a. ballestrero infn and dip. fisica teorica torino

Alessandro Ballestrero Frascati LC Panda Meeting 25 Oct 06 1

A. Ballestrero INFN and Dip. Fisica Teorica

Torino

From SIXPHACT to PHANTOM

A short history of SIXPHACT

Future programs for ILC

PHANTOM now

This is rather a letter of intent than a presentation



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

Other six fermion MonteCarlos for Linear Collider have then appeared in these yearsWizard, Lusifer,...

All general purpose programs (Amegic, Phelac, Madevent,...) can now compute six fermion final states.

Many comparisons have been done at subsequent ILC meetings



e+e¡ ! ¹ ¹ºu¹db¹bdiagrams for

with the use of subdiagramscomputed only once.

Method for computing amplitudes:

helicity amplitudeswritten with PHACT



Examples of subdiagrams



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

NWA, SIGNAL and FULL as a function of cut

for the two quark pairs

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

dot, dashed



a further cut on e reduces the effect for



gaussian smearing

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



EW and QCD Higgs backgroundas a function of

real, reconstructed, missing mass



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

e+e¡ ! ¹ ¡ ¹+u¹de¡ ¹º

e+e¡ ! ¹ ¡ ¹+u¹dd¹u

2Z2W

4Ze+e¡ ! ¹ ¡ ¹+u¹uc¹cMixed

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

−

therefore only 2Z2W amplitudes were implemented

e.g.

For these final states and for the cuts used one optimized phase space at a time integrated with an adaptive routine (VEGAS) was enough:

no multichannel technique was adopted


PHANTOM now

PHANTOM 1.0 Belhouari Bevilacqua Maina AB

Butterworth et al, Chanowitz


PHANTOM now

● 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

● contains important, expecially for LHC

● complete : 4w + 2z2w + 4z + mixed

● extension and generalization of subdiagram method: 3 master amplitudes for 4w, 2z2w, 4z computed in this way all the rest by repeated calls

PHANTOM main features:

● oneshot generation: possibility of unweighted generation of any number of processes at the same time. Useful: 4q at LHC needs more that 160 processes !

● separation of various color contributions: les Houches accord 2

● first 6f program for LHC

O(®2s £ ®4em)


PHANTOM now

PHANTOM has been used for boson boson scattering physics

WW scattering effects are buried in WW fusion processesImportant for EWSB studies

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


PHANTOM nowExample of results



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. + quarks or six quarks)is much lower but 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



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 onBoson 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.


BACKUP


Must be prepared for the unexpectedMust know SM “background” e.g VTVT

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

a. ballestrero infn and dip. fisica teorica torino

Documents