

500 GeV 

(m(! 

) > 150 GeV) 

~ 

1 

~ 

0 

520 GeV 

~ 

t 2 

mass (m( t ) = m( 

% 

! ) + 180 GeV) 

1 1 

0 

l mass (m( 

% 

! ) = 0) 

1 

% ± 

0 

~ 

± 0 

! mass (m( 

% 

! ) < 10 GeV, m( l,$ % ) = 

1 

(m( 

% 

! ) + m( 

% 

110-340 GeV 

! ))) 

% ± 1 

1 

0 

± 0 

! mass (m( 

% 

! ) < 10 GeV, m( 

% 

#,$ % 2 1 1 

) = 

1 

(m( 

% 

! ) + m( 

% 

180-330 GeV 

! ))) 

1 

1 

2 1 1 

% ± 

± 0 0 ~ 

600 GeV ! mass (m( 

% 

! ) = m( 

% 

! ), m( 

% 

! ) = 0, m( l,$ % ) as above) 

% ± 

1 

1 2 1 

± 0 0 

! mass (m( 

% 

! ) = m( 

% 

! ), m( 

% 

315 GeV 

! ) = 0, sleptons decoupled) 

% ± 1 

1 2 1 

± 

! mass (1 < #( 

% 

! ) < 10 ns) 

1 

1 

~ 

985 GeV g mass 

% 

300 GeV # mass (5 < tan' < 20) 

% 0 

0 

! mass (0.4 < #( 

% 

! ) < 2 ns) 

1 

1~ 

q mass (1 mm 

~ 

700 GeV 

$ % $ % < c# < 1 m, g decoupled) 

, 

1.61 TeV # mass (! =0.10, ! =0.05) 

311 

132 

, 

1.10 TeV # mass (! =0.10, ! =0.05) 

311 

1(2)33 

% + 

! 

% + 

! 

~ 

q = 

~ 

1.2 TeV g mass (c# < 1 mm) 

mass (m( 

% 

760 GeV 

! 

0 

LSP 

) > 300 GeV, ( 

1 

> 0) 

mass (m( 

% 

350 GeV 

! 

0 

1 

121 

) > 80 GeV, ( 

1 

~ 

> 0) 

1 

133 

666 GeV g mass 

~ 

~ 

880 GeV g mass (any m( t)) 

sgluon mass (incl. limit from 1110.2693) 

704 GeV M* scale (m ! < 80 GeV, limit of < 687 GeV for D8) 

220 GeV 

230 GeV 

100-287 GeV 

*Only a selection of the available mass limits on new states or phenomena shown. 

All limits quoted are observed minus 1# theoretical signal cross section uncertainty. 

-1 

10 1 10 

Mass scale [TeV] 



ATLAS Exotica Search 

ATLAS Exotics Searches* - 95% CL Lower Limits (Status: HCP 2012) 

New quarks LQ V' CI Extra dimensions 

Other Excit. 

ferm. 

Large ED (ADD) : monojet + E T ,miss 

Large ED (ADD) : monophoton + E T ,miss 

Large ED (ADD) : diphoton & dilepton, m # # / ll 

UED : diphoton + E T ,miss 

1 

S /Z 2 

ED : dilepton, m ll 

RS1 : diphoton & dilepton, m # # / ll 

RS1 : ZZ resonance, m llll / lljj 

RS1 : WW resonance, m T ,l" l" 

RS g !tt (BR=0.925) : tt ! l+jets, m 

KK 

tt,boosted 

ADD BH (M TH 

/M D 

=3) : SS dimuon, N ch. part. 

