the physics of the lhc
DESCRIPTION
The Physics of the LHC. The Compact Muon Solenoid at the Large Hadron Collider Dan Green Fermilab US CMS Project Manager. Outline. Why do we go to the energy frontier? What is the CMS collaboration? - PowerPoint PPT PresentationTRANSCRIPT
Slide Title Goes Here*
The Compact Muon Solenoid at the Large Hadron Collider
Dan Green
*
What is the CMS collaboration?
What is the Standard Model? How do we detect the fundamental particles contained in the SM?
The Higgs boson is the missing object in the SM “periodic table”. What is the CMS strategy to discover it?
What might we find at CMS in addition to the Higgs?
US CMS Colloquium: Dec., 2000
*
European Center for Nuclear Research (CERN)
Large
Hadron
Collider
(LHC)
*
High Energy Physics-”Natural Units”
Dimensions are taken to be energy in HEP. Momentum and mass are given the dimensions of energy, pc, mc2. The basic energy unit is the electron Volt, the energy gained when an electron falls through a potential of 1 Volt = 1.6 x 10 -19 Joule.
The connection between energy and time, position and momentum is supplied by Planck's constant, , where 1 fm = 10-13 cm. Thus, inverse length and inverse time have the units of energy. The Heisenberg uncertainty relation is
Charge and spin are "quantized"; they only take discrete values, e or . Fermions have spin 1/2, 3/2 ..., while bosons have spin 0,1,.… The statistics obeyed by fermions and bosons differs profoundly. Bosons can occupy the same quantum state - e.g. superconductors, laser. Fermions cannot (Pauli Exclusion Principle) - e.g. the shell structure of atoms.
US CMS Colloquium: Dec., 2000
*
Size and the Energy of the Probe Particle
In order to "see" an object of size r one must use "light" with a wavelength l < r. Thus, visible light with l ~ 3000 A ( 1 A = 10-8 cm, ~ size of an atom) can resolve bacteria. Visible light comes from atomic transitions with ~ eV energies ( = 2000 eV*A).
To resolve a virus, the electron microscope with keV energies was developed, leading to an increase of ~ 1000 in resolving power.
To resolve the nucleus, 105 time smaller than the atom one needs probes in the GeV (109 eV) range. The size of a proton is ~ 1 fm = 10-13 cm.
The large Hadron Collider (LHC) at the CERN will explore Nature at the TeV scale or down to distances ~ 0.0002 fm.
US CMS Colloquium: Dec., 2000
*
Higgs boson
t quark
b quark
s quark
*
*
US CMS Colloquium: Dec., 2000
*
CMS Collaboration
CMS Collaboration
*
“Particle Physics” in the 20th Century
The e- was discovered by Thompson ~ 1900. The nucleus was discovered by Rutherford in ~ 1920. The e+, the first antiparticle, was found in ~ 1930. The m , indicating a second “generation”, was discovered in ~ 1936.
There was an explosion of baryons and mesons discovered in the 1950s and 1960s. They were classified in a "periodic table" using the SU(3) symmetry group, whose physical realization was point like, strongly interacting, fractionally charged "quarks". Direct evidence for quarks and gluons came in the early 1970s.
The exposition of the 3 generations of quarks and leptons is only just, 1996, completed. In the mid 1980s the unification of the weak and electromagnetic force was confirmed by the W and Z discoveries.
The LHC, starting in 2005, will be THE tool to explore the origin of the breaking of the electroweak symmetry (Higgs field?) and the origin of mass itself.
US CMS Colloquium: Dec., 2000
*
Electro - Weak Unification
The weak interactions are responsible for nuclear beta decay. The observed rates are slow, indicating weak effective coupling. The decays of the nuclei, n, and m are parametrized as an effective 4 fermion interaction with coupling, G ~ 10-5 GeV-2, Gm ~ G2Mm5.
