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A. Ballestrero INFN and Dip. Fisica Teorica Torino

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From SIXPHACT to PHANTOM

A. Ballestrero

INFN and Dip. Fisica Teorica

Torino

A short history of SIXPHACT

PHANTOM now

Future programs for ILC

This is rather a letter of intent than a presentation

Alessandro Ballestrero

A short history of SIXPHACT

Six fermion calculations for LC are now 10 years old !

The first Joint ECFA/DESY Study: Physics and Detectors for a Linear Collider took place in 2006

First meeting in FRASCATI (5-6 February 1996)

In one of the subsequent meeting (Munich September?) we presented

the first completecalculations for six fermion final state.

This was the first result with SIXPHACT ( Accomando Pizzio A.B.)

For the following meeting GRACE produced results to compare with ours

and immediately also SIXFAP (M. Moretti and PV group)entered the game

Other six fermion MonteCarlos for Linear Collider have then appeared in these years

Wizard, Lusifer,...

All general purpose programs (Amegic, Phelac, Madevent,...) can now compute

six fermion final states.

Many comparisons have been done at subsequent ILC meetings

Alessandro Ballestrero

A short history of SIXPHACT

Method for computing

amplitudes:

diagrams for

¹

¹

+

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d

b

b

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e

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!

withthe use of subdiagrams

computed only once.

helicity amplitudes

written with PHACT

Alessandro Ballestrero

A short history of SIXPHACT

Examples of subdiagrams

Alessandro Ballestrero

A short history of SIXPHACT

−

SIXPHACT was used for studies of t t higgs and 3 boson physics

Example of results : comparison of full 6f and approximations for 3 boson production

NWA, SIGNAL and FULL as a function of cut

dot, dashed

for the two quark pairs

Alessandro Ballestrero

A short history of SIXPHACT

a further cut on e n reduces the effect for

Alessandro Ballestrero

A short history of SIXPHACT

Example of results : top and irreducible background for Higgs signal of different masses

gaussian smearing

Alessandro Ballestrero

A short history of SIXPHACT

EW and QCD Higgs background

as a function of

real, reconstructed, missing mass

Alessandro Ballestrero

A short history of SIXPHACT

¹

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2Z2W

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4Z

Mixed

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SIXPHACT was used for studies of t t higgs and 3 boson physics

Final states with a neutrino were therefore considered

as they implied W+W- production

SIXPHACT has not been extended to cover all possible final states

If one consider all particles as outgoing, an 8 fermion process

can be classified according to how can be grouped in pairs

as 4Z, 2Z 2W, 4W or as mixed.

e.g.

therefore only 2Z2W amplitudes were implemented

no multichannel technique was adopted

For these final states and for the cuts used one optimized phase space

at a time integrated with an adaptive routine (VEGAS) was enough:

Alessandro Ballestrero

PHANTOM now

PHANTOM 1.0

Belhouari Bevilacqua Maina AB

Butterworth et al, Chanowitz

Alessandro Ballestrero

PHANTOM now

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PHANTOM main features:

●first 6f program for LHC

●complete : 4w + 2z2w + 4z + mixed

●new integration method developed for the first time in PHASE (Accomando Maina AB)

Iterative-Adaptive Multichannel

Merges best feautures of both! Adapts well to cuts

Small number of channels required (Multimapping). Good efficiency

● amplitudes with PHACT

●extension and generalization of subdiagram method:

3 master amplitudes for 4w, 2z2w, 4z computed in this way

all the rest by repeated calls

●oneshot generation: possibility of unweighted generation of any number of processes

at the same time. Useful: 4q mn at LHC needs more that 160 processes !

● contains

important, expecially for LHC

●separation of various color contributions: les Houches accord 2

Alessandro Ballestrero

PHANTOM now

PHANTOM has been used for boson boson scattering physics

in collaboration with CMS groups of Torino and Rio for full analysis

WW scattering effects are buried in

WW fusion processes

Important for EWSB studies

Alessandro Ballestrero

Example of results

PHANTOM now

Alessandro Ballestrero

Example of results

PHANTOM now

Alessandro Ballestrero

Future programs for ILC

WE INTEND TO EXTEND PHANTOM TO e+ e- COLLIDERS

Integration methods, oneshot generation, amplitudes have a general validity

They should work very well also in this case

PDF should be substituted by isr and beamstrahlung.

This implies two more variables of integration or unweighted generation of beamstrahlung.

Should be no problem

Number of possible processes for a given final state (eg. m n + quarks or six quarks)

is much lowerbut it is important for physical studies to generate them simultaneously

Many technical points remain to be fixed or changed,

but the structure of the program should remain the same

We plan to have the possibility to use both fully massive and massless amplitudes:

Massless are more efficient and sufficient for many studies,

but some require fully massive at least for comparison

Alessandro Ballestrero

Future programs for ILC

PHANTOM will have features and efficiency competitive with the other 6f MC for ILC

But our main purpose in its extension is to use it

as a tool for physics analyses and phenomenology

It will be particularly suited for comparative studies

between LHC and ILC physics potential

We are in particular interested in extending to ILC our studies on

Boson Boson scattering and alternative EWSB scenarios

Several studies in this direction have already appeared (Chierici, Barklow,...)

For discovering strong scattering effects the energy of the machine will be crucial.

LHC can reach higher energies for parton interactions,

but the luminosity is rapidly decreasing

ILC on the other hand should have a much lower QCD background

So it will be interesting to compare the reach of the two colliders in this field.

A realistic study with all processes and detector simulation seems worthwhile

We look forward for possible collaborations on our physics program.

Alessandro Ballestrero

BACKUP

Alessandro Ballestrero

Unitarization: eg: Butterworth,Cox,Forshaw PRD65(02)96014different ways of constructing amplitudes which are unitary from low order amp

Must be prepared for the unexpected

Must know SM “background” e.g VTVT

Alessandro Ballestrero