ADD BH (M TH 

/M D 

=3) : leptons + jets, 'p 

Quantum black hole : dijet, F & 

(m T 

jj 

) 

qqqq contact interaction : &(m ) 

jj 

qqll CI : ee & µµ, m 

ll 

uutt CI : SS dilepton + jets + E T ,miss 

Z' (SSM) : m ee/µµ 

Z' (SSM) : m $$ 

W' (SSM) : m T,e/µ 

W' (! tq, g =1) : m 

R tq 

W' R 

(! tb, SSM) : m 

W* : m T,e/µ 

Scalar LQ pair (!=1) : kin. vars. in eejj, e"jj 

Scalar LQ pair (!=1) : kin. vars. in µµjj, µ"jj 

Scalar LQ pair (%=1) : kin. vars. in $$jj, $"jj 

th 

4 generation : t't'! WbWb 

th 

4 generation : b'b'(T T 5/3 

)! WtWt 

5/3 

New quark b' : b'b'! Zb+X, m 

Top partner : TT ! tt + A 0 

A 0 

(dilepton, M ) 

T2 

Vector-like quark : CC, m l" q 

Vector-like quark : NC, m llq 

Excited quarks : #-jet resonance, m 

Excited quarks : dijet resonance, m # jet 

jj 

Excited lepton : l-# resonance, m 

l# 

Techni-hadrons (LSTC) : dilepton, m ee/µµ 

Techni-hadrons (LSTC) : WZ resonance ("lll), m 

T ,WZ 

Major. neutr. (LRSM, no mixing) : 2-lep + jets 

W R 

(LRSM, no mixing) : 2-lep + jets 

±± 

±± 

HL 

(DY prod., BR(H !ll)=1) : SS ee (µµ), m 

±± 

L ±± 

ll 

H (DY prod., BR(H !eµ)=1) : SS eµ, m 

L 

L 

eµ 

Color octet scalar : dijet resonance, m jj 

tb 

Zb 

-1 

L=4.7 fb , 7 TeV [1210.4491] 

-1 

L=4.6 fb , 7 TeV [1209.4625] 

-1 

L=4.7 fb , 7 TeV [1211.1150] 

-1 


-1 

L=4.9-5.0 fb , 7 TeV [1209.2535] 

-1 

L=4.7-5.0 fb , 7 TeV [1210.8389] 

-1 

L=1.0 fb , 7 TeV [1203.0718] 

-1 

L=4.7 fb , 7 TeV [1208.2880] 

-1 


-1 

L=1.3 fb , 7 TeV [1111.0080] 

-1 

L=1.0 fb , 7 TeV [1204.4646] 

-1 

L=4.7 fb , 7 TeV [1210.1718] 

-1 


-1 

L=4.9-5.0 fb , 7 TeV [1211.1150] 

-1 

L=1.0 fb , 7 TeV [1202.5520] 

-1 

L=5.9-6.1 fb , 8 TeV [ATLAS-CONF-2012-129] 

-1 

L=4.7 fb , 7 TeV [1210.6604] 

-1 

L=4.7 fb , 7 TeV [1209.4446] 

-1 

L=4.7 fb , 7 TeV [1209.6593] 

-1 

L=1.0 fb , 7 TeV [1205.1016] 

-1 

L=4.7 fb , 7 TeV [1209.4446] 

-1 

L=1.0 fb , 7 TeV [1112.4828] 

-1 

L=1.0 fb , 7 TeV [1203.3172] 

-1 

L=4.7 fb , 7 TeV [Preliminary] 

-1 

L=4.7 fb , 7 TeV [1210.5468] 

-1 


-1 

L=2.0 fb , 7 TeV [1204.1265] 

-1 

L=4.7 fb , 7 TeV [1209.4186] 

-1 


-1 


-1 

L=2.1 fb , 7 TeV [1112.3580] 

-1 


-1 


-1 

L=4.9-5.0 fb , 7 TeV [1209.2535] 

-1 

L=1.0 fb , 7 TeV [1204.1648] 

-1 

L=2.1 fb , 7 TeV [1203.5420] 

-1 

L=2.1 fb , 7 TeV [1203.5420] 

-1 

L=4.7 fb , 7 TeV [1210.5070] 

-1 

L=4.7 fb , 7 TeV [1210.5070] 

-1 

L=4.8 fb , 7 TeV [1210.1718] 

