higgs physics at the large hadron collider

Higgs Physics at the Large Hadron Collider

Markus Schumacher , Bonn University

19th International Workshop on Weak Interactions and Neutrinos

WIN03

Lake Geneva, Wisconsin, Oct. 6th to 11th, 2003

• Discovery Potential in the SM

• Investigations of the Higgs Boson Profile

• Discovery Potential in the MSSM

• MSSM versus SM (a first look) ??

• Invisible Higgs

Markus Schumacher, Bonn University Higgs Physics at LHC WIN03 Lake Geneva, Wisconsin2

Production and Decay of the SM Higgs Boson at LHC

Having available four production mechanisms and observing several decay modes is the key for investigations of the Higgs boson profile

50 100 200 100010-3

10-2

10-1

100

bb cc tt gg WW ZZ

Bra

nching

ratio

(Higgs

)

mH (GeV)

bb WW

ZZ

tt

cc

gg

K>1.7

K~1.2

K~1.1

K~1.3

HDECAY: Djouadi, Spira et al.


Discovery Potential 2001 + Main Channels

light Higgs boson M<2MZ:gluon fusion GF with: H , H ZZ 4l H WW ll

associated production: tth, Hbb

2001: 10fb-1 from both experiments for discovery of small mass Higgs

New: weak boson fusion WBF qqqqH with H and HWW

heavy Higgs boson M>2MZ

GF: HZZ4l,

WBF: qqqqH with

HZZll

HZZlljj

HWWljj

Require forward jet tagging

Status 2001


Detectors optimised for low mass Higgs discovery

current LHC schedule: start 2007> 10 fb-1 / yr at low luminosity (few 1033cm-2s-1) runninglater 100 fb-1 /year at high luminosity (1034cm-2s-1) running

pixel vertex and strip track detectors b andtagging (H, bb)

homogenous calorimeters to large e/ measurement (Hgg, H4 leptons) forward jet tagging (VBF), missing energy (HHinvisible)

complex myon spectrometers momentum accuracy and efficient trigger (HZZ4 leptons, A/H)

uds = 0.005

key performance numbers obtained from full GEANT simulationmass resolutions, b+ tagging efficiencies and rejection factors

forward jet tagging, trigger efficiencies, PID,….


Gluon Fusion: H and HZZ4 leptons

100 fb-1

MH=130GeV

Inclusive analysis: two high Pt

Even

ts /

GeV

M: ~1GeV

K=1.6

S/BG ~ 1/20NLO MC for signal + irreducible BG available (Binoth et al., Bern et al.):

Preliminary ATLAS study: S/B from 4 to ~6 for 30 fb-1,M= 120 GeV

Born

Cross sections under control (MH=120 GeV): =20 pb (LO), 38pb (NLO), 44pb (NNLO)(Ravindran et al., Harlander et al.)

4 high pt leptons narrow mass peak, very small background irreducible BG: ZZ reducible BG: tt, Zbbrejection via lepton isolation and b-veto

ATLAS: preliminary study with NLO-MC indicates

increase of significance by ~25%

HZZ4 leptons:

Irreducible BG dominant, estimate from sidebands


ttH, Hbb

signal: bqq bl bb lepton for trigger

background processes: reducible tt+jets,W+jets (1/3)irreducible: ttbb (2/3 in ATLAS study)

L = 30 fb-1 k = 1.5

M ~ 15 GeV CMS: K=1.5 (signal, ttZbb): S/ B = 5.3 K=1 for all processes: S/ B = 3.8

For L = 30 fb-1 and MH = 115 GeVK=1.2 for QCD-Scale=(Mt+MH/2)

(Beenakker et al., Dawson et al.)

ATLAS: TDR: S/ B = 3.6 for MH=120 GeV, L = 30 fb-1, K=1

New analysis: S/ B = 2.8ttbb from AcerMC, new PDF, new QCD-scale

Selection: 4 b jets + 1 lepton full reconstruction of ttH final state

b-tagging and jet energy performance crucial !


