september 29, 2005andrey korytov, uf physics colloquium 1 on the verge of pivotal discoveries at the...

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


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?


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


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


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...


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



1919: Weyl points out that is not uniquely

defined

gauge transformation

does not change physical fields,

A

( )A A x

and E B



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



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



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



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


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


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..

.


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


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


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


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


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


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?


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


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


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


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


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...


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


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


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


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


LHC Experiments: ATLAS, LHC Experiments: ATLAS, CMSCMS, LHC-b, ALICE, LHC-b, ALICE


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)


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!


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


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...


Muon Detectors for CMSMuon Detectors for CMS

UF made this happen

2

?


First Full Scale Muon DetectorFirst Full Scale Muon Detector

We need

500 of these!


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


Muon Detectors: all finishedMuon Detectors: all finished


What’s next?What’s next?

Get Ready to Run the Experiment

Get Ready to Discover Higgs


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

qq

most of the time

• looks nearly identical• happens 1011 times more often

SIGNALMH=200 GeV


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


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


Higgs = Peak in 4-muon invariant Higgs = Peak in 4-muon invariant massmass

Higgs Signal

Various Bkgd’s


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!


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


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...


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


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


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

september 29, 2005andrey korytov, uf physics colloquium 1 on the verge of pivotal discoveries at the...

Documents

em force

massless standard model

em fields

weak force ux

renormalizablestandard

strong force ux

local gauge invariance

gauge fields gluons