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Bruce Mellado University of Wisconsin-Madison HEP Seminar, EPFL, Lausanne 29/02/08 Higgs Searches with the ATLAS Experiment at the LHC
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Page 1: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce MelladoUniversity of Wisconsin-Madison

HEP Seminar, EPFL, Lausanne 29/02/08

Higgs Searches with the ATLAS Experiment at the LHC

Page 2: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 2

OutlineIntroductionMost relevant observation channels (SM)H→γγ

H→ττH→ZZ(*)→4lH→WW(*)→llνν

MSSM HiggsWhat can the Tevatron tell us?Feasibility of searches

Focus on what we can do with 10 fb-1 of data at the LHC

Page 3: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 3

A Higgs boson in predicted and

required to give mass to particles

Standard Model of Particle PhysicsQuarks and Leptons interact via the exchange of force carriers

?Gravitation

Electro-weak bosons (γ,W,Z)Electro-Weak

Gluons (g)StrongCarrierForce

quark, lepton

quark, lepton

force carrier

Page 4: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 4

What is the origin of the particle masses?

Why some particles are heavier than others?

The discovery of the Higgs boson should answer these questions

Page 5: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 5

The Quest for the Higgs

Experimentalists have been looking for the Higgs since the 70’s and 80’s in decays of nuclei, π, K, B, Y, etc… yielding mass limit <5 GeVOne of the goals of the LEP experiments (e+e-

collisions 1989-2000) was to search for a Higgs boson. The most stringent limit to date comes from the LEP experiments

Page 6: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 6≈ ≈2.6%

LEP

Higgs

Sea

rche

s (M

H=1

15)

Page 7: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 7

First Possible Hint for a Higgs boson (2000)

ALEPH observed three golden candidates in the four-jet channel

Input MH=115GeV/c2

Page 8: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 8

The LEP Limit

Above 0 favors

Background-only

hypothesis

Below 0 favors

Signal+background

hypothesis

ALEPH observed an excess over background-onlyprediction with significance of 2.8σ at 115 GeV/c2

Overall significance of LEP experiments ~1.8 σ→ limit setting MH>114.4

Page 9: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 9

Electro-Weak FitsExperimental constraints so far:

Indirect measurements from fitting the EW data using new world average for Mtop=170.9±1.8 GeV and Mw=80.398±0.025 GeV:

mH = 76+33-24 GeV

mH<144 GeV @ 95%CL (including LEP exclusion mH<182 GeV)

Data prefers low mass Higgs

Page 10: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 10

Present Tevatron Exclusion Limit

Note: the combined result is essentially equivalent to one experiment with 1.3 fb-1, since both experiments have “complementary” statistics at low and high mass

Page 11: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 11

The LHC 25 nsBunch spacing10 hLuminosity Lifetime1034 cm-2 s-1Design Luminosity14 TeVCenter of mass E

Page 12: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 12

Z’→ee

W’SUSY

Higgs

2009

2008

LHC Discovery ReachApp

roxi

mat

e disc

over

y re

ach

for

one

Expe

rimen

t

Page 13: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 13

Higgs Production at LHC

Leading Process (gg fusion)

Sub-leading Process (VBF)

Page 14: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 14

Main Decay Modes

Close to LEP limit: H→γγ,ττ,bb

For MH>140 GeV: H→WW(*),ZZ(*)

Djouadi, Kalinowski, Spira

Page 15: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 15

Cross-sections at LHC

Search for Higgs and new physics hindered by huge background rates

Known SM particles produced much more copiously

This makes low mass Higgs especially challenging

Narrow resonancesComplex signatures

Higgs in association with tops and jets.

Page 16: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 16

Low Mass Higgs Associated with Jets

Inclusive

Analyses in TDR were mostly inclusive

H+2jetTag jet

Tag jet

Applied to H→γγ,ττ,WW(*)

H+1jet

Tag jet

Tag jet

Not Tagged

φ

η

Forward jets

Higgs Decay

Not tagged

Not tagged

Slicing phase space in regions with different S/B seems more optimal when inclusive analysis has little S/B

Page 17: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 17

SM Higgs + ≥2jets at the LHCWisconsin Pheno (D.Zeppenfeld, D.Rainwater, et al.) proposed to search for a Low Mass Higgs in association with two jets with jet veto

Central jet veto initially suggested in V.Barger, K.Cheung and T.Han in PRD 42 3052 (1990)

Jet

Jet

Higgs Decay Products

Tagging Jets

Central Jet Veto.v.j.c

GeV700500M45.3

0

JJ

JJ

2J1J

÷>÷>η∆

<η⋅η

η

ϕ

Page 18: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 18

SM Higgs + ≥1jet at the LHC1.Large invariant mass of leading

jet and Higgs candidate2. Large PT of Higgs candidate3. Leading jet is more forward

than in QCD background

η

ϕ

Higgs Decay Products

Quasi-central Tagging Jet

Loose Central Jet Veto(“top killer”)