Forward tagging jets

Higgs Decay

Proposed by Rainwater, Zeppenfeld et al.Strong discovery potential for low MH

Allows to measure Higgs couplings Good for invisible decays

Weak Boson Fusion Channels

Two forward tagging jets

at large , large

+ little central detector activity

Jet

Jet


High Lumi

Low Lumi

Central Forward

Channels considered:

all by ATLAS, red by CMS

HWWll and ljj

Hll lhad

H

Experimental Issues

pT>20GeV

Forward jet reconstruction jet-veto fake rate due to pile up

Careful investigation of jet tagging with full simulation

ATLAS ATLAS

Only low lumi running

investigated so far

Low Lumi


MH=160 GeVWWe

Weak Boson Fusion: HWW

tt WWjj, W + 4 jets

Dominant backgrounds

ATLASCMS

Selection: tag jets with rapididty gap, central jet veto, b-jet veto, mjj, lepton angles (Spin 01), transverse mass (llET

miss)

significance > 5

for 10 fb-1 and

MH=135 to 190 GeV

(WWll and ljj, incl. BG = 10%)

Cross section: 500 to 2000 fb for MH = 120 to 190 GeV

10 fb-1

60 fb-1


Evidence for Spin 0 in H->WW->ll mode

between leptons W from H opposite spins leptons same direction

+ add. BG normalisation

MT>175 GeVMT<175 GeV

Signal Region

Outside Signal Region

Weak Boson Fusion: HWW

mT(ll) with (left) and w/o (right) lepton cuts

background estimation at level of 10% from data + shape from MC

ATLAS

Transverse mass


Weak Boson Fusion: H

Zjj, Wjj EW&QCD tt production

Dominant backgrounds:

Cross section: 300 to 64 fb for MH = 120 to 150 GeV

angle between tagging jets

Sensitive to CP structure of couplings

Plehn et al.

Selection: VBF cuts as for WW +

reconstruction of and M


Mass can be reconstructed in collinear approximation

He30 fb-1

ATLAS

M = 11 to 12 GeV

Weak Boson Fusion: H

background estimate: ~10%

for MH>125 GeV from side bands

for MH>125 GeV from normalisation of Zpeak

significance > 5 for 30 fb-1 and

MH=110 to 140 GeV (e ll lhad)

30 fb-1

H Wjj

x=momentum fraction carried by tau decay products


SM Higgs: Discovery potential incl. VBF

VBF channels largely increase discovery potential for low mass region

10fb-1 at one experiment sufficient for discovery

several channels observable over full mass range robust discovery and coupling dtermination

Future work on VBF channels:high lumi running performancemass measurementreinvestigate potential with

NLO-MC (not yet avaiable) improved matching ME to parton shower


Higgs Boson Mass

1fb300L

ATLAS

M/M: 0.1% to 1%

Uncertainties considered:

“Indirect” from Likelihoodfit to transverse mass spectrum: HWWllWHWWWlll

Direct where Higgs mass can be reconstructed: HHbb HZZ4l

VBF with H or WW not studied yet !

No theoretical errors considered:Effect of PDF <<10 MeVLarge MH, shift in position due to interference of Higgs signal and non resonant background

i) statistical ii) absolute energy scale 0.1% (goal: 0.02%) for l, 1% for jets iii) 5% on BG and signal rates for HWW channels


Spin and CP Quantum Numbers

- angle between decay planes in the rest frame of the Higgs boson

- angle between leptons and the momentum of the Z in the rest frame of the Z (Gottfried Jackson angle).

SN-ATLAS-2003-025

observation of Hor ggH rules out Spin=1 (Young theorem)

sensitivity through polarisation correlations of Higgs decay products one possibility HZZ4 leptons

Sensitive observables investigated:

Higgs rest frame


Theoretical prediction

)cos()cos()( 21F ))(cos()(sin)( 22 1TLGTL

TLR


Exp. Results after L=100fb-1

After background subtraction : for MH>250 GeV clear discrimination between Spin = 0 or 1 and CP even or odd

MH<250 GeV: only dicrimination between SM-Higgs and S=0, CP=-1



discrimination of CP via tth(A) production under study !

Discrimination dominated by (polarisqation) especially for larger masses

For MH>250 clear

discrimination between

Spin = 0 and 1

CP = even or odd


Higgs Couplings to Bosons

Couplings to bosons W and ZCouplings to bosons W and Z

1) direct:

Z

W

GF

GF

ZZ)xBR(HWW)xBR(H

Z

W

ZGF

GF

ZZ)BR(H)BR(H

W =

2) indirect:

3) indirect:

Z

W

QCDGF

VBF CorrZZ*)→BR(HWW*)→BR(H

Assuming uncertainties of 20% gluon fusion, 5% VBF

Uncertainties on rates: statistics, 2% efficieny, 10% luminosity, 5% background


Coupling to Fermions and tot

Assume: (Zeppenfeld et al.)

