Higgs and beyond at the LHC with a little help from QCD - CERN...Higgs boson. W+ W− H 2i M2 W v...

Higgs and beyond at the LHCwith a little help from QCD

Gavin Salam

CERN, Princeton University & LPTHE/CNRS (Paris)

MIT Physics Colloquium6 September 2012

The LHC has been colliding protons since late 2009

The world’s largest fundamental physics endeavour

Involving O (10 000) scientists and engineersFrom about 60 countries across the worldAt a cost of several billion US dollars

Gavin Salam (CERN/Princeton/Paris) Higgs@LHC and QCD MIT 2012-09-06 2 / 40

The scales at play[Introduction]


tµ τneutrinos e

ud s cb


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l. P

hys.

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mis

try

tµ τneutrinos e

ud s cb


1 century

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try

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v. fa

ctor

ies

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neutrinoexperiments

tµ τneutrinos e

ud s cb


1 century

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hys.

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try

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neutrinoexperiments

LHC

tµ τneutrinos e

ud s cb


happens here...get clues as to what

The hope:

matter−antimatter asymmetry+ other questions, e.g.

nature of dark matter/energy

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l. P

hys.

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mis

try

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neutrinoexperiments

LHC

tµ τneutrinos e

ud s cb

The Standard Model[Higgs mechanism]


Higgs/ABEHGHK’tH in an (oversimplified) slide[Higgs mechanism]

Among the terms in theStandard Model Lagrangian:

g2w

φ2 ZµZµ



g2w

φ2 ZµZµ

Z-boson fields



g2w

φ2 ZµZµ

gauge coupling Z-boson fields



g2w

φ2 ZµZµ

gauge coupling

scalar field

Z-boson fields



g2w

φ2 ZµZµ

gauge coupling

scalar field

Z-boson fields

0 v

V(φ)

φPotential for scalar field is

V (φ) = −µ2φ2 + λφ4

Universe lives at minimum of poten-tial, φ ≃ v . Rewrite φ in terms ofperturbations H around minimum



g2w

φ2 ZµZµ

gauge coupling

scalar field

Z-boson fields

0 v

V(φ)

φ

Minimum of potential at

φ = v ≡√

µ2

2λ

Potential for scalar field is

V (φ) = −µ2φ2 + λφ4




g2w

φ2 ZµZµ

gauge coupling

scalar field

Z-boson fields

0 v

V(φ)

φ


φ = v ≡√

µ2

2λ


V (φ) = −µ2φ2 + λφ4


φ ≡ v +H → φ2 = v2 +2vH +H2H is the Higgs-boson field



g2w

φ2 ZµZµ

gauge coupling

scalar field

Z-boson fields

0 v

V(φ)

φ


φ = v ≡√

µ2

2λ


V (φ) = −µ2φ2 + λφ4


φ ≡ v +H → φ2 = v2 +2vH +H2H is the Higgs-boson field

g2wφ2ZµZ

µ → g2wv2︸︷︷︸

Z mass2

ZµZµ + 2g2w v

︸︷︷︸

HZZ coupling

HZµZµ

Mechanism generatesparticle masses

And a “Higgs” boson

A similar mechanism holds for fermions, with a Yukawa coupling yf ,yf φf f̄ → yf v f f̄

︸︷︷︸

fermion mass

+ yf H f f̄︸︷︷︸

interaction

Higgs mechanism gives massto all fundamental particles(except maybe neutrinos).

It predicts characteristic rela-tionship between their massesand their interactions with theHiggs boson.

