Determination of the Higgs-Fermion Yukawa couplings at future colliders

Determination of the Determination of the Higgs-Fermion Yukawa couplings Higgs-Fermion Yukawa couplings

at future collidersat future collidersMarkus Schumacher, Bonn University

WE Heraeus Summer School on Flavour Physics and CP Violation Dresden, 29 August to 7 September

IntroductionIntroduction

Higgs boson discovery and Higgs boson discovery and

1st measurements at LHC 1st measurements at LHC

Precision measurements at ILC Precision measurements at ILC

Synergy of LHC and ILC for gSynergy of LHC and ILC for gtt

ConclusionsConclusions

Markus Schumacher, Higgs Fermion Yukawa Couplings at LHC and ILC, Summer School Dresden 2005 2 / 45

The Higgs Mechanism in the Nut Shell

gauge symmetry no masses for W and Z

different reps. for left- a. rightchiral fields no masses for fermions

The problem: (for details see lecture by Marek Jezabek)

The „standard“ solution:

new doublet of scalar fields

with appropiately choosen potential V

vacuum spontaneously breaks gauge symmetry

one new particle: the Higgs boson H

= v + H

effective mass terms =

friction of particles

with omnipresent „Äther“

v =247 GeVx

fermion

gf

mf = gf v / sqrt(2)

gf is Yukawa coupling


The Higgs Mechanism in the Nut Shell

Higgs Boson couplings:

one unknown parameter in SM: mass of Higgs boson MH

MH completely determines Higgs phenomenology in SM

Loop induced effective couplings:

(sensitive to new physics)

Photon: g = gW “+“ gt “+“…

Gluon: g = gt “+“ gb “+“…

Hx

x

Born level couplings:

Fermions gf= mf / v

W/Z Bosons: gV= 2 MV / v

v = (sqrt(2) G)-1/2 =247GeV

2


The situation after LEP and from TEVATRON

Today: only discuss SM like Higgs boson with mass below 200 GeV

MH < 186 GeV

from EW fit (EPS05)

direct search:

MH<114.4 GeV

excluded by LEP

at 95% CL

MSSM: theory Mh <134 GeV (MSUSY=1TeV, mtop =175 GeV)

LEP Mh<92.9 GeV MA<93.4 excluded at 95% CL


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

channels which can be identified and observed:

LHC: WW,ZZ, bb,

ILC: WW,ZZ,,Z bb,, cc udsg ()

HDECAY: Djouadi, Spira et al.


1) mass (LHC, ILC)

2) quantum numbers: spin and CP (LHC, ILC dep. on MH)

3) BRs, total width, couplings

4) self coupling (non vanishing at SLHC?, meas. only at ILC)

Higgs Physics at Future Colliders

discovery at LHC (SM like or at least one in MSSM)

investigation of Higgs boson profile

start at LHC and continue with higher precision at ILC

future colliders:

LHC: pp collisions at 14 TeV start in 2007

ILC: e+e- collisions between 90 and 800++ GEV start in 201x?


Why and how to access the couplings ?

partial width: Hz ~ gHz2

experiment measures rate: rate = Nsig+NBG

Nsig=L x efficiency x Hx x BR

need to know: luminosity, efficiency, background

Hx x BR ~ HX Hy

tot

tasks: disentangle contribution from production and decay

determine tot (tot << mass resolution for MH <200 GeV)

Why ? precision test of the hopefully discovered Higgs sector

look for deviations from SM prediction

hint towards new physics (SUSY, ED, Little H, TC)

Higgs couplings enter production and decay

Hx = const x Hx BR(Hyy) = Hy / tot

How ?

