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EW precision tests before the LHC. Paolo Gambino Università di Torino INFN Torino HEP 2007 Manchester. Precision tests in the last few years. (g-2) µ remains a puzzle - PowerPoint PPT Presentation

EW precision tests before the LHC Paolo Gambino Universit di Torino INFN Torino

HEP 2007 Manchester

P.Gambino HEP 2007 Manchester

Precision tests in the last few years(g-2) remains a puzzle Great improvement in Mt and smaller one in MW at the TevatronSmall improvements in h determination Most LEP results finalized, final E158 result. Some possible anomalies faded away (weak universality, NuTeV)ongoing theoretical effort to improve accuracy: important for the future, especially for ILC

Overall the SM performs well, but some cracks in its building have deepened during the last few years.

P.Gambino HEP 2007 Manchester

The ups and downs of (g-2)taue+e-

P.Gambino HEP 2007 Manchester

Can we test the SM with (g-2)?~3 discrepancy: New Physics (Supersymmetry?) or due to uncalculable strong interaction effects? Non-QED effects are suppressed by m2/2 but starting at 2loops can also be the scale of strong interactions ~M~700MeV ! Excellent place for new physics, no MH sensitivity: loop effects ~m2/2 but needs chiral enhancement: SUSY natural candidate at moderate/large tanQED diagrams

P.Gambino HEP 2007 Manchester

The spectral function The pion form factor> 70% of ahad,LOThe spectral function can be measured in e+ e- hadr, in decays, and with radiative returnradiative returnthe pionform factor

P.Gambino HEP 2007 Manchester

Experimental situation is improving but tau data must be understood (experimental or theoretical problem?)Passera Tau06Light by lightThe main open problemsSpectral functionfrom tau decays implies extra theory input

P.Gambino HEP 2007 Manchester

Status of (g-2) At present still problematic. Exp problems will be solved in the near future.LxL eventual bottleneck, but has the wrong sign and theory evolves.The proposed new experiments at Brookhaven and J-PARC should be fundedAleph e+e-LxL: MelnikovVainshteinPassera, hep-ph/0702027

P.Gambino HEP 2007 Manchester

(g-2) in the MSSMEllis et al, arXiv:0706.0652EW fit in the CMSSM: the existence of the dip (preference for light superpartners)in 2 rests almost exclusively on this piece of data

P.Gambino HEP 2007 Manchester

Low energy tests of NC couplingsLow energy measurementsof sin2W can be presentedas tests of its runningNeeds to reanalyzedataNuTeV uncertaintyfrom PDFs, imple-mentation of NLO and EW correctionsAtomic ParityViolation Moller scattering

P.Gambino HEP 2007 Manchester

Indirect determination of MH Best known EW observables: G(0.9 10-5) MZ (2 10-5) (MZ) (3 10-4) MW (4 10-3) sin2efflept (0.8 10-3) l (10-3)

(Mz),G,Mw f(Mt,MH) or (Mz),G,sin2efflept g(Mt,MH)

Since Mt is now known to 1% MHr is an observable quadratic (logarithmic) function of Mt (MH), known withtheory precision close to 10-4. Analogous relations hold for sin2efflept etc.

Recent calculations: complete 2loop EW, leading 3 and 4 loop effects Awramik,Czakon,Freitas,Feisst,Uccirati,Sturm, Weiglein,Boughezal,Van der Bij,Tausk,Chetyrkin,Kuehn,Meier,Hollik...

EW loops

P.Gambino HEP 2007 Manchester

Mtop-MH correlationsStrong correlation becausethey enter the same loopsPositive correlation:higher Mt higher MH

The constraining power of MW and sin2eff is similar at current precision

P.Gambino HEP 2007 Manchester

MW and Mtop history The low value of Mtop implies a preference for lower MH

Which mass is being measured? Its time to goto NLO and adopt a well-defined mass that induces small radiative corrections, eg MS mt(mt)

P.Gambino HEP 2007 Manchester

Pointing to a light HiggsMW likes a very light Higgs

Almost too light...

A heavy Higgs can be accomodated by many types of New Physics, ex: 4th generation.It needs an accidental cancellation we cannot exclude

NB further improvementson mt will have a more limitedeffect on MH constraints

P.Gambino HEP 2007 Manchester

The global EWWG fit

OVERALL, SM fares well(does not include NuTeV, APV, g-2) Strong preference for light Higgs, below 150 GeV, even including infofrom direct searches

P.Gambino HEP 2007 Manchester

The blue bandLEP-SLD EW Working Group http://lepewwg.web.cern.ch/LEPEWWG

P.Gambino HEP 2007 Manchester

The MH fitEWWG fits an arbitrary setno (g-2), no universality, no b s

Only a subset of observables is sensitive to MH A fit only to the observablessensitive to MH has the same central value and much LOWER probabilityof about 2%

P.Gambino HEP 2007 Manchester

New physics in the b couplings?Root of the problem: old ~3 discrepancy between LR asymmetry of SLD and FB b asymmetry of LEP: in SM they measure the same quantity, sin2eff (Ab is practically fixed in SM)New Physics in the b couplings couldexplain it, but it should be tree level and such that |gRb|>>|gLb| Problematic and ad-hoc Choudhury et al, He-Valencia

P.Gambino HEP 2007 Manchester

The Chanowitz argument2 possibilities, both involving new physics: a) AFB(b) points to new physicsb) its a fluctuation or is due to unknown systematicsIf true, not difficult to find NP that mimics a light Higgs. Non-trivially, SUSY can do that with light sleptons, tan>4 Altarelli et alStatistically not very strong (114.4 GeV Even worse if (MZ) from tau is used

P.Gambino HEP 2007 Manchester

Precision tests and LHCHiggs discovery or disproval remains the first task of LHC. We have growing evidence that the SM Higgs must be very close to the LEP exclusion bound, if it exists. A heavy H can describe data only with new physics (and a conspiracy)

Whatever LHC observes will need to be understood: is this the SM Higgs or not? are these heavy charged scalars squarks o KK excitations? The constraints from EWPT enhance significantly the analyzing power for LHC results.

LHC will also have its own EW program, including the study of Higgs properties (mass, width, couplings), W mass (goal 10 MeV) and width, top mass (probably th limited) and properties, sin2efflept from FB asymmetries, triple gauge couplings.

Muon g-2 and AFB(b) are puzzling (3!) anomalies. Had AFB(b) not been measured, we would face a similar puzzle, with the conflict of direct and indirect MH determinations.

P.Gambino HEP 2007 Manchester

Cracks in the egg?

P.Gambino HEP 2007 Manchester

Possibility n.1Susy?

P.Gambino HEP 2007 Manchester

Possibility n.2

P.Gambino HEP 2007 Manchester

We wont need to wait long for an answer

P.Gambino HEP 2007 Manchester

Overview of precision testsEWSB: O(0.1%), > 5 TeV (roughly)Flavor: O(2-10%), > 2 TeV (roughly)The modern version of Weak Universality

P.Gambino HEP 2007 Manchester