W+

W−

H

2iM2Wv

gµν

Z

ZH

2iM2Zv

gµν

f

f_

Himfv

v ≃ 246 GeV is known as vacuum expectation value of Higgs field


Higgs Mass ↔ no-lose proposition[Higgs mechanism]

V (φ) = −µ2φ2 + λφ4 −→ MH =√2λv

quartic coupling λ unknown, so no prediction about Higgs mass

Still, strong arguments say

◮ it cannot be below 70 GeV, because λ too small — renormalisation groupevolution drives it negative and our universe is unstable

◮ if MH & 800 GeV, λ is large and we see new non-perturbative physics at∼ 1 TeV

So ideally build a collider that can discover Higgs-boson upto 800 GeV and perform WW scattering up to ≃ 1 TeV


LHC concept got serious in first half of 80’s[LHC]

From the CERN Courier in 1984:

The installation of a hadron collider inthe [27km] LEP tunnel, using supercon-ducting magnets, has always been fore-seen by ECFA and CERN as the naturallong term extension of the CERN facili-ties beyond LEP. [...]

Although the installation of such ahadron collider in the LEP tunnel mightappear still a long way off [...], it [is] anopportune moment for ECFA, in collabo-ration with CERN, to organize a ’Work-shop on the Feasibility of a Hadron Col-lider in the LEP Tunnel’ [...]

E ∝ BR

ring radius R ∼ 4×Tevatronsuperconduction magnets: B = 8 T

(2× Tevatron)

Tevatron ∼ 2∼ 2∼ 2TeV −→−→−→ LHC ∼ 14∼ 14∼ 14TeVGavin Salam (CERN/Princeton/Paris) Higgs@LHC and QCD MIT 2012-09-06 10 / 40

Interconnection betweentwo “dipoles” (bendingmagnets) in the LHCtunnel.

Cryogenics plant: 96 000 kg of Helium circulate through the machine at 1.9K

The detectors:

To accumulate 5× 1016 collisions over a few years, theyhave to be able to handle a pp collision rate of 109Hz

[25 collisions every 25 ns]

Typically, about 100 000 000 channels to read out.[must be examined 40 000 000 times/s,

interesting events written to long-term storage ∼400–1000 times/s]


ATLAS: general purpose CMS: general purpose

ALICE: heavy-ion physics LHCb: B-physics

+ TOTEM, LHCf

HIGGSPRODUCTION CHANNELS

(always indirect, because H couples

only weakly to light quarks)

cross section ≃ 20 pb∼ 1 Higgs every 5× 109 pp collisions

[for mH = 125.5 GeV]

protonproton

gluon gluon

Higgs

top

87%

W+ W−Z Z

quarkquark

Higgs

or

7%

5%

quarkantiquark

W or Z Higgs

0.6%

gluon gluon

topanti−top

Higgs


DECAY CHANNELS[for mH = 125.5 GeV]

WW and ZZ suppressed relative to

simple coupling proportionality,

because they cannot be produced

on-shell

Best channels for detection areγγ and ZZ ∗(→ 4e, µ), becauseof excellent experimental massresolution and manageable

backgrounds

b57%

b

Z Z * 2.8%

0.01% for 4 e, µ

6%τ+ τ−

0.2%

photonphoton

top

photonphotonW

W W

22%W W*

1% for 2 e, µ + 2ν


γγ pair invariant mass distribution[Higgs searches]

100 110 120 130 140 150 160

Eve

nts

/ 2 G

eV

500

1000

1500

2000

2500

3000

3500 ATLAS

γγ→H

Data

Sig+Bkg Fit

Bkg (4th order polynomial)

-1Ldt=4.8fb∫=7 TeV, s-1Ldt=5.9fb∫=8 TeV, s

(a)

=126.5 GeV)H

(m

100 110 120 130 140 150 160

Eve

nts

- B

kg

-200-100

0100200

(b)

100 110 120 130 140 150 160

wei

ghts

/ 2

GeV

Σ

20

40

60

80

100Data S/B Weighted

Sig+Bkg Fit

Bkg (4th order polynomial)

=126.5 GeV)H

(m

(c)

[GeV]γγm100 110 120 130 140 150 160

w

eigh

ts -

Bkg

Σ -8-4048

(d)

