Electroweak Symmetry Breaking: experimental investigations

Alain Blondel WIN 05 June 2005

Electroweak Symmetry Breaking: experimental investigations

1. The question2. The tools : accelerators and detectors3. The status from precision electroweak measurements4. The status of direct searches5. The near future (Tevatron, LHC)6. The Susy factory: ILC7. The Higgs factory: muon collider8. Conclusions


The Question: Why do W’s have mass (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 w to give Z and

mW+=mW

-=mW0=mZcosw

mThis important test of the model (or is it?) is verified with high precisionspeed of em radiation is independent of wavelengthresidual energy carriedby vector potential (Arhonov-Boehm effect)

Magneto hydrodynamics of solar plasma m< 6 10 –17eV(new, PDG 2004)

and of course is respected by em gauge invariance


L E P

ran around Z peak Z mass and widththen up to 209 GeVcollected 20MZ,& 80 kW


Slac Linear Collider

ran at Z peak (500kZ)observed first Z event polarized beam (~77%)very small vertex excellent b, c tag

92 GeV polarized e+e- collider


TeVatron

p. 20

CDF detector

New

Old

Partiallynew

Forward muonEndplugcalorimeter

Silicon and drift chamber trackers

Central muonCentral calorimeters

Solenoid

Front endTriggerDAQOffline

TOF

WZ event in D0

2 TeV proton-antiproton collider

1000


These are real magnets now!

LHC


PROGRAMME

measure Z and W masses

measure W

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 QED

= mtop/mZ)2

- log mh/mZ)2

at first order:

= cos2w log mh/mZ)2

b=20/13 mtop/mZ)2

complete formulae at 2d orderincluding strong corrections are available in fitting codes

e.g. ZFITTER

EWRCs


Parameters of the SM: (M(Mzz22))

Using the latest experimental Using the latest experimental data from BESII: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 These data has also confirm the

validity validity of extending the use of of extending the use of perturbative perturbative

QCDQCD in the calculation of in the calculation of 55

hadronhadron . . The most precise of these theory-The most precise of these theory-

driven driven calculations gives,calculations gives,

5hadron = 0.02747 0.00012

(Troconiz and Yndurain 2001))

hep-ph/0312250

is not anymore the limiting is not anymore the limiting factor in the SM fits… factor in the SM fits…

thanks BES !!!thanks BES !!!

using CMD-2 latest data

using CMD-2 and KLOE latest data, seem to cancel out


Parameters of the SM: (~M(~M22))

e+ e-

π- π+

γ

τ- ν

π- π0

W

(11658472.07± 0.11)10-

10

(692.4 to 694.4 ± 7)10-10 [e+e- -based 04]

(12.0 ± 3.5)10-10 [Melnikov & Vainshtein 03]


(g-2)

New - data collected in 2001, confirms previous measurements using +

(a(a++ - 11659000) - 11659000) x 10x 10-10-10 = = 203 ± (6 stat. 203 ± (6 stat. 5 syst.) 5 syst.)

(a(a-- - 11659000) x 10 - 11659000) x 10-10-10 = = 214 ± (6 stat. 214 ± (6 stat. 5 syst.) 5 syst.)

(a(a - 11659000)exp x 10 - 11659000)exp x 10-10-10 = = 208 ± (5 stat. 208 ± (5 stat. 4 syst.) 4 syst.)

(a(a - 11659000)th x 10 - 11659000)th x 10-10-10 = = 183 ± 7183 ± 7 [e+e-] DEHZ04[e+e-] DEHZ04

including including KLOEKLOE

2.72.7 from prediction from prediction

(was (was 1.91.9 before inclusion of 2001 data) before inclusion of 2001 data)

(0.7 ppm)

BNL00

BNL01

(0.7 ppm)


luminosity measurement to 6 10-4!

LEP: N = 2.9841 0.0083

inv (new) < 2.1 MeV

NB this is 2low


energy resolution (resonant depolarization)+-200 keV! variations due to tides, trains, rain,etc..

mZ= 91187.5 +-2.1 MeV


Note relative insensitivity of z to Higgs mass. Was the dominant new factor in 1994 when results from the 1993 scan (with res. dep. on each point)

= 2494.8 +- 2.5 MeV

mtop = 174 +- 12 +- 18 GeVBolek Pietrzyk Moriond March 1994 vs mtop = 174 +- 16 GeV

CDF may 1994

!


Measuring sin2Weff (mZ)

sin2Weff ¼ (1- gV/gA)

gV = gL + gR

gA = gL - gR

Alain Blondel WIN 05 June 2005 WZ event in D0

ALEPH evts

e+e- qq

e+e- q1 q2 q3 q4

W mass



SM: combination of and yields mW and sin2Weff(Q2)

experiment expresses result in terms of sin2W = 1 – m2W/m2

Z

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?

NUTeV

R R


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 SINGLETSwhich in principle shouldnt talk to each other

Is this true? It has been suspected thatthere may be some O(s

2) correction leading for example to

1. Bose Einstein correlations between (BEB)the two systems2. Color reconnection effects 3. there has been some progress in trying to see such effects in data.

This can affect WW 4q mass by > 100 MeV


four quark channel is severely affeced by hadronization uncertainties!


BEC in W+W- events

BEC effects experimentally established in Z jets at LEP1Inter-W BEC? Analyses performed in 4 LEP experiments to search/limit themObservable: distance in p-space between pairs of charged pions:

Q2ij=-(pi-pj)2

Inter-W BEC correlations disfavoured Limit on systematic: MW ~ 15 MeV

L3

0 1 Q(GeV)

LEPWW/FSI/2002-02

fraction of model seen


The particle flow analysis

CR models predict a modified particle flow in W+W- events:

CR:

No CR:

W-

W+

W-

W+

Observable: ratio of particle flow between the inter and intra-W regions:

(A + B) / (C + D)

A

B

C

D

• Data

- SK1 (extreme parameter)- Jetset


Results from particle flow

CR Prob

For SK1:Preferred value of the parameter

(0.5 + 0.2 - 0.3)

corresponds to MW ~ 100 MeV!!

