September 29, 2005 Andrey Korytov, UF Physics Colloquium 1
On the verge of pivotal discoveriesOn the verge of pivotal discoveriesat the new energy frontierat the new energy frontier
Andrey KorytovAndrey Korytov
September 29, 2005 Andrey Korytov, UF Physics Colloquium 2
Next 45 minutes...Next 45 minutes...
Palace of the Standard Model of elementary particles
Cracks in the Palace
Higgs boson to hold it all together...
Where is the Higgs boson?
The answer is just around the corner...
How do we get there?
September 29, 2005 Andrey Korytov, UF Physics Colloquium 3
SM: Three Generations of Fermions (s=1/2)SM: Three Generations of Fermions (s=1/2)
neutrino
"electron"
"up"-quark
"down"-quark
3
ee
dududu
dudusc
muon
dudubt
Caveat: quarks come in three different “colors” andexist only in bound “colorless” states, e.g.:
proton neutron pion and many more...u dd
du
u ud
September 29, 2005 Andrey Korytov, UF Physics Colloquium 4
time
SM: Three Fundamental ForcesSM: Three Fundamental Forces
dud
uud
d u
e-
neutron proton
uud
uud
proton proton
e- e-
pp
ELECTROMAGNETIC: photon () couples to electrically charged
particles no self-interaction, massless
STRONG: 8 gluons (g) couple to color-charged quarks change color charge of quarks self-interacting, massless
WEAK: W and Z0 bosons couple to all fermions W transforms particles self-interacting, MASSIVE
September 29, 2005 Andrey Korytov, UF Physics Colloquium 5
Beautiful Palace of Standard ModelBeautiful Palace of Standard Model
Origin of beauty—symmetries: all three forces can be related to local gauge invariance...local gauge invariance is a highly sought after symmetry...
September 29, 2005 Andrey Korytov, UF Physics Colloquium 6
Standard Model: EM Force Standard Model: EM Force (1)(1)
EM fields can be described by one 4-vector field
0
0 , A
E AA A A t
B A
Introduce:
1Free Field Lagrangian:
4EM
F A A
L F F
September 29, 2005 Andrey Korytov, UF Physics Colloquium 7
Standard Model: EM Force Standard Model: EM Force (2)(2)
1919: Weyl points out that is not uniquely
defined
gauge transformation
does not change physical fields,
A
( )A A x
and E B
September 29, 2005 Andrey Korytov, UF Physics Colloquium 8
Standard Model: EM Force Standard Model: EM Force (3)(3)
Late 1920s: Relativistic Quantum Mechanics
Wave function x Relativistic equations for spin=0 particle
Lagrangian:
with potential energy density:
2 2 2ˆ
ˆ
E E itE p m
p p i
2 0m
*0
22 L VT m
22V m
September 29, 2005 Andrey Korytov, UF Physics Colloquium 9
Standard Model: EM Force Standard Model: EM Force (4)(4)
Phase Invariance?
rotate x by an arbitrary phase
probabilities of locating particle at x, |x|2, do not change...
one may expect that the new wave function would also be a solution...
BUT Lagrangian is NOT invariant!
( )( ) ( )ig xx e x
2*0
2 L m
September 29, 2005 Andrey Korytov, UF Physics Colloquium 10
Standard Model: EM Force Standard Model: EM Force (5)(5)
Solution: add EM field and make A and interact
Building Full Lagrangian
Full Lagrangian is now invariant w.r.t. all terms popping up from field derivatives can be absorbed in
However, EM field must remain massless... Otherwise, the term in the form would break
the Lagrangian invariance
* 220
2 *int
1
4EML L L L J A g A Fm A F
( )x ( )x( )A A x
2m A A
g g2
igA
( )( ) ( )ig xx e x
September 29, 2005 Andrey Korytov, UF Physics Colloquium 11
Standard Model: EM Force Standard Model: EM Force (6)(6)
1930s: Relativistic Quantum Mechanics is stalled... only leading order perturbation is calculable higher order loop corrections diverge!
