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Electroweak Symmetry Breaking: experimental investigations. The question The tools : accelerators and detectors The status from precision electroweak measurements The status of direct searches The near future (Tevatron, LHC) The Susy factory: ILC The Higgs factory: muon collider
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(and photons dont)?
The Standard Model answer:
a complex doublet of self coupling scalars with weak isospin ½
splits off into
W+L W-L W0L (additional degrees of freedom of massive particle) and h0
Furthermore, W0 and B field mix by angle qw to give Z and g
mg = 0
This important test of the model (or is it?) is verified with high precision
speed of em radiation is independent of wavelength
residual energy carriedby vector potential (Arhonov-Boehm effect)
Magneto hydrodynamics of solar plasma mg< 6 10 –17eV(new, PDG 2004)
and of course is respected by em gauge invariance
ran around Z peak
Z mass and width
then up to 209 GeV
collected 20MZ,& 80 kW
92 GeV polarized e+e- collider
ran at Z peak (500kZ)
observed first Z event
polarized beam (~77%)
very small vertex
excellent b, c tag
2 TeV proton-antiproton collider
WZ event in D0
These are real magnets now!
measure Z and W masses
check relation mW= mZcosW
see that it is affected by Electroweak Radiative corrections
use these to predict top quark mass
find the top and check its mass
use mass to refine Higgs boson mass from EWRCs
try to find a physical h particle
what if not? verify properties of W and Z, WW, WZ, ZZ scattering
If yes, identify its properties, Susy or not – other Higgses
relations to the well measured
GF mZ aQED
at first order:
Dr = a /p (mtop/mZ)2
- a /4p log (mh/mZ)2
e3 = cos2qwa /9p log (mh/mZ)2
dnb=20/13 a /p (mtop/mZ)2
complete formulae at 2d order
including strong corrections
are available in fitting codes
Using the latest experimental data from BESII:
5hadron = 0.02761 0.00036
(Burkhardt and Pietrzyk 2001)
5hadron = 0.02755 0.00023
(Hagiwara et al. 2003)
These data has also confirm the validity
of extending the use of perturbative QCD
in the calculation of 5hadron.
The most precise of these theory-driven
5hadron = 0.02747 0.00012
(Troconiz and Yndurain 2001)
using CMD-2 and KLOE
latest data, seem to cancel out
using CMD-2 latest data
is not anymore the limiting factor in the SM fits…
thanks BES !!!
(692.4 to 694.4 ± 7)10-10 [e+e- -based 04]
(12.0 ± 3.5)10-10 [Melnikov & Vainshtein 03]
New -data collected in 2001, confirms previous measurements using +
(a+ - 11659000)x 10-10 = 203 ± (6 stat. 5 syst.)
(a- - 11659000) x 10-10 = 214 ± (6 stat. 5 syst.)
(a - 11659000)exp x 10-10 = 208 ± (5 stat. 4 syst.)
(a - 11659000)th x 10-10 = 183 ± 7[e+e-] DEHZ04
2.7 from prediction
(was 1.9 before inclusion of 2001 data)
LEP: N = 2.9841 0.0083
Ginv (new)< 2.1 MeV
NB this is 2s low
+-200 keV! variations due to tides,
mZ= 91187.5 +-2.1 MeV
Was the dominant new factor
in 1994 when results from the 1993 scan
(with res. dep. on each point)
GZ = 2494.8 +- 2.5 MeV
mtop = 174 +- 12 +- 18 GeV
Bolek Pietrzyk Moriond March 1994
mtop = 174 +- 16 GeV
CDF may 1994
sin2qWeff ¼ (1- gV/gA)
gV = gL + gR
gA = gL - gR
e+e- q1 q2 q3 q4
WZ event in D0
SM: combination of and yields mW and sin2qWeff(Q2)
experiment expresses result in terms of sin2qW = 1 – m2W/m2Z
which is strictly and obviously equivalent to mW once mZ is so well measured.
beyond SM: sensitivity to unexpted Q2 dep. of couplings and or propagators (Z’)
Trivial problems: predictions are sensitive to assumptions about
isospin symmetry violations
is u(x) in neutron strictly equal to d(x) in proton? charm production?
four quark channel is severely affeced by hadronization uncertainties!
fraction of model seen
BEC effects experimentally established in Z jets at LEP1
Inter-W BEC? Analyses performed in 4 LEP experiments to search/limit them
Observable: distance in p-space between pairs of charged pions:
0 1 Q(GeV)
Observable: ratio of particle flow between the inter and intra-W regions:
(A + B) / (C + D)
CR models predict a modified particle flow in W+W- events:
‘Asymmetry’ from experiments combined in a c2
Preferred value of the parameter
(0.5 + 0.2 - 0.3)
corresponds to dMW ~ 100 MeV!!
idea is to reduce effects by excluding particles situated outside
angular cones around the jets.
Some resolution is lost but systematic error is reduced.
Good reduction factors are obtained for all available models
Example: Cone (R=0.5 rad), with a statistical loss of ~ 25%:
Cone radius (rad)
Results in CERN-EP/2003-091, LEPEWWG/2003-02
still with standard jet algorithms
DmW = 22 ± 43 MeV
errors expected for
summer ‘05 conferences:
there will also be an
improvement on the
beam energy error
due to usage of LEP
lots of hard work, and improved understanding … but diminishing returns
n exchange t channel ONLY
Clear proof of SU(2)xU(1) gauge couplings !