(GeV)γγm110 120 130 140 150S

/(S

+B

) W

eig

hte

d E

ve

nts

/ 1

.5 G

eV

0

500

1000

1500

Data

S+B Fit

B Fit Component

σ1±

σ2±

-1 = 8 TeV, L = 5.3 fbs

-1 = 7 TeV, L = 5.1 fbsCMS

(GeV)γγm120 130

Eve

nts

/ 1

.5 G

eV

1000

1500

Unweighted

ZZ ∗ (4-lepton) invariant mass distribution[Higgs searches]

[GeV]4lm100 150 200 250

Eve

nts/

5 G

eV

0

5

10

15

20

25

-1Ldt = 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 fb∫ = 8 TeV: s

4l→(*)ZZ→H

Data(*)Background ZZ

tBackground Z+jets, t

=125 GeV)H

Signal (m

Syst.Unc.

ATLAS

✹

✽� ✶�� ✶✁� ✶✂� ✶✄� ✶✽��

✁

✂

✄

✽

✶�

✶✁

✶✂

✶✄❉☎✆☎

❩✝✞

✯✟ ❩❩✤❩

❂✠✡☛ ☞✌✍❍♠

❈✎❙✲✏✥ ✑ ✒❡✓✱ ▲ ✥ ✺✔✸ ❢✕s✲✏✥ ✖ ✒❡✓✱ ▲ ✥ ✺✔✗ ❢✕s

✘✙✚✛✜✢✣✦✧★ ✦✢★ ✦✩★

❊✪✫✬✭✮✰✳✴✫✵

✷

✻

✼

✾

✿

❀

❁ ❃ ✷❄❀❅❑


Significance of the “bumps”?[Higgs searches]

p0 value = probability background fluctuated to produce observed “bumps”.

[GeV]Hm110 115 120 125 130 135 140 145 150

0L

oca

l p

-1110

-1010

-910

-810

-710

-610

-510

-410

-310

-210

-110

1

Obs. Exp.

σ1 ±-1Ldt = 5.8-5.9 fb∫ = 8 TeV: s-1Ldt = 4.6-4.8 fb∫ = 7 TeV: s

ATLAS 2011 - 2012

σ0σ1σ2

σ3

σ4

σ5

σ6

(GeV)Hm116 118 120 122 124 126 128 130

Local p-v

alu

e-1210

-1110

-1010

-910

-810

-710

-610

-510

-410

-310

-210

-110

11

2

3

4

5

6

7

Combined obs.

Expected for SM H

= 7 TeVs

= 8 TeVs

CMS-1

= 8 TeV, L = 5.3 fbs-1

= 7 TeV, L = 5.1 fbs

ZZ✣ + H ✢✢✣ H

≥ 5σ≥ 5σ≥ 5σ: OBSERVATION OF A NEW PARTICLEBY BOTH ATLAS AND CMS!


Properties of this new “Higgs-like” particle[Higgs searches]

◮ decay to γγ indicates either spin 0 or 2data by end of year should pin down spin and parity

◮ Mass: ATLAS: 126.0± 0.4± 0.4 GeVCMS: 125.3± 0.4± 0.5 GeV

◮ Couplings to other SM particles (key prediction of Higgs mechanism)


Properties of this new “Higgs-like” particle[Higgs searches]

◮ decay to γγ indicates either spin 0 or 2data by end of year should pin down spin and parity

◮ Mass: ATLAS: 126.0± 0.4± 0.4 GeVCMS: 125.3± 0.4± 0.5 GeV

◮ Couplings to other SM particles (key prediction of Higgs mechanism)

)µSignal strength (

-1 0 1

Combined

4l→ (*) ZZ→H

γγ →H

νlν l→ (*) WW→H

ττ →H

bb→W,Z H

-1Ldt = 4.6 - 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 - 5.9 fb∫ = 8 TeV: s




