Future perspective in Elementary Particle Physics - Carlo Rubbia CERN, Geneva, Switzerland Laboratori Nazionali del Gran Sasso, INFN, Assergi ...
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Future perspective in Elementary
Particle Physics
Carlo Rubbia
CERN, Geneva, Switzerland
Laboratori Nazionali del Gran Sasso, INFN, Assergi, Italy
1
A new revival of Astro-particle Physics Nobel Physics 2006 to Mather and Smoot “for work that looks back into the infancy of the Universe and attempts to gain some understanding of the origin of galaxies and stars”. It is based on measurements made with the help of the COBE satellite launched by NASA in 1989. Nobel Physics 2008 to Nambu “for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics” and to Kobayashi and Maskawa “for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature”. Initial operation of the LHC, with the search for Higgs particle and for the possible existence of Supersymmetry A revival of major experiments in space and underground to look for dark matter, neutrinos, gravitational waves and proton decay (diamonds are not for ever). Vienna Presentation, Oct 2008 Slide# : 2
Composition of the present Universe (Nobel Physics 2006)
Ωtot = 1
73% Dark Energy 23% Dark Matter
3.6% Intergalactic Gas
0.4% Stars, etc.
Only about 4 % of the Universe is ordinary, hadronic matter
(inanimate and living) of which we are made of and that we
perceive.
The remaining 96% is invisible and completely unknown.
This is a major experimental result of immense consequence
Vienna Presentation, Oct 2008 Slide# : 3
Visible and invisible phenomena
The earliest visible object in the sky is the observation of
CMB image (WMAP), some 300’000 years after the BigBang,
when radiation and matter started to separate
Power Spectrum Ω = 1!
Ωm = 0.3!
Contrast 1 : 105
All the rest is astronomically invisible since the Universe was
opaque to light. However the Universe was then extremely
uniform and it is now possible to reconstruct experimentally
these phenomena with and without accelerators.
Vienna Presentation, Oct 2008 Slide# : 4
WMAP results Parameter Value Baryon Density Ωbh2 = 0.024 ± 0.001 Matter Density Ωmh2 = 0.14 ± 0.02 Hubble Constant h = 0.72 ± 0.05 Baryon Density/Critical Density Ωb = 0.044 ± 0.004 Matter Density/Critical Density Ωm = 0.27 ± 0.04 Age of the Universe to = 13.7 ± 0.2 Vienna Presentation, Oct 2008 Slide# : 5
Weak lensing observations of cluster merger
Visible plasma (stars)
By now at least four
examples have been seen
Gravitational mass
(lensing)
Clowe, Bradac et al.
The gravitational potential does not trace the plasma
distribution, the dominant baryonic mass component; the
majority of the matter in the system is unseen.
Vienna Presentation, Oct 2008 Slide# : 6
Dark Matter Candidates ?
Despite the impressive amount of •Kaluza-Klein DM inUED
•Kaluza-Klein DM in RS
astrophysical evidence, the exact •Axion
•Axino
nature of Dark Matter is still unknown. •Gravitino
All present evidence is now limited to
•Photino
•SM Neutrino
gravitational effects. The main •Sterile Neutrino
•Sneutrino
question is that if other types of •Light DM
interactions may be also connected to •Little Higgs DM
•Wimpzillas
DM. A key question is the presence of •Q-balls
•Mirror Matter
a electro-weak coupling to ordinary •Champs (charged DM)
matter. •D-matter
•Cryptons
Elementary particle physics provides a •Self-interacting
•Superweakly interacting
number of possible candidates in the •Braneworls DM
•Heavy neutrino
form of long lived, Weakly Interacting •NEUTRALINO
Massive Particles (WIMPs). •Messenger States in GMSB
•Branons
“Popular” bets are, at the moment, the •Chaplygin Gas
•Split SUSY
lightest SUSY particle (the Neutralino) •Primordial Black Holes
and the Axion.