SU(2) relation for W/Z

b/ = 3c(mb/m)2

tot =(detectable)+(in SM mainly Hcc)indirect determinationof tot

t

W

Wg

WW

WW)→BR(HWW)→BR(H

GF

WH

Direct: VBF

W

W

WW

ττ)→BR(HWW)→BR(H

VBF

VBF

Indirect: e.g.


Coupling Determination: New Study

Production Decay Mass range

Gluon fusion

HHZZ(*)4l HWW(*) l l

110 – 150 GeV 120 – 200 GeV 110 – 200 GeV

Vector Boson Fusion

HH HWW(*)l lHZZ4l

110 – 150 GeV 110 – 150 GeV 110 – 190 GeV 110 – 200 GeV

ttH

HHbbHWW(*)l l

110 – 120 GeV 110 – 140 GeV 120 – 200 GeV

WHHHWW(*

) l ll

110 – 120 GeV 150 – 190 GeV

ZH H 110 – 120 GeV

Analysis used in this study (ATLAS)

ttH with Halso avaiable, but not yet included

for VBF channels only int. luminosity of 30 fb-1 assumed


Parameter Determination: 4 Scenarios

CP-even, Spin=0 (several mass degenerate states fine) measurement of rates

only one Higgs boson measurement of ratios of branching ratios = measurement of ratios of partial decay widths

only dominant SM couplings are present, no extra particles or strong couplings to light fermions measurement of ratios of couplings and lower limit on total width from visible decays

visible decays ~ visible decays in SM measurement of absolute couplings and

total decay width


CP even Spin 0: Measurement of RatesSimultaneous global likelihood fit of signal rates xBR in all channels to number of selected events

Takes into account: cross talk between channels (e.g. GF events selected in VBF analysis) statistical fluctuations detector effects: uncertainties of lumi measurement ,

efficiencies for tau, b-, forward jet tagging, and electron reconstruction background estimates: sidebands + shape + theoretical prediction uncertainties to signal rate from PDFs and QCD corrections


1 Higgs Boson: Ratio of Partial Widths

WWHZH,

WWHWH,

WWHttH,

WWHVBF,

WWHGF,

BR)(

BR)(

BR)(

BR)(

BR)(

W

b

WWW

Z

fit parameters:

All rates can be expressed by above parameters

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


Ratio of Couplings

H

2w

2W

2t

2W

2b

2W

2

2W

2Z g

gg

gg

gg

gg

fit parameters:

2ZZHZH

2WWHWH

2tttHttH

2ZZF

2wWFVBF

2tggHggH

g

g

g

gg

g

Fix scale as H not

measurable

Production cross sections

7%

15%

4%

20%

WH

ttH

ZFWF

ggH

from theory with assumed uncertainty

b loop neglected for now in ggH

assumptions: only SM particles couple to Higgs boson no large couplings of light fermions


2W

2W

2Z

2W

2W

2t

ggH

ZZHggH,

g

g

gg

g

g

BR)(

H

2b

b

H

2

H

t(t)W(W)

H

2Z

Z

H

2W

W

g bb)BR(H

g )BR(H

gg )BR(H

g ZZ)BR(H

g WW)BR(H

2

Branching ratios

Rate as function of xi, e.g.

=1%

Ratio of Couplings


Top Quark Yukawa Coupling: effect of b-loop

Effect of b loop: ~5% in SM

For MH<150 GeV b-coupling determined from ttH,Hbb

For larger MH, b coupling only via GF effects top coupling determination

1) Limit b coupling to less that 10 (50) x SM value

2) No b-loop determination only via ttH, HWW

+ t b


Total Decay Width H

for MH200 GeV, tot>1GeV direct measurement from mass peak in ZZ4 leptonsBelow 200 GeV: indirect split

g

H

2w

g 2W into and

lower limit on H


Absolute Coupling Measurement + H

detect.)BR(H

detect.)BR(H

SMSM

detect.)BR(HSMSM 1

Assume: sum of visible BRs have SM value

ZZ, WW

ZZ, WW bb

detectable

only detectable

SMSM


MSSM: Heavy Higgs Bosons H,A,H+-

Neutral: H and A

•Main discovery decay modes: H/A and H/A enhanced with tan

•Production: direct gg->H/A and associated ggbbH/A

MA>300, tan>10: >90% from ass.

