New Views in Particle
Physics
Vemes Rencontres du Vietnam
Conference Summary
Stanley Wojcicki
Stanford University
Hanoi, Vietnam
August 11, 2004
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The Main Themes at the Meeting
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Past and Future of Particle Physics
CP Violation
Electroweak Physics
Neutrino Physics
Heavy Flavor Physics
QCD
New Facilities
Physics in Vietnam
Astrophysics/Cosmology Connection
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Plan of This Talk
• Cannot possibly cover all the material that was presented
• Will focus on few topics that represent the main activities in
the field today
• Because of time limitations had to exclude a number of
important topics
• Gave short shrift to theory, technology, astrophysics
• Hopefully, the talk will be on the level understandable and of
interest to both particle and astrophysics communities
• Start with historical perspective, end with a look at the future
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Particle Physics - The Past
• Particle Physics was born a little over 60 years ago, a child of:
– Cosmic Ray Physics (phenomena)
– Nuclear Physics (methodology)
• Its growth was aided by World War II related developments:
– Acceptance of big science
– Respect for physics as a “useful” science
– Cold war
• Its remarkable evolution was a result of successful interplay of:
– Theory
– Experiment
– Technology (accelerators and detectors)
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How Discoveries Happen?
• Theory motivated (predicted):
– positron, parity violation, neutrino, charm
quark, W-, gluons, neutral currents
• Unexpected experimental:
– muon, strange particles, CP violation, third
generation, neutrino masses, dark energy
• Technology enabled:
– antiproton, two neutrinos, nucleon
substructure, W and Z bosons, top quark
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Then and Now
The first “Barkas and
Rosenfeld wallet card ”
from 1957, the forerunner
of the current PDG
summary.
The latest, 2002 edition
of PDG Review of
Particle Properties,
contains 974 pages.
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Elementary Particles in1957
Our “Playground”
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Quarks
Leptons
Force Carriers
“New” Phenomena
– Via quantum loops
– Through direct observations
Will organize talk around these points
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The Quark Sector
• The quark mass states and flavor states are different
• The are connected by a unitary transformation, VCKM
• The sector can be characterized by 10 measurable
parameters, 6 masses, 3 angles, and 1 phase
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Quark Masses
• Quark masses are very
hierarchical
• The knowledge of heavy quark
masses is needed to extract
CKM matrix elements with
precision and to calculate loop
corrections
• The top quark mass is
especially important:
– it allows one to set limit on Higgs
mass
– its knowledge is needed for
precision tests of EW theory
• Top quark decays before it
hadronizes
• Its many decay modes call for
several different analyses
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Top mass - an example
Multivariate Template Method, 33 Lepton+Jets Events with SVX b-tag
Combined D0 and CDF measurement from Run 1: mtop = 178.0+-4.3GeV
Run 2 goal is uncertainty of 1% (1.5 - 2.0 GeV)
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CKM Matrix
• Consider first absolute
values of VCKM
elements
• Can be determined
from inclusive and
exclusive decay rates
and loop diagrams
• The matrix is almost
diagonal
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CKM Matrix (ctd)
• For only 3 generations, CKM matrix has to be
unitary
• Unitarity is satisfied but not a stringent test because
of diagonal nature of the matrix
• There was a small deviation from unitarity (row 1)
• Recent measurements move Vus upward, giving a
better agreement with unitarity
PDG: 0.2196 (15)
Unitarity: 0.2265 (23)
(8,21)
Hyperons: 0.2250 (27)
K+->p0e+n: 0.2272 (22,7,18)
K0L->pln: 0.2252
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Vub - small element
• Information comes from
charmless B decays
• Small branching ratios is
one experimental
problem
• Difference between B’s
and b quarks is another
– Lattice gauge calculations
– Better new data (CLEO)
– Inclusive/exclusive difference
(3.23 +- .62)
x 10-3
(4.57 +-.61)
x 10-3
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Vtb - Better Direct Measurement?