Vienna Presentation, Oct 2008 Slide# : 7
Broken symmetries in the early Universe (Physics 2008) Initially, at the time of the BigBang, matter and anti-matter were probably equally produced. In 1964 Fitch and Cronin found a very tiny phenomenon of a incredibly small CP violation in the K neutral system. It took 35 years before it was detected also in B- decays. In 1967 Sakharov pointed out that CP violation could be the cause of the resulting today’s asymmetry of the Universe. We now know that this is possible only if at least 3 families of quarks co-exist in Nature: without the B and T quarks our Universe could not have existed ! It was only in 1994 that the sixth quark was discovered with the p-pbar collider at Fermilab. This has been experimentally demonstrated by the so-called B-Factories accelerators and the theoretical prediction of this year’s Nobel Prizes that this model passes successfully all checks that physicists have set-up. Vienna Presentation, Oct 2008 Slide# : 8
A few comments about Dark Energy.
Several increasingly accurate Astronomical observations
have strengthened the evidence that today’s Universe is
dominated by an exotic nearly homogeneous energy density
with negative pressure. The vacuum space is not empty: it
contains a huge amount of gravitational energy. The simplest
candidate is a cosmological term in Einstein's field
equations.
The energy density is constant in time, while the matter
energy density decreases as the Universe expands, why are
the two comparable at about the present time, tiny in the
early Universe and very large in the distant future ?
The problem is one of the greatest questions of the
Universe, all along from its introduction in 1917 by Einstein:
It has now become widely clear that we are facing a deep
mystery and that the problem will presumably stay with us
forPresentation,
Vienna alongOcttime
2008 . Slide# : 9
Gravitational waves: coming and how soon?
In spite of the large
investments in LIGO
and VIRGO, no
gravitational event
has been so far
detected.
Some better hope with
the Advanced LIGO
and VIRGO, enhancing
sensitivity between 3
and 10 times present
status.
Third generation cryogenic interferometers, to improve x 100 times the
present sensitivity to the frequencies 1-10 Hz. In Europe the Einstein
Telescope (ET), while similar initiatives are growing in US and Japan.
A completely different frequency range (0.0001-0.1 Hz) will be the LISA
space project supported by ESA and NASA. It will comprise three
satellites flying five million kilometres apart, in an equilateral triangle.
Vienna Presentation, Oct 2008 Slide# : 10The LHC: “the unstoppable collider”. Vienna Presentation, Oct 2008 Slide# : 11
Vienna Presentation, Oct 2008 Slide# : 12
Quantum corrections: the great triumph of QED
In Dirac’s theory a point like spin
1/2 object of mass m has a given
magnetic moment.
The first-order radiative correction
of the electron contributes an
anomalous magnetic moment of α/2π
≈ 0.00116 (Schwinger)
Basic interaction First order correction
with B field photon
[Theory - experiment] is in agreement to:
(-0.5 ±2.1 ) x 10-12 for the electron
(5.4 ± 3.3 ) x 10-10 for the muon
Vienna Presentation, Oct 2008 3rd order corrections Slide# : 13Extremely precise higher
order corrections for the
electromagnetism: Lamb
shift, G-2 of muon and
electron and so on
Most likely also the same
with higher order Experimental observation
renormalizable corrections
of electro-weak interactions
Indirect Determinations of the top mass
Vienna Presentation, Oct 2008 Slide# : 14Will the same be true for the Higgs ?
MH between 114 and ~200 GeV
Prediction of the range for the Higgs mass
Vienna Presentation, Oct 2008 Slide# : 15The so called ”no fail” theorem for LHC ?
Central to the Standard Model is the experimental observation
of the Higgs boson, for which a very strong evidence for a
relatively low mass comes from the remarkable findings of LEP
and of SLAC.
Due to higher order fermion corrections, the mass of an
elementary Higgs, becomes quadratically divergent. This would
shift its physical mass far away, near to the presumed limit of
validity of quantum mechanics.
To “protect” it, we may need an extremely precise graph
cancellation to compensate for the divergence of the fermions.
With a sofar unknown SUSY partner for each and every known
fermion, a symmetric cancellation amongst fermions is becoming
possible. A low predicted Higgs mass tells us that the mass
range of the SUSY partners must be not too far away.
If SUSY does not exist, something else, like for instance
“Technicolor” must exist !!!! ( so theorists think they know)
Vienna Presentation, Oct 2008 Slide# : 16The case of superconductivity
In the old Lindau-Ginzberg theory the phenomenon of
superconductivity was due to the presence of a neutral
scalar particle.
In reality the phenomenon of superconductivity is generated
dynamically by the presence of the so called Cooper pairs,
i.e. the dynamic creation of a scalar by electron pairs.