-1Ldt = 4.7 fb∫ = 7 TeV: s

-1Ldt = 4.6-4.7 fb∫ = 7 TeV: s

= 126.0 GeVHm

0.3± = 1.4 µ

ATLAS 2011 - 2012

SM/Best fit

-1 0 1 2 3

bb✣H

✢✢✣H

WW✣H

ZZ✣H

✜✜✣H

CMS-1

= 8 TeV, L = 5.3 fbs-1

= 7 TeV, L = 5.1 fbs

= 125.5 GeVH

m


Interpretations. . .[Higgs searches]

Fits to underlying couplings Stability of universe at Mplanck

Degrassi et al

Since the discovery, a slew of papers have discussed couplings,proposed new physics explanations of deviations, etc.

The forthcoming installments of data will tell us more.

Behind the scenes. . .


Oneof

theenablers

fortheLHC’ssuccess

isourunderstan

dingof

the

stronginteraction

Quantum

Chromodynamics

—QCD

0

0.2

0.4

0.6

0.8 1

fraction of ATLAS & CMS papers that cite them

Papers com

monly cited by A

TLA

S and C

MS

as of 2012−06−

28, from ’papers’, excluding self−

citations

Plot by GP Salam based on data from ATLAS, CMS and INSPIREHEP

Pythia 6.4 MCGEANT4Anti−kt jet alg.CTEQ6 PDFs

Herwig 6 MCALPGENCTEQ6.6 PDFsMSTW2008 PDFs

MC@NLOJIMMYRPP2010LO* PDFsPOWHEG (2007)

MadGraph4MC@NLO heavy−flavour

FastJetHerwig++ MCCT10 PDFsFEWZ NNLOCL(s) techniqueLHC MachineZ1 UE TunePythia 8.1PDF4LHC

QC

D

Gavin

Salam

(CERN/Prin

ceton/Paris)

Higgs@

LHC

andQCD

MIT

2012-09-06

24/40

Rough combination of ATLAS and CMS H → γγ signal strengths: they see1.6± 0.3 times the standard model expectation — a little high, but stillconsistent

The standard-model cross section for gluon-fusion Higgs production iswritten as a perturbative expansion in powers of the strong couplingconstant, with a leading-order (LO) term:

Higgs productioncross section

gluon gluon

Higgs

top

number of colliding gluon pairsper pp collision ~ 100

Higgs field vacuum expectation value

strong coupling constant ~ 0.11


If ATLAS and CMS had used the previous page’s formula they would havefound

σobservedσLO

= 5.6± 1.1

This would have been a strong sign (4σ) of physics beyond the standardmodel!

Where’s the catch? Higher orders of QCD perturbation theory:

σgg→H = σLO(1 + 11.4αs + 63α

2s + · · ·

)

= σLO (1 + 1.27 + 0.79 + · · · )≃ σLO × 3.4

NLO: Dawson ’91; Djouadi, Spira & Zerwas ’91

NNLO: Harlander & Kilgore ’02; Anastasiou & Melnikov ’02; Ravindran, Smith & van Neerven ’03


Corrections to total σgg→H are tip of QCD iceberg

Experimental searches break analysisinto sub-channels, which can differ interms of signal process, backgrounds,resolutions, etc. Need QCD predic-tions in each sub-channel.

W+ W−

quarkquark

Higgs

gluon gluon

Higgs

top

One or richest aspects of this kind of event characterization involves jets,which help count the number of energetic quarks and gluons in an event.


Quarks & gluons? We only ever see “jets”[Jets]

q

q

Start off with quark and anti-quark, qq̄



In perturbative quantum chromody-namics (QCD), probability that aquark or gluon emits a gluon:

∼ αsdE

E

dθ

θ

Diverges for small gluon energies E

Diverges for small angles θ

θ

q

q

A quark never survives unchangedit always emits a gluon (usually low-energy, at small angles)




∼ αsdE

E

dθ

θ



q

q

Each gluon radiates a further gluon




∼ αsdE

E

dθ

θ



q

q

And so forth




∼ αsdE

E

dθ

θ



q

q

And then a non-perturbative transition occurs



jet

jet

q

q

π, K, p, ...

