J. Brau, APS NW, May 30, 2003 1 Particles, Mysteries, and Linear Colliders Jim Brau APSNW 2003 Reed College May 30, 2003

J. Brau, APS NW, May 30, 20031

Particles,Mysteries,

and Linear Colliders

Jim BrauAPSNW 2003Reed CollegeMay 30, 2003


Particles• Particle Physics left the 20th Century with a

triumphant model of the fundamental particles and interactions - the Standard Model– quarks, leptons, gauge bosons mediating gauge interactions

– thoroughly tested – no confirmed violations*

– * neglecting neutrino mixing

e+e- W+W- (LEP)


Mysteries

• We enter the 21st Century with mysteries of monumental significance in particle physics:

20th CenturyParticle Physics

– Physics behind Electroweak unification?• The top quark mass

– Ultimate unification of the interactions?– Hidden spacetime dimensions?– Supersymmetry? - doubling Nature’s fundamental

particles– Cosmological discoveries?• What is dark matter?• What is dark energy?

electron spin =1/2

selectronspin = 0


Linear Colliders

• The electron-positron Linear Collider is a critical tool in our probe of these secrets of Nature

The First Linear Collider

SLAC Linear Collider (SLC)built on existing SLAC linacOperated 1989-98

3 KM

future Linear Collider

500 GeV - 1 TeV and beyond

could operate by 2015

25 KM

expanded horizontal scale


Electroweak Symmetry Breaking

• One of the major mysteries in particle physics today is the origin of Electroweak Symmetry Breaking

– Weak nuclear force and the electromagnetic force unified

• SU(2) x U(1)Y with massless gauge fields

– Why is this symmetry hidden?• The physical bosons are not all massless

• M = 0 MW = 80. 4260.034 GeV/c2 MZ = 91.1880.002 GeV/c2

– The full understanding of this mystery appears to promise deep understanding of fundamental physics

• the origin of mass• supersymmetry and possibly the origin of dark matter• additional unification (strong force, gravity) and possibly hidden space-

time dimensions


( )Complex spin

0 Higgs doublet

Electroweak Unification

• The massless gauge fields are mixed into the massive gauge bosons

tan W = g’/g

sin2W=g’2/(g’2+g2)

e = g sin W = g’ cos

W

e J(em) A

W W

Z

( ) Physical bosons

Electroweak symmetry breaking

b ( )Massless

gauge bosons in symmetry limit

by the Higgs mechanism


The Higgs Boson• The quantum(a) of the Higgs Mechanism is(are) the

Higgs Boson or Bosons– Minimal model - one complex doublet 4 fields

– 3 “eaten” by W+, W-, Z to give mass– 1 left as physical Higgs

• This spontaneously broken local gauge

theory is renormalizable - t’Hooft (1971)• The Higgs boson properties

– Mass < ~ 800 GeV/c2 (unitarity arguments)– Strength of Higgs coupling increases with mass

• fermions: gffh = mf / v v = 246 GeV

• gauge boson: gwwh = 2 mZ2/v


Standard Model Fit

• MH = 91 GeV/c2

+58-37

LEPEWWG


(SM) Mhiggs < 211 GeV at 95% CL. LEP2 limit Mhiggs > 114.4 GeV. Tevatron discovery reach ~180 GeV

W mass ( 80.426 0.034 MeV) and top mass ( 174.3 5.1 GeV) agree with precision measures and indicate low SM Higgs mass

LEP Higgs search – Maximum Likelihood for Higgs signal at mH = 115.6 GeV with overall significance (4 experiments) ~ 2

Indications for a Light Standard Model-like Higgs


History of Anticipated Particles

Positron 1932 - Dirac theory of the electron

Pi meson 1947 - Yukawa’s theory of strong interaction

Neutrino 1955 - missing energy in beta decay

Quark 1968 - patterns of observed particles

Charmed quark 1974 - absence of flavor changing neutral currents

Bottom quark 1977 - Kobayashi-Maskawa theory of CP violation

W boson 1983 - Weinberg-Salam electroweak theory

Z boson 1984 - “ “Top quark 1997 - Expected once Bottom was discovered

Mass predicted by precision Z0 measurements

Higgs boson ???? - Electroweak theory and experiments


The Search for the Higgs Boson

• LHC at CERN– Proton/proton collisions at

Ecm=14,000 GeV

– Begins operation ~2007

8.6 km

2 km

• Tevatron at Fermilab– Proton/anti-proton

collisions at Ecm=2000 GeV

– Collecting data now• discovery possible by ~2008?


precision studies of the Higgs boson will be requiredto understand Electroweak Symmetry Breaking;

just finding the Higgs is of limited value

We expect the Higgs to be discovered at LHC(or Tevatron) and the measurement of its properties will begin at the LHC

We need to measure the full nature of the Higgsto understand EWSB

The 500 GeV (and beyond) Linear Collider is the toolneeded to complete these precision studies

References: TESLA Technical Design Report Linear Collider Physics Resource Book for Snowmass 2001

(contain references to many studies)

Establishing Standard Model Higgs


Some Candidate Models for Electroweak Symmetry Breaking

Standard Model Higgsexcellent agreement with EW precision measurementsimplies MH < 200 GeV (but theoretically ugly - h’archy prob.)