In the case of the Higgs particle similar alternatives are
conceivable.
If Higgs is elementary, the super-symmetric cancellation
is highly probable.
If Higgs is the complex resultant for instance of fermions
or other combinations there no reason to justify the
presence of such huge cancellation.
Even if a Higgs particle is detected, there is no need of “no
-fail theorem” unless one can prove that Higgs is
“elementary”.
Vienna Presentation, Oct 2008 Slide# : 17Running coupling constants
LEP: running coupling constants
Running coupling constants α1-1(Q)
are modified above SUSY Strong
With SUSY
threshold, and the three α2-1(Q)
main interactions converge E.M.
to a common Grand Unified Without SUSY
Theory at about 1016 GeV
α3-1(Q)
but provided that SUSY is Weak
there at a not too high
masses
Proton decay ?
A discovery of a “low mass” elementary Higgs may become an
important hint to the existence of an extremely rich realm of
new physics, a real blessing for LHC.
A doubling of the number of elementary particles, is a result
of gigantic magnitude.
Vienna Presentation, Oct 2008 Slide# : 18LHC as sources of SUSY
The experimental signature of a SUSY type particle is
generally very characteristic and it deeply affects the
number and the kinematical configuration of large p⊥ events.
2 leptons p⊥>15 GeV+ E⊥miss> 100 GeV
mo = 200 GeV
m1/2 = 160 GeV
tgβ = 2
Ao = 0
µSUSY as the source of non-baryonic matter ? The relation between dark matter and SUSY matter is far from being immediate: however the fact that such SUSY particles may also eventually account for the non baryonic dark matter is therefore either a big coincidence or a big hint. However in order to be also the origin of dark mass, the lowest lying neutral SUSY particle must be able to survive the 13.7 billion years of the Universe The lifetime of an otherwise fully “permitted” SUSY particle decay is typically ≈10-18 sec ! We need to postulate some strictly conserved quantum number (R-symmetry) capable of an almost absolute conservation, with a forbidness factor well in excess of 4x10+17/ 10-18 =4x1035 !!! Vienna Presentation, Oct 2008 Slide# : 20
Predictions of relic Susy/WIMP
WIMP
Target Atom
(mass MA)
β ≈ 10-3
WIMP
Recoil
Tmax ≈ 2 MAc2β2
10-46 cm2
The “ultimate” WIMP
detector requires some
10-30 active tons, a very
strong rejection of
cosmic neutron
backgrounds and a vast
international investment.
Typical recoil threshold for elastic nuclear recoils > 30 keV
Vienna Presentation, Oct 2008 Slide# : 21Competition
DAMA/LIBRA
NaIAD CRESST II WARP
EDELWEISS II CUORICINO
ZEPLIN I Germany
UK
ZEPLIN III France USA
ZEPLIN II
HDMS/Genino
DRIFT I Bubble Russia
Chamber Japan
PICASSO
XMASS (DM) LiF
USA
CDMS II Canada ELEGANTS V & VI
IGEX
Spain
XENON
MAJORANA (DM)
ANAIS ROSEBUD
ArDM
Vienna Presentation, Oct 2008 Slide# : 22PAMELA space experiment Current measurements of the positron cosmic rays exhibit a bump around 10 GeV which is still hardly explained by standard secondary astrophysical processes, i.e. spallation of cosmic rays off the interstellar gas. Many scenarios have been invoked as potential solutions to this excess, among them being some additional primary Result Embargoed by Nature, positrons originating awaiting for publication from dark matter annihilation in the Galaxy. Vienna Presentation, Oct 2008 Slide# : 23
Proton decay Proton (nucleon) decay should occur but at an insignificant rate at the Planck mass. Grand Unified gauge Theories predict a much larger decay rates, but still smaller than the present limits of about 1034 y. Running coupling constants might converge according to LEP extrapolations and SUSY to a necessary common value: it would predict Higgs dominance converging to the heaviest quark and lepton, hence dominance of exotic channels, like K+ντ, K+µ, etc. An adequate sensitivity improvement would require detectors of extremely large sensitive mass and of remarkable quality in order to identify the signal over the many other backgrounds. The detector should be combined with a long baseline accelerator experiment to study CP-violation in the neutrino oscillation. Vienna Presentation, Oct 2008 Slide# : 24
Proton decay: sensitivity WITH LAr vs exposure
65 cm
p→K+ν
p→e+π0 p → K+ νe
MC
≈ 1 ev/Mton y
“Single” event detection capability
e+ 1035
K+
10 34
6 × 1034 nucleons (100 kton) ⇒ µ+
τp /Br > 2 1034 years × T(yr) × ε @ 90 CL Data
Vienna Presentation, Oct 2008
T600: Run 939 Event 46 Slide# : 25Nucleon decay searches
Icarus Icarus
p→e+ π0
Icarus
p→νK+ n→νK0
Channel Eff(%) SK eff(%) ICARUS
p →e+ πο 43 45
p →k+ νο 6.5 97
If SUSY dominated, proton decay
prefers heaviest quark & lepton
SuperK
Vienna Presentation, Oct 2008 Slide# : 26Neutrinos
Are neutrino a simple carbon copy repetition of quarks?
