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Particles, Mysteries, and Linear Colliders. Jim Brau APSNW 2003 Reed College May 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.

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particles mysteries and linear colliders

Particles,Mysteries,and Linear Colliders

Jim Brau

APSNW 2003

Reed College

May 30, 2003

J. Brau, APS NW, May 30, 2003

particles
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)

J. Brau, APS NW, May 30, 2003

mysteries

selectron

spin = 0

electron spin =1/2

20th Century

Particle Physics

Mysteries
  • We enter the 21st Century with mysteries of monumental significance in particle 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?

J. Brau, APS NW, May 30, 2003

linear colliders

The First Linear Collider

future Linear Collider

SLAC Linear Collider (SLC)

built on existing SLAC linac

Operated 1989-98

500 GeV

- 1 TeV

and beyond

could operate

by 2015

3 KM

25 KM

expanded horizontal scale

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

J. Brau, APS NW, May 30, 2003

electroweak symmetry breaking
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
      • Mg = 0 MW = 80. 4260.034 GeV/c2 MZ = 91.1880.002 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

J. Brau, APS NW, May 30, 2003

electroweak unification

(

)

Massless gauge bosons in symmetry limit

b w-w0 w+

(

)

g

W- W+

Z0

Physical bosons

(

)

f1 f2

Complex spin 0 Higgs doublet

Electroweak symmetry breaking

Electroweak Unification

by the Higgs mechanism

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

tanqW = g’/g

sin2qW=g’2/(g’2+g2)

e Jm(em) Am

e = g sinqW = g’ cosqW

J. Brau, APS NW, May 30, 2003

the higgs boson
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

J. Brau, APS NW, May 30, 2003

standard model fit
Standard Model Fit

+58

-37

  • MH = 91 GeV/c2

LEPEWWG

J. Brau, APS NW, May 30, 2003

indications for a light standard model like higgs
Indications for a Light Standard Model-like Higgs

(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) ~ 2s

J. Brau, APS NW, May 30, 2003

history of anticipated particles
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

Quark1968 - 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

J. Brau, APS NW, May 30, 2003

the search for the higgs boson

Tevatron at Fermilab

    • Proton/anti-proton collisions at Ecm=2000 GeV
    • Collecting data now
      • discovery possible by~2008?

2 km

The Search for the Higgs Boson
  • LHC at CERN
    • Proton/proton collisions at Ecm=14,000 GeV
    • Begins operation ~2007

8.6 km

J. Brau, APS NW, May 30, 2003

establishing standard model higgs
Establishing Standard Model Higgs

precision studies of the Higgs boson will be required

to 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 Higgs

to understand EWSB

The 500 GeV (and beyond) Linear Collider is the tool

needed to complete these precision studies

References: TESLA Technical Design Report

Linear Collider Physics Resource Book for Snowmass 2001

(contain references to many studies)

J. Brau, APS NW, May 30, 2003

some candidate models for electroweak symmetry breaking
Some Candidate Models for Electroweak Symmetry Breaking

Standard Model Higgs

excellent agreement with EW precision measurements

implies MH < 200 GeV (but theoretically ugly - h’archy prob.)

Minimal Supersymmetric Standard Model (MSSM) Higgs

expect Mh< ~135 GeV

light Higgs boson (h) may be very “SM Higgs-like”

with small differences (de-coupling limit)

Non-exotic extended Higgs sector

eg. 2HDM

Strong Coupling Models

New strong interaction

The LC will provide critical data to resolve these possibilities

J. Brau, APS NW, May 30, 2003

the next linear collider
The Next Linear Collider
  • Acceleration of electrons in a circular accelerator is plagued byNature’s resistance to acceleration
    • Synchrotron radiation
    • DE = 4p/3 (e2b3g4 / R) per turn (recall g = E/m, so DE ~ E4/m4)
    • eg. LEP2 DE = 4 GeV Power ~ 20 MW
  • For this reason, at very high energy it is preferable to accelerate electrons in a linear accelerator, rather than a circular accelerator

electrons

positrons

J. Brau, APS NW, May 30, 2003

cost advantage of linear colliders

Optimization R ~ E2 Cost ~c E2

  • Cost (linear) ~ aL, where L ~ E

Circular

Collider

At high energy,

linear collider is

more cost effective

cost

Linear Collider

Energy

Cost Advantage of Linear Colliders

m,E

  • Synchrotron radiation
    • DE ~ (E4 /m4 R)

R

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

J. Brau, APS NW, May 30, 2003

the linear collider

25 KM

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

expanded horizontal scale

Warm X-band version

J. Brau, APS NW, May 30, 2003

the first linear collider
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 the

80’s within the existing

SLAC 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

J. Brau, APS NW, May 30, 2003

the next linear collider1
The “next” Linear Collider

The next Linear Collider proposals include plans to

deliver a few hundred fb-1 of integrated lum. per year

TESLA JLC-C NLC/JLC-X *

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

SuperconductingRoom T Room T

RF cavities structures structures

Ldesign (1034)3.45.80.432.23.4

ECM (GeV)500  800 500 500  1000

Eff. Gradient (MV/m) 23.4  353465

RF freq. (GHz) 1.35.7 11.4

Dtbunch (ns)337  1762.8 1.4

#bunch/train2820  4886 72 190

Beamstrahlung (%) 3.2  4.4 4.6  8.8

There will only be one in the world

ILC-Technical Review Committee

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

J. Brau, APS NW, May 30, 2003

the next linear collider2
The “next” Linear Collider

Standard Package:

e+e-Collisions

Initially at 500 GeV

Electron Polarization  80%

Options:

Energy upgrades to ~ 1.0 -1.5 TeV

Positron Polarization (~ 40 - 60% ?)