Minimal Supersymmetric Standard Model (MSSM) Higgsexpect Mh< ~135 GeVlight Higgs boson (h) may be very “SM Higgs-like” with small differences (de-coupling limit)

Non-exotic extended Higgs sectoreg. 2HDM

Strong Coupling ModelsNew strong interaction

The LC will provide critical data to resolve these possibilities


The Next Linear Collider

• Acceleration of electrons in a circular accelerator is plagued by Nature’s resistance to acceleration– Synchrotron radiation– E = 4/3 (e234 / R) per turn (recall = E/m, so E ~ E4/m4)– eg. LEP2 E = 4 GeV Power ~ 20 MW

electrons positrons

• For this reason, at very high energy it is preferable to accelerate electrons in a linear accelerator, rather than a circular accelerator


• Therefore– Cost (circular) ~ a R + b E ~ a R + b (E4 /m4 R)

• Synchrotron radiation– E ~ (E4 /m4 R)

Cost Advantage of Linear Colliders

cost

Energy

CircularCollider

• Optimization R ~ E2 Cost ~ c E2

Linear Collider

– Cost (linear) ~ aL, where L ~ E

At high energy,linear collider ismore cost effective

Rm,E


The Linear Collider

• A plan for a high-energy, high-luminosity, electron-positron collider (international project)– Ecm = 500 - 1000 GeV– Length ~25 km

• Physics Motivation for the LC– Elucidate Electroweak Interaction

• particular symmetry breaking• This includes

– Higgs bosons– supersymmetric particles– extra dimensions

• Construction could begin around 2009 following intensive pre-construction R&D with operation beginning around 2015

Warm X-band version

25 KM

expanded horizontal scale


The First Linear Collider• This concept was demonstrated at SLAC in a linear

collider prototype operating at ~91 GeV (the SLC)

• SLC was built in the80’s within the existingSLAC linear accelerator

• Operated 1989-98– precision Z0 measurements

• ALR = 0.1513 0.0021 (SLD)

asymmetry in Z0 production with L and R electrons

– established Linear Collider concepts


The next Linear Collider proposals include plans todeliver a few hundred fb-1 of integrated lum. per year

TESLA JLC-C NLC/JLC-X *

(DESY-Germany) (Japan) (SLAC/KEK-Japan)

Superconducting Room T Room T RF cavities structures structures

Ldesign (1034) 3.4 5.8 0.43 2.2 3.4

ECM (GeV) 500 800 500 500 1000

Eff. Gradient (MV/m) 23.4 35 34 65

RF freq. (GHz) 1.3 5.7 11.4

tbunch (ns) 337 176 2.8 1.4

#bunch/train 2820 4886 72 190

Beamstrahlung (%) 3.2 4.4 4.6 8.8

* US and Japanese X-band R&D cooperation, but machine parameters may differ

There will only be one in the worldILC-Technical Review Committee

The “next” Linear Collider


Standard Package:e e CollisionsInitially at 500 GeVElectron Polarization 80%

Options:Energy upgrades to 1.0 -1.5 TeVPositron Polarization (~ 40 - 60% ?)Collisionse e and eCollisionsGiga-Z (precision measurements)

The “next” Linear Collider


Elementary interactions at known Ecm*

eg. e+e Z H

Democratic Cross sectionseg. (e+e ZH) 1/2 (e+e d d)

Inclusive Triggertotal cross-section

Highly Polarized Electron Beam ~ 80%

Exquisite vertex detectioneg. Rbeampipe 1 cm and hit 3 m

Calorimetry with Jet Energy Flow E/E 30-40%/E

* beamstrahlung must be dealt with, but it’s manageable

Special Advantages of Experiments at the Linear Collider


NLC a TESLA

Linear Collider Detectors

The Linear Collider provides very special experimentalconditions (eg. superb vertexing and jet calorimetry)

CCD Vertex Detectors Silicon/Tungsten Calorimetry

SLD Lum (1990)Aleph Lum (1993)Opal Lum (1993)

Snowmass - 96 Proceedings NLC Detector - fine gran. Si/W

Now TESLA & NLD have proposed Si/W as central elements in jet flow measurement

SLD’s VXD3

NLC

TESLA


For MH = 140 GeV, 500 fb-1 @ 500 GeV

Mass Measurement MH 60 MeV 5 x 10-4 MH

Total width 3 % Particle couplings

tt needs higher s for 140 GeV, except through H gg)

bb gbb / gbb2 %cc gcc / gcc22.5 % g / g 5 %WW* gww/ gHww2 %ZZ g/ gHZZ6 % gg ggg / ggg12.5 % g / g 10 %