• Today our information on Vtb comes from
dominance of t->bl+nl over those without b
and is quite poor = 0.94+0.31-0.24
• Single top production proportional to |Vtb|2
• Full Run2 Tevatron data might make
observation possible
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CKM Phase - CP Violation
• CKM matrix unitarity implies that sum of
products over elements of row and column must
vanish - equivalent to a triangle
• 1st and 3rd rows - all sides O(l3) -> large angles
V*tbVud
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CKM Triangle (ctd)
• Closing of a triangle is an important check of
validity of Standard Model
• Different measurements place different constraints
on the triangle with different levels of accuracy:
– First class, uncertainties in 2nd order (B->J/ K0s)
– Second class, uncertainties ~10% but constrained (eK)
– Third class, accuracies are model dependent (B->Kp)
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CP violation - History
• 1964 - CP discovered through observation of decay
K0L->p+p- ; measurement of e
• 1974 - Kobayashi-Maskawa paper, three generations
needed for CP violation in SM
• ~2000 - Determination that e’is not zero, ie existence
of direct CP violation
• ~2000 - initiation of study of CP violation in B decays
with asymmetric B factories at SLAC & KEK
• ~2004 - very strong constraint on SM CKM phase as
responsible for CP violation observed
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Different CP violation mechanisms
• CP violation occurs when different amplitudes, with a relative phase,
contribute to the same final state
• Unlike the K system, the B system has many channels with potential
CP violation with varying level of quality of theoretical predictability.
• The B->J/ K0S is the “golden”channel, A a sin(2b)sin(Dmt)
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The Richness of B Physics
a

b
fKs, ’Ks,
Ksp0…
The ability to investigate all these channels has been made
possible by the excellent performance of the 2 colliders
(285 and 244 fb-1 accumulated so far)
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CP violation in the B system
• One can observe time
dependent asymmetries
by tagging the other B
• The asymmetries occur
on a scale of fraction of a
mm
• The golden B decay
channel, B->J/K, gives
sin2b=0.736+-.049
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Global Unitary Triangle Fit
Excellent agreement
between different
measurements, both
CP violating and CP
conserving
More measurements
to come in the future
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Other CP Results
• Other measurements in the B and K system consistent with the Standard Model
• Only potential anomaly in fKS final state:
– BELLE -> A = -0.96+-.50
– BaBar -> A = +.47+-.34
– Expect similar A as in J/ K0S decay (~0.74)
• Direct CP violation; recent evidence from the
rates for B->Kp decay channels:
– BaBar: A = 0.133 +- .030
– BELLE: A = 0.088 +- .035 ,the B0->K+p- is higher
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CKM Matrix Summary
• The parameters are now measured quite well
• The overall picture is consistent with the
Standard Model expectations
• Regarding CP: “We left the era of hoping for
New Physics alternatives to CKM; we are in
the era of seeking corrections from NP to
CKM” (Y.Nir)
• Now is “the time for theory of quark masses
and CKM elements” (J.Rosner)
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Leptons (mainly neutrinos)
• The last decade has seen a revolution
in neutrino physics
• Contrary to Standard Model picture,
there is good evidence that neutrinos
have masses and do change flavor
• Thus they have a great similarity to
quarks: mass states and flavor states
are related by a unitary matrix.
• CKM matrix -> PMNS matrix
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Neutrino Oscillations
Fraction of I in a
Fraction of b in 1
Change in
phase
Uai*, Ubi, mi2 are constants of nature; L,E experimental parameters
Dm2 and L/E scales
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• To obtain maximum oscillations, we want phase, ie.
