+ All Categories
Home > Documents > Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology...

Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology...

Date post: 26-Mar-2015
Category:
Upload: brianna-myers
View: 220 times
Download: 4 times
Share this document with a friend
Popular Tags:
32
Higgs Physics at the Higgs Physics at the Large Hadron Collider Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006
Transcript
Page 1: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Higgs Physics at theHiggs Physics at the

Large Hadron ColliderLarge Hadron ColliderMarkus Schumacher, Bonn University

NRW Phenomenology Meeting 2006, Bad Honnef, January 2006

Page 2: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 2

Outline

the Higgs Mechanism and SM Higgs phenomenology at LHC

• discovery of 1 neutral scalar SM like Higgs boson

(determination of mass, spin, CP)

quantum numbers: spin and CP

BRs, total width, couplings

self coupling at SLHC

direct observation of

additional Higgs bosons

determination of Higgs profile:

deviations from SM prediction

- > 1 neutral Higgs boson

- charged Higgs boson

- exotic decays:Hinvisible

Higgs physics program at the LHC

•discrimination: SM or extended Higgs sectors (e.g. MSSM)

Page 3: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 3

The Higgs Mechanism in the Nut Shell

consistent description of nature seems to be based on gauge symmetry

SU(2)LxU(1) gauge symmetry no masses for W and Z and fermions „ad hoc“ mass terms spoil

The problem:

The „standard“ solution:

new doublet of complex scalar fields

with appropiately choosen potential V

vacuum spontaneously breaks gauge symmetry

one new particle: the Higgs boson H

= v + H

renormalisibility no precise calculation of observables bad high energy behaviour WLWL scattering violates unitarity at ECM~1.2 TeV

Higgs boson mass unknown: theory: unitarity MH<1TeV

LEP search: MH<114.4 GeV electroweak fit: MH<186 GeV excluded at 95% CL at 95%CL

Page 4: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 4

Mass generation and Higgs couplings: = v + H

effective mass = friction of particles

with omnipresent „Äther“

v =247 GeVx

fermion

gf

mf ~ gf v Yukawa coupling

MV ~ g v gauge coupling

x x

W/Z boson

g gauge

Interaction of particles with v=247 GeV

Fermions gf ~ mf / v

W/Z Bosons: gV ~ 2 MV / v

Interaction of particles with Higgs H

fermion

gf

x

W/Z boson

g gauge

Higgs

Higgs v

2

2VVH coupling ~ vev

only present after EWSB breaking !!!

unknown Higgs mass fixes Higgs profile completely

Page 5: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 5

50 100 200 100010-3

10-2

10-1

100

bb cc tt gg WW ZZ

Bra

nchi

ng r

atio (Higgs

)

mH (GeV)

bb

WW

ZZ

tt

ccgg

Higgs Boson Decays in SM

for M<135 GeV: H bb, dominant

for M>135 GeV: H WW, ZZ dominant

tiny: H also important

HDECAY: Djouadi, Spira et al.

Page 6: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 6

LHC

SPPS

pp collisions at the Large Hadron Collider

start in 2007 at ECM of 14 TeV

first years: low lumi running 10 fb-1/year

later (x10): high lumi running 100 fb-1/year

Page 7: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 7

Complexity of a LHC event

+ ~23 additional pp-interactions per bunch crossing at high lumi

~109 proton-proton collisions / sec

~1600 charged particles in detector per event

hard process

+ ISR,FSR

+ underlying

event

Page 8: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 8

The challenge of reconstruction

low lumi. high lumi.

Page 9: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 9

Production of the SM Higgs Boson at LHC

K = (N)NLO/LO

K ~ 1.2

K ~ 2

K ~ 1.4

K ~ 1.1

~4 to 15% + from PDF (5 to15%)

signal MC at NLO only avaiable for GGF

background: NLO calculations often not avaiable

ATLAS: use K=1 and LO MC for signal and BG

CMS:K-factor for GGF + „guestimated“ K for BG

Page 10: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 10

Cross sections for background processes

Higgs 150 GeV: S/B <= 10-10

overwhelming background

trigger: 10-7 reduction

on leptons, photons, missing E

p pqq

q

p pqq

qq

H

WW

l

l

background: mainly QCD driven

signal: often electroweak interaction

photons, leptons, …

q

Page 11: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 11

Considerations for Discovery Channels

sufficient signal rate no sensitivity to H in SM

efficient trigger (,e,, …) no sensitivity for: GGF, WBF: Hbb

H mass reconstructable? yes: H, ZZ, bb, no: HWW

control of background

- signal-to-background ratio - estimate of BG from data possible?

