Precision Tests of the SM,

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PASCOS, Mumbai, 4 January '03
Precision Tests of the SM, the Higgs and New
Physics
G. Altarelli CERN
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The Standard Model


Electroweak
Strong
SU(3) colour symmetry is exact!
The EW symmetry is spont. broken down to U(1)Q
Higgs sector (???)
Gauge Bosons
8 gluons gA
W, Z, g
Matter fields 3 generations of quarks
(coloured) and leptons
2 more replicas
mW, mZGF-1/2 Fermi scale of mass(???)
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The EW theory L L symm L Higgs
A chiral theory
-
with
L symm well tested (LEP, SLC, Tevatron), L
Higgs untested
Rad. corr's -gt mH193 GeV but no Higgs seen
mHgt114.4 GeV (mH115 GeV ?) Only hint
mWmZcosqW doublet Higgs
LEP 2.1s
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Overall the EW precision tests support the SM
and a light Higgs.
The c2 is reasonable but not perfect
?2/ndof29.7/15 (1.3)
Note includes NuTeV and APV not (g-2)m?
Without NuTeV and APV (th. error questionable)
?2/ndof18.2/13 (14.9)
NuTeV
APV
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copied from Grunewald, Amsterdam 02 talk
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copied from Grunewald, Amsterdam 02 talk
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My opinion the NuTeV anomaly could simply arise
from a large underestimation of the theoretical
error
The QCD LO parton analysis is too crude to
match the required accuracy A small asymmetry
in the momentum carried by s-s could have a large
effect They claim to have measured this asymmetry
from dimuons. But a LO analysis of s-s makes no
sense and cannot be directly transplanted here
(asvalence corrections are large and process
dependent) A tiny violation of isospin symmetry
in parton distribs can also be important.
S. Davidson, S. Forte, P. Gambino, N. Rius, A.
Strumia
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Atomic Parity Violation (APV)
QW is an idealised pseudo-observable
corresponding to the naïve value for a N
neutron-Z proton nucleus
The theoretical best fit value from ZFITTER
is
(QW)th -72.8800.003
The experimental value contains a variety of
QED and nuclear effects that keep changing all
the time
Since the last LEP EWWG fit (showing a 1.52s
deviation) a new evaluation of the QED
corrections led to
Kuchiev, Flambaum02
(QW)exp -72.710.49
So in this very moment APV is OK!
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(g-2)m 3s discrepancy shown by the BNL02 data
EW 15.20.4 LO hadr 683.16.2 NLO hadr
-100.6 Light-by-Light 84 (was -8.52.5)
These units
hadr.
L by L
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Question Marks on EW Precision Tests
The measured values of sin2qeff from leptonic
(ALR) and from hadronic (AbFB) asymmetries are
3s away
The measured value of mW is somewhat high
The central value of mH (mH8350-33 GeV) from
the fit is below the direct lower limit (mH114.4
GeV at 95) more so if sin2qeff is close to that
from leptonic (ALR) asymm. mH lt 110 GeV
Chanowitz GA, F. Caravaglios, G. Giudice, P.
Gambino, G. Ridolfi
Hints of new physics effects??
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copied from Grunewald, Amsterdam 02 talk
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Plot sin2qeff vs mH
Exp. values are plotted at the mH point
that better fits given mtexp
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Plot mW vs mH
mW points to a light Higgs
Like sin2qeffl
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Sensitivities to mH
The central value of mH would be even lower
if not for AbFB
AbFB
One bad feature helpes the other AbFB vs ALR
cures the problem of ALR, mW clashing with
mHgt114.4 GeV
ALR
mW
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Some indicative fits
Most important observables mt, mW, Gl, Rb,
as(mZ), a???, sin2qeff
Taking sin2qeff from leptonic or hadronic
asymmetries as separate inputs, sin2qeffl and
sin2qeffh, with a-1QED128.9360.049 (BP01) we
obtain
c2/ndof18.4/4, CL0.001 mHcentral100 GeV, mH
212 GeV at 95
Taking sin2qeff from only hadronic asymm.
sin2qeffh
c2/ndof15.3/3, CL0.0016
Taking sin2qeff from only leptonic asymm.
sin2qeffl
c2/ndof2.5/3, CL0.33 mHcentral42 GeV, mH 109
GeV at 95
Much better c2 but clash with direct limit!
