Model independent FCNC top physics at the LHC

Pedro Ferreira

ISEL e CFTC, Universidade de Lisboa

Jornadas do LIP 2008, 12/1/08

• P. M. Ferreira, O. Oliveira and R. Santos, PHYSICAL REVIEW D 73, 034011 (2006)

• P. M. Ferreira and R. Santos, PHYSICAL REVIEW D 73, 054025 (2006)

• P. M. Ferreira and R. Santos, PHYSICAL REVIEW D 74, 014006 (2006)

• P. M. Ferreira, R. B. Guedes and R. Santos, PHYSICAL REVIEW D 75, 055015 (2007)

• Contribution to the Yellow Report for the CERN Workshop “Flavour in the Era of the LHC” (2007) (in the arXiv on Monday!)

• Two more being produced as we speak…

THE WORK…

Projects:

POCI/FP/81950/2007 PTDC/FIS/70156/2006POCI/FP/63926/2005POCI/FP/63420/2005POCTI/FIS/59741/2004PDCTI/FP/FNU/50155/2003

People:

Juan Aguilar-Saavedra, Augusto Barroso, João Bastos, João Carvalho, Matilde Castanheira, Nuno Castro, Pedro Ferreira, Miguel Fiolhais, Agostinho Gomes, Renato Guedes, Amélia Maio, Paulo Martins, Rita Monteiro, Miguel Oliveira, Orlando Oliveira,

Sancho Oliveira, António Onofre, Rui Santos, Sergey Slabospitsky, Filipe Veloso, Helmut Wolters, Miguel Won.

THE TEAM…

LIP CFTC

Granada

Valencia

NExT

RHULLONDON

Southampton

RAL

top FCNCcombination

tbW measurements(BSM physics)tbW

measurements

Generators, tbW physics

THE CONNECTIONS…

EFFECTIVE OPERATOR FORMALISM

New physics “generated” in extensions of the standard model would manifest itself at lower energy scales in the form of effective operators of dimension superior to 4.

Complete list of dimension 5 and 6 effective operators: Buchmüller e Wyler, Nucl. Phys. B268 (1986) 621.

Dimension 5 operators violate baryon/lepton number.

Dimension 6 operators: a great many of them….

We are interested in processes of single top production via flavour changing neutral currents (FCNC’s) at the LHC.

All terms are invariant under the SM gauge group; Λ is the energy scale of new physics. This formalism allows us to make predictions in a model-independent

manner.

EFFECTIVE OPERATOR FORMALISM

To select among the many dimension 6 terms, we employed some physical selection criteria:

• The operators must contribute to FCNC’s involving the top quark and the strong interaction, with impact on single top production.

•They must not have sizeable contributions to physics below the TeV scale, so as to not ruin the successful predictions of the SM.

Strong FCNC contributions – decays t → q g, with q = u, c.

Weak FCNC contributions – decays t → q Z and t → q γ

0Z

RESULTS

We found a direct proportionality between the cross sections of several FCNC processes and the FCNC Branching ratios. For instance, for single top production of a top quark at the LHC (in picobarn):

In the SM,

BR(t→cg) ~ 10-12

In other models, it can reach

BR(t→cg) ~ 10-4

RESULTS

The branching ratios of t → q Z and t → q γ are related:

RESULTS FOR t + γ PRODUCTION

Analysing the combined effects of FCNC in the strong and weak sector yields information on the sum of the branching ratios.

DIFFERENTIAL CROSS SECTIONS ALLOW TO DISTINGUISH STRONG AND WEAK FCNC CONTRIBUTIONS:

THE FUTURE…

• Continue (and survive) the fruitful collaboration between theoreticians and experimentalists.

• Top gluon FCNC interactions have been introduced in an event generator (latest version of TopReX). We wish to implement ALL FCNC interactions in generators and study their effects in LHC physics.

• Publish loads of very nice papers…

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