- sometimes: shape from MC needed

excl

ud

ed b

y

LEP

main discovery channels

GGF: H GGF: H ZZ 4l+-

GGF: HWW2(l)

ttH: H bb

VBF: H

VBF: H WW

ATLAS

since

2000

Page 12: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 12

H 2 Photons

signal: two photons background:

- reducible: pp j+x, jj+x,..

photon vs. jet seperation

- irreducible: pp+X

diphoton mass

mass resolution M/M = 0.7%

- uniformity/understanding of ECAL

- dead material: % of unconverted

- pile up: vtx constraint

background estimate from sidebands

no Monte Carlo needed

exp. uncertainty: O(0.1%)

S/BG ~ 1/10

CMS 100fb-1

red./irred. BG: 2 to 1 after final cut

LO NLO: increase of S/B ~ 5060%

(K-factor ~ 2, larger Higgs Pt)

NLO

CMS

Page 13: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 13

H ZZ(*)4 Leptons

reducible BG:

tt, Zbb 4 leptons

lepton isolation and

veto against b-jets

good mass resolution M: <~1% muon spectrometer + tracking detectors

small and flat background easy estimate from sidebands no Monte Carlo needed

CMS

CMS

100fb-1

NLO

signal: 4 iso. leptons

1(2) dilepton mass = MZ

irreducible BG:

ZZ 4 leptons

four lepton mass

Page 14: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 14

signal:

- 2 leptons + missing ET

- lepton spin corrleations

- no mass peak transverse mass

H WW l l

ATLAS

M=160GeV

30fb-1

transverse mass

BG: WW, WZ, tt

lepton iso., missing E resolution

jet (b-jet) veto against tt

BG estimate in data from ll

normalisation rom sideband

shape from MC

NLO effect on spin corr.

ggWW contribution signal like

Dührssen, prel.

ll

Page 15: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 15

Vector Boson Fusion: ppqqH

signature:2 forward jets with

large rapidity gap only Higgs decay products

in central part of detector

rapidity of tag jets rapidity difference

Page 16: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 16

Vector Boson Fusion: ppqqH

Page 17: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 17

Vector Boson Fusion: challenges

pT>20GeV

forward jet reconstruction

influence of UE and pile up?

so far only for low lumi

ATLAS

central jet veto:

influence of UE and pile up?

so far only for low lumi

efficiency of jet veto at NLO.?

distributions at NLO calculated

but: need NLO MC generator

for signal and BG

Zeppenfeld et al.

Page 18: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 18

Vector Boson Fusion: H tau tau ll 4 (or l had 3 ) signature: tagging jets + 2 high pt leptons + large missing ET

backgrounds: tt,Zjjcentral jet veto

reconstruction of m

mass resolution ~ 10% dominated bei Emiss resolution

He

ATLAS30 fb-1

expected BG uncertainty ~ 5 to 10%

for MH > 125 GeV: flat sideband

for MH < 125 normalisation from Z peak, but shape?

collinear approximation

Page 19: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 19

Idea: jjZandjjZ

look almost the same, esp. in calos

same missing energy

only momenta different

Method: select Z events

randomise momenta

apply „normal“ mass reco.

Vector Boson Fusion, Hestimate of BG shape from data

PTmiss,final (GeV) M (GeV)

promising prel. results from ongoing diploma thesis in BN (M. Schmitz)

Page 20: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 20

Weak Boson Fusion: HWWll (lqq)

HWWeATLAS

10 fb-1

MH=160 GeV

H2 photons

S/BG ~ 1/1

S/BG ~1/10

VBF versus inclusive channel

ATLAS

M=160GeV

30fb-1HWWll

S/BG ~ 4/1

S/BG ~ 2/3

smaller rate larger sig-to-BG ratio smaller K-factor

more challenging for detector understanding

order of significance depends on channel and Higgs mass

CMS

Page 21: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 21

Discovery Potential for light SM Higgs boson

excl

ud

ed b

y

LEP

for GGF: raise of significance by ~ 50% from LO to NLO

results for cut based analysis improvement by multivariate methods

discovery from LEP exclusion until 1 TeV

from combination of search channels with 15 fb-1 of well understood data

with individual search channels with 30 fb-1 of well understood data

Page 22: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 22

Measurement of Higgs Boson Mass

1fb300L

ATLAS

M/M: 0.1% to 1%

Uncertainties considered:

“Indirect” from Likelihood fit to transverse mass spectrum: HWWllWHWWWlll

Direct from mass peak: HHbb HZZ4l

VBF with H or WW

not studied yet !

i) statistical

ii) absolute energy scale

0.1 (0.02) % for l,,1% for jets

iii) 5% on BG + signal for HWW

Page 23: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 23

Determination of Higgs boson couplings

couplings in production Hx= const x Hx and decay BR(Hyy) = Hy / tot

Hx x BR ~ HX Hy

tot

prod decay

partial width: Hz ~ gHz2

tasks: - disentangle contribution from production and decay

- determine tot

H WW chosen as reference as best measured for MH>120 GeV

for 30fb-1 worse by factor 1.5 to 2

model independent:

only ratio or partial decay widths

13 signal rates used in global fit

(incl. various syst. uncertainties)

Page 24: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 24

for MH<200 GeV, tot<<mass resolution

no direct determination

have to use indirect constraints on tot

Absolute couplings with gV < gVSM constraint

coupling to W, Z, , b, t

Dührssen et al.

lower limit from observable rates:

tot > W+Z+t+g+....

upper limit needs input from theory:

mild assumption: gV<gVSM

rate(VBF,HWW)~V2/tot<(V

2 in SM)/tot

tot< rate/(V2 in SM)

Page 25: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 25

MH2 = 2 =MPlanck

Motivation for Supersymmetry from Higgs Sector

Higgs mass problem in SM: 2

“solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ?