The weak SU(2) gauge bosons, W+ Zo W- , acquire a mass by interacting with the "Higgs boson vacuum expectation value" of the field, while the U(1) photon, g , remains massless. MW ~ gW<f>
The SU(2) and U(1) couplings are "unified" in that e = gWsin(qW). The parameter qW can be measured by studying the scattering of n + p, since this is a purely weak interaction process.
The coupling gW can be connected to G by noting that the 4 fermion Feynman diagram can be related to the effective 4 fermion interaction by the Feynman "propagator", G ~ gW2/MW2. Thus, from G and sin(qW) one can predict MW. The result, MW ~ 80 GeV was confirmed at CERN in the pp collider. The vacuum Higgs field has <f> ~ 250 GeV.
US CMS Colloquium: Dec., 2000
*
Matter consists of half integral spin fermions. The strongly interacting fermions are called quarks. The fermions with electroweak interactions are called leptons. The uncharged leptons are called neutrinos.
The forces are carried by integral spin bosons. The strong force is carried by 8 gluons (g), the electromagnetic force by the photon (), and the weak interaction by the W+ Zo and W-. The g and are massless, while the W and Z have ~ 80, 91 GeV mass.
J = 1
*
Tracker
ECAL
HCAL
Magnet
Muon
*
(ECAL shower, no track)
(ionization only)
q = u, d, s Jet (narrow) in ECAL+HCAL
q = c, b Jet (narrow) + Decay Vertex
t --> W +b W + b
e Et missing in ECAL+HCAL
-->l + +l Et missing + charged lepton
W --> l + l Et missing + charged lepton,
Et~M/2
--> l + l Et missing in ECAL+HCAL
US CMS Colloquium: Dec., 2000
*
Dijet Events at the Tevatron
The scattering of quarks inside the proton leads to a "jet" of particles traveling in the direction of, and taking the momentum of, the parent quark. Since there is no initial state Pt, the 2 quarks in the final state are "back to back" in azimuth.
US CMS Colloquium: Dec., 2000
*
A FNAL Collider (D0) Event
The D0 detector has 3 main detector systems; ionization tracking,liquid argon calorimetry ( EM , e , and HAD , jets ,), and magnetized steel + ionization tracker muon , m , detection/identification. This event has jets, a muon, an electron and missing energy , n.
US CMS Colloquium: Dec., 2000
*
A FNAL Collider (CDF) Event
The CDF detector has 3 main detector systems; tracking - Si + ionization in a magnetic field, scintillator sampling calorimetry, (EM - e, g and HAD - h), and ionization tracking for muon measurements. Missing energy indicates n in the final state.Si vertex detectors allow one to identify b and c quarks in the event.
US CMS Colloquium: Dec., 2000
*
W --> e + at the Tevatron
The W gauge bosons can decay into quark-antiquarks, e.g. u + d, or into lepton pairs, e + ne, m + nm, t+ nt. There can also be radiation associated with the W, gluons which evolve into jets.
US CMS Colloquium: Dec., 2000
*
Z --> e + e and + Events at the Tevatron
The e appear in the EM and not the HAD compartment of the calorimetry, while the m penetrate thick material.
US CMS Colloquium: Dec., 2000
*
The Generation of Mass by the Higgs Mechanism
The vacuum expectation value of the Higgs field, <f>, gives mass to the W and Z gauge bosons, MW ~ gW<f>. Thus the Higgs field acts somewhat like the "ether". Similarly the fermions gain a mass by Yukawa interactions with the Higgs field, mf = gf<f>. Although the couplings are not predicted, the Higgs field gives us a compact mechanism to generate all the masses in the Universe.
G(H->ff) ~ gf2MH ~ g2(Mf/MW)2MH , g = gW
G(H->WW) ~ g2MH3/MW2 ~ g2(MH/MW)2MH
G ~ MH3 or G/MH ~ MH2 ==> G/MH ~ 1 @ MH ~ 1 TeV
H
g
*
Higgs Cross section
CDF and D0 successfully found the top quark, which has a cross section ~ 10-10 the total cross section.