Giving a pattern of hadrons that “remembers” the gluon branchingHadrons mostly produced at small angle wrt qq̄ directions or with low energy


Jets made systematic: jet definitions[Jets]

jet 1 jet 2

LO partons

Jet Def n

jet 1 jet 2

Jet Def n

NLO partons

jet 1 jet 2

Jet Def n

parton shower

jet 1 jet 2

Jet Def n

hadron level

π π

K

p φ

LHC events may be discussed in terms of quarks, quarks+gluon, or hadrons

A jet definition provides common representation of different “levels” ofevent complexity.


A $100 000 000, 20-year old problem[Jets]

QCD theorists have spent the past 10–15 years making accuratecalculations of signals and backgrounds at the LHC, many of them with jets(with remarkable advances in field theory on the way)

O (100) people × 10 years ≃ $100 000 000

Problem 1: the jet definitions originally foreseen by LHC experiments werenot compatible with these calculations — they “leaked” infinities:

σ = σLO(1 + c1 αs + c2 α

2s +∞∞∞α3s + · · ·

)

Problem 2: the jet definitions advocated by theorists since 1990’s hadbeen mostly shunned by proton-collider experiments

a) bad response to experimental noiseb) severe computational issues (1 minute/event ×1010 recorded events)


Solving the jets problem[Jets]

Discovered a link between QCD jet-finding and problemsof 2D computational geometry

Cacciari & GPS ’05

Jet clustering reduces to 2D dynamic nearest neighbour problem

time to cluster N particles reduced from N3 → N lnN (or N 32 )

Developed a theory of the interplay between jet-finding,

QCD radiation and experimental noiseCacciari, GPS & Soyez ’08

A crucial element was linearity of response

Spin-off applications for γ and lepton ID in Higgs searches

Proposed a new jet-definition based on what we’d learntanti-kt

Cacciari, GPS & Soyez ’08


Anti-kt algorithm[Jets]

simple agglomerative clustering algorithm

repeatedly cluster objects with smallest dij =∆R2ij

max(k2ti , k2tj)


Coefficient of “infinity”

10-5 10-4 10-3 10-2 10-1 1

Fraction of hard events failing IR safety test

JetClu

SearchCone

PxCone

MidPoint

Midpoint-3

Seedless [SM-pt]

Seedless [SM-MIP]

Anti-Kt, SISCone

50.1%

48.2%

16.4%

15.6%

9.3%

1.6%

0.17%

0 (none in 4x109)

Safe for perturbative QCD:No infinities

Speed

10-4

10-3

10-2

10-1

1

10

102

102 103 104 105t

[s]

N

time to cluster N particles

OLD

: KtJ

et (s

afe

for t

heor

y)

OLD

: CDF

JetCl

u (ver

y un

safe)

NEW

: Fas

tJet a

nti-k t

LHC lo-lumi LHC hi-lumi LHC Pb-Pb

∼ 1000 times faster than previouscodes


anti-kt used in nearly all jetmeasurements at the LHC

→ possible to make accuratepredictions for range of

measurements, including Higgs

allowing the experiments to pindown Higgs couplings moreaccurately in years to come

e.g.: fraction of Higgs eventsthat pass a “jet veto,” which

matters for measuring H → WW

ε(p t

,vet

o)

gg → H, mH = 125 GeV

NNLO

NNLL+NNLO

HqT-rescaled POWHEG + Pythia 0.2

0.4

0.6

0.8

1

pp, 8 TeVmH /4 < µR,F , Q < mH , schemes a,b,cMSTW2008 NNLO PDFsanti-kt, R = 0.5Pythia partons, Perugia 2011 tune