NB this is really non trivial. W3= Z cosqW + B sinqW
Alas, beam polarization vanishes at LEP above E=65 GeV
res. dep. will not work for linear collider
idea: use e+e- Z g to measure Ebeam given that mZ is so well known
lead to non trivial systematics!
Tesla TDR mW +- 6 MeV … hmmmm …
the calorimeter and tracker
will have to be very carefully designed,
and full identification of final state
hadrons (incl. neutrons, L and K)
will be needed.
This method gives a statistical error that
matches that of the W mass measurement
in the lvqq channel.
using muons instead would require
20 times more stats.
Similar results by L3, OPAL
Status as of Moriond 2005
Method similar to mw at LEP II: form ‘estimator’ and compare measured distribution
to templates with different top masses as input.
(this cannot be done by rescaling since top is too narrow)
Progress was noted when a ‘likelihood’ was built including event by event error estimate
There is a flurry of new measurements and measurement techniques at RUNII.
In most cases the limitation comes from the JET ENERGY CORRECTIONS.
Top Mass determined using maximum likelihood
Expected statistical error
Expected 5.4 GeV
Observed 3.6 GeV
Jet energy scale syst: 3.3 GeV/c2
Mtop = 180.1 ± 3.6 (stat) ± 3.9 (sys) GeV/c2
Comparable precision to all previous measurements combined
(some luck involved!)
error bars: red=stat, blue=total
LO ME final state:
Largest uncertainty: Jet Energy Measurement
Determine true “particle”, “parton” E,p from measured jet E, q
but: top is NOT a color singlet, nor is tt pair.
This method requires that the effect on the mass reconstructed using
a specific jet rec. algorithm is perfectly modelled by the MC
in a situation where there is no conservation law to prevent large effects.
* There is no calibration of this! *
(At LEP a light quark typically acquires 5-10 GeV due to fragmentation.
This is not particularly well modelled in qqbar situation. But what about ppbar?)
W (color singlet)
W (color singlet)
W (color singlet)
W (color singlet)
Tevatron aims at measuring mtop with a precision of 2-3 GeV.
This would be a remarkable achievement and progress.
LHC hopes to be able to reach 1 GeV
ATLAS note (SN-ATLAS-2004-040) mentions testing top mass
against varying the jet cuts.
Because of all the gluons around this may be a very sticky business!
this in fact is a verification
of the validity of the relation
mW = mZ cosqW at tree level.
(up to corrections due to mHiggs
and any new physics cancellation)
these plots show the fact that
sin2qeffW i the most sensitive
estimator of the Higgs mass,
but the limitation will soon come
from the top mass meast
with a 2/d.o.f. = 15.8/13 and
a 67% correlation between
mtop and log(mHiggs).
The largest contribution to the
2 is AbFBwith 2.4. It pulls for
a large mHiggs in opposition to l,
mW and leptonic asymmetries.
5hadron = 0.02769 0.00035
s(mZ) = 0.1186 0.0027
mtop = 178.2 3.9 GeV
log(mHiggs) = 2.06 0.21
MH= 126+73-48 GeV
MH 280 GeV @ 95% C.L.
Is there any chance to improve this constraints?
[log(mHiggs)]2 = [exp]2 + [mt]2 + 2 + [s]2
Z asymmetries,sin2eff :[0.22]2 = [0.15]2 +[0.12]2+ [0.10]2 + [0.01]2
all high Q2 data:[0.21]2 = [0.12]2 +[0.13]2 + [0.10]2 + [0.04]2
[0.03] if theory-driven
The reduction in mtop (5.1 4.3 GeV) has reduced the uncertainty on mHiggs , but still the TOP priority is to reduce the uncertainty on mtop ,which is limited by systematic uncertainties!
@ 114 GeV : s ~ 0.1 pb
BR(Hbb) ~ 74% BR(Htt) ~ 7%
ALEPH 4-Jet candidate
Consistency with BG
Mass limit via
CLS = CLS+B/CLB
Mass spectrum after tight selection cuts
Observed Limit: 114.4 GeVExpected Limit: 115.3 GeV
Phy. Lett. B565 (2003) 61
Updated in 2003 in the low Higgs mass region
W(Z)Hln(nn,ll)bb to include VBF
better detector understanding
optimization of analysis
Tevatron will begin sensitivity to LEP Higgs limit (or signal?) when >2.5 fb-1
will have been accumulated … it could be quite soon (Moriond 2007?)
CMS note 03 033 ATLAS SN-ATLAS-2003-024
NB in this channel,
it is easy to determine
the spin of the Higgs!
striking now: there is aways at least two channels of which at least one allows
determination of spin of Higgs and, if mH<160 GeV
the ratio of couplings to bosons vs fermions.
The standard Model has been verified in many ways experimentally
(boson couplings, masses properties)
its structure is still mysterious, and the mechanism by which
masses are given is still unclear.
It all works as if there was a Higgs, although one could not help notice that
the radiative corrections assocaited to it as consistent with
log (mH/mZ)=0 ….
If the Higgs is indeed lower in mass than 280 GeV it will be discovered at
LHC rather rapidly, and thanks to the realization of the importance of VBF
we should be able if it is not of mass higher than 2 mW to measure its
mass spin and parity
Precision physics with jets is delicate (color reconnection) and will reserve much
fun in the near future.
we are living in exciting times!