A 500 GeV Higgs has a cross section ratio of ~ 10-11, which requires great rejection power against backgrounds and a high luminosity.
24.unknown
*
CMS Tracking System
The Higgs is weakly coupled to ordinary matter. Thus, high interaction rates are required. The CMS pixel Si system has ~ 100 million elements so as to accommodate the resulting track densities..
Si pixels + Si Strips - an all Si detector is demanded by the high luminosity required to do the Physics of the LHC
US CMS Colloquium: Dec., 2000
*
If MH < 160 GeV use H --> ZZ --> 4e or 4
Fully active crystals are the best resolution possible needed for 2 photon decays of the Higgs.
US CMS Colloquium: Dec., 2000
*
The Hadron Calorimeter
HCAL detects jets from quarks and gluons. Neutrinos are inferred from missing Et.
Scintillator + WLS gives “hermetic” readout for neutrinos
US CMS Colloquium: Dec., 2000
*
The CMS Muon System
The Higgs decay into ZZ to 4 is preferred for Higgs masses > 160 GeV. Coverage to || < 2.5 is required ( > 6 degrees)
US CMS Colloquium: Dec., 2000
*
1 GHz interactions
storage medium
The telecomm technology is moving very rapidly. A L2 and L3 in software using the full event is possible
13.unknown
*
At high masses larger branching ratios are needed.
At lower masses the ZZ* and final states are used.
LEP II will set a limit ~ 110 GeV.
CMS will cover the full range from LEPII to 1 TeV.
23.unknown
*
US CMS Colloquium: Dec., 2000
*
Higgs Mass - Upper Limit
In quantum field theories the constants are altered in high order processed (e.g. loops). Asking that the Higgs mass be well behaved up to a high mass scale (no new Physics) implies a low mass Higgs.
US CMS Colloquium: Dec., 2000
*
12 Unresolved Fundamental Questions in HEP
How do the Z and W acquire mass and not the photon?
What is MH and how do we measure it?
Why are there 3 and only 3 light “generations”?
What explains the pattern of quark and lepton masses and mixing?
Why are the known mass scales so different? QCD ~ 0.2 GeV << EW vev ~ 246 GeV << MGUT ~ 1016 GeV << MPL ~ 1019 GeV
Why is charge quantized?
Why is matter (protons) ~ stable?
Why is the Universe made of matter?
What is “dark matter” made of?
Why is the cosmological constant small?
How does gravity fit in with the strong, electromagnetic and weak forces?
US CMS Colloquium: Dec., 2000
*
Grand Unified Theories
Perhaps the strong and electroweak forces are related. In that case leptons and quarks would make transitions and p would be unstable. The unification mass scale of a GUT must be large enough so that the decay rate for p is < the rate limit set by experiment.
The coupling constants "run" in quantum field theories due to vacuum fluctuations. For example, in EM the e charge is shielded by virtual fluctuations into e+e- pairs on a distance scale set by, le ~ 1/me. Thus a increases as M decreases, a(0) = 1/137, a(MZ) = 1/128.
US CMS Colloquium: Dec., 2000
*
Why is charge quantized?
There appears to be approximate unification of the couplings at a mass scale MGUT ~ 1014 GeV.
Then we combine quarks and leptons into GUT multiplets - the simplest possibility being SU(5).
[d1 d2 d3 e ] = 3(-1/3 ) + 1 + 0 = 0
Since the sum of the projections of a group generator in a group multiplet is = 0 (e.g. the angular momentum sum of m), then charge must be quantized in units of the electron charge.
In addition, we see that quarks must have 1/3 fractional charge because there are 3 colors of quarks - SU(3).
US CMS Colloquium: Dec., 2000
*
GUT Predicts W
A GUT has a single gauge coupling constant. Thus, and W must be related. The SU(5) prediction is that sin(W) = e/g = 3/8.