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It is not simple to explain the difference
sin2ql vs sin2qh in terms of new physics. A
modification of the Z-gtbb vertex (but Rb and
Ab(SLD) look normal)?
Probably it arises from an experimental problem
Then it is very unfortunate because sin2ql vs
sin2qh makes the interpretation of precision
tests ambigous
Choose sin2qh bad c2 (clashes with mW,
) Choose sin2ql good c2, but mH clashes
with direct limit
In the last case, SUSY effects from light
s-leptons, charginos and neutralinos, with
moderately large tanb???? solve the mH problem
and lead to a better fit of the data
GA, F. Caravaglios, G. Giudice, P. Gambino, G.
Ridolfi
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AbFB vs sin2qlept New physics in Zbb vertex?
Unlikely!! (but not impossible-gt)
For b
From AbFB0.09950.0017, using sin2qlept
0.231130.00020 or Ae0.15010.0016, one
obtains Ab0.8840.018
(Ab)SM - Ab 0.052 0.018 -gt 2.9 s
A large dgR needed (by about 30!)
But note (Ab)SLD 0.9220.020,
Rb0.216440.00065 (RbSM0.2157)
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Choudhury, Tait, Wagner
dgR
Ab(from AbSLD and AbFB)
0.992 gL(SM), 1.26 gR(SM)
Rb
SM
dgL
A possible model involves mixing of the b quark
with a vectorlike doublet (w,c) with charges
(-1/3, -4/3)
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EW DATA and New Physics
For an analysis of the data beyond the SM we use
the ? formalism
GA, R.Barbieri, F.Caravaglios, S. Jadach
One introduces ???? ???? ???? ?? such that
Focus on pure weak rad. corrects, i.e. vanish
in limit of tree level SM pure QED and/or QCD
corrects a good first approximation to the data
Z,W
Are sensitive to vacuum pol. and Z-gtbb vertex
corr.s (but also include non oblique terms)
???? ???? ???
b
Z
??
b
Can be measured from the data with no reference
to mt and mH (as opposed to S, T, U)
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One starts from a set of defining observables
Oi mW/mZ, Gm, AmFB, Rb
e1
e3
e2
eb
Oiek OiBorn1 Aik ek
OiBorn includes pure QED and/or QCD
corrs. Aik is independent of mt and mH
Assuming lepton universality Gm, AmFB --gt G?,
A?FB
To test lepton-hadron universality one can
add GZ, sh, Rl to Gl etc.
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GA, R. Barbieri, F.Caravaglios
??vs mtop
With sin2qeff from all data ?????? -gt -gt mW
large. ?1,3,b OK
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GA, R. Barbieri, F.Caravaglios
??vs mtop
With sin2qeff from leptons ?????? -gt -gt mW
large. ?3 also low-gt -gt mH below direct
limit. ?1, b OK
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a mW, Gl, Rb, sin2ql b mW, Gl, Rb, GZ, sh,
Rl, sin2ql c mW, Gl, Rb, GZ, sh, Rl,
sin2qlsin2qh
Note 1s ellipses (39 cl)
??
??
??
??
????? OK, ??????????? (mW), ?? depends on
sin2q????? for sin2ql (mH)
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MSSM me-L 96-300 GeV, mc- 105-300 GeV, m
(-1)-(1) TeV, tgb 10, mh 113 GeV, mA me-R
mq 1 TeV



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s-leptons and s-ns plus gauginos must be as
light as possible given the present exp. bounds!


In general in MSSM m2e-m2nm2Wcos2b
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Light charginos also help by making ?2
corrs larger than those of e3
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(No Transcript)
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The sign of ? is irrelevant here. But crucial
for (g-2)m
This model can also fit (g-2)m
Approx. at large tgb
Exp. 300

am 130 10-11(100 GeV/m)2 tgb
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tanb40, A0, sign(m)gt0
Djouadi, Kneur, Moultaka
m0
b-gts-g
(g-2)m
m1/2
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The Standard Model works very well
So, why not find the Higgs and declare particle
physics solved?
