future e + e - collider sensitivity to the hz coupling

H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002

Future e+e- Collider Sensitivity to the HZ Coupling

M. Dubinin, H.J. Schreiber and A. Vologdin

Standard Model-like Higgs couplings to

studied

in

detail

fermions

W, Z boson

and

trilinear Higgs self-coupling

- another important set of couplings

induced by loops of heavy particles

So far, Hgg in e+e- collisions and at LHC investigated

H either in e+e- interactions and at LHC investigated

or fusion process H X

Hgg, H and HZ vertices

1


We explore the potential of linear e+e- collider

HZ coupling through rare decay H Z

Reaction (2-to-4 particle reaction):

Zee ee

H signal events (H Z) are imbedded

account for complete irreducible background

Assuming MH = 120, 140, 160 GeV

at s 500 GeV and

Ldt = 1 ab-1

Event generation: CompHEP

PYTHIA (for some reducible background reactions)

Higgs boson width and H Z branching fractions

imported from HDECAY

2


Typically, we expect~ 100 H Z signal events

and~ 50.000 irreducible background events

principal cuts (at generation level)

E 10 GeV

5o 175o

96 %Higgs eventssurvive

~ 50 % background discarded

Even after these cuts

small H event rate vs. huge irreducible background and background events have similar final state signatures as H Z events

So far, qqZ

2 hadronic jets orginating

from the Z boson together

with an energetic photon and large missing energy

signal event topology:

3


Possible reducible background

ee

)(

)(

)(

)(

)(

)(

ZZZ

WWZ

tt

Zee

We

WW

millionsofevents;small part might mimic the signal

)(),(),( ZZZWWZttcould be effectively removedby selection procedures applied

some surviving contributions from

)()/(

)(

)(

*

Zee

We

WWee

which are included in the final M(Z) and in

BF(HZ) / BF (H Z)

4


Large background and tiny signal event rates

different strateties for extracting signal events

consecutive cuts jet finder(s)„Higgs likeness“

Independent of the selection technique chosen

event (quality) cuts:

- Evis < 240 GeV

- ET < 210 GeV

- # of charged particles > 3

- missing mass: 180 - 400 GeV ensures clean elimination of

)()( ZHZee

• Ejet > 8 GeV• |cos jet| < 0.95 (between 2 jets) > 20o

• # of particles/jet > 3

)~( Zqq MM

jet (quality) cuts:

5


Event selection using consecutive cuts

Out of all photons

• E > 20 GeV with ET > 15 GeV

• no further particle in a cone of half-angle 10o

• if more than 1 photon, the one with largest energy is selected

• all remaining particles

2 jets

• Mjj MZ (84 - 105 GeV)

Finally, M(Z)

• Higgs signals clearly established• accounting for all Z decays and irreducible and

reducible background (~ 17 % of the irreducible) and uncertainty of )( Hee ee

%)41%,23(%52)(

)(

ZHB

ZHB

for MH = 120 (140, 160) GeV

e+

e-

ZH

H

6


All particles reconstructed by SIMDET were passed through a jet cluster algorithm

aim: isolate from H Z; one of the jets compatible with an isolated high-energy photon andall remaining jets should be compatible with Z

Two jet finder:

PUCLUS (PYTHIA)

DURHAM (ycut = 0.004)

Results very similar;

PUCLUS somewhat less reducible background

Resulting M(Z)|PUCLUS

• Higgs signal clearly visible

• %)52%,28(%61)(

)(

ZHB

ZHB

for MH = 120 (140, 160) GeV

Event selection using jet finders

7


Probability PH is constructed giving a measure that an event is part of the signal

PH : [0, 1 ]

background events have preferably low PH

signal events PH close to 1

Variables taken into account:

E() , polar cms() , polar cms (Z)

-decay angels in H rest frame

angles between (, Z)|cms

collinearity (beam, )

coplanarity (beam, , Z)

coplanarity (beam, H, )

transverse mass (, missing system)

transverse mass (H, missing system)

Finally PH > 0.98

Event selection by ‚Higgs-likeness‘

8


• Higgs bosons clearly established

• ‚Higgs-likeness‘ method

best signal-to-background ratios

(due to best reducible background rejection)

%)39%,23(%44)(

)(

ZHBF

ZHBF•

for MH = 120 (140, 160) GeV

Significant improvement by longitudinally

polarized beams:

e.g. e- polarisation: - 80 %

e+ polarisation: + 60 % (ambitious)

%)23%,15(%26)(

)(

ZHBF

ZHBF

%)24%,16(%27)(

)(

ZH

ZH

if tot (H) has an error of 5 %

%)12%,8(%14

HZ

HZ

g

g

9


•Overlap of hadrons to H signal events after passing selection procedures

- no loss or distortions

ZZHZee )(

including huge reducible and irreducible backgrounds

at e.g.

less precision on BF (H Z )

• Due to our present knowledge, Higgs-strahlung

• Inclusion of leptonic Z decays, Z ,llor Z Z fusion events,

neglected so far

only slight

GeVs 300

• Completely open whether full luminosity of 1 ab-1 at = 500 GeV with desired beam plarisation is

delivered to this measurements

)(

)(

ZHBF

ZHBF

improvement on

lower bounds on HZy

HZy

g

g

10

H. Jürgen Schreiber, ECFA/DESY Prague, Nov. 2002 11

future e + e - collider sensitivity to the hz coupling

Documents

h signal events h z

h z eventsso

h z branching

h z signal eventsand

e e collisions

e e interactions

cuts small h event rate

photons e