prod decay


pp collider /LHC and e+e- collider / ILCcollision of pointlike particle with known energy ECM = 2 Ebeam

high enery difficult to achieve

well defined quantum numbersand four momentum of initial state

production via el.-weak interaction smaller theo. uncertainties

“simple” final states, “moderate” background

no trigger needed

purely hadronic final statesselectable and reconstructable

Higgs: decay mode independent observation

moderate radiation exposure

suited for discoveries and precision measurements

collision of composed particleswith unknown energy ECM< 2 Ebeam

high energies easily achievable

quantum numbers of hard processnot known, only PT=0

production via strong interaction QCD uncertainty, PDF uncertainty

complex final states, overlaping events, huge background sophisticated trigger needed

purely hadronic final states can hardly be triggered and selected

Higgs: need identification of decay for observation

very high radiation level best suited for discoveries (energy frontier) and first measurementshadron and lepton collider are complementary !!


Comparison of cross sections

LHC: Higgs 150 GeV

S/B <= 10-10

ILC: Higgs 120 GeV

S/B >= 10-2


LHCLHCpp collisions

ECM = 14 TeV

start: 2007

tbunch = 25 ns

Luminosity:

first years: L= 12 1033/(cm2s) >10 fb-1 / year

later: L= 1034/(cm2s) 100 fb-1 / year

~23 overlaying minimum bias events


Production of the SM Higgs Boson at LHC

K~2.0

K~1.2

K~1.1

K~1.3

K = NLO / LO


uds = 0.005

Two multipurpose detectors at LHC: ATLAS and CMS

pixel vertex a. strip tracking detectors b andtagging (H, bb)

homogenous calorimeters up to e/ meas. (H,H4

lept.)

(pseudorapidtiy = -ln tan forward jet tagging (VBF)

missing energy (HHinv.)

complex myon spectrometers momentum accuracy and

eff. trigger (HZZ4 , A/H)

ATLAS CMS

detectors optimised for discovery of low mass Higgs boson


Discovery Potential for light SM Higgs boson

discovery channels:

GGF: H GGF: H ZZ 4l+-

GGF: H WW2(l)

tth: H bb

VBF: H

VBF: H WW

discovery with 10fb-1 for masses between LEP exclusion and 1 TeV

Exclu

ded

by

LEP

need photon, lepton or missing energy for trigger a. background supp. no sensitivity for fully hadronic final states signal processes with largest rate not useable e.g. GGF with Hbb

need identification of Higgs boson decay mode for observation !!!


Gluon Fusion: H and H ZZ 4 leptons

100 fb-1

MH=130GeVH signature two high Pt

Even

ts /

GeV

M: ~1GeV

K=1.6

S/BG ~ 1/20

4 high pt leptons narrow mass peak, small and flat background irreducible BG: ZZ reducible BG: tt, Zbb rejection via lepton isolation and b-veto mass resolution M: ~1%

HZZ4 leptons:

irreducible BG: pp +x mass resolution M: ~1% precise background estimate from sidebands ~ 0.1%


ttH with Hbb

signature: 1 lepton, missing energy,

6 jets of which 4 b-tagged

mbb ~ mH

mass resolution M: ~ 15%

difficult background estimate from

data foreseen, uncertainty ~ O(10 %)

reducible BG: tt+jets,W+jets b-tagging irreducible BG: ttbb reconstruct mass peak

exp. issue: full reconstruction of ttH final state b-tagging + jet/missing energy performance understanding of whole detector needed !

S/BG ~ 1/6

30 fb-1

only channel to see Hbb


Forward tagging jets

Higgs Decay

signature: - 2 forward jets with large

- only Higgs decay products

in central part of detector

Jet

Jet

Vector Boson Fusion

- forward jet reconstruction

- jet-veto fake rate due to pile up

- missing energy resolution

exp. issues:

