looking for new effects in electroweak precision data
DESCRIPTION
Looking for New Effects in Electroweak Precision Data. J. de Blas In collaboration with F. del Águila & M. Pérez-Victoria. XXXI Reunión Bienal de la Real Sociedad Española de Física. Granada, 11 de Septiembre de 2007. Introduction. SM is a great success - PowerPoint PPT PresentationTRANSCRIPT
Looking for New Effects in Electroweak Precision Data
J. de BlasIn collaboration with F. del Águila & M. Pérez-Victoria
XXXI Reunión Bienal de la Real Sociedad Española de Física
Granada, 11 de Septiembre de 2007
Introduction
SM is a great success
Good agreement with experimental data.
But:
Theoretical Problems: Hierarchy problem.
SM must be considered as an effective theory with a cutoff Λ<ΛPlanck.
Naturalness → Λ~1 TeV
Discrepancies (≥ 2σ) with some measuments: AbFB, σHad…:
Maybe statistical fluctuations.
Otherwise, one could use these small discrepancies to obtain some information about the theory at energies E> Λ.
Introduction
We would like to parametrize the new physics in a model independent way
→→ Effective Lagrangians
Precise measurements are necessary to constrain or exclude indirect new physics effects:
→→ Precision Electroweak Data
We have developed a code that allows us to:
Select different classes of new physics.
Incorporate different sets of Data.
Study specific models.
Outline
Effective lagrangians:
Heavy vectors
Heavy fermions: Dirac, Majorana
Electroweak Precision Data:
Effects of new physics.
Example: Bounds on heavy fermions
Conclusions
Effective Lagrangians
Beyond usual oblique analysis.
Decoupling scenario, weak coupling.
Heavy (~ Λ) states are integrated out
Ln involves only SM fields. LEff valid for E<< Λ.
We consider only operators up to dimension 6, classified in the basis of 1 (dim. 5) +81 (dim. 6) operators of W. Buchmüller & D. Wyler .
Integration at tree-level ( only gives a subset of the above)→ Big Effects
After EWSB L6 corrects the SM:
Nuc. Phys B268 (1986) 621-653)
Heavy Vectors
Construct the most general lagrangian for a heavy vector coupled to the SM particles.
Renormalizability+Lorentz&Gauge invariance leaves two possibilities:
Heavy Vectors: Operators
Vector Vector
EffectEffect
4-Fermion4-Fermion
Vector-Fermion Vector-Fermion vertexvertex
, ,Fermion Fermion massesmasses
,Vector Boson Vector Boson
massesmasses
,Higgs PotentialHiggs Potential
Heavy vector-like Dirac Fermions
Vector-like Quarks: F.del Águila et al.
Easily generalized for vector-like Leptons:
JHEP 09 (2000) 011
Heavy Dirac Quarks: Operators
EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
-
Heavy Dirac Leptons: Operators
Heavy Majorana Fermions
Renormalizability+Invariance & Majorana condition leaves only two types:
Integration similar to Dirac’s case but gives also the only dimension five operator of the basis:
•Majorana mass for neutrinos
•Lepton number violation ∆L=2→→
EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
Heavy Majorana Leptons: Operators
Electroweak Precision Data
The program includes:
Z-pole measurements:
Low-Energy measurements:
LEP II measurements:
New physics effects linear in . 2
2v
MW Z-pole Low-Energy LEP IISM Inputs:
GF, MZ
W ± & Z0
mass W ±
FF
&
Z0 FF
Vertex
Effects of new physics
4-F
erm
ion
Example: Bounds on SM-like Heavy Fermions
Bounds at 1-σ:
Bound [x (M/1TeV)]Bound [x (M/1TeV)]
<(0.31 0.32 ----- )
<(0.40 0.30 0.16)
<(0.42 0.46 ----- )
<(0.17 0.70 0.30)
<(0.05 0.15 0.10)
<(0.06 0.25 0.11)
Mixing with the SM b quark?→ → , v=246 GeV.
Example: Bounds on SM-like Heavy Fermions
B
DQM
vY
23
Example: Heavy B quark singlet with mass MB=500 GeV. (D type)
Read the bound on YDQ3 and apply the formula.
MixingbB < 0.03
Conclusions
The Effective Lagrangian parametrizes heavy physics at low energies in a model independent way.
Constraints on masses and couplings of generic new particles.
Specific Models can be easily analyzed.
Electroweak Precision Tests are complementary to LHC searches.
Looking for New Effects in Electroweak Precision Data
Backup slides
Effects of new physics II
Best measurements: Z-pole and Low-Energy experiments.
Z-pole is the main constraint over operators that modify vector-fermion vertex.
Low-Energy and LEP II: 4-fermion operators becomes relevant.
• Heavy fermion corrections are mainly constrained by Z-pole.
• Heavy vector corrections constrained by all data.
→→
Example II: Bounds over Exotic Heavy Fermions
Bounds at 1-σ:Bound [x (M/1TeV)]Bound [x (M/1TeV)]
<(0.15 0.24 ---- )
<(0.39 0.33 0.51)
<(0.14 0.24 0.25)
<(0.37 0.37 0.32)
<(0.23 0.22 0.66)
<(0.19 0.09 0.29)
<(0.27 0.17 0.40)
<(0.09 0.21 0.14)