TESLA - The TEV-Energy Superconducting Linear Accelerator Light Higgs Production at the Tesla Photon...

TESLA - The TEV-Energy Superconducting Linear Accelerator

Light Higgs Production at the Tesla Photon Collider

Aura RoscaDESY Zeuthen

Amsterdam, Netherlands, 1-4 April 2003

April 2003 Aura Rosca DESY-Zeuthen 2


Motivation

• Measure the two-photon partial width:– Contribution to the two photon

decay width from any kind of massive charged particles. Any deviation of the partial width from SM prediction:

• Evidence for new physics;• Can be directly compared to

predictions of alternative models (MSSM, NMSSM, general 2HDM).



How to Get Widths?• The Higgs mass peak gives

• Taking and from LHC or LC,

• This is proposed as the way to get the total width. This would be a model-independent result.

)bbBR(h)(h γγΓ

γγ)BR(h )bbBR(h

)BR(h

)bbBR(h)bbBR(h)(h

tot γγ

ΓΓ

γγΓΓ

γγ

γγ

GeV) 140(mh



Realistic Luminosity Spectra and Polarization for the Photon Beams•

• Luminosity spectra for J=0,2 with

• Total luminosity for

1.8x

100%P 85%,2

GeV 210s

ce

ee

λ

GeV, 80 sz γγ. fb 80 1-L

Circe 2.0

/GeVfb 1.57sd

dL 1-γγ



• Higgs boson has spin-0– It is produced from J=0

revents/yea 20000NS helicities photon ),(1

m)bb)BR(h(h4

sd

dL )bbh(N

i21

2

2

m

S

λλλ

γγΓπγγ

hγγ

γγ

• Adjust beam polarization to increase the signal cross section;

• If know, adjust photon energies to have .

0.22%)BR(h

68%)bbBR(h

MeV 4

GeV 120m

tot

h

γγ

Γ

hm

hms

The Signal

/GeVfb 1.57sd

dL 1-γγ



Higgs Decay

• Light Higgs

• Signature– 2-jet events

• Background

– large cross sections, can be suppressed exploiting the polarization dependence of the cross section.

dominant )bbBR(h

b

b

(g)cc

(g)bb

γγ

γγ

GeV) 140(mh



The Background

))cos(1)(2cos(1)cos(1s

Q12

dcos2)(Jd

)(1)cos(1s

Q12

dcos0)(Jd

222222

34q

2

zLO

422

4q

2

zLO

θβθθβ

βπα

θ

σ

βθβ

βπα

θ

σ

γγ

γγ

γγs

m2q

)bbσ(γγ )ccσ(γγ ,Qσ 4q

2)σ(J orespect tin s

m0)σ(J z

γγ

2q

z

• Suppression removed for

• Need to take into account the NLO corrections!

Need b-tag to reduce bkg.cc

Photons of the same helicity suppress continuum .bb

γγβ /s4m1 2q

(g)bbγγ



Background Cross Sections

• NLO cross sections include:– Exact one-loop QCD

corrections (Jikia, Tkabladze)

– Non-Sudakov form factors (Melles, Stirling, Khoze)



Simulation• Results include realistic photon spectrum for ++

and +- helicities simulated with Circe 2.0;

• Signal MC generated with Pythia and passed through the TESLA fast simulation, Simdet 4.02;

• Background MC generated with Pythia and passed through the TESLA fast simulation:– – Convolution with the realistic photon spectrum for ++

and +- helicities – Events weighted by the NLO Xsec for ++ and +-

helicities

• B-tagging

GeV 80s γγ



Cross SectionsCross

section(pb)

Number of expected

ev.

Number of generated

ev.

Signal process0.25

~20 000 50 000

Background

J=0

(from Pythia)

0.7544 175.0 600 000

J=24.79 102 314.4 600 000

J=013.4 789 260.0 600 000

J=285.1 1 817 734.0 600 000

1 80fbL,eff

bbh

)g(bb

)g(bb

)g(cc

)g(cc

)L 10J 58.9fb(

)L 12J 21.1fb(

GeV 80s γγ



Selection Requirements• Isotropic angular distributions for signal and

forward peaked for the background:

• • Jet clustering using Durham with y=0.02;• Other cuts on

0.7cosθT

0.1/EE GeV, 95E vislongvis 2,3N jet



B-tagging Performance

98%purity

% 70 0.95NN bbout

εEvents containing at least one jet with two reconstructed vertices:

GeV 91.2sqqZee ee ,

cc

bb



Invariant Mass Spectrum• It is possible to isolate the signal from the

background.

events 7111N

events 6018 N

bkg

sig



Partial Width Uncertainty

• This is one of the main justifications for a Photon Collider.

1.9%NN

N

)bb)BR(h(h

bb)BR(h(h

bobs

obs

γγΓ

γγΓΔ



Summary

• Measure with a precision of 1.9% by:

– Taking into account the QCD radiative corrections to the background process (Pythia + NLO Xsec.) through a reweighting procedure;

– Adopting a b-quark tagging algorithm based on a neural network.

)bbBR(h)(h γγΓ

qqγγ



Summary

• Measure with a precision of 1.9% by:– Taking into account the QCD

radiative corrections to the background process (Pythia + NLO Xsec.) through a reweighting procedure;

– Adopting a b-quark tagging algorithm based on a neural network.

)bbBR(h)(h γγΓ

qqγγ

events 7111N

events 6018 N

bkg

sig

TESLA - The TEV-Energy Superconducting Linear Accelerator Light Higgs Production at the Tesla Photon...

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