1940s: Way out—Renormalization procedureabsorb all divergences into definition of coupling constants (sweeping the problem under the rug)remnant of the procedure: charge, mass, magnetic moment become energy-dependentit all works to astonishing precision: ~10-10
1970s: Gauge-invariant theories are renormalizable
strong force coupling
September 29, 2005 Andrey Korytov, UF Physics Colloquium 12
Standard Model: Strong ForceStandard Model: Strong Force Building Strong Force
U(x) = 3x3 unitary matrix 8 independent phases 8 gauge fields (gluons) self-interacting all massless
( ) ( ) (
( )
( )) )
(
(
)
g
r
b
d
x x U x
d
d
x
x
x
x
September 29, 2005 Andrey Korytov, UF Physics Colloquium 13
Standard Model: Weak ForceStandard Model: Weak Force
Building Weak Force
U(x) = 2x2 unitary matrix 3 independent phases
3 gauge fields: W+, W-, Z0
self-interacting all massless
( ) or ( ) ( ) ( )u
x x U x xe d
Predicted theoretically!Was found later...Oops..
.
September 29, 2005 Andrey Korytov, UF Physics Colloquium 14
Cracks in the PalaceCracks in the Palace
Gauge bosons W & Z have massesThis is why the weak force is weak...Putting them in by hand breaks the gauge invariance, the very same symmetry that their existence is derived from
Fermions have masses Parity violation in weak interactions can be accommodated without breaking the gauge invariance only if fermion masses are zeros
September 29, 2005 Andrey Korytov, UF Physics Colloquium 15
Cracks in the PalaceCracks in the Palace
Why worry? Let it be broken...
theory is not renormalizable, needs new physics at some scale ; this new physics must take care of the divergences somehow...
for some processes this scale had better be below 1 TeV
September 29, 2005 Andrey Korytov, UF Physics Colloquium 16
Higgs Boson fieldHiggs Boson field
1964: Peter Higgs – one can give mass to vector field without breaking gauge invariance!
potential of conventional complex scalar field (s=0)
consider complex field with weird potential
the lowest energy state for is not =0 field has non-zero vacuum expectation value vacuum is going to be filled with non-zero field—
New Age Ether!
22( )V m
2 42( )2
V
September 29, 2005 Andrey Korytov, UF Physics Colloquium 17
Higgs Boson trickHiggs Boson trick
Require local gauge invariance for
Expand around local minimum:
Re-write L in terms real h(x) and x Behold! EM field appears to have mass:
Mass is proportional to vacuum expectation value v0 and coupling g
2 4* 2 2 * 1
2 4L J A g A A F F
( )0( ) ( )i xx e v h x
2 22*0
2 +... +... g v A Ag A A hA A h A A
September 29, 2005 Andrey Korytov, UF Physics Colloquium 18
Standard Model MassesStandard Model MassesApply the trick to the Weak Force
get masses for W and Z(effectively, they acquire masses by interacting with all penetrating Higgs field, the Ether of 21 century)
How about fermions?start from massless fermionsforce Higgs field interact with fermions, with different hand-picked couplings; hmm...
expand around its vacuum expectation value... now fermions appear to have masses, too; their masses proportional to the picked couplings
September 29, 2005 Andrey Korytov, UF Physics Colloquium 19
So, what is all this trickery, after all?So, what is all this trickery, after all?
Free Lunch?.. Hocus-Pocus?.. Intelligent Design?..
Can it be tested?
September 29, 2005 Andrey Korytov, UF Physics Colloquium 20
Higgs Boson MassHiggs Boson Mass
If you have field, you can make splashes...waves = particles, Higgs particles...
What is the Higgs boson mass?
is the only free parameter in theoryall other parameters are fixed by observed couplings and masses
Can the Higgs mass be anything?