Tag jet

Not Tagged

Tag jet

MHJ

S.Abdullin et al PL B431 (1998) for H→γγB.Mellado, W.Quayle and Sau Lan Wu Phys.Lett.B611:60-65,2005 for H→ττB.Mellado, W.Quayle and Sau lan Wu

Phys.Rev.D76:093007,2007 for H→WW(*)

Page 19: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 19Weight: 7000 t 44 m

22 m

ATLAS

Page 20: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 20

Low Mass SM Higgs: H→γγ

Page 21: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 21

ATLAS

Page 22: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 22

Higgs decay to γγ

γγ Backgrounds Reducible γj and jjBackgrounds

q→π0

Page 23: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 23

CMS

and

ATL

AS

analys

es f

or 1

00 f

b-1

CMS

ATLAS

Page 24: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 24

Higgs Mass ReconstructionIn ATLAS Expect about 50% of events to have at least one converted photon, but can achieve <1.2% mass resolution

σ=1.36 GeV σ=1.59 GeVLow Lumi High Lumi

Events with at least one conversion

Page 25: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 25

Photon IdentificationTo separate jets from photons is crucial for Higgs discovery

Need rejection of > 1000 against quark-initiated jets for εγ=80% to keep fake background about 20% of total backgroundExpect rejection against gluon-jets to be 4-5 times greater

Jet rejection will be evaluated with data

Look into sub-leading jets in multi-jet final states with different PT thresholds

Avoid trigger biasApply trigger pre-scaling if neededCorrect for contribution from prompt photons

ATLA

S TDR (1999)

Page 26: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 26

Inclusive H→γγ

ATLAS

Page 27: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 27

h,A→ττ; H±→τ±ν

Page 28: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 28

Central Jet Veto Higgs Decay Products

Tagging Jets

η

ϕ

Low Mass SM H→ττ + jets

η

ϕ

Higgs Decay Products

Quasi-central Tagging Jet

Loose Central Jet Veto(“top killer”)

GeV700500M45.3

0

JJ

JJ

2J1J

÷>

÷>

<⋅

η∆ηη

GeV 700MGeV 100P

JH

TH

>

>

Because of the poor Higgs mass resolution obtained with H→ττ, inclusive analysis not possible. Need to reduce QCD backgrounds by using distinct topology of jets produced in association with Higgs

H→ττ + ≥2 jets H→ττ + ≥1 jets

Page 29: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 29

In order to reconstruct the Z mass need to use the collinear approximation Tau decay products are collinear to tau direction

H→ττ Mass Reconstruction

xτ1 and xτ2 can be calculated if the missing ET is knownGood missing ET reconstruction is essential

τ

τxPP l=

21

ll

xxMM

ττττ ≈

Tmiss2Tl1Tl2T1T PPPPP ++=+ ττ

Fraction of τ momentum carried by visible τ decay

l

h

νν

νν

H

Page 30: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 30

Low Mass SM H→ττ+jetsReconstruct Higgs mass with collinear approxim.

30 fb-1

H(→ττ→ll) +≥2jets H(→ττ→lh) +≥1jet

MH=120 GeV

Page 31: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 31

Control Sample 3Z →ee,µµTight cuts on Jets

MC extrap. is validated

Control Sample 1Z →ee,µµLoose cuts on Jets

Control Sample 2Z →ττLoose cuts on Jets

Signal Region

Z →ττTight cuts on Jets

MC extrap.

Replace Z→ ee,µµby Z→ ττ

Determine shape and normalization of Z →ττbackground

Two independent ways of extracting Z→ττ shapeData driven and MC drivenSimilar procedure has been defined for H→WW(*)

MHJ, ∆ηJJ

Mll <75 GeV

85<Mll <95 GeV

Page 32: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 32

Normalization of Z→ττ using Z→ee,µµZ→ee,µµ offers about 35 times more statistics w.r.t to Z→ττ→ll

Ratio of efficiencies depends weakly with MHJ and can be easily determined with MC after validation with data

)llZ(B),eeZ(B

dM),eeZ(d

dM)llZ(d

R

ZJ

ZJ

→→→

•→

→→

=ττ

µµµµσ

ττσ

),eeZ()llZ(R

µµεττε

→→→

=

Page 33: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 33

SM Higgs: H→ZZ(*)→4l

Page 34: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 34

Irreducible Z0Z0 backgrounds

Higgs decay to Z0Z0

Z

Z

Reducible 4l backgrounds

Page 35: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 35

ll

lll l

ll

l

l l

l

ν

νb b

bb

ZbbZbbtt WbWbZZ*/ γ*→4l

l

l

l

l

ν

ν

ν

ν

τ

τZZ*/ γ*→2l 2τ

BackgroundsHiggs→ZZ(*)→4l

(l=eµ)