ε(p t

,vet

o) /

ε cen

tral

(pt,v

eto)

pt,veto [GeV]

0.8

0.9

1

1.1

1.2

10 20 30 50 70 100

Banfi, Monni, GPS & Zanderighi ’12

cf. talk tomorrow by Pier Monni


QCD is, in part, about predicting properties of collisions

But also about devising techniques to carry out more

effective searches


H → bb̄ (57% of decays) v. hard to see[Jet substructure]

Best hope is pp → W±H (and ZH), W± → ℓ±ν, H → bb̄.

e,µ

b

νb

H

W




pp → WH → ℓνbb̄ + bkgds

ATLAS TDR

Conclusion (ATLAS TDR):

“The extraction of a signal from H → bb̄decays in the WH channel will be verydifficult at the LHC, even under the mostoptimistic assumptions [...]”

Low efficiency, huge backgrounds, e.g. tt̄

NB: Evidence of this channel seen recently

at Tevatron, but similar difficulties

e,µ

b

νb

H

W




pp → WH → ℓνbb̄ + bkgds

ATLAS TDR

Conclusion (ATLAS TDR):

“The extraction of a signal from H → bb̄decays in the WH channel will be verydifficult at the LHC, even under the mostoptimistic assumptions [...]”

Low efficiency, huge backgrounds, e.g. tt̄

Analysis of signal/bkgd suggests:

◮ Go to high pt (ptH , ptW > 200 GeV)◮ Lose 95% of signal, but more efficient?◮ Maybe kill tt̄ & gain clarity?

W

H

bb

e,µ ν


pp → ZH → νν̄bb̄, @14TeV, mH=115GeV[Jet substructure]

Herwig 6.510 + Jimmy 4.31 + FastJet 2.3

Cluster event, C/A, R=1.2

Butterworth, Davison, Rubin & GPS ’08

also earlier work by Seymour; Butterworth et al




Fill it in, → show jets more clearly






Consider hardest jet, m = 150 GeV






split: m = 150 GeV, max(m1,m2)m

= 0.92 → repeat






split: m = 139 GeV, max(m1,m2)m

= 0.37 → mass drop






check: y12 ≃pt2pt1

≃ 0.7 → OK + 2 b-tags (anti-QCD)






Rfilt = 0.3






Rfilt = 0.3: take 3 hardest, m = 117 GeV




“substructure” techniques haveapplications in many searches,

e.g. tt̄ resonances

very active field,(including MIT group!)


An overview of some new-physics searches[Jet substructure]


LHC Outlook[Outlook]

rest of 2012

continue running at 8 TeV to reach ∼ 30 fb−1 per experiment (a factor of 3more data than used for discovery). Higgs features should emerge more clearly

2013

short proton-lead runfollowed by ∼18 month shutdown to complete LHC repairs

late 2014-

Running at 13− 14 TeVAccumulating several 100 fb−1 over a few years

Cover a large chunk of LHC’s potential to search for new physics

Beyond

LHC luminosity upgrades: factor 5-10?

Linear collider (to study Higgs in detail)?

Higher-energy LHC?Gavin Salam (CERN/Princeton/Paris) Higgs@LHC and QCD MIT 2012-09-06 40 / 40

EXTRAS


Energy–frontier colliders of the past 25 years[Extras]

Collider Lab Date Collided C.o.M. Energy

Tevatron Fermilab/USA 1987 – pp̄ @ 1960 GeVSLC SLAC/USA 1989 – 1998 e+e− @ 100 GeVLEP CERN/Europe 1989 – 2000 e+e− @ 209 GeVHERA DESY/Germany 1992 – 2007 e±p @ 330 GeV

Protons are made of quarks, anti-quarks and gluons. It’s the individualquarks and gluons that collide. Only a fraction of the proton’s energy isactually available in a single quark/gluon collision.