202 250 GeV 2Hm v
September 29, 2005 Andrey Korytov, UF Physics Colloquium 21
Can Higgs Boson mass be anything? Can Higgs Boson mass be anything? (theory) (theory)
No, unless there is new physics at some scale energy Given mass MH, as measured at 100-1000 GeV energy scale, we know coupling at this energy scale
Renormalization makes coupling “run” with energy
MH cannot be too light: flips sign at some scale
(and vacuum breaks loose—potential does not have minimum)
MH cannot be too heavy: gets large and
theory becomes non-perturbative (and all theorists can retire)
Whatever MH might be, corrections to it diverge ~2
fine tuning of seemingly unrelated parameters is required atthe level of ~(200/)2 ~10% at 1 TeV, 0.1% at 10 TeV
2~ Hm
non-p
ert
urb
ati
ve
un
sta
ble
vacu
um
N
ew
Ph
ysic
s E
ner
gy
Sca
le (
Ge
V)
1
03
10
6
1
09
10
12
1
01
5
10
18
0 200 400 600
Higgs mass MH (GeV)
10% tuning 0.1% tuning
0.001% tuning
September 29, 2005 Andrey Korytov, UF Physics Colloquium 22
How can we see Higgs experimentally?How can we see Higgs experimentally?
Particle Masses proportional to Particle-Higgs couplings...
to give birth to Higgs boson, one needs to produce a heavy particle first
Higgs boson will decay to the heaviest pair of particles accessible to it by kinematics: m < MH/2
HZ
ZMH=200 GeV
Hb
bMH=100 GeV
H
Z
Z
e+
e-
Htop-quark loopgluon
gluonMZ=90 GeV
Mtop=170 GeV
September 29, 2005 Andrey Korytov, UF Physics Colloquium 23
Higgs Boson mass: experimental limits (1)Higgs Boson mass: experimental limits (1)
If Higgs mass were small, we would’ve seen it directly at Large Electron-Positron
Collider, but we have not seen it: MH>114 GeV
If Higgs was lighter that 209-91=118 GeV,LEP would have enough energy and intensity to produce it...
}MJJ=MH =?
}MJJ=MZ=91 GeVZ0
H bb
jet (b-tagged)
jet (b-tagged)
q
q jet
jet
e+
e-
Z0
LEP Energy209 GeV
CERN, near Genevae+e- collisions energy 209 GeV4 ExperimentsOperated 1989-2000
September 29, 2005 Andrey Korytov, UF Physics Colloquium 24
WW
H
Higgs Boson mass: experimental limits (2)Higgs Boson mass: experimental limits (2)
New Global Fit of Precision Data
MH = 117+65-45 GeV
MH < 250 GeV (95% CL)
If Higgs boson were too light or too heavy, its presence in virtual loops would alter various SM parameters: - masses, - couplings, - decay branching ratios, - scattering asymmetries...
September 29, 2005 Andrey Korytov, UF Physics Colloquium 25
Can we find Higgs at Tevatron?Can we find Higgs at Tevatron?
TEVATRON, near ChicagoTEVATRON, near Chicagoproton-antiproton collisionsproton-antiproton collisionsEnergy 2,000 GeVEnergy 2,000 GeV2 Experiments: CDF and D02 Experiments: CDF and D0Will operate till 2009Will operate till 2009
UF is a member of CDF
CDFCDF D0D0
September 29, 2005 Andrey Korytov, UF Physics Colloquium 26
Can we find Higgs at Tevatron?Can we find Higgs at Tevatron?
Center of Mass Energy, TeV
Pro
ton
– P
roto
n C
ross
Sec
tio
n
Tevatron
Signal—a few events over 10 yrsSignal : Background = 1 : 1014
Maybe, by 2009, if MH<120 GeV...
Large Hadron Collider• larger x-section by 1000• larger intensity by 100
Signal—lots of eventsSignal : Background = 1 : 1011
Odds look better...