Masses were once taken as zeros “by ignorance”
Oscillations are an extension of KM-C mixing
Matter oscillations are due to neutral currents
But this is’t all ! Important discoveries are ahead:
CP violation in the lepton sector
Majorana or Dirac ν’s;ν-less β-decay,ν-masses
Sterile neutrino and other “surprises”
Right handed neutrinos and see-saw mechanisms
from Nature 455,156
Very large and expensive experiments both without and with
new long baseline accelerators (β- and νµ- beams) are required.
Of course the astronomical importance of neutrinos from space
is immense so is their role in the cosmic evolution.
Vienna Presentation, Oct 2008 Slide# : 27CP violation of the leptonic sector Crucial but very difficult experiments are needed in order to complete the phenomenology of the neutrino sector. Such a wide programme demands new accelerated neutrino beams with well identified initial species, long decay distances and novel technologies. Cosmological arguments have suggested that in order to ensure dominance of matter over anti-matter, the CP violation of the quark sector must be extended to the leptonic sector, with of a new phase δ. To this effect, all the three neutrino mixing angles must have non zero values, including the presently unknown θ13, for which the CHOOZ experiment has given only the upper limit sin2(2 θ13) < 0.14 (0.18). Provided θ13≠0, the leptonic CP violating phase δ becomes accessible with sufficient statistics and in absence of backgrounds. Conventional horns and high energy proton beams in MWatt region may be capable of pushing the sensitivity up to sin2(2 θ13) > 0.02, the limit due to the tiny natural νe contamination of the horn driven νµ beam. Entirely new methods are required if sin2(2 θ13) would turn out to have an even smaller value. Vienna Presentation, Oct 2008 Slide# : 28
Double Chooz in France, Daya Bay in China and so on
Θ13
0.28 km 1.05 km
Suekane DBD07
Near Far
Vienna Presentation, Oct 2008 Slide# : 29Future options
Starting either from an initial high purity νµ or νe sin2(2 θ13)=2.5 10-3
source, the key physical process is the
observation of tiny O (≈ 10-3) oscillation mixing
between νµ↔ νe related to θ13.
Two advanced methods both based on cooling
technologies are being considered:
1) Muon beams, following a method by Skrinsky
4 MW Proton driver: production target
Target, capture channel: Create π, decay to µ
Cooling:Reduce transverse emittance (1.7 µ/p)
Muon acceleration: ~130 MeV to 20-50 GeV
Decay ring(s): Store for ~500 turn;Long straights π − → µ− + ν µ Lepton sign
identification
2) Beta-beams: Zucchelli has proposed a neutrino µ− → e − + ν µ + ν e required !
beam from the β-decay of a short lived nucleus
followed by acceleration and decay in a dedicated ν µ → µ −
[ O (1) ] ν µ → e −
O( [
10 −3
) ]
high energy storage ring. It was originally based ν → e + O 1 ν → µ + O 10−3
on He-6 and Ne-19(?), produced by many MW
e [ ( )] e [
( ) ]
Aspallation source/reactor.