‘Asymmetry’ from experiments combined in a 2


Reduction of MW

MW (MeV)

Model Standard Cone R=0.5 rad

SK1, kI~2 100 40

Herwig 35 10

AR 2 50 20

Rathsman

40 15

Good reduction factors are obtained for all available models

Example: Cone (R=0.5 rad), with a statistical loss of ~ 25%:

idea is to reduce effects by excluding particles situated outside angular cones around the jets.

Some resolution is lost but systematic error is reduced.

Cone radius (rad)

ALEPH

SK1 k=2.13

MW (

GeV

)MW


mW from direct reconstruction

Non-4q 4q

mW = 22 ± 43 MeV

Results in CERN-EP/2003-091, LEPEWWG/2003-02still with standard jet algorithms


errors expected for summer ‘05 conferences:

errors as of summer 2003

lots of hard work, and improved understanding … but diminishing returns

there will also be an improvement on the beam energy error due to usage of LEP spectrometer.


Physics processes at LEP2

~100k evts

~10k evts

~1k evts

~100 evts


W-pair cross sections

exchange t channel ONLY


exchange and WW vertex


Clear proof of SU(2)xU(1) gauge couplings !agreement to 0.6+-0.9%

NB this is really non trivial. W3= Z cosW + B sinW


LEPII (and LC) energy calibration

idea: use e+e- Z to measure Ebeam given that mZ is so well known

Alas, beam polarization vanishes at LEP above E=65 GeV res. dep. will not work for linear collider

2GeV/cZm

ALEPH


MeV 54Total

MeV 24anglePolar

MeV 16 tracksForward

MeV 12stat MC

MeV 16background

MeV 7ISR

MeV 20methodFit

MeV 30rsCalorimete

MeV 19ionFragmentat

effect mSource 12

Systematic uncertainties

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 statehadrons (incl. neutrons, 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


TOP mass measurementCDF, 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.


Top Mass determined using maximum likelihood

D0 Run I - Top Mass Analysis Using ME Method

Mtop = 180.1 ± 3.6 (stat) ± 3.9 (sys) GeV/c2

Nature 429, 638-642 (2004)

Comparable precision to all previous measurements combined(some luck involved!)

Expected 5.4 GeVObserved 3.6 GeV

• 91 candidate tt events • 77 with exactly 4 jets selected• 22 passing cut on background

probability (Pbkg < 10-11)

Jet energy scale syst: 3.3 GeV/c2

Expected statistical errorpseudo-experiments


Mtop Measurements

• Combined RunI mass: mt=178.0 ± 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 m~2-3 GeV/c2

error bars: red=stat, blue=total


Measuring Mtop

LO ME final state:

CDF sees:

•Lepton+jets•Undetected neutrino

•Px and Py from Et conservation•2 solutions for Pz from MW=Ml

•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

Challenging:

Largest uncertainty: Jet Energy Measurement


Jet Energy Corrections

Determine true “particle”, “parton” E,p from measured jet E,

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

Jargon:

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)b

Color flow must be broken, but where?

top

top


W (color singlet)

W (color singlet)b

and why not this?

toptop


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!

top mass outlook


ELECTROWEAK fits (as of Moriond 2005)

this in fact is a verification of the validity of the relation

mW = mZ cosW at tree level.

(up to corrections due to mHiggs

and any new physics cancellation)


ELECTROWEAK fits (as of Moriond 2005)

these plots show the fact that sin2eff

W i the most sensitive estimator of the Higgs mass,

but the limitation will soon come from the top mass meast


Consistency with the SM

SM fits:SM fits:

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 Ab

FB with 2.4. It pulls for a large mHiggs in opposition to l, mW and leptonic asymmetries.

55hadronhadron = 0.02769 = 0.02769

0.000350.00035

ss(m(mZZ) = 0.1186 ) = 0.1186 0.00270.0027

mmtoptop = 178.2 = 178.2 3.9 GeV 3.9 GeV

log(mlog(mHiggsHiggs) = 2.06 ) = 2.06

0.210.21


Constraints on mHiggs

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

Constraints on mHiggs

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!

[0.03] if theory-driven


Search for the SM Higgs BosonMass determines Higgs boson profile:

@ 114 GeV : ~ 0.1 pb

BR(Hbb) ~ 74% BR(H) ~ 7%

SM searches exploited b-tagging extensively

ALEPH 4-Jet candidate

Mbb=114.3 GeV

two b-tags


SM Higgs: the final word from LEP

Observed Limit: 114.4 GeV Expected Limit: 115.3 GeV

Phy. Lett. B565 (2003) 61

Mass limit via

CLS = CLS+B/CLB

Mass spectrum after tight selection cuts

signal + background: CLS+B= 0.15 @ 115 GeV

Consistency with BG only hypothesis:

Consistency with:

background only: 1-CLB = 0.09 @ 115 GeV (1.7excess)


Higgs at Tevatron?

Updated in 2003 in the low Higgs mass region

W(Z)Hl(,ll)bb to include VBF

better detector understanding

optimization of analysis

LEP

Tevatron

Ldt (fb-

1)

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?)


Higgs at LHC



Signature:

CMS note 03 033 ATLAS SN-ATLAS-2003-024more on-going


H →WW (*) →ℓ ν ℓ ν

MC

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.


ConclusionsThe 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 VBFwe 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!

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Electroweak Symmetry Breaking: experimental investigations