SLIDE 1
M d l i d d t FCNC t h i t Model independent FCNC top physics at the LHC
P d F i Pedro Ferreira ISEL CFTC U i id d d Li b ISEL e CFTC, Universidade de Lisboa
Jornadas do LIP 2008, 12/1/08
SLIDE 2 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…
SLIDE 3
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.
SLIDE 4
THE CONNECTIONS…
Granada Southampton NExT
tbW measurements tbW measurements (BSM physics) (BSM physics) tbW tbW
LIP CFTC RAL
tbW tbW measurements measurements
Valencia RHUL LONDON
top FCNC top FCNC combination combination Generators, Generators, tbW physics tbW physics
Valencia
SLIDE 5 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
- f 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.
SLIDE 6 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.
SLIDE 7 Strong FCNC contributions – decays t → q g, with q = u, c.
λa Λ2
jtqν) + v σµν (βtjγR + β∗ jtγL)
p
③
Λ
j
k, α; a t q
③
λa Λ2
tjqν) + v σµν (βjtγR + β∗ tjγL)
uj p
③
(kµ gνα − kν gµα) k, α; a t q
i gs Λ2
jtqν) + γνγR(αtjpµ − α∗ jtqµ)
+2v σµν (βjtγR + β∗
tjγL)
k1, µ; a uj p
③
+
µν (βjtγR + βtjγL)
gs 2Λ2
k1gµν − k1νγµ) γR
jt
(/ k2g − k2 γ ) γR
j
t q (/ k2gµν k2νγµ) γR
;
SLIDE 8 Weak FCNC contributions – decays t → q Z and t → q γ
③
1 Λ2
ut pν + αγ R∗ tu
qν) k, α t p
③
+ v σµν (βγ
utγR + βγ∗ tu γL)
¯ u q
γ
t p
③
1 Λ2
ut pν + αZ R∗ tu
qν) + v σµν (βZ
utγR + βZ∗ tu γL)
k, α t p
Z
Λ2 [iγR (ηut pα − ¯
ηut qα) + θ v γα γR)] ¯ u q
SLIDE 9
RESULTS
We found a direct proportionality between the cross sections of l FCNC d th FCNC B hi ti F several FCNC processes and the FCNC Branching ratios. For instance, for single top production of a top quark at the LHC (in picobarn):
SLIDE 10
SLIDE 11
The branching ratios of t → q Z and t → q γ are related:
SLIDE 12 RESULTS FOR t + γ PRODUCTION
10
2
10 10
Analysing the combined effects
10
−4
10
−2
→ t γ) (pb)
combined effects
strong and weak sector yields
−8
10
−6
σ(pp → u g →
sector yields information on the sum of the branching ratios.
10
−10
10
−8
σ
g
10
−15
10
−10
10
−5
10 10
−12
BR(t → u g) + BR(t → u γ)
SLIDE 13 DIFFERENTIAL CROSS SECTIONS ALLOW TO DISTINGUISH STRONG AND WEAK FCNC CONTRIBUTIONS:
10
2
10
−2
10
BR(t → u g ) ~ 10−2 BR(t u ) ~ 10−7 10
−4
d σ/d cos BR(t → u γ ) ~ 10−7
10 10
1
−1 −0.5 0.5 1 10
−6
cosθ
10
−2
10
−1
s θ (pb) BR(t → u g ) ~ 10−7
−2
cos
10
−5
10
−4
10
−3
d σ/d cos θ BR(t → u γ ) ~ 10−2 −1 −0.5 0.5 1 10
−7
10
−6
10 −1 −0.5 0.5 1 cosθ
SLIDE 14 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…
SLIDE 15
NEXT THEORETICIANS + EXPERIMENTALISTS’ PAPER