First of all one has to find it! Difficult
because it is only coupled to heavy particles
H
e-
e.g. at LEP
e
Z
Because of both
Z
Conceptual problems
Mainly the hierarchy problem
and experimental clues
Coupling unification Neutrino masses Dark
matter Baryogenesis
New results from KamLAND
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First results from KamLAND
Solar oscill.s confirmed on earth
Large angle sol. established ??????????Dm27.10-
5 eV2, sin22q 1
ne from reactors behave as ne from
sun Constraint on CPT models
Best fit
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Conceptual problems of the SM
No quantum gravity (MPl 1019 GeV)
Most clearly
But a direct extrapolation of the SM leads
directly to GUT's (MGUT 1016 GeV)
MGUT close to MPl
suggests unification with gravity as in
superstring theories poses the problem of the
relation mW vs MGUT- MPl
The hierarchy problem
Can the SM be valid up to MGUT- MPl??
Not only it looks very unlikely, but the new
physics must be near the weak scale!
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Indeed in SM mh, mW... are linear in L!
e.g. the top loop (the most pressing)
mh2m2baredmh2
t
h
h
The hierarchy problem demands new physics near
the weak scale
Lo(1TeV)
L scale of new physics beyond the SM
LgtgtmZ the SM is so good at LEP L few times
GF-1/2 o(1TeV) for a natural explanation of mh
or mW
Barbieri, Strumia
The LEP Paradox mh light, new physics must be so
close but its effects are not directly visible
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Examples
SUSY
Supersymmetry boson-fermion symm. exact
(unrealistic) cancellation of dm2 approximate
(possible) L mSUSY-mord
The most widely accepted
The Higgs is a yy condensate. No fund. scalars.
But needs new very strong binding force
Lnew103LQCD (technicolor).
Strongly disfavoured by LEP
Large extra spacetime dimensions that bring
MPl down to o(1TeV)
Elegant and exciting. Does it work?
Models where extra symmetries allow mh only at
2 loops and non pert. regime starts at L10
TeV "Little Higgs" models. Now extremely popular
around Boston. Does it work?
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SUSY at the Fermi scale
Many theorists consider SUSY as established at
MPl (superstring theory).
Why not try to use it also at low energy to fix
some important SM problems.
Possible viable models exists MSSM softly
broken with gravity mediation or with gauge
messengers or with anomaly mediation
Maximally rewarding for theorists Degrees of
freedom identified Hamiltonian specified Theory
formulated, finite and computable up to MPl
Unique!
Fully compatible with, actually supported by GUTs
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Coupling unification Precise matching of gauge
couplings at MGUT fails in SM and is well
compatible in SUSY
SUSY fits with GUT's
From aQED(mZ), sin2qW measured at LEP predict
as(mZ) for unification (assuming desert)
Non SUSY GUT's
as(mZ)0.0730.002
SUSY GUT's
as(mZ)0.1300.010
EXP as(mZ)0.1190.003 Present world average
Langacker, Polonski
Dominant error thresholds near MGUT
Proton decay Far too fast without SUSY
MGUT 1015GeV non SUSY -gt1016GeV SUSY
Dominant decay Higgsino exchange
While GUT's and SUSY very well match, (best
phenomenological hint for SUSY!) in technicolor ,
large extra dimensions, little higgs etc., there
is no ground for GUT's
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But
Lack of SUSY signals at LEP lower limit on mH
problems for minimal
SUSY
In MSSM
So mH gt 114 GeV considerably reduces available
parameter space.
In SUSY EW symm. breaking is induced by Hu
running
Exact location implies constraints
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mZ can be expressed in terms of SUSY parameters
For example, assuming universal masses at MGUT
for scalars and for gauginos
caca(mt,ai,...)
Clearly if m1/2, m0,... gtgt mZ Fine tuning!