ContinuumIrreducible

Non-Resonantreducible

Resonantreducible

Page 36: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 36

H[130 GeV] 2e2µH[130 GeV] 4µH[130 GeV] 4e

SM Higgs→ZZ(*)→4lAble to reconstruct a narrow resonance, with mass resolution close to 1%. Can achieve excellent signal-to-background > 1

Major issue: Lepton ID and rejection of semi-leptonic decays of B decays. Suppress reducible background Zbb,tt→4l

ATLAS TDR

Page 37: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 37

Sum of Pt of tracks around each µ in GeV

Σ of calo energy around each µ in GeV

ATLAS

ATLAS

ATLA

S TD

RReducible background

ATLA

S TD

R

Page 38: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 38

Page 39: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 39

SM Higgs: H→WW(*)→2l2ν

Page 40: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 40

+ Single top & non-resonant WWbb

W+W- backgrounds

Higgs decay to W+W-

Page 41: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 41

SM Higgs H→WW(*)→2l2ν

∆φll (rad)

Strong potential due to large signal yield, but no narrow resonance. Left basically with event counting experiment

H→WW+0j

Transverse Mass (Gev)

H→WW+2j

Page 42: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 42

SM H→WW +0,1,2 jets

Defined three independent analysis, depending on the number of tagged jets

Systematic errors added in significance calculation

WW+1jet ATLAS

WW+2jet ATLAS

WW+0jet ATLAS

Page 43: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 43

Background Suppression and ExtractionNot able to use side-bands to subtract background. This makes signal extraction more challenging. Need to rely on data rather than on theoretical predictionsDefinition & understanding of control samples is crucial

ttbar suppression Non-resonant WW suppression

EW WW QCD WW

Jet veto (understand low PT jets)Semi-inclusive b-tagging or “top killing” algorithmCombined rejection of >10 times

∆φll and Mll, very important variablesTransverse momentum of WW system

Higgs production is harderMissing ET reconstruction plays a role

Page 44: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 44

Control Samples for H→WW(*)

Main control sample is defined with two cuts∆φll>1.5 rad. and Mll>80 GeV

Because of tt contamination in main control sample, need b-tagged sample (Mll cut is removed)

Page 45: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 45

MSSM HiggsMinimal super-symmetric extension of Higgs sector

Five Higgs: h (light), H, A, H± (heavy)Parameter space reduced to two: MA,tanβTheoretical limit on light MSSM Higgs: h<135 GeV

Page 46: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 46

MSSM Higgs (cont)

Large number of discovery modes:SUSY particles heavy:

SM-like: h→γγ,bb,ττ,WW; H→4lMSSM-specific: A/H→µµ,ττ,tt; H→hh, A→Zh; H±→τ±ν

SUSY accessible:H/A → χ0

2 χ02, χ0

2 → h χ01

Small impact on Higgs branching ratio to SM particles

q

qg

gt

t

t

gg

q

qW

W

t

H

H

H

H

bt

g

H+

Page 47: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Mt = 171.4 GeVMW = 80.398 GeV

Does the data favor a MSSM Higgs?

Slepton/squarkone loop corrections

Contributions from MSSM Higgs bosons

Caution: This is not the only way of achieving agreement with data

Page 48: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 48

MSSM Higgs Cross-sections (large tanβ)

Tevatron LHC

Page 49: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 49

Heavy CP-odd Higgs boson (A) branching ratios

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Bruce Mellado, HEP Seminar, EPFL 29/02/08 50

MSSM Higgs Search at the Tevatron

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Bruce Mellado, HEP Seminar, EPFL 29/02/08 51

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Bruce Mellado, HEP Seminar, EPFL 29/02/08 52

D0 3b-jet Analysis

Page 53: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 53

D0 3b-jet Analysis

Page 54: Higgs Searches with the ATLAS Experiment at the LHC · 2018. 5. 15. · Higgs Searches with the ATLAS Experiment at the LHC. ... SUSY Higgs 2009 2008 LHC Discovery Reach Approximate

Bruce Mellado, HEP Seminar, EPFL 29/02/08 54

LHC Discovery Potential

ATLAS30 fb-1

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Bruce Mellado, HEP Seminar, EPFL 29/02/08 55

Outlook and ConclusionsThe search for a Higgs boson is a priority of CMS and ATLAS. One experiment should be able to observe a SM Higgs with O(10) fb-1 and also cover most of the MSSM planeHiggs searches at the LHC comprise a large number of final states involving all the signatures that the CMS and ATLAS detectors can reconstruct

Electrons, muons, photons, τ, jets, b-jetsNeed to understand V,VV, (V=Z,W), tt, γγ, jγ and their

production in association with jetsHiggs searches at the LHC promise is a rich program that promises to turn the LHC era into fascinating times for High Energy Physics


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