proton
September 29, 2005 Andrey Korytov, UF Physics Colloquium 27
Large Hadron Collider (LHC)Large Hadron Collider (LHC)
LHC is Proton-Proton Collider at CERNtunnel 27 km in circumference, 100 m underground1,300 14-m long 8-T field magnets to keep protons on orbitstart of operation 2007
Switzerland
France
Geneva airport
6 miles
September 29, 2005 Andrey Korytov, UF Physics Colloquium 28
Proton-Proton Collision at LHCProton-Proton Collision at LHC
Collision Energy: 14,000 GeV (7 times Tevatron)Particles per Collision: ~100 (similar to Tevatron)Collision Rate: 109 Hz (100 times Tevatron)
proton proton
September 29, 2005 Andrey Korytov, UF Physics Colloquium 29
LHC Experiments: ATLAS, LHC Experiments: ATLAS, CMSCMS, LHC-b, ALICE, LHC-b, ALICE
September 29, 2005 Andrey Korytov, UF Physics Colloquium 30
Compact Muon Solenoid ExperimentCompact Muon Solenoid Experiment
Compact Muon Solenoid TriviaSolenoid: 4 T field, 8 m diameter, 16 m length, 3109 J
Overall size: 12,500 ton weight, 15 m diameter, 22 m long
Electronics channels: 50 million
Collaboration38 countries
168 institutions2220 physicists
UF role in CMS Muon System (GM) Endcap muon detectors (AK) Endcap muon trigger (DA) Computing (PA) Physics with CMS (ALL)
September 29, 2005 Andrey Korytov, UF Physics Colloquium 31
Why Muons?Why Muons?
When in 1940s it became clear that the newly discovered particle (muon) was not a long sought after Yukawa particle (pion), but rather it behaved more like a very heavy electron, Rabi exclaimed “Who ordered that?!”
Experimentalists!
September 29, 2005 Andrey Korytov, UF Physics Colloquium 32
Why Muons?Why Muons?
HZZ+-+-
Higgs decay into 4 muons is called “golden” channel, since muons can be easily filtered from background particles by placing material on their way
Muons will be similarly effective in many - new physics searches and - Standard Model precision measurements
September 29, 2005 Andrey Korytov, UF Physics Colloquium 33
Muon Detectors for CMSMuon Detectors for CMS
Requirements: high precision (100 m), fast (5 ns), ... huge sensitive area: 6,000 m2 (football field)
Does such technology exist?The answer for the first point is Yes, Cathode Strip Chambersinvented by Charpak in 1979,but never attempted at scale over few m2 as it did not appear to be feasible...
September 29, 2005 Andrey Korytov, UF Physics Colloquium 34
Muon Detectors for CMSMuon Detectors for CMS
UF made this happen
2
?
September 29, 2005 Andrey Korytov, UF Physics Colloquium 35
First Full Scale Muon DetectorFirst Full Scale Muon Detector
We need
500 of these!
September 29, 2005 Andrey Korytov, UF Physics Colloquium 36
Muon Detectors at UFMuon Detectors at UFUF developed comprehensive program of chamber testing
6 Sites world-wide commissioned 500 chambers using these tests
Half of the US-made chambers were commissioned at UFUF HEE Lab
September 29, 2005 Andrey Korytov, UF Physics Colloquium 37
Muon Detectors: all finishedMuon Detectors: all finished
September 29, 2005 Andrey Korytov, UF Physics Colloquium 38
What’s next?What’s next?
Get Ready to Run the Experiment
Get Ready to Discover Higgs
September 29, 2005 Andrey Korytov, UF Physics Colloquium 39
BACKGROUNDjet
jet
jet
jet
How we will sort out Higgs from BackgroundHow we will sort out Higgs from Background
g
g
tH
Z
Z
q
q
most of the time
• looks nearly identical• happens 1011 times more often
SIGNALMH=200 GeV
September 29, 2005 Andrey Korytov, UF Physics Colloquium 40
BACKGROUND
How we will sort out Higgs from BackgroundHow we will sort out Higgs from Background
g
g
tH
Z
Z
We keep 1 event out of 1000 HOnly ~100 events in 3 years
g
g
3%
3%
10%
10%
10%
10%
Top quarks are now BACKGROUND!~20,000 events in 3 yearsKill by requiring no muons in jets
t
t
b
b
W-
W+
c
c
jet
jet
SIGNALMH=200 GeV
September 29, 2005 Andrey Korytov, UF Physics Colloquium 41
BACKGROUND
How we will sort out Higgs from BackgroundHow we will sort out Higgs from Background
g
g
tH
Z
Z
We keep 1 event out of 1000 HOnly ~100 events in 3 years
3%
3%
Looks very much the same as HiggsBut 4 muons do not come from one particle!