decay modes: H WW l l and l j j

H l l and l had

only studied for low luminosity running results for 30 fb-1


MH=160 GeVHWWe

ATLAS

10 fb-1

ATLAS

He

Vector Boson Fusion

S/BG ~ 3.5/1

background: tt

no mass peak transverse mass

BG uncertainty ~ 10 %

S/BG ~ 1 to 2 / 1

background: Zjj

mass resolution ~ 10%

BG uncertainty ~ 5 to 10%

30 fb-1

MH=120 GeV

only channel to see H


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

No theoretical errors considered: effect of PDF <<10 MeV

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


Strategy of Coupling Determination at LHC

assumption: CP-even, Spin=0 (several mass degenerate states fine)

only measurement of rates

only one Higgs boson

ratios of BRs = ratios of partial decay widths

= ratios of squared couplings, if only Born level couplings involved

further theoretical assumptions needed in order to constrain tot

measurement of couplings

t

W

Wg

WW

CorrWW)BR(HWW)BR(H

GF

WH

→

→

Direct: VBF

Indirect: e.g.

W

W

WW

ττ)BR(HWW)BR(H

VBF

VBF

→

→old study, Zeppenfeld et al.


Overview of 13 Channels used in new ATLAS Study

Production Decay Mass range

Gluon fusion

HHZZ4l 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

HHbbHWWl l

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

WHHHWWl ll

110 – 120 GeV 150 – 190 GeV

ZH H 110 – 120 GeV* only studied for low lumi running, L= 30fb-1


CP even Spin 0: Measurement of Rates

Simultaneous fit of signal rates x BR in all 13 channels

Takes into account: cross talk between channels (e.g. GF events selected in VBF analysis) statistical fluctuations detector effects: Lumi, eff. tau, b-, forward jet tagging, and e background estimates: sidebands + shape + theoretical prediction uncertainties to signal rate from PDFs and QCD corrections


One CP even Higgs Boson: Ratio of Partial Widths

WWHZH,

WWHWH,

WWHttH,

WWHVBF,

WWHGF,

BR)(

BR)(

BR)(

BR)(

BR)(

W

b

WWW

Z

9 fit parameters:

all rates can

be expressed

by those 9

parameters

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

For 30fb-1 worse by factor 1.5 to 2


Total Decay Width H

for MH>200 GeV, tot>1GeV measurement from peak width in ZZ4 l

for MH<200 GeV, tot<< mass resolution no direct determination

upper limit needs input from theory:

mild assumption: gV<gVSM

valid in models with only Higgs doublets and singlets

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

2 in SM)/ tot

tot< rate/(V2 in SM)

lower limit from rate measurements: tot > W+Z+t+g+....

have to use indirect constraints on tot


Fit of couplings with gV < gVSM constraint

8 fit parameters:

coupling to W, Z, , b, t

inv for undetactable decays

e.g. c, gluons,newphoton (new), gluon (new):

non SM contribution to loopsg/g = ½ g2)/g2


ILCILCECM: 90 GeV bis 800++ GeV

5 Bunch Trains/s tbunch=337 ns 950 µs 199 ms 950 µs

2820 bunches

Lumi.: 3.4 to 5 x 1034cm-2s-1 (6000xLEP)

L = 500 fb-1 @ 500 GeV ~ 2 to 3 years

L = 1000 fb-1 @ 800 GeV ~ 3 to 4 years

Polarisation: 80% electrons, 60% positrons

No hardware trigger deadtime free

contineous readout for bunch train

Superconducting cavities


SM Higgs Boson Production at ILC

17 Higgs events per hour

ECM=500 GeV, MH=120 GeV

Higgs factory

Higgs-Strahlung WW-Fusion

e+e- qq 330/h e+e- WW 930/h e+e- tt 70/h


Strategy for e+e- collider

decay mode independent observation in Higgs-Strahlung

from recoil mass spectrum model independent determination of mass, Spin, CP and coupling to Z boson gHZ

rate measurement in Higgs Strahlung with Hxx: gHZ x BR(Hxx) branching ratios BR(Hxx)

indirect but model independent determination of total width tot

BR(Hxx) + tot partial width x coupling gHx

Yukawa coupling from rate in ttH associated production

need: accelerator with luminosity ILC

highly performing detector

2


Performance Requirements

Momentum: Higgs mass,…

(1/p) = 7 x 10-5/GeV (1/10xLEP 1/7xLHC)