430 GeV 

400 GeV 

409 GeV 

375 GeV 

483 GeV 

483 GeV 

4.37 TeV M D (-=2) 

1.93 TeV M D (-=2) 

M S (HLZ -=3, NLO) ATLAS 

4.18 TeV 

-1 

Preliminary 

1.41 TeV Compact. scale R 

-1 

4.71 TeV M KK ~ R 

2.23 TeV Graviton mass (k/M Pl = 0.1) 

845 GeV Graviton mass (k/M Pl = 0.1) 

-1 

1.23 TeV Graviton mass (k/M Pl = 0.1) . Ldt = (1.0 - 13.0) fb 

1.9 TeV g mass 

KK 

M (-=6) 

s = 7, 8 TeV 

1.25 TeV D 

1.5 TeV M D (-=6) 

4.11 TeV M D (-=6) 

7.8 TeV + 

13.9 TeV + (constructive int.) 

1.7 TeV + 

2.49 TeV Z' mass 

1.4 TeV Z' mass 

2.55 TeV W' mass 

W' mass 

1.13 TeV W' mass 

2.42 TeV W* mass 

st 

660 GeV 1 gen. LQ mass 

nd 

685 GeV 2 gen. LQ mass 

rd 

3 gen. LQ mass 

656 GeV t' mass 

670 GeV b' (T ) mass 

5/3 

b' mass 

T mass (m(A ) < 100 GeV) 

0 

1.12 TeV VLQ mass (charge -1/3, coupling , qQ = "/m Q 

) 

1.08 TeV VLQ mass (charge 2/3, coupling , qQ = "/m Q 

) 

2.46 TeV q* mass 

3.84 TeV q* mass 

2.2 TeV l* mass (+ = m(l*)) 

850 GeV ( T 

/* T 

mass (m(( /* T 

) - m() T 

) = M ) 

T 

W 

( mass (m(( ) = m() T 

) + m W , m(a ) = 1.1 m(( )) 

T 

T 

T 

T 

1.5 TeV N mass (m(W ) = 2 TeV) 

R 

2.4 TeV W R mass (m(N) < 1.4 TeV) 

±± 

HL 

mass (limit at 398 GeV for µµ) 

±± 

HL 

mass 

Scalar resonance mass 

538 GeV 

1.86 TeV 

*Only a selection of the available mass limits on new states or phenomena shown 

-1 

10 1 10 

10 

Mass scale [TeV] 



2

CMS Exotica Search 

CMS EXOTICA 95% CL EXCLUSION LIMITS (TEV) 

q* (qg), dijet 

q* (qW) 

q* (qZ) 

q* , dijet pair 

q* , boosted Z 

e*, ! = 2 TeV 

"*, ! = 2 TeV 

Z’SSM (ee, µµ) 

Z’SSM (##) 

Z’ (tt hadronic) width=1.2% 

Z’ (dijet) 

Z’ (tt lep+jet) width=1.2% 

Z’SSM (ll) fbb=0.2 

G (dijet) 

G (ttbar hadronic) 

G (jet+MET) k/M = 0.2 

G ($$) k/M = 0.1 

G (Z(ll)Z(qq)) k/M = 0.1 

W’ (l%) 

W’ (dijet) 

W’ (td) 

W’→ WZ(leptonic) 

WR’ (tb) 

WR, MNR=MWR/2 

WKK " = 10 TeV 

&TC, 'TC > 700 GeV 

String Resonances (qg) 

s8 Resonance (gg) 

E6 diquarks (qq) 

Axigluon/Coloron (qqbar) 

gluino, 3jet, RPV 

gluino, Stopped Gluino 

stop, HSCP 

stop, Stopped Gluino 

stau, HSCP, GMSB 

hyper-K, hyper-&=1.2 TeV 

neutralino, c#

LHC Future Prospects 

• LHC ran pp at 8 TeV until end of 2012 

✤ 

23 fb -1 begins to test main Higgs properties 

✤ 

No sign of beyond-Standard-Model processes yet 

• Restart late 2014 at 13 TeV 

✤ ~300 fb -1 by 2021: Higgs properties to ~10% 

✤ 

New physics searches to multi-TeV range 

• Luminosity upgrade ~2023 3000 fb -1 by 2030? 