This prediction applies at MGUT
Running back down to the Z mass, the prediction becomes; 3/8[1 - 109 /18(ln(MGUT/MZ))]1/2
This prediction is in ~ agreement with the measurement of W from the W and Z masses.
US CMS Colloquium: Dec., 2000
*
There is no gauge motivated conservation law making protons stable.
Indeed, SU(5) relates quarks and leptons and possesses “leptoquarks” with masses ~ the GUT mass scale.
Thus we expect protons (uud) to decay via uu --> e+d , ud --> d. Thus p --> e+o or +
Looking at the GUT extrapolation, we find 1/ ~ 40 at a GUT mass of ~ 1014 GeV.
One dimensional grounds, the proton lifetime should be
p = 1/p ~ GUT2(Mp/MGUT)4Mp or p ~ 4 x 1031 yr.
The current experimental limit is 1032 yr. The limit is in disagreement with a careful estimate of the p decay lifetime in simple SU(5) GUT models. Thus we need to look a bit harder at the grand unification scheme.
US CMS Colloquium: Dec., 2000
*
The present state of the Universe is very matter-antimatter asymmetric.
The necessary conditions for such an asymmetry are the CP is violated, that Baryon number is not conserved, and that the Universe went through a phase out of thermal equilibrium.
The existence of 3 generations allows for CP violation.
The GUT has, of necessity, baryon non-conserving reactions due to lepto-quarks.
Thus the possibility to explain the asymmetry exists in GUTs, although agreement with the data, NB/N ~ 10-9, and calculation may not be plausible.
US CMS Colloquium: Dec., 2000
*
SUSY and Evolution of
It is impossible to maintain the big gap between the Higgs mass scale and the GUT mass scale in the presence of quantum radiative corrections. One way to restore the gap is to postulate a relationship between fermions and bosons. Each SM particle has a supersymmetric (SUSY) partner with spin 1/2 difference. If the mass of the SUSY partners is ~ 1 TeV, then the GUT unification is good - at 1016 GeV
US CMS Colloquium: Dec., 2000
*
Galactic Rotation Curves
The rise of v as r (Keplers law) is observed, but no falloff is observed out to 60 kpc, well beyond the luminous region of typical galaxies. There must be a new “dark matter”.
22.unknown
*
Summary for CMS Physics
CMS will explore the full (100 - 1000 GeV) allowed region of Higgs masses. Precision data indicates that the Higgs is light.
The generational regularities in mass and CKM matrix elements will probably not be informed by data taken at CMS.
There appears to be a GUT scale which indicates new dynamics. The GUT explains charge quantization, the value of W and perhaps the matter dominance of the Universe and the small values of the neutrino masses. However it fails in p decay and quadratic radiative corrections to Higgs mass scales..
Preserving the scales, (hierarchy problem) can be accomplished in SUSY. SUSY raises the GUT scale, making the p quasi-stable. The SUSY LSP provides a candidate to explain the observation of galactic “dark matter”. A local SUSY GUT naturally incorporates gravity. It can also possibly provide a small cosmological constant. A common GUT coupling and preservation of loop cancellations requires SUSY mass < 1 TeV. CMS will fully explore this SUSY mass range either proving or disproving this attractive hypothesis.
US CMS Colloquium: Dec., 2000
*
What will we find at the LHC?
There is a single fundamental Higgs scalar field. This appears to be incomplete and unsatisfying.
Another layer of the “cosmic onion” is uncovered. Quarks and/or leptons are composites of some new point like entity. This is historically plausible – atoms nuclei nucleons quarks.
There is a deep connection between Lorentz generators and spin generators. Each known SM particle has a “super partner” differing by ½ unit in spin. An extended set of Higgs particles exists and a whole new “SUSY” spectroscopy exists for us to explore.
The weak interactions become strong. Resonances appear in WW and WZ scattering as in + . A new force manifests itself, leading to a new spectroscopy.