ATLAS[Extras]

A slice of CMS[Extras]


LHC has now been operating for three years[Extras][Operation]

1995: LHC approved2000: LEP closed

2008/09: LHC beams circulated

2008/09: severe “incident”poor electrical connection, arc, catastrophic Helium release, much damage

Followed by reviews, the fixes that could be made in ∼ 1 year

2009/11: LHC starts up again, 900 GeV pp collisions2009/12: 2360 GeV pp collisions2010/03: 7000 GeV pp collisions (∼ 50 pb−1)

“reduced-energy” target for safe operation

2010/11: 2760 GeV PbPb collisions2011/03: 7 TeV pp collisions (∼ 5 fb−1)2011/11: 2760 GeV PbPb collisions2012/03: 8 TeV pp collisions (∼ 6 fb−1 published, ∼ 14 fb−1 delivered)Gavin Salam (CERN/Princeton/Paris) Higgs@LHC and QCD MIT 2012-09-06 45 / 40

The challenges in reaching high energies[Extras][Operation]

Circular e+e− collider. Basic issue is synchrotron radiation

Energy loss per orbit ∼ E4

m4R

At LEP the numbers are O (10%) of the electron’s energy per orbit.

Circular pp collider

Proton mass 2000 times larger, so synchrotron radiation not a problem.The limitation is magnetic field needed to bend the protons round

B ∼ ER

Tevatron: R ∼ 1 km, Ec.o.m ∼ 2 TeV =⇒ B = 4 TeV.


The challenges in reaching high energies[Extras][Operation]

Circular e+e− collider. Basic issue is synchrotron radiation

Energy loss per orbit ∼ E4

m4R

At LEP the numbers are O (10%) of the electron’s energy per orbit.

Circular pp collider

Proton mass 2000 times larger, so synchrotron radiation not a problem.The limitation is magnetic field needed to bend the protons round

B ∼ ER

Tevatron: R ∼ 1 km, Ec.o.m ∼ 2 TeV =⇒ B = 4 TeV.

So what energy do you need?


Higgs mass and Higgs decays?[Extras][EW precision]

[GeV]HM50 100 150 200 250 300 350 400

[G

eV]

top

m

150

155

160

165

170

175

180

185

190

WAtop band for mσ1

WAtop

68%, 95%, 99% CL fit contours excl. m

LE

P 9

5% C

L

Tev

atro

n 9

5% C

L

WAtop

68%, 95%, 99% CL fit contours incl. m

68%, 95%, 99% CL fit contours incl. WA and direct Higgs searchestopm

[GeV]HM50 100 150 200 250 300 350 400

[G

eV]

top

m

150

155

160

165

170

175

180

185

190

G fitter SM

Nov 10

Likely Higgs Mass

There’s some likelihood thatthe Higgs boson will be“light”, MH ∼ 120 GeV


Higgs mass and Higgs decays?[Extras][EW precision]

[GeV]HM50 100 150 200 250 300 350 400

[G

eV]

top

m

150

155

160

165

170

175

180

185

190

WAtop band for mσ1

WAtop

68%, 95%, 99% CL fit contours excl. m

LE

P 9

5% C

L

Tev

atro

n 9

5% C

L

WAtop

68%, 95%, 99% CL fit contours incl. m

68%, 95%, 99% CL fit contours incl. WA and direct Higgs searchestopm

[GeV]HM50 100 150 200 250 300 350 400

[G

eV]

top

m

150

155

160

165

170

175

180

185

190

G fitter SM

Nov 10

Likely Higgs Mass

BR(H)

bb_

τ+τ−

cc_

gg

WW

ZZ

tt-

γγ Zγ

MH [GeV]50 100 200 500 1000

10-3

10-2

10-1

1

Higgs decayproducts v. MHMHMH

There’s some likelihood thatthe Higgs boson will be“light”, MH ∼ 120 GeV

If it is, crucial test of whetherit is the Higgs, will comefrom measuring several dif-ferent decays