H+-and H+-tb for MH>Mt

Charged: H+-

Decay modes:

Production:1) MH<Mt: top pair production with decay tb H+-

2) gbt H+- gg(qq)tb H+- qqH+-

2 to 2 2 to 3

Transistion region around mt

not studied yet (now in HERWIG)

M. Guchait a. S. Moretti, T.Plehn

NLO-MC needed for more sophisticated studies!


H/A and

good mass resolution ~1% might allow

to disentangle A,H for specific scenarios (e.g. intense coupling scenario)

determine total width of A which may be a few to 10 GeV

require two and 1 or 2 b-tagged jets

M(GEV)

CMS:20fb-1

tan=30M=130 GeV

H/A

CMS 30fb-1

Low mass <~ 400: lep. lep. lep. had.

Large mass >~400: had. had.

larger rate, trigger on hard tau jets

Eff.(LV1TR)= 80% =95% offline selected events

Tau ID: Eff(tau)=55% Rejection(QCD)=2500

Tau ID and missing E resolution crucial

H/A

ATLAS 30fb-1


Discovery Potential for H and A

CMS L=100 fb-1

e.g. A,H

4 leptons + Emiss

00

isolation + Z veto SM BGveto nr. and energies of jets,limit on EmissSUSY-BG

discovery potential depends on SUSY parameters: BR, M signal and BG

intermediate tanregion not coverable by SM decay modes

consider SUSY decays of H/A or H/A in SUSY decay decades

(proposed e.g. by Djouadi et al.)

signal

BG: SM+SUSY


Higgs Decays to Gauginos

ATLAS:Scan in mSUGRAM1/2= 100 to 300 GeVM = 50,100,150,200 GeVSign()=+

CMS:

Specific set

M1=60 GeV

M2=120/180 GeV

M=-500GeV

Ml=250GeV

Mq,g=1TeV

300 fb-1

5 contours


Masses and tan from neutral Higgs bosons

Error on masses

m/m = 0.1 to few %

Error on tan

tan/tan

= 15 to 5 %

from rates of H/A

VBF h/Hnot studied yet ATLAS TDR


MH<mt: tt, tbH+- ,H+-

Leptonic channel (ATLAS and CMS):

tH+b; H+; hadr. + t bW bl

Look for an excess of leptons over SM predictions

BR (H±) 100 % for mH<mtop

Hadronic channel (ATLAS):

tH+b; H+; hadr. + tbWbqq

Transverse mass ( jet, Emiss) can be used

for mass measurement in likelihood fit:

Mgen=127.0 GeV Mrec=128.4±1.0 (stat) GeV

but error dominated by systematics (~4 GeV)energy scale, background shape,....

t

ATLAS 10 fb-1


reconstruct had. top decay and taujetuse spin corr. in decay

(spin 1 versus spin 0)

->

L

,a1

TL ,a1L

tt background

Signal

MH>mt: gbtH+- H+-and H+-tb

H+; hadr. t bW bqq

large background (tt+jets)

reconstruct tops and Higgs MH

H+tb t bW blqq

CMS L= 30 fb-1

CMS L= 30 fb-1

determine MT(jet, ETmiss)

P/E(-jet)


M2 = 210 GeV, = 135 GeV,Msleptons = 110 GeV,Msquark, gluino = 1TeV

CMS: gbtH+, H 2,30 1,2

3l+ETmiss

Discovery Potential for Charged Higgs Boson

Hadronic channel analysis closes „hole“ at tan~7Further studies

(proposed by Moretti et al)

1) correct handle of

2 to 3 process transition

2) ggtbHtbtbblbqq for high mass region

3) investigate decay modes in SUSY particles

ATLAS, 30fb-1

(1) (3)

(2)


ATLAS study

tb

From transverse mass in H case.From invariant mass in Htb case.Precision dominated by statistics. Systematics: bg rate and shape,

energy scale.

xBR ~ tan2 for large tan

Precision limited by uncertainties in luminosity and systematics.

Masses and tan from charged Higgs bosons

tan/tanM/M


Updated MSSM Scan (ATLAS)

Influence mainly phenomenology of light Higgs boson h

1) MHMAX scenario (MSUSY=1 TeV ) maximal theoretically allowed region for mh

2) Nomixing scenario (now MSUSY= 2 TeV, 1TeV almost excluded by LEP )

small mh difficult for LHC

3) Gluophobic scenario (MSUSY=350GeV)

coupling to gluons suppressed (cancellation of top + stop loops)

small rate for gluon gluon H, Hand Z4 leptons

4) Small scenario (MSUSY = 800 GeV) coupling to b (and ) suppressed (cancellation of sbottom, gluino loops) for large tanb and MA 100 to 500 GeV

New calculations for masses and branching ratios (Feynhiggs1.3, Heinemeyer et al., HDECAY3.0, Spira et al.)