“There are more things in heaven and earth than are dreamt of”
Higgs boson
t quark
b quark
s quark
Mass(GeV)
1/
a
a
3
a
2
a
1
10
0
10
5
10
10
10
15
10
20
100
200
300
400
500
600
700
800
L
(GeV)
Mass(GeV)
1/
a
a
3
a
2
a
1
The Compact Muon Solenoid at the Large Hadron Collider
Dan Green
*
What is the CMS collaboration?
What is the Standard Model? How do we detect the fundamental particles contained in the SM?
The Higgs boson is the missing object in the SM “periodic table”. What is the CMS strategy to discover it?
What might we find at CMS in addition to the Higgs?
US CMS Colloquium: Dec., 2000
*
European Center for Nuclear Research (CERN)
Large
Hadron
Collider
(LHC)
*
High Energy Physics-”Natural Units”
Dimensions are taken to be energy in HEP. Momentum and mass are given the dimensions of energy, pc, mc2. The basic energy unit is the electron Volt, the energy gained when an electron falls through a potential of 1 Volt = 1.6 x 10 -19 Joule.
The connection between energy and time, position and momentum is supplied by Planck's constant, , where 1 fm = 10-13 cm. Thus, inverse length and inverse time have the units of energy. The Heisenberg uncertainty relation is
Charge and spin are "quantized"; they only take discrete values, e or . Fermions have spin 1/2, 3/2 ..., while bosons have spin 0,1,.… The statistics obeyed by fermions and bosons differs profoundly. Bosons can occupy the same quantum state - e.g. superconductors, laser. Fermions cannot (Pauli Exclusion Principle) - e.g. the shell structure of atoms.
US CMS Colloquium: Dec., 2000
*
Size and the Energy of the Probe Particle
In order to "see" an object of size r one must use "light" with a wavelength l < r. Thus, visible light with l ~ 3000 A ( 1 A = 10-8 cm, ~ size of an atom) can resolve bacteria. Visible light comes from atomic transitions with ~ eV energies ( = 2000 eV*A).
To resolve a virus, the electron microscope with keV energies was developed, leading to an increase of ~ 1000 in resolving power.
To resolve the nucleus, 105 time smaller than the atom one needs probes in the GeV (109 eV) range. The size of a proton is ~ 1 fm = 10-13 cm.
The large Hadron Collider (LHC) at the CERN will explore Nature at the TeV scale or down to distances ~ 0.0002 fm.
US CMS Colloquium: Dec., 2000
*
Higgs boson
t quark
b quark
s quark
*
*
US CMS Colloquium: Dec., 2000
*
CMS Collaboration
CMS Collaboration
*
“Particle Physics” in the 20th Century
The e- was discovered by Thompson ~ 1900. The nucleus was discovered by Rutherford in ~ 1920. The e+, the first antiparticle, was found in ~ 1930. The m , indicating a second “generation”, was discovered in ~ 1936.
There was an explosion of baryons and mesons discovered in the 1950s and 1960s. They were classified in a "periodic table" using the SU(3) symmetry group, whose physical realization was point like, strongly interacting, fractionally charged "quarks". Direct evidence for quarks and gluons came in the early 1970s.
The exposition of the 3 generations of quarks and leptons is only just, 1996, completed. In the mid 1980s the unification of the weak and electromagnetic force was confirmed by the W and Z discoveries.
The LHC, starting in 2005, will be THE tool to explore the origin of the breaking of the electroweak symmetry (Higgs field?) and the origin of mass itself.
US CMS Colloquium: Dec., 2000
*
Electro - Weak Unification
The weak interactions are responsible for nuclear beta decay. The observed rates are slow, indicating weak effective coupling. The decays of the nuclei, n, and m are parametrized as an effective 4 fermion interaction with coupling, G ~ 10-5 GeV-2, Gm ~ G2Mm5.