Collisions

e-e-and e-Collisions

Giga-Z (precision measurements)

J. Brau, APS NW, May 30, 2003

special advantages of experiments at the linear collider
Special Advantages of Experiments at the Linear Collider

Elementary interactions at known Ecm*

eg. e+e- Z H

Democratic Cross sections

eg. (e+e -ZH) ~ 1/2 (e+e -d d)

Inclusive Trigger

total cross-section

Highly Polarized Electron Beam

~ 80%

Exquisite vertex detection

eg. Rbeampipe ~ 1 cm and hit ~ 3 mm

Calorimetry with Jet Energy Flow

E/E ~ 30-40%/E

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

J. Brau, APS NW, May 30, 2003

linear collider detectors
Linear Collider Detectors

The Linear Collider provides very special experimental

conditions (eg. superb vertexing and jet calorimetry)

Silicon/Tungsten Calorimetry

CCD Vertex Detectors

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

NLC a TESLA

TESLA

NLC

SLD’s VXD3

J. Brau, APS NW, May 30, 2003

example of precision of higgs measurements at the next linear collider
Example of Precision of Higgs Measurements at the Next Linear Collider

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

Mass Measurement MH  60 MeV  5 x 10-4 MH

Total width  H / H  3 %

Particle couplings

tt(needs higher s for 140 GeV,

except through H  gg)

bbgHbb / gHbb  2 %

ccgHcc / gHcc  22.5 %

+- gH / gH    5 %

WW* gHww/ gHww  2 %

ZZgHZZ/ gHZZ  6 %

gg gHgg / gHgg  12.5 %

gg gHgg/ gHgg  10 %

Spin-parity-charge conjugation

establish JPC = 0++

Self-coupling

HHH/ HHH 32 %

(statistics limited)

If Higgs is lighter, precision is often better

J. Brau, APS NW, May 30, 2003

higgs studies the power of simple reactions
Higgs Studies- the Power of Simple Reactions

Higgs recoiling from a Z0 (nothing else)

known CM energy (powerful for unbiassed tagging of Higgs decays) measurement even of invisible decays

  • Tag Zl+ l
  • Select Mrecoil = MHiggs

> 10,000 ZH events/year

for mH = 120 GeV

at 500 GeV

Invisible decays are included

( - some beamstrahlung)

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

J. Brau, APS NW, May 30, 2003

higgs couplings the branching ratios
Higgs Couplings - the Branching Ratios

bbgHbb / gHbb  2 %

ccgHcc / gHcc  22.5 %

+- gH / gH    5 %

WW* gHww/ gHww  2 %

ZZgHZZ/ gHZZ  6 %

gg gHgg / gHgg  12.5 %

gg gHgg/ gHgg  10 %

SM predictions

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.

J. Brau, APS NW, May 30, 2003

higgs spin parity and charge conjugation j pc 0
Higgs Spin Parity and Charge Conjugation (JPC = 0++)

Threshold cross section (e+ e- Z H)for J=0

s ~ b , while for J > 0, generally higher

power of b (assuming n = (-1)J P)

Production angle (q) and Z decay angle in Higgs-strahlung

reveals JP (e+ e- Z H ffH)

JP = 0+ JP = 0-

ds/dcosq sin2q (1 - sin2q )

ds/dcosf sin2f (1 +/- cosf )2 f is angle of the fermion,

relative to the Z direction

of flight, in Z rest frame

LC Physics Resource Book,

Fig 3.23(a)

Also e+e-  e+e-Z

Han, Jiang

TESLA TDR, Fig 2.2.8

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

J. Brau, APS NW, May 30, 2003

is this the standard model higgs
Is This the Standard Model Higgs?

Z vs. W

b vs. c

Arrows at:

MA = 200-400

MA = 400-600

MA = 600-800

MA = 800-1000

HFITTER output

conclusion:

for MA < 600,

likely distinguish

b vs. tau

b vs. W

J. Brau, APS NW, May 30, 2003

TESLA TDR, Fig 2.2.6

supersymmetry

eg. selectron pair

production

e+e- e+e-

 

LC Resource Book,

Fig 4.3

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

J. Brau, APS NW, May 30, 2003

extra dimensions

g

e+

e-

Gn

Our 4-d world (brane)

e+e- + -

e+e-  Gn

LC Resource Book,

Fig 5.17

LC Resource Book,

Fig 5.13

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

J. Brau, APS NW, May 30, 2003

adding value to lhc measurements
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

J. Brau, APS NW, May 30, 2003

political developments
Political Developments
  • 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

Japanese Roadmap Report (2003)

German Science Council (2001)

requests gov’t consent

German 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 . . . . . .

J. Brau, APS NW, May 30, 2003

conclusion
Conclusion

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

J. Brau, APS NW, May 30, 2003