(L/E )Dm2, to be around p/2:
• For atmospheric Dm2 (2-3 x 10-3 eV2)
– Atmospheric - E~1 GeV, L~10-104 km
– Accelerator - E~GeV’s -> L~few hundred km
– Reactor - E~MeV’s -> L ~km,
• For solar Dm2 (6-8 x 10-5 eV2)
– Reactor - E~MeV’s -> L~100 km
– Sun - E~MeV’s but mass eigenstate so L~108 km OK
• LSND region - Dm2 (0.1 - 1 eV2)
– Ignore in this summary; being addressed by MiniBooNE
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Atmospheric neutrinos
• Primary cosmic ray protons interact in the atmosphere to
give hadronic showers
• Large fraction of resulting p’s and m’s will decay giving
nm’s and ne’s
• At medium and high energies nm flux will be up/down
symmetric
• But upward going nm’s have longer pathlength
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SuperK Results on nm Rates
No oscillations
Oscillations
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K2K Experiment
Experiment using SuperK and a nm beam from K2K with L=250km
(normalized by area)
No Oscillation
(KS prob: 0.11%)
Best Fit
(KS prob: 52%)
108 events observed
151+-11 expected (no osc)
Best fit parameters:
Maximum mixing
Dm2 = 2.73 x 10-3
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K2K/SuperK Comparison
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SNO Basic Idea
• Use deuterons (heavy water) as target
• This allows three separate measurements:
 ne + d -> e- + p +p gives Fcc = Fe
 nx + d -> nx + p + n gives Fnc = Fe + (Fm + Ft)
 nx + e- -> nx + e- gives Fes = Fe + .154(Fm + Ft)
• Each measurement gives a line in the space
defined by Fe and (Fm + Ft)
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SNO Results Summary
BP04 nSSM = 5.8 (13)
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KamLAND Experiment
• A 1 kt underground liquid scintillator
detector in Japan detecting ne’s from
many reactors about 180 km away
• In 766.3 ton-yr exposure, there are:
– 258 observed events
– 365 +- 24 expected if no oscillations
– 7.5 +- 1.3 background events
• Observed energy spectrum is distorted
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Combined SNO/KamLAND Fit
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Summary of Oscillation Results
The Unknowns:
a) Value of q13
b) Value of d (CP)
c) Mass hierarchy
d) Is q23 = 45o ?
e) Nature of LSND
anomaly
Mass Differences:
Dm12 ~ 8 meV
Dm13 ~ 50 meV
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Nature of neutrinos
• Are neutrinos their own antiparticles, ie Majorana n’s?
• No reason why not. No distinguishing quantum number if
no lepton number conservation
• If so, neutrinoless double beta decay possible
• Probably only practical way to resolve the question
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Experimental Status
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Today a questionable claim to a signal in
Germanium by a subset of Moscow
Heidelberg group; meff=.39eV
Want to reach sensitivity of at least 20
meV
That would allow observable signal if
masses degenerate (ie lowest mass >>
20 meV) or if inverted hierarchy
This will require:
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About 1 ton of right isotope
Good resolution (2b2n suppression)
Low external background
Better knowledge of matrix elements
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Summary of Double b Possibilities
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Lepton number violation in l+• Currently no lepton flavor violation observed in charged
leptons
• Best limit in m-->e- capture: 6 x 10-13
• There are good prospects for improving sensitivity in
the future to 10-16 - 10-18
• That would give sensitivity to new physics:
supersymmetry, heavy neutrinos, leptoquarks…
• Flavor violation in n’s gives negligible effect
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Forces and Force Carriers
• The topics of interest in electroweak and
strong forces are quite different
• In the former we want to test SM predictions
and/or make precise measurements
• In the latter the interesting issues are either
calculational or involve new phenomena
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Direct W Mass Measurements
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Tevatron, leptonic decay - 80.452 (059)
LEP2 - cross section evolution - 80.411 (044)
LEP2 - direct reconstruction - 80.420 (107)
Good agreement
DELPHI
enqq
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Triple Gauge Couplings
• Several Born level diagrams have to be
combined to calculate W+W- pair production in
e+e- collisions
• The correct shape and agreement of W mass
with direct masurements provides validation of
theory
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Radiative corrections
• In comparing results of measurements
with each other (or with theory) it is
essential to include one loop corrections
Oi  fia MZ ), GF , MZ , mtop, MHiggs,as 
• Thus the MW, MZ relationship will be
2

MW  pa 1
2

1 + Dr )
MW 1 
2 
2 GF
 MZ 