q
q
Z
Z
SIGNALMH=200 GeV
September 29, 2005 Andrey Korytov, UF Physics Colloquium 42
Higgs = Peak in 4-muon invariant Higgs = Peak in 4-muon invariant massmass
Higgs Signal
Various Bkgd’s
September 29, 2005 Andrey Korytov, UF Physics Colloquium 43
Finding Golden Needles in HaystackFinding Golden Needles in Haystack
Start from Signal : Background = 1 : 1011
Look for 4 muons: 1 : 200Put haystack in water, collect sunk needles! And...most of sunk needles are made of iron, but we need golden ones...
None of muons inside particle jets: 1 : 10Use magnet to sort out iron needles, collect non-magnetic ones. And...most of non-magnetic needles are copper, but we need gold...
Look at invariant mass of 4 muons: 10:1 (we got it!)Sort out remaining needles by weight. And...the golden needles group around the same weight!
September 29, 2005 Andrey Korytov, UF Physics Colloquium 44
CMS Higgs Boson Discovery ReachCMS Higgs Boson Discovery Reach
By 2010 Assuming LHC startup in 2007 and nominal operation
Standard Model Higgs
whatever mass it hasand if it exists at all
will be discovered by 2010 or earlier...
discovery thresholdof 5 significance
September 29, 2005 Andrey Korytov, UF Physics Colloquium 45
Is the Higgs Boson the End of Journey?Is the Higgs Boson the End of Journey?
If we DO find Higgs,What keeps its mass small? Expect new physics at 1 TeV scale...Why does it couple so differently to different particles?How shall we deal with so “thick” vacuum energy density?
(1054 times more than what we see in the Universe)
If we do NOT find Higgs, Expect new exotic physics at 1 TeV scale...
Why do we have three nearly identical generations?Pattern of masses clearly signifies something...Pattern of mixing angles is a telltale sign of something...
Do three forces unite at some high energy scale?
New physics at 1 TeV scale is needed to make it happen...
September 29, 2005 Andrey Korytov, UF Physics Colloquium 46
SummarySummary
The Standard Model of elementary particles and fundamental forces, however beautiful it may be, is incomplete and breaks at 1 TeV scale
Higgs Boson is the most elegant hypothesis known so far that would give particle masses
Higgs Boson comes with its own bag of problems, more new physics is just around the corner at 1 TeV scale
Higgs Boson AND/OR more “new physics” will be discovered at LHCHiggs boson hypothesis has been around for 40 years... And now we seem to see light at the end of tunnel...
LHC tunnel
September 29, 2005 Andrey Korytov, UF Physics Colloquium 47
Higgs boson: have we seen it at LEP?Higgs boson: have we seen it at LEP?
MH (GeV/c2)
Points—dataDashed line—expected background (no-Higgs processes)
ALEPH Collaboration data - 2000
small excess?Formally, it looked like 4 effect!If it was Higgs, they saw too many...Other 3 experiments did not see it...
LEP was let run longer to get more data
Tight Cuts
After taking more data and combining results of all 4 experiments,
the final word from LEP:
No discovery...
Consistency with background: ~1.7
Limit on Higgs mass:
MH > 114.4 GeV @95% CL
Phys. Lett. B565 (2003) 61
September 29, 2005 Andrey Korytov, UF Physics Colloquium 48
TEVATRON, near ChicagoTEVATRON, near Chicagoproton-antiproton collisionsproton-antiproton collisionsEnergy 2,000 GeVEnergy 2,000 GeV2 Experiments: CDF and D02 Experiments: CDF and D0Will operate till 2009Will operate till 2009
UF is a member of CDF
CDFCDF D0D0
Higgs boson: can we discover it at Higgs boson: can we discover it at Tevatron?Tevatron?
only if MH<125 GeV
only 3-evidence, hard to claim discovery...with some luck we may see more events...
excludedat LEP
expected integrated luminosity by 2009L = 4 – 8 fb-1
current integrated luminosity (2001-2005)L = 1 fb-1