Impact parameter : Yukawa couplingsd=510/p(GeV)m (1/3xSLD, 1/2,1/5LHC)

Jet energy: Higgs selfcoupling, ttH

E/E = 0.3/E(GeV) (<1/2xLEP 2/3xLHC)

reconstruction of complex multi jet final states (even 8 or more)

hermeticity down to small angles 5 mrad

Design determined by precision physics, not by radiation hardness or event rate !!!

radiation hardness (almost) no problem compared to LHC

1st layer of vertex detector: 109 n/cm2/yr at TESLA = 0.00001 LHC

time structure of collisions and background vom beamstrahlung

read out speed / granularity


Detector Concept (TESLA/Large Detector)

tracking system and both calorimeters inside coil

magnetic field B = 4 Tesla

large gaseous central tracking device

precision vertex detector

instrumented mask for background shielding

no hardware trigger

different bunch separation / background level w.r.t to LHC

other technology options possible at ILC e.g. gaseous tracking

all silicium tracking also studied for ILC


Why (1/p) = 7 x 10-5/GeV? Higgs mass meas.

independent of H decay model independent

recoil mass to :

MH, ZH, gZZH, Spin

goal: M<0.1x

(1/p)

< 7x10-5/GeV

efficient supression of background

good resolution for recoil mass

e+e-ZZHX

Higgs-Strahlung

precise measurement of lepton momenta


Tracking System

Barrel region:Pixel vertex detector (VTX)Silicon strip tracker (SIT)Time projection chamber (TPC)

Forward region: Silicon Disks (FTD) Forward Tracking Chambers (FCH)(e.g. Strawtubes, Si strips)

Momentum resolution:

TPC only: (1/p) = 2.0 x 10-4 /GeV (1/6 x LEP)

TPC+VTX: (1/p) = 0.7 x 10-4 /GeV (1/9 x LEP)

TPC+VTX+SIT: (1/p) = 0.5 x 10-4 /GeV (below the goal)

E and B field

Efficient and robust track reconstruction, seperately in

TPC: 200 space point + VTX+SIT: 7 space points

global track finding: =98.4% (including background)


Mass and Coupling to the Z Boson

~ 5 bis 6%m ~ 100 MeV

ZH ~ gZH2 model independent

determination of gZH

decay mode independent selection of ZH with Z or ee

peak position peak height

fit to spectrum of the recoil mass to leptons

gZH/gZH~ 2-3%

m ~ 40 bis 80 MeV with complete reconstruction of the Higgs decay

500fb-1


Why d=510/p(GeV)m? Higgs Yukawa Couplings

efficient ID of b,c and light jets

reconstruction of secondary vtx.

with all tracks M, /, Q

Precise measurement of impact par. do

b: 300 m „state of the art“ c 75 m „challenging“<p> = 1 bis 2 GeV

d = a b/p(GeV)

goal: 5m 10m

LHC: 12m 57m

goal: determination of BR(Hbb, cc, light q+g) with O(%) precision

M

IP

Secundary vtx.

l ~ 8 mm

do .

IP

d= a b/p


Vertex detector: concept and expected performance

5 pixel layers R1 = 15 mm (1/2SLD, 1/4LEP,1/3LHC)

pixel size: 20x20m2, Punkt < 3 m

thin: 0.1 % X0 pro Lage (1/4 SLD) read out at ladder ends

no hybrid pixels a la LHC

M

e.g. vertex mass

•LEP-c

Expected resolution: = 4.2 4.0/p(GeV)m


Fermionic Branching Ratios

Select ZHqq/ll qq events by kinematic cuts

calculate likelihood for Hbb,cc,gg from

precise measurements of tracks at IP

perform fit of MC likelihood distributions to data

event rates

data =

Hbb backgroundHggHcc


( )( )

