The MICE collaboration

1
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
• Conclusions

2
The Question Why do Ws have mass
(and photons dont)?
The Standard Model answer a complex doublet of
self coupling scalars with weak isospin ½ splits
off into WL 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 mWmW-mW0mZcosqw 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
lt 6 10 17 eV (new, PDG 2004) and of course is
respected by em gauge invariance
3
L E P
ran around Z peak Z mass and width then up to
209 GeV collected 20MZ, 80 kW
4
Slac Linear Collider
92 GeV polarized ee- collider
ran at Z peak (500kZ) observed first Z event
polarized beam (77) very small vertex ?
excellent b, c tag
5
TeVatron
2 TeV proton-antiproton collider
WZ event in D0
1000
6
LHC
These are real magnets now!
7
PROGRAMME measure Z and W masses measure
?W check relation mW mZcos?W 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
8
EWRCs
relations to the well measured GF mZ aQED
at first order
Dr a /p (mtop/mZ)2 - a /4p log
(mh/mZ)2
e3 cos2qw a /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 e.g.
ZFITTER
9
Parameters of the SM ?(Mz2)
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
calculations gives,

??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 !!!
hep-ph/0312250
10
Parameters of the SM ?(M?2)
(11658472.07 0.11)10-10
(692.4 to 694.4 7)10-10 ee- -based 04
(12.0 3.5)10-10 Melnikov Vainshtein 03
11
(g-2)?
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
ee- DEHZ04
including KLOE 2.7?
from prediction (was 1.9? before inclusion of
2001 data)
12
luminosity measurement to 6 10-4!
LEP N? 2.9841 ?0.0083
Ginv (new) lt 2.1 MeV NB this is 2s low
13
energy resolution (resonant depolarization) -200
keV! variations due to tides, trains,
rain, etc..
mZ 91187.5 -2.1 MeV
14
Note relative insensitivity of Gz to Higgs mass.
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 vs mtop 174 - 16 GeV CDF may
1994
!
15
Measuring sin2qWeff (mZ) sin2qWeff ? ¼ (1-
gV/gA) gV gL gR gA gL - gR
16
ee- ? mn qq
W mass
ALEPH evts
ee- ? q1 q2 q3 q4
WZ event in D0
17
(No Transcript)
18
NUTeV
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?
19

• Measuring masses with JETs
• which may not be independent
• LEP mW from the 4quark channel
• W ? qq gives two dependent jets
• (in JETSET language these jets are part
• of one single string) but they form a
• COLOR SINGLET
• WW? qq qq gives two COLOR SINGLETS
• which in principle shouldnt talk to each other
• Is this true? It has been suspected that
• there may be some O(as2) correction leading
• for example to
• Bose Einstein correlations between (BEB)
• the two systems

20
four quark channel is severely affeced by
hadronization uncertainties!
21
BEC in WW- events

• 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
• Q2ij-(pi-pj)2

0 1 Q(GeV)

• Inter-W BEC correlations disfavoured
• Limit on systematic dMW 15 MeV

22
The particle flow analysis

• CR models predict a modified particle flow in
  WW- events

23
Results from particle flow
Asymmetry from experiments combined in a c2
For SK1 Preferred value of the parameter (0.5
0.2 - 0.3) corresponds to dMW 100 MeV!!
24
Reduction of dMW
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 (R0.5 rad), with a statistical
  loss of 25

MW (GeV)
ALEPH SK1 k2.13
Cone radius (rad)
25
mW from direct reconstruction
Results in CERN-EP/2003-091, LEPEWWG/2003-02
still with standard jet algorithms
DmW 22 43 MeV
26
? errors as of summer 2003
errors expected for summer 05 conferences
there will also be an improvement on the beam
energy error due to usage of LEP spectrometer.
lots of hard work, and improved understanding
but diminishing returns
27
Physics processes at LEP2
100k evts
10k evts
1k evts
100 evts
28
W-pair cross sections
n exchange t channel ONLY
29
n exchange and gWW vertex
30
agreement to 0.6-0.9
Clear proof of SU(2)xU(1) gauge couplings !
NB this is really non trivial. W3 Z cosqW B
sinqW
31
LEPII (and LC) energy calibration
Alas, beam polarization vanishes at LEP above
E65 GeV res. dep. will not work for linear
collider
idea use ee- ? Z g to measure Ebeam given
that mZ is so well known
ALEPH
32
Jets that are boosted 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.
Systematic uncertainties
Similar results by L3, OPAL
33
TOP mass measurement CDF, D0
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 (D0, CDF) There is a flurry of new
measurements and measurement techniques at RUNII.
In most cases the limitation comes from the JET
ENERGY CORRECTIONS.
34
D0 Run I - Top Mass Analysis Using ME Method
Top Mass determined using maximum likelihood