The weak SU(2) gauge bosons, W+ Zo W- , acquire a mass by interacting with the "Higgs boson vacuum expectation value" of the field, while the U(1) photon, g , remains massless. MW ~ gW<f>
The SU(2) and U(1) couplings are "unified" in that e = gWsin(qW). The parameter qW can be measured by studying the scattering of n + p, since this is a purely weak interaction process.
The coupling gW can be connected to G by noting that the 4 fermion Feynman diagram can be related to the effective 4 fermion interaction by the Feynman "propagator", G ~ gW2/MW2. Thus, from G and sin(qW) one can predict MW. The result, MW ~ 80 GeV was confirmed at CERN in the pp collider. The vacuum Higgs field has <f> ~ 250 GeV.
US CMS Colloquium: Dec., 2000
*
Matter consists of half integral spin fermions. The strongly interacting fermions are called quarks. The fermions with electroweak interactions are called leptons. The uncharged leptons are called neutrinos.
The forces are carried by integral spin bosons. The strong force is carried by 8 gluons (g), the electromagnetic force by the photon (), and the weak interaction by the W+ Zo and W-. The g and are massless, while the W and Z have ~ 80, 91 GeV mass.
J = 1
*
Tracker
ECAL
HCAL
Magnet
Muon
*
(ECAL shower, no track)
(ionization only)
q = u, d, s Jet (narrow) in ECAL+HCAL
q = c, b Jet (narrow) + Decay Vertex
t --> W +b W + b
e Et missing in ECAL+HCAL
-->l + +l Et missing + charged lepton
W --> l + l Et missing + charged lepton,
Et~M/2
--> l + l Et missing in ECAL+HCAL
US CMS Colloquium: Dec., 2000
*
Dijet Events at the Tevatron
The scattering of quarks inside the proton leads to a "jet" of particles traveling in the direction of, and taking the momentum of, the parent quark. Since there is no initial state Pt, the 2 quarks in the final state are "back to back" in azimuth.
US CMS Colloquium: Dec., 2000
*
A FNAL Collider (D0) Event
The D0 detector has 3 main detector systems; ionization tracking,liquid argon calorimetry ( EM , e , and HAD , jets ,), and magnetized steel + ionization tracker muon , m , detection/identification. This event has jets, a muon, an electron and missing energy , n.
US CMS Colloquium: Dec., 2000
*
A FNAL Collider (CDF) Event
The CDF detector has 3 main detector systems; tracking - Si + ionization in a magnetic field, scintillator sampling calorimetry, (EM - e, g and HAD - h), and ionization tracking for muon measurements. Missing energy indicates n in the final state.Si vertex detectors allow one to identify b and c quarks in the event.
US CMS Colloquium: Dec., 2000
*
W --> e + at the Tevatron
The W gauge bosons can decay into quark-antiquarks, e.g. u + d, or into lepton pairs, e + ne, m + nm, t+ nt. There can also be radiation associated with the W, gluons which evolve into jets.
US CMS Colloquium: Dec., 2000
*
Z --> e + e and + Events at the Tevatron
The e appear in the EM and not the HAD compartment of the calorimetry, while the m penetrate thick material.
US CMS Colloquium: Dec., 2000
*
The Generation of Mass by the Higgs Mechanism
The vacuum expectation value of the Higgs field, <f>, gives mass to the W and Z gauge bosons, MW ~ gW<f>. Thus the Higgs field acts somewhat like the "ether". Similarly the fermions gain a mass by Yukawa interactions with the Higgs field, mf = gf<f>. Although the couplings are not predicted, the Higgs field gives us a compact mechanism to generate all the masses in the Universe.
G(H->ff) ~ gf2MH ~ g2(Mf/MW)2MH , g = gW
G(H->WW) ~ g2MH3/MW2 ~ g2(MH/MW)2MH
G ~ MH3 or G/MH ~ MH2 ==> G/MH ~ 1 @ MH ~ 1 TeV
H
g
*
Higgs Cross section
CDF and D0 successfully found the top quark, which has a cross section ~ 10-10 the total cross section.