New channels added, in particular VBF channels

New benchmark scenarios considered (proposed by Carena et al.)


VBF, HiggsNo Lose in MSSM

ATLAS: MHMAX scenario

Parton level study by Plehn, Rainwater, Zeppenfeld

Maximal Mixing Scenario ,MSUSY=1TeV

(for Mh/H>100 GeV)

No lose in MSSM with 40 fb-1

ATLAS: (for Mh/H>110 GeV)

h, H

MHMAX Scenario, MSUSY=1TeV

Area not excluded by LEP covered with 30 fb-1

Other benchmark scenarios not yet checked

h

H


Mass of the light Higgs boson h

130GeV<Mh

120<Mh<130GeV

110<Mh<120GeV

100<Mh<110GeV

90<Mh<100GeV

Mh<90GeV


Light Higgs boson h: 30 fb -1

bbh

VBF, h

VBF,h+WW

tthbb

WWhlbb

VBF,hWW

VBF channels

cover large part of

MSSM plane

combined

Excluded by LEP


Light Higgs boson h: 10 fb -1

5 discovery

3observation

5 discovery

3observation

Almost no individual channel observable

need combination of all channels

Excluded by LEP


Light Higgs boson h: 300 fb-1

All three

only B

A and B

A and C

For high lumi.: A: h B: tthbb C: hZZ4l contribute

Excluded by LEP

bbh


h: Number of observable final states

1 channel

2 channels

3 channels

4 channels

5 channels

several channels

observable

allows parameter determination

300 fb-1

Excluded by LEP


How many can be seen: h,H,A,H+- ?

MHMAX scenario 300 fb-1

1 boson

2 bosons

3 bosons

All 4 bosons

h only

h,H,A,H+-

h,H,A

No holes !

Complete plane covered

h,H,A

(also in other 3 benchmark scenarios)

Excluded by LEP


Only h seen: is it the SM or the MSSM ?

BR(h) BR(hWW)

R =

From VBF (30fb-1)

=(RMSSM-RSM)exp

> 2 >1

First preliminary look

532

>1 Higgs boson

only h

> 1 Higgs boson

MHMAX scenario, 300fb-1

Only statistical error

Excluded by LEP

Future work: apply coupling measurement study to MSSM

How far SM vs MSSM discrimination in „wegde area“ ?


Invisible Decays of the Higgs

VBF most promising process !!

Trigger on forward jets + missing ET

CMS fine ! (eff.>95%)

ATLAS: cal. trigger only up to 3.2 so far

studies in progress ! going to 4.9 increase

significance by factor 2.5

Selection:

1) VBF cuts: forward jet tagging central jet-veto, Mjj

2) lepton veto, ptmiss

3) jj <1

Background estimate from qqZ(W) with Zll (Wlto level of 3%

Jet

Jet

ATLAS

MH=130GeV


Sensitivity to Invisible Decays of Higgs

ATLAS: preliminary investigations of tthblnbqq inv. + Zhll inv

Sensitivity lower by 1/3 to 1/6ATLAS

Difference due to survival probability of jet veto

CMS: parametrisations by Zeppenfeld et al.

ATLAS: cuts on PYTHIA MC

Both include 3% uncertainty on background estimation

w/o syst uncertainty sensitivity increased by factor 2


Conclusions and Outlook

Very good SM and MSSM discovery potential in first years increased significantly by VBF channels light Higgs boson can be observed in several channels

Progress on coupling measurement also driven by VBF channels might be useful for discrimination between SM and MSSM

Sensitivity of LHC for invisible Higgs decays shown

Continue and reinvestigate channel studies with full simulation, NLO calculations, high luminosity scenario (e.g. potential of VBF, mass measurements) need NLC MC (e.e. bbA/H), matching ME to parton shower

Consider new Higgs scenarios MSSM with CP violation, NMSSM, Little Higgs (work started)

Improve and use coupling measurement to discriminate SM Higgs sector from ist extensions

higgs physics at the large hadron collider

Documents

bonn university higgs

sm higgs boson

lhc win03 lake geneva

higgs boson profilek1

b jets

higgs couplings good

sidebandsmarkus schumacher

jet tagging vbf