Model independent FCNC top physics at M d l i d d t FCNC t h i - PowerPoint PPT Presentation

Model independent FCNC top physics at M d l i d d t FCNC t h i t the LHC Pedro Ferreira P d F i ISEL ISEL e CFTC, Universidade de Lisboa CFTC U i id d d Li b Jornadas do LIP 2008, 12/1/08

THE WORK… • 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 and R. Santos, PHYSICAL REVIEW D 74, 014006 (2006) • P. M. Ferreira, R. B. Guedes and R. Santos, PHYSICAL REVIEW D 75, 055015 (2007) (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 TEAM… Projects: Projects: POCI/FP/81950/2007 PTDC/FIS/70156/2006 POCI/FP/63926/2005 POCI/FP/63420/2005 POCTI/FIS/59741/2004 PDCTI/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 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 CONNECTIONS… Southampton Granada tbW measurements tbW measurements (BSM physics) (BSM physics) NExT tbW tbW tbW tbW RAL measurements measurements CFTC LIP Generators, Generators, top FCNC top FCNC tbW physics tbW physics RHUL combination combination LONDON Valencia Valencia

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 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.

EFFECTIVE OPERATOR FORMALISM 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. 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. u j p � � � � λ a γ µ γ R ( α tj p ν + α ∗ jt q ν ) + v σ µν ( β tj γ R + β ∗ jt γ L ) Λ 2 j j Λ k, α ; a ③ ( k µ g να − k ν g µα ) q t p u j � � λ a γ µ γ R ( α jt p ν + α ∗ tj q ν ) + v σ µν ( β jt γ R + β ∗ tj γ L ) Λ 2 k, α ; a k α ; a ③ ③ ( k µ g να − k ν g µα ) q t λ c f abc � � i g s γ µ γ R ( − α tj p ν + α ∗ jt q ν ) + γ ν γ R ( α tj p µ − α ∗ jt q µ ) Λ 2 k 1 , µ ; a u j p �� �� + +2 v σ µν ( β jt γ R + β ∗ µν ( β jt γ R + β tj γ L ) tj γ L ) + + ③ � � � g s ( / k 1 g µν − k 1 ν γ µ ) γ R λ a λ b α tj + λ b λ a α ∗ + 2Λ 2 jt q t � � �� �� k 2 , ν ; b 2 , ; ( / ( / k 2 g k 2 g µν − k 2 γ ) γ R k 2 ν γ µ ) γ R λ b λ a α tj + λ a λ b α jt λ b λ α tj + λ λ b α ∗ j

Weak FCNC contributions – decays t → q Z and t → q γ p t � γ µ γ R ( α γ R ut p ν + α γ R ∗ 1 q ν ) tu Λ 2 k, α ③ ③ ( k µ g να − k ν g µα ) � + v σ µν ( β γ ut γ R + β γ ∗ tu γ L ) q u ¯ γ p p t t � 0 1 γ µ γ R ( α Z R ut p ν + α Z R ∗ q ν ) Z Λ 2 tu ( k µ g να − k ν g µα )+ k, α � � ③ + v σ µν ( β Z ut γ R + β Z ∗ tu γ L ) v Λ 2 [ iγ R ( η ut p α − ¯ η ut q α ) + θ v γ α γ R )] q u ¯

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

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

RESULTS FOR t + γ PRODUCTION 2 10 10 0 10 Analysing the combined effects combined effects −2 10 of FCNC in the → t γ ) (pb) strong and weak −4 10 sector yields sector yields σ (pp → u g → information on −6 10 the sum of the branching ratios. g σ −8 −8 10 −10 10 −12 10 −15 −10 −5 0 10 10 10 10 BR(t → u g) + BR(t → u γ )

DIFFERENTIAL CROSS SECTIONS ALLOW TO DISTINGUISH STRONG AND WEAK FCNC CONTRIBUTIONS: 2 10 0 10 os θ (pb) BR(t → u g ) ~ 10 −2 −2 10 BR(t → u γ ) ~ 10 −7 u ) ~ 10 −7 d σ /d cos BR(t 1 10 −4 10 0 10 −1 10 −6 10 −2 BR(t → u g ) ~ 10 −7 s θ (pb) 10 −1 −0.5 0 0.5 1 cos θ cos d σ /d cos θ BR(t → u γ ) ~ 10 −2 −2 −3 10 −4 10 −5 10 10 −6 10 −7 10 −1 −1 −0.5 −0.5 0 0 0.5 0.5 1 1 cos θ

THE FUTURE… • Continue (and survive) the fruitful collaboration between 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 implement ALL FCNC interactions in generators and study their effects in LHC physics. • Publish loads of very nice papers…

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