Remember: Higgs couplings

intimately related to origin

of particle masses


✲�

✲✁✂✄

✁

✁✂✄

�

�✂✄

❉❍

❉❱

❉❢

❉❲

❉❩

❉t

❉❜

❉☎

❉❣

❉❩✆❲

❉☎✆❜

❉❜✆❲

✝① ✥ ✝①❙✞

✟✠✡☛①✮

▲☞✌✍✎✏✑✍✒✓✔ ✕✖✗✘✙✑✍✒✏✑✍✚✓✛ ✕✖✗✘ ✜✢✣✤✱ ✎✛✦ ✧▲★ ✩✕▲✩❙ ✙ ✧✞❙

✪✫ ✬✭✯✰

❞✳✴✳

❞✳✴✳ ✵✶☛✷✸

ICHEP 2012

Plehn & Rauch


0-jet events

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

10

20

30

40

50

60

70

80

90

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

10

20

30

40

50

60

70

80

90 =125 GeVH m data WW *γ Z/ Top VZ W+jets

CMS Preliminary = 8 TeVs

-1L = 5.10 fb

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

10

20

30

40

50

60

70

80

90

mainly WW ∗

background

1-jet events

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

5

10

15

20

25

30

35

40

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

5

10

15

20

25

30

35

40=125 GeVH m data

WW *γ Z/ Top VZ W+jets

CMS Preliminary = 8 TeVs

-1L = 5.10 fb

[GeV]l,lm50 100 150 200

eve

nts

/6.7

Ge

V

0

5

10

15

20

25

30

35

40

also some tt̄background

≥ 2-jet events

not usedtoo much background


How does anti-kt fare?[Extras]

[anti-kt ]

Timing v. particle multiplicity 2005

10-4

10-3

10-2

10-1

1

101

102

100 1000 10000 100000

t / s

N

KtJe

t k t

CDF M

idPoin

t (see

ds >

0 GeV

)

CDF M

idPoin

t (seed

s > 1 G

eV)

CDF J

etClu (

very u

nsafe)

3.4 GHz P4, 2 GB

R=0.7

Tevatron LHC lo-lumi LHC hi-lumi LHC Pb-Pb



[anti-kt ]

Timing v. particle multiplicity 2008

10-4

10-3

10-2

10-1

1

101

102

100 1000 10000 100000

t / s

N

KtJe

t k t

CDF M

idPoin

t (see

ds >

0 GeV

)

CDF M

idPoin

t (seed

s > 1 G

eV)

CDF J

etClu (

very u

nsafe)

FastJe

t

Seedl

ess IR

Safe C

one

(SISC

one)

Cam/Aac

hen

R=0.7

anti-k t

LHC lo-lumi LHC hi-lumi LHC Pb-Pb

k t

in critical region of N ∼ 2000− 40001000 times faster than previous attempts with similar jet algorithms



[anti-kt ]

Experimental sensitivity to noise

As good as, orbetter than allpreviousexperimentally-favouredalgorithms



[anti-kt ]

Coefficient of “infinity”

10-5 10-4 10-3 10-2 10-1 1

Fraction of hard events failing IR safety test

JetClu

SearchCone

PxCone

MidPoint

Midpoint-3

Seedless [SM-pt]

Seedless [SM-MIP]

Anti-Kt, SISCone

50.1%

48.2%

16.4%

15.6%

9.3%

1.6%

0.17%

0 (none in 4x109)

Safe for perturbative QCDpredictions:

No “leakage” of infinitiesto higher orders


IntroductionHiggs mechanismLHCHiggs searchesQCDJetsJet substructureOutlookExtrasOperationEW precisionfits etc.WW channelanti-kt

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Higgs and beyond at the LHC with a little help from QCD - CERN...Higgs boson. W+ W− H 2i M2 W v...

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