• 91 candidate tt events
• 77 with exactly 4 jets selected
• 22 passing cut on background probability (Pbkg lt
  10-11)

Expected statistical error
pseudo-experiments
Nature 429, 638-642 (2004)
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!)
35
Mtop Measurements

• Combined RunI mass
• mt178.0 4.3 GeV/c2
• was 174.3 5.1 GeV/c2
• Run II measurements
• Systematic uncertainty largely dominated by jet
  energy correction will be reduced
• RunII goal is dm2-3 GeV/c2

error bars redstat, bluetotal
36
Measuring Mtop
Challenging
LO ME final state

• Leptonjets
• Undetected neutrino
• Px and Py from Et conservation
• 2 solutions for Pz from MWMln
• Leading 4 jets combinatorics
• 12 possible jet-parton assignments
• 6 with 1 b-tag
• 2 with 2 b-tags
• ISR FSR
• Dileptons
• Less statistics
• 2 undetected neutrinos
• Less combinatorics 2 jets

CDF sees
Largest uncertainty Jet Energy Measurement
37
Jet Energy Corrections
Determine true particle, parton E,p from
measured jet E, q
Jargon

• Non-linear response
• Uninstrumented regions
• Response to different particles
• Out of cone E loss
• Spectator interactions
• Underlying event

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?)
38
Color flow must be broken, but where?
top
top
W (color singlet)
b
W (color singlet)
39
and why not this?
top
top
W (color singlet)
b
W (color singlet)
40
top mass outlook
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!
41
ELECTROWEAK fits (as of Moriond 2005)
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)
42
ELECTROWEAK fits (as of Moriond 2005)
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
43
Consistency with the SM

• SM fits
• with a ?2/d.o.f. 15.8/13 and
• a 67 correlation between

??5hadron 0.02769? 0.00035 ?s(mZ) 0.1186 ?
0.0027 mtop 178.2 ? 3.9 GeV log(mHiggs) 2.06
? 0.21
44
Constraints on mHiggs

• MH 12673-48 GeV
• MH ? 280 GeV _at_ 95 C.L.

45
Constraints on mHiggs

• Is there any chance to improve this constraints?
• 
  ?log(mHiggs)2 ?exp2 ?mt2 ??2
  ??s2
• Z asymmetries, sin2?eff 0.222
  0.152 0.122 0.102 0.012
• all high Q2 data 0.212
  0.122 0.132 0.102
  0.042

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!
46
Search for the SM Higgs Boson

• Mass determines Higgs boson profile
• _at_ 114 GeV s 0.1 pb
• BR(H?bb) 74 BR(H?tt)
  7
• SM searches exploited b-tagging extensively

ALEPH 4-Jet candidate Mbb114.3 GeV two b-tags
47
SM Higgs the final word from LEP
Mass limit via CLS CLSB/CLB
Consistency with BG only hypothesis
Mass spectrum after tight selection cuts
Consistency with

• background only 1-CLB 0.09 _at_ 115 GeV
  (1.7s excess)

• signal background CLSB 0.15 _at_ 115 GeV

Observed Limit 114.4 GeV Expected Limit
115.3 GeV
Phy. Lett. B565 (2003) 61
48
Higgs at Tevatron?
Ldt (fb-1)
LEP
Updated in 2003 in the low Higgs mass region
W(Z)H?ln(nn,ll)bb to include VBF ? better
detector understanding ? optimization of analysis
Tevatron
Tevatron will begin sensitivity to LEP Higgs
limit (or signal?) when gt2.5 fb-1 will have been
accumulated it could be quite soon (Moriond
2007?)
49
Higgs at LHC
50
(No Transcript)
51
Signature
CMS note 03 033 ATLAS SN-ATLAS-2003-024 more
on-going
52
H ?WW () ?l ? l ?
NB in this channel, it is easy to determine the
spin of the Higgs!
MC
53
striking now there is aways at least two
channels of which at least one allows
determination of spin of Higgs and, if mHlt160
GeV the ratio of couplings to bosons vs
fermions.
54
Conclusions
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!