( ) / ( )

HZ X Z

BR H XHZ H BR Z

Higgs Boson Branching Ratios

Decay Rel.Error

for 500 fb , m=120 GeV-1

TDR study: two independent measurements of

alternative approach: measure fraction of Hxx events within an unbiased sample of HZHll events

disadvantage: smaller event sample

advantage : binomial errors smaller than gaussian errors

(one measurement instead of two)

23%


Total Decay Width

Indirect determination for M < 180 GeV:

tot << detector resolution no info in width of mass peak

Idea: use tot = (Hxx) / BR(Hxx)

best precision: W Boson

(HWW): from measurement of cross section of WW fusion

BR(HWW): from Higgs-Strahlung ZH with HWW

needed for determination of

Yukawa couplings to fermions

gf2 ~ ff = BR(Hff) x tot

direct determination from peak width


Coupling to W Boson and Total Width

WW fusion process:

b

b

fit to missing mass spectrum:

~ gw2xBR(Hbb)

+ meas. of BR(Hbb) in ZH

model independent determination of gw

gW/gW ~ 3 to 13%

= 6 to 16 %

for MH = 120 to 160 GeV

LHC

+BR (H>WW)


Top Quark Yukawa Coupling

gttH/gttH = 7 to 15 %

for mH =120 to 200 GeV

including 5% systematic

uncertainty on BG

small cross section and

„a lot of mass“ in the final state

large ECM = 800 GeV high luminosity L = 1 ab-1

challenging analysis (ANN):


Top Quark Coupling:Synergy of LHC and ILC

ILC: measurement of branching ratio BR(Hbb) BR(HWW)

LHC: measurement of rate tth x BR(Hbb)

tth x BR(HWW)

gt x BR(Hxx)

ILC at ??

2

combination of both measurementsmodel independent determination of top quark Yukawa coupling

H

xx

x

x


Determination of gt

gt ~ 13 to 17 % (7 to 11%)

combination of

LHC and ILC

assume Born level relation: ~ gt2

synergy of LHC and ILC allows 1st

model independent determination

of top Yuakwa coupling


The Higgs Boson Profile from ILC

PDG Booklet 201x ?

Why aim for this precision ?

precise test of the SM

discrimination between SM Higgs sector extensions or alternatives

(SUSY, ED, Little H, TC, …)

E. Gross

10-3

rel. error on Higgs boson couplings

expected accuracy: 1 to 5 %

g/g = ½


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

LHC: discrimination using

rate measurements from

VBF channels (30fb-1)

R = BR(h WW) BR(h )

300 fb-1

assume Higgs mass well measured no systematic errors considered

compare expected

measurement of R in MSSM

with prediction from SM

for same value of MH

systematic error from lumi,

PDFs, QCD in production cancel


SM or Extended Higgs Sector ?

ATLASprel.

300 fb-1

ILC

=|RMSSM-RSM|exp

similar study by Duehrssen et al.:

VBF dominates discrimination

comparison of all couplings

discrimination from profile measurements at 2 level

observation of additional Higgs bosons at LHC and ILC500/800


Summary

LHC: discovery over full mass range 110 to 1000 GeV

1st measurements e.g.: mass ~ 0.1%, CP, Spinratios of partial width: W/Z, W/t, W/W/b ~10 to 60 %

absolute couplings only with further theoretical input = 5 to 45% depending on mass and particle

ILC: decay mode independent observation mass, CP, Spin mass determination: ~ 0.04 % total width determinable w/o theoretical assumptions absolute couplings (also 2nd generation) =1 to 5 %

LHC+ILC: 1st model independent determination of top quark coupling from synergy of data: ~15%

Let’s hope for unexpected deviations from the SM at LHC and ILCand also other collider and non collider experiments!

Documents

Determination of the Higgs-Fermion Yukawa couplings at future colliders