A 500 GeV Higgs has a cross section ratio of ~ 10-11, which requires great rejection power against backgrounds and a high luminosity.
24.unknown
*
CMS Tracking System
The Higgs is weakly coupled to ordinary matter. Thus, high interaction rates are required. The CMS pixel Si system has ~ 100 million elements so as to accommodate the resulting track densities..
Si pixels + Si Strips - an all Si detector is demanded by the high luminosity required to do the Physics of the LHC
US CMS Colloquium: Dec., 2000
*
If MH < 160 GeV use H --> ZZ --> 4e or 4
Fully active crystals are the best resolution possible needed for 2 photon decays of the Higgs.
US CMS Colloquium: Dec., 2000
*
The Hadron Calorimeter
HCAL detects jets from quarks and gluons. Neutrinos are inferred from missing Et.
Scintillator + WLS gives “hermetic” readout for neutrinos
US CMS Colloquium: Dec., 2000
*
The CMS Muon System
The Higgs decay into ZZ to 4 is preferred for Higgs masses > 160 GeV. Coverage to || < 2.5 is required ( > 6 degrees)
US CMS Colloquium: Dec., 2000
*
1 GHz interactions
storage medium
The telecomm technology is moving very rapidly. A L2 and L3 in software using the full event is possible
13.unknown
*
At high masses larger branching ratios are needed.
At lower masses the ZZ* and final states are used.
LEP II will set a limit ~ 110 GeV.
CMS will cover the full range from LEPII to 1 TeV.
23.unknown
*
US CMS Colloquium: Dec., 2000
*
Higgs Mass - Upper Limit
In quantum field theories the constants are altered in high order processed (e.g. loops). Asking that the Higgs mass be well behaved up to a high mass scale (no new Physics) implies a low mass Higgs.
US CMS Colloquium: Dec., 2000
*
12 Unresolved Fundamental Questions in HEP
How do the Z and W acquire mass and not the photon?
What is MH and how do we measure it?
Why are there 3 and only 3 light “generations”?
What explains the pattern of quark and lepton masses and mixing?
Why are the known mass scales so different? QCD ~ 0.2 GeV << EW vev ~ 246 GeV << MGUT ~ 1016 GeV << MPL ~ 1019 GeV
Why is charge quantized?
Why is matter (protons) ~ stable?
Why is the Universe made of matter?
What is “dark matter” made of?
Why is the cosmological constant small?
How does gravity fit in with the strong, electromagnetic and weak forces?
US CMS Colloquium: Dec., 2000
*
Grand Unified Theories
Perhaps the strong and electroweak forces are related. In that case leptons and quarks would make transitions and p would be unstable. The unification mass scale of a GUT must be large enough so that the decay rate for p is < the rate limit set by experiment.
The coupling constants "run" in quantum field theories due to vacuum fluctuations. For example, in EM the e charge is shielded by virtual fluctuations into e+e- pairs on a distance scale set by, le ~ 1/me. Thus a increases as M decreases, a(0) = 1/137, a(MZ) = 1/128.
US CMS Colloquium: Dec., 2000
*
Why is charge quantized?
There appears to be approximate unification of the couplings at a mass scale MGUT ~ 1014 GeV.
Then we combine quarks and leptons into GUT multiplets - the simplest possibility being SU(5).
[d1 d2 d3 e ] = 3(-1/3 ) + 1 + 0 = 0
Since the sum of the projections of a group generator in a group multiplet is = 0 (e.g. the angular momentum sum of m), then charge must be quantized in units of the electron charge.
In addition, we see that quarks must have 1/3 fractional charge because there are 3 colors of quarks - SU(3).
US CMS Colloquium: Dec., 2000
*
GUT Predicts W
A GUT has a single gauge coupling constant. Thus, and W must be related. The SU(5) prediction is that sin(W) = e/g = 3/8.