Spin-parity-charge conjugationestablish JPC = 0++

Self-couplingHHH / HHH 32 %(statistics limited)

If Higgs is lighter, precision is often better

Example of Precision of Higgs Measurements at the Next Linear Collider


Higgs recoiling from a Z0 (nothing else)known CM energy (powerful for unbiassed tagging of Higgs

decays) measurement even of invisible decays

•Tag Zl+ l

•Select Mrecoil = MHiggs

500 fb-1 @ 500 GeV, TESLA TDR, Fig 2.1.4

Invisible decays are included

Higgs Studies- the Power of Simple Reactions

> 10,000 ZH events/year for mH = 120 GeV at 500 GeV

( - some beamstrahlung)


Higgs Couplings - the Branching Ratios

Measurement of BR’s is powerful indicator of new physics

e.g. in MSSM, these differ from the SM in a characteristic way.

Higgs BR must agree with MSSM parameters from many other measurements.

bb gbb / gbb2 % cc gcc / gcc22.5 % g / g 5 % WW* gww/ gHww2 % ZZ g/ gHZZ6 % gg ggg / ggg12.5 % g / g 10 %

SM predictions


H or H rules out J=1 and indicates C=+1

Higgs Spin Parity and Charge Conjugation (JPC = 0+

+)

LC Physics Resource Book, Fig 3.23(a)

Threshold cross section ( e+ e Z H) for J=0, while for J > 0, generally higherpower of (assuming n = (-1)J P)

TESLA TDR, Fig 2.2.8

Also ee eeZHan, Jiang

Production angle () and Z decay angle in Higgs-strahlung reveals JP (e+ e Z H ffH)

JP = 0+ JP = 0 d/dcos sin2 (1 - sin2 ) d/dcossin2 (1 +/- cos )2 is angle of the fermion,

relative to the Z direction

of flight, in Z rest frame


TESLA TDR, Fig 2.2.6

Is This the Standard Model Higgs?

Arrows at: MA = 200-400 MA = 400-600 MA = 600-800 MA = 800-1000

HFITTER output

conclusion: for MA < 600, likely distinguish

Z vs. W

b vs. taub vs. W

b vs. c


Supersymmetry

• Supersymmetry– all particles matched by super-partners

• super-partners of fermions are bosons• super-partners of bosons are fermions

– inspired by string theory– high energy cancellation of divergences– could play role in dark matter (stable neutral particle)– many new particles (detailed properties at LC)

Arkani-Hamed, Dimopoulos, Dvali

eg. selectron pair production

e+e- e+e- LC Resource Book, Fig 4.3


Extra Dimensions

• Extra Dimensions– string theory predicts them

– solves hierarchy problem (Mplanck >> MEW) if extra dimensions are large (or why gravity is so weak)

– large extra dimensions would be observable at LC

e+e- + -

LC Resource Book, Fig 5.17

Our 4-d

world

(brane)

e-

e+

Gn

e+e- Gn

LC Resource Book, Fig 5.13


Adding Value to LHC measurements

The Linear Collider will enhance the LHC measurements (“enabling technology”)

How this happens depends on the Physics:

•Add precision to the discoveries of LHC•eg. light higgs measurements

•Measure superpartner masses•SUSY parameters may fall in the tan /MA wedge.•Directly observed strong WW/ZZ resonances at LHC

are understood from asymmetries at Linear Collider•Analyze extra neutral gauge bosons•Giga-Z constraints


In US, HEPAP subpanel endorsed LC as the highest priority future project for the US program (2002)

DOE Off. of Science 20 year Roadmap for new facilities(2003)

• HEP Facilities Committee •LC gets top marks for science and feasibility•Recommended

Political Developments

Japanese Roadmap Report (2003)

German Science Council (2001)

requests gov’t consentGerman Government (2003)

formal statement - supports project- wait for int’l plan

OECD Global Science Forum Report strongly endorses LC project as next facility in Elem. Particle Physics (2002)

Discussions between governmental representatives from countries interested in the LC have been active recently and are continuing . . . . . .


The Linear Collider will be a powerful tool for studying Electroweak Symmetry Breaking and the Higgs Mechanism, as well as the other possible scenarios for TeV physics

Current status of Electroweak Precision measurements strongly suggests that the physics at the LC will be rich.

We can expect these studies to further our knowledge of fundamental physics in unanticipated ways

Conclusion


Documents

J. Brau, APS NW, May 30, 2003 1 Particles, Mysteries, and Linear Colliders Jim Brau APSNW 2003 Reed College May 30, 2003