MH2 = (MSM-MSUSY)

2 2

W W+ HH natural value ~ MPl

vs electroweak fit MH~O(100GeV)

SUSY solution: - partner with spin difference by ½ cancel divergence exactly if same M - SUSY broken in nature, but hierarchy still fine if MSUSY~1 TeV

H H

-

SUSY breaking in MSSM: parametrised by 105 additional parameters too many constrained MSSM with O(5) additional parameters

Page 26: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 26

The MSSM Higgs sector in a tiny Nut Shell

SUSY: 2 Higgs doublets 5 physical bosons real MSSM: 2 CP even h, H, 1 CP odd A, charged H+, H-

at Born level 2 parameters: tan, m A mh < MZ

large corrections: mh < 133 GeV for mtop=175 GeV, MSUSY=1TeV

corrections depend on 5 SUSY parameters: Xt, M0 , M2, Mgluino,

fixed in the benchmark scenarios e.g. MHMAX scenario

maximal Mh conservative LEP exclusion

Mtop=174.3 GeVmain questions for LHC: at least 1 Higgs boson observable in the entire parameter space?

how many Higgs bosons can be observed?

can the SM be discriminated from

extended Higgs sectors?

calculated with

FeynHiggs

Page 27: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 27

Light Higgs Boson h

large area covered by many channels

sure discovery and parameter

determination possible

small area uncovered @ mh~95 GeV

300 fb-130 fb-1

VBF dominates observation

small area from bbh,h

for small Mh

ATLAS preliminaryATLAS preliminary

VBF, H covers hole plane

from either H or h observation

with 30fb-1

Page 28: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 28

Overall Discovery Potential: 300 fb-1

at least one Higgs boson

observable for all parameters

in all CPC benchmark scenarios

significant area where only lightest Higgs boson h is observable

can H SUSY decays or

Higgs from SUSY decays

provide observation?

discrimination via h profile

determination?

similar results in other benchmark scenarios

VBF channels , H/Aonly used with 30fb-1

300 fb-1

ATLAS preliminary

Page 29: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 29

Higgs Decays to Gauginos

Msleptons=250 GeV

e.g. H0 20 2

0 10 1

0+4l

dominant background from SUSY

• results for most optimistic scenarios shown fine tuned• require small slepton masses

for large BR(2 1 +2 leptons )• reduced sensitivity for other channels, consistent interpretation needed

CMS 100fb-1

Page 30: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 30

ATLASprel.

300 fb-1

SM or Extended Higgs Sector e.g. Minimal SUSY ?

discrimination via rates from VBF

R = BR(h WW) BR(h )

assume Higgs mass well measured no systematic errors considered same contribution from GGF

compare expected

measurement of R in MSSM

with prediction from SM

for same value of MH

=|RMSSM-RSM|exp

Page 31: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 31

CP-Violating MSSM: Overall Discovery Potential

MH1: < 70 GeVMH2: 105 to 120 GeV

MH3: 140 to 180 GeV

small masses below 70 GeVnot yet studied in ATLAS

300 fb-1 yet uncovered area size and location of „hole“ depends on Mtop and program for calculation

ATLAS preliminary

at Born level: CP symmetry conserved in Higgs sector

complex SUSY parameters mixing between neutral CP eigenstates

no absolute mass limit from LEP

Page 32: Higgs Physics at the Large Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006.

Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006 32

Conclusion and Outlook

Standard model: discovery of SM Higgs boson with 15 fb-1

• requires good understanding of whole detector• multiple channels with larger luminosity Higgs profile investigaton

CP conserving MSSM: at least one Higgs boson observable • only h observable in wedge area at intermediate tan• maybe Higgs to SUSY or SUSY to Higgs observable?• discrimination via Higgs parameter determination seems promising

CP violating MSSM: probably a „hole“ with current MC studies• promising MC studies on the way see 2nd next talk

more realistic MC studies: • influence of miscalibrated and misaligned detector• improved methods for background estimation from data• use of NLO calcluations and MCs for signal and background

additional extended models + seach channels:• CPV MSSM, NMSSM, 2HDM• Higgs SUSY, SUSYHiggs• VBF, Hbb (b-trigger at LV2), VBF,Hinv. (add. forward jet trigger)


Recommended