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Test of one-loop corrections
• We can compare direct
measurements of top quark
and W masses with those
optained from global
electroweak fit
• There is good agreement
• Relatively light Higgs
appears to be favored
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Potential Problems
• The decade old issue of conflict
between ALR from SLD and
AFB(b) from LEP has not gone
away
• Recent checks of LEP data
found no systematic problems
or independent evidence for
anomalous b couplings
• W->t coupling is somewhat
high
g( m )
 0.997  0.010
g( e)
g(t )
 1.034  0.015
g( e)
g(t )
 1.037  0.014
g( m )
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QCD Topics
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Heavy ions; new state of matter
New narrow states
Parton distribution functions
State of as
“From quarks to particles” issues
– Interpretation of CP asymmetries
– Calculation of CKM matrix elements
– Understanding cross sections, lifetimes
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Why do we need to understand QCD
Heavy Ion Collisions
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• 241 mb-1 of 200 GeV/nucleon data accumulated at
RHIC at BNL
• Unprecedented energy density in collision, many
times the nuclear density
• Allows one to search for and study a new state of
matter - Quark Gluon Plasma, predicted to occur at
T~175 MeV (1 GeV/fm3)
• Is there evidence for such a state - deconfined
quarks and gluons, as in early universe, t < 10-5 sec
• “Little Big Bang” experiment
A sample of results
• Energy density about 30 times
nuclear density
• Particle/antiparticle balance
around y=0
• Transparency in collisions
• Lack of low momenta
• Still not enough data for J/
detailed study
• Jet quenching (high pT
suppression) - gluon radiation in
high color density environment
(predicted by Bjorken in 1976)
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Jet Quenching Evidence
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Potential New Narrow States
• According to the quark model, the observed states
will be composed of either 2 (mesons) or 3
(baryons) quarks
• That restriction limits quantum numbers of
allowable states and the allowable SU(3)
representations (1,8,10)
• Observation of a state with “forbidden” quantum
numbers will indicate more complex combinations
(pentaquarks, quark molecules, etc)
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Experimental Indications
• Recently there has been several
reports of new narrow states
• There have been some
confirmations but also some
contradictory experimental results
• The most interesting of these is a
state with mass around 1540
MeV, with quantum numbers of
K+n
• Such state has been predicted in
1997 as S=1 member of an
antidecuplet; it would be most
likely a pentaquark
Predicted state
Diakonov,Petrov,Polyakov
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Examples of Mass Distributions
“Discovery”
“Confirmation”
 + n -> K+ K- n
The Jury is still out
Negative result
Secondary K interactions
in BELLE
Running of as
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The strong coupling constant, as will have q2 dependence,
known as running. This dependence can be obtained in
a number of ways, eg by looking at gluon radiation as
function of cm energy in e+e- collisions:
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Summary of as measurements
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•
LEPI - as(mZ) = 0.1199
LEPII - as(mZ) = 0.1202
R value in e+e- - as(mZ) = 0.1200
4 jet analysis - as(mZ) = 0.1170
Tau BR (hadrons/leptons) - as(mZ) = 0.1181
Hadronic collisions - experimental precision
equally good; but large theoretical
uncertainties at this time
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Structure Functions
• The range in x and q2 greatly
extended by HERA
• One can make accurate gluon
distribution measurements at
high x at the Tevatron; currently
interpretation limited by
theoretical uncertainties
• Knowledge of parton distribution
functions important for future
searches for new physics at
LHC
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Progress in understanding cross sections
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CP violation and QCD
• Relating experimental values
from CP violation experiments
to fundamental parameters will
require better ability to calculate
QCD effects
• Some of the examples are eK,
eK’, B->Kp asymmetry
• Many of the CP violation effects
in the B system involve
interference effects with (or
between) different penguin
diagrams
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Higgs Situation
Current Situation
8.5 fm-1
4.4 fm-1
Potential Tevatron Sensitivity
MHiggs < 237 GeV (95% CL)
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The Road Ahead of Us
• I will end by attempting to look
into the future
• First I want to say few words
about physics possibilities