LEP results (e.g. mc gt100 GeV) exclude gaugino
universality if no FT by gt 20 times is allowed
Without gaugino univ. the constraint only remains
on mgluino and is not incompatible
Exp. mgluino gt200GeV
Barbieri, Giudice de Carlos, Casas Barbieri,
Strumia Kane, King Kane, Lykken, Nelson,
Wang......
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Large Extra Dimensions
Solve the hierachy problem by bringing gravity
down from MPl to o(1TeV)
Arkani-Hamed, Dimopoulos, DvaliAntoniadis
Randall,Sundrun..
Inspired by string theory, one assumes
Large compactified extra dimensions SM
fields are on a brane Gravity propagates in
the whole bulk
y extra dimension R compact'n radius
R
GN1/M2Pl Newton const.
y
MPl large as GN weak
y0 "our" brane
The idea is that gravity appears weak as a lot
of lines of force escape in extra dimensions
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r gtgt R ordinary Newton law
y0 brane
r ltlt R lines in all dimensions
Gauss in d dim rd-2 r m
By matching at rR
For m 1 TeV, (d-4 n )
n 1 R 1015 cm (excluded) n 2 R 1mm (close
to limits) n 3 R 10-9 cm
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Limits on deviations from Newton law
Hoyle et al, PRL 86,1418,2001
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Generic feature compact dim.
Kaluza-Klein (KK) modes
pn/R m2n2/R2
(quantization in a box)
SM fields on a brane
The brane can itself have a thickness r 1/r
gt1TeV r lt10-17 cm
KK recurrences of SM fields Wn,Zn etc
cfr Gravity on bulk 1/R gt10-3 eV R lt0.1 mm
Many possibilities
Factorized metric
Warped metric
Randall-Sundrum
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Large Extra Dimensions to solve the hierarchy
problem is a very exciting scenario.
However, by itself it is difficult to see how
it can solve the main problem (the LEP Paradox)
??L 1/R must be small (mH light)
But precision tests put very strong lower
limits on L (several TeV)
In fact in typical models of this class there
is no mechanism to sufficiently quench the
corrections
No simple baseline model has yet emerged
But could be part of the truth
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Georgi (moose), Arkani-Hamed C.
Little Higgs Models
SM
gauged
global
H is (pseudo)-Goldstone boson of G takes mass
only at 2-loops (needs breaking of 2 subgroups
or 2 couplings)
cut off L
10 TeV
L2 divergences canceled by
dm2Htop new coloured fermion c dm2Hgauge
W', Z', g' dm2HHiggs new scalars
1 TeV
2 Higgs doublets
0.2 TeV
E-W Precision Tests? Problems GUT's? But
signatures at LHC clear
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e.g. enlarge SU(2)weak global SU(3)

quark doublet triplet
SU(3) broken spont.ly
Yukawa coupling
expl. SU(3) breaking
lf
tL
top loop
cL
tR
coeff. L2
- l/f
l2
tR
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Little Higgs Big Problems with Precision Tests
Hewett, Petriello, Rizzo/ Csaki, Hubisz, Kribs,
Meade, Terning
Even with vectorlike new fermions large
corrections arise mainly from Wi, Z
exchange. lack of custodial SU(2) symmetry
A combination of LEP and Tevatron limits gives
f gt 4 TeV at 95 (L 4pf)
Fine tuning gt 100 needed to get mh 200 GeV
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Summarizing
SUSY remains the Standard Way beyond the SM
What is unique of SUSY is that it works up to
GUT's .
GUT's are part of our culture! Coupling
unification, neutrino masses, dark matter, ....
give important support to SUSY
It is true that the train of SUSY is already a
bit late (this is why there is a revival of
alternative model building)
No complete, realistic alternative so far
developed (not an argument! But)
Extra dim.s is an attractive, exciting
possibility. Little Higgs models look as just
a postponement (both interesting to keep in
mind)
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SUSY The standard way beyond the SM
LSM Lsymm LHiggs
Untested
n masses via L Baryogenesis via
leptogenesis Unification of couplings No
clash with unobs p decay (yet) Neutralino
as CDM
GUT's MGuts MPl
mW ltlt mPl
Hierarchy problem
SUSY GUT's
SUSY