• Energy upgrade > 2035 would need new magnets or tunnel 



Conclusions and Prospects 

• Standard Model has (so far) been spectacularly 

confirmed at the LHC 

• Monte Carlo event generation of (SM and BSM) 

signals and backgrounds plays a big part 

• Matched NLO and merged multi-jet generators 

have proved essential 

✤ Automation and NLO merging in progress 

✤ 

NNLO much more challenging 

• Still plenty of scope for new discoveries! 



Thanks for listening! 



Backup 



LHC Future Prospects 

Under way 

"#$%&'("#') 

Highly speculative 

Previous machine 

!"#$%&'(()'*+&',-.."/0&'1"2&0"3&'-4'567'839'"1.'$,#%89&.)' 

Present machine 

Brüling et al., CERN-ATS-2012-237 

(submission to European Strategy 

Symposium, Krakow, Sept 2012) 

&'#%(#)*'#+%,,-./'#%+)-%0,#%(#1#2-3*#40'536#728#-0#)*'#728#)900'/:#;-)*#1#+

MC@NLO matching 

dσ NLO = 

≡ 

 

finite virtual 

B (Φ B )+V (Φ B ) − 

 

B + V − 

 

C dΦ R 

 

 

i 

S Frixione & BW, JHEP 06(2002)029 

divergent 

C i (Φ B , Φ R )dΦ R 

 

dΦ B + R (Φ B , Φ R )dΦ B dΦ R 

dΦ B + R dΦ B dΦ R 

 

dσ MC = B (Φ B )dΦ B ∆ MC (0) + R 

MC (Φ B , Φ R ) 

∆ MC (k T (Φ B , Φ R )) dΦ R 

B (Φ B ) 

≡ B dΦ B [∆ MC (0) + (R MC /B) ∆ MC (k T )dΦ R ] 

dσ MC@NLO = 

 

B + V + 

 

(R MC − C) dΦ R 

 

dΦ B [∆ MC (0) + (R MC /B) ∆ MC (k T )dΦ R ] 

finite > < 0 

+(R − R MC )∆ MC (k T )dΦ B dΦ R 

• Expanding gives NLO result 

MC starting from no emission 

MC starting from one emission 



POWHEG matching 

dσ MC = B (Φ B )dΦ B 

 

∆ MC (0) + R MC (Φ B , Φ R ) 

B (Φ B ) 

dσ PH = B (Φ B )dΦ B 

 

∆ R (0) + R (Φ B, Φ R ) 

B (Φ B ) 

B (Φ B )=B (Φ B )+V (Φ B )+ 

∆ R (p T )=exp 

 

− 

dΦ R 

R (Φ B , Φ R ) 

B (Φ B ) 

R (Φ B , Φ R ) − i 

P Nason, JHEP 11(2004)040 

 

∆ MC (k T (Φ B , Φ R )) dΦ R 

∆ R (k T (Φ B , Φ R )) dΦ R 

 

C i (Φ B , Φ R ) 

 

dΦ R 

 

θ (k T (Φ B , Φ R ) − p T ) 

• NLO with (almost) no negative weights 

• High pT always enhanced by 

arbitrary NNLO 

K = B/B =1+O(α S ) 



W & Z 0 at Tevatron 

Z boson pT spectrum compared to D0 run II data 

rell-Yan vector boson production Drell-Yan vector boson production 

W boson pT spectrum compared to D0 run I data 

D0 Run I: W 

D0 Run II: Z 0 

(with MEC) 

(with MEC) 

• 

Blue dashes: MC@NLO 

Herwig++ includes W/Z+jet (MEC) 

• All agree (tuned) at Tevatron 

• Normalized to data 

lid line: NLO Herwig++ POWHEG 

Red dashes: Herwig++ with ME corrections 

Solid line: NLO Herwig++ POWHEG Blue dashes: MC@NLO 

Red dashes: Herwig++ with ME corrections 

Hamilton, Richardson, Tully JHEP10(2008)015

Event Simulation for the LHC - High Energy Physics Group ...

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