novel method based on ion cooling of Li-8 and B-8 is here described
Vienna Presentation, Oct 2008 Slide# : 30
€Beta beams: A = 8: the Li/Be/B triplet Isospin triplet with A = 8 (Li-8, Be-8, B-8), decaying to the fundamental level of Be-8. In absence of Coulomb corrections, the three states would have identical nucleons configurations because of charge independence. The actual experimental values of the beta decaying doublet Li-8 with = 0.84 s and B-8 with τ 1/2 = 0.77 s are respectively Q* = 16.005 MeV and Q* = 16.957 MeV. Vienna Presentation, Oct 2008 Slide# : 31
Detection rates The detector distance is 730 km, corresponding to the Soudan from LNAL or LNGS from CERN. We have considered a LAr detector of 50 kton (35’000 m3) if sin2(2 θ13) > 2.7 x 10-3, doubled to 100 kton for an ultimate experimental sensitivity as small as ≈ 6 x 10-4. Rates before cuts refer to a 5 years exposure with 200 d/y. Vienna Presentation, Oct 2008 Slide# : 32
High Energy Colliders: ILC (Ecm up to ~ 500 GeV) Vienna Presentation, Oct 2008 Slide# : 33
High Energy Colliders: CLIC (Ecm up to ~ 3TeV)
CLIC TUNNEL
• High acceleration gradient: ~ 100 MV/m CROSS-SECTION
“Compact” collider – total length < 50 km at 3 TeV
Normal conducting acceleration structures at high
frequency
Novel Two-Beam Acceleration Scheme
Cost effective, reliable, efficient
Simple tunnel, no active elements
Modular, easy energy upgrade in stages
QUAD
QUAD
POWER EXTRACTION
STRUCTURE
4.5 m diameter
ACCELERATING Drive beam - 95 A, 300 ns
STRUCTURES
12 GHz – 140 MW
from 2.4 GeV to 240 MeV
Main beam – 1 A, 200 ns
from 9 GeV to 1.5 TeV BPM
Vienna Presentation, Oct 2008 Slide# : 34Mainmain
New CLIC CLICparameters
parameters
Center-of-mass energy 3 TeV
Peak Luminosity 7·1034 cm-2 s-1
Peak luminosity (in 1% of energy) 2·1034 cm-2 s-1
Repetition rate 50 Hz
Loaded accelerating gradient 100 MV/m
Main linac RF frequency 12 GHz
Overall two-linac length 41.7 km
Bunch charge 4·109
Beam pulse length 200 ns
Average current in pulse 1A
Hor./vert. normalized emittance 660 / 20 nm rad
Hor./vert. IP beam size bef. pinch 53 / ~1 nm
Total site length 48.25 km
Total power consumption 390 MW
Vienna Presentation, Oct 2008 Slide# : 35Short, “political” touch
The last decades have witnessed a profound change in the
experimental Elementary Particle Physics:
From world-wide competition to world-wide collaboration
Key element in this has been the role of CERN and of the LHC,
in which teams coming from all countries are joining in
conditions of total equality to a competitive participation.
In the future it is expected that such globalization of the
scientific participation will be further pursued, characterized
by a growing complementarity amongst at least the largest
installations world-wide.
No single country is capable of holding alone the burden of
curiosity driven scientific programmes of such a magnitude.
But there is an additional “value plus” in combining strengths
internationally, still maintaining the competition in the field.
We should prime “who did it” with respect to “where he did it”
Vienna Presentation, Oct 2008 Slide# : 36Conclusions
Frank Wilczek (Physics, 2004) has said that “only the LHC stands a real
chance of breaking the existing paradigm” and Nature has named it “the
unstoppable collider”.
I have been for decades one of the most strenuous supporters of the LHC.
However I believe that we cannot predict where the next major
discoveries/surprises may come from. Ultimately the LHC and the other
complementary experiments are competing together, like David and
Goliath.
The discovery of SUSY may be a real “bonanza” for the present (and
future) colliders but its relation to the now credible dark matter is by no
mean obvious or granted.
Likewise the neutrino sector may reserve for us incredible new discoveries.
Proton decay will never be observable with accelerators. Gravitational
waves are about to be discovered in the laboratory and in space.
Events from the sky and underground have an immense role to play in the
future. Now that LHC is on the verge of operation, European physics and
CERN have the obligation of concentrating some of the efforts and
funding also on a broader range of these other activities in the framework
of a wider
Vienna collaborative
Presentation, Oct 2008 effort with the rest of the world. Slide# : 37Thank you ! Vienna Presentation, Oct 2008 Slide# : 38
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