This prediction applies at MGUT
Running back down to the Z mass, the prediction becomes; 3/8[1 - 109 /18(ln(MGUT/MZ))]1/2
This prediction is in ~ agreement with the measurement of W from the W and Z masses.
US CMS Colloquium: Dec., 2000
*
There is no gauge motivated conservation law making protons stable.
Indeed, SU(5) relates quarks and leptons and possesses “leptoquarks” with masses ~ the GUT mass scale.
Thus we expect protons (uud) to decay via uu --> e+d , ud --> d. Thus p --> e+o or +
Looking at the GUT extrapolation, we find 1/ ~ 40 at a GUT mass of ~ 1014 GeV.
One dimensional grounds, the proton lifetime should be
p = 1/p ~ GUT2(Mp/MGUT)4Mp or p ~ 4 x 1031 yr.
The current experimental limit is 1032 yr. The limit is in disagreement with a careful estimate of the p decay lifetime in simple SU(5) GUT models. Thus we need to look a bit harder at the grand unification scheme.
US CMS Colloquium: Dec., 2000
*
The present state of the Universe is very matter-antimatter asymmetric.
The necessary conditions for such an asymmetry are the CP is violated, that Baryon number is not conserved, and that the Universe went through a phase out of thermal equilibrium.
The existence of 3 generations allows for CP violation.
The GUT has, of necessity, baryon non-conserving reactions due to lepto-quarks.
Thus the possibility to explain the asymmetry exists in GUTs, although agreement with the data, NB/N ~ 10-9, and calculation may not be plausible.
US CMS Colloquium: Dec., 2000
*
SUSY and Evolution of
It is impossible to maintain the big gap between the Higgs mass scale and the GUT mass scale in the presence of quantum radiative corrections. One way to restore the gap is to postulate a relationship between fermions and bosons. Each SM particle has a supersymmetric (SUSY) partner with spin 1/2 difference. If the mass of the SUSY partners is ~ 1 TeV, then the GUT unification is good - at 1016 GeV
US CMS Colloquium: Dec., 2000
*
Galactic Rotation Curves
The rise of v as r (Keplers law) is observed, but no falloff is observed out to 60 kpc, well beyond the luminous region of typical galaxies. There must be a new “dark matter”.
22.unknown
*
Summary for CMS Physics
CMS will explore the full (100 - 1000 GeV) allowed region of Higgs masses. Precision data indicates that the Higgs is light.
The generational regularities in mass and CKM matrix elements will probably not be informed by data taken at CMS.
There appears to be a GUT scale which indicates new dynamics. The GUT explains charge quantization, the value of W and perhaps the matter dominance of the Universe and the small values of the neutrino masses. However it fails in p decay and quadratic radiative corrections to Higgs mass scales..
Preserving the scales, (hierarchy problem) can be accomplished in SUSY. SUSY raises the GUT scale, making the p quasi-stable. The SUSY LSP provides a candidate to explain the observation of galactic “dark matter”. A local SUSY GUT naturally incorporates gravity. It can also possibly provide a small cosmological constant. A common GUT coupling and preservation of loop cancellations requires SUSY mass < 1 TeV. CMS will fully explore this SUSY mass range either proving or disproving this attractive hypothesis.
US CMS Colloquium: Dec., 2000
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What will we find at the LHC?
There is a single fundamental Higgs scalar field. This appears to be incomplete and unsatisfying.
Another layer of the “cosmic onion” is uncovered. Quarks and/or leptons are composites of some new point like entity. This is historically plausible – atoms nuclei nucleons quarks.
There is a deep connection between Lorentz generators and spin generators. Each known SM particle has a “super partner” differing by ½ unit in spin. An extended set of Higgs particles exists and a whole new “SUSY” spectroscopy exists for us to explore.
The weak interactions become strong. Resonances appear in WW and WZ scattering as in + . A new force manifests itself, leading to a new spectroscopy.
“There are more things in heaven and earth than are dreamt of”
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