• Then I want to make few
general comments about some
aspects of our field
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Where are we today
• A great deal of progress has been achieved over the last 60
years
• The particle physics phenomena are well described by our
Standard Model
• Much work and very precise experiments have confirmed
various features of the SM
• Only neutrino physics has shown verified departures from
Standard Model
• We know that Standard Model is only an effective theory
and deeper theory must exist
• We look to the future to find the answers to what it is
Future (next 10 years)
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Predictions are hard, especially if they are about future (Yogi Berra)
• Electroweak Physics (Tevatron, LHC)
– Existence of Higgs, its mass
– Supersymmetry and its mass scale
– Overall consistency of electroweak parameters
• Neutrino Physics (Accelerator beams, reactors, nuclear physics expts)
– Value of q13 or a better limit
– Resolution of LSND anomaly
– Double beta decay with 100 kg detector
• CP violation (B-factories, LHCb, BTeV)
– Better statistics, better calculations
– Maaybe disagreements with Standard Model
– K0L -> p0 n n
• New Phenomena (Muon and/or n factories)
– mu-e capture
– New surprises
• Astrophysics (IceCube, ANTARES, NESTOR, underground DM detectors)
– Dark matter
– Neutrino astronomy
– High energy cosmic rays
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Higgs at LHC
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Other Physics
Dark matter searches
Optimistic SUSY models tested
NOnA and
T2K q13
sensitivities
Double b decay sensitivity
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Future (10 years after that)
• Electroweak physics (Linear Collider, SLHC)
– Detailed studies of Higgs, its couplings
– Precision mass of SUSY particles
– New phenomena (WLWL scattering)
• New Neutrino Facilities (superbeams, n factories,
beta beams)
– Mass hierarchy
– CP violation
– New phenomena
• Megaton Detector
– Nucleon decay
– Precision neutrino studies
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Electroweak Physics at Linear Collider
Higgs mass
measurement
Top mass measurement from
energy scan (mt=175 GeV)
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The Astrophysics Connection
• The field started out looking up to the
“heavens” and trying to understand its “gifts”,
ie cosmic rays
• We are once again looking to the heavens
and now try to understand “it” from what we
learn on earth
• Astrophysics/cosmology/particle physics
connection may well be one of the most
exciting developments in the field in the last
decade
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Historical Comment
• Particle Physics was in its infancy in
the 1956-1965 decade
• Many key discovery were made then:
parity violation, neutrino, V-A, 2 n’s, CP
violation, SU(3), W• Astrophysics/cosmology are in the
same phase today
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Big Science, Long Time Scales
• Over the last 50 years the field has grown very much in
complexity
• Single purpose experiments, tend now to give way to
programmatic approach with large multipurpose detectors
• One consequence of this is large collaborations: in my first
publication there were 6 authors; there were 79 institutions in
the most recent BABAR publication; 19 authors with last name
of Zhang in last BES publication.
• Another one is long time scales - in MINOS, 10 years from first
collaboration meeting to the present (first accelerator n this
December)
• Needless to say, that presents problems for postdocs and
graduate students.
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The Quest for Higher Energies
• The progress in particle physics has been made possible
in the past by the availability of ever higher energies
• All indications are that the progress in the future will also
require new colliders with ever higher energies
• LHC will open up a new, and hopefully very fruitful, domain
for exploration
• Further ahead, ever increasing size and hence cost of new
facilities (accelerators and detector systems) will make this
more and more difficult
• The challenge in front of us is to make it nevertheless
possible
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Internationalization
• The next big machine will have to be INTERNATIONAL in
true meaning of the word
• This will not be easy (look at ITER) but we must
overcome the challenges if we want to maintain progress
• Our record in bringing in new areas in the world into the
community of particle physicists is quite good - this
Conference is a good example
• Somehow we have to learn from our very good record in
building detectors, and extrapolate them to the
accelerators
• The reward will hopefully be not only progress in particle
physics but also progress in mutual understanding
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Final Words (from Judy Jackson)