WoP Particles of the Standard Model
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Transcript of WoP Particles of the Standard Model
VU lecture – World of Particles Thomas Gajdosik, FI & VU
World of Particleso d o a t c es
Th P ti l Z Thomas Gajdosik
Vilnius Universitetas, Teorinės Fizikos Katedra
The Particle Zoo Symmetries The Standard Model
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model:Particles of the Standard Model: Fermions
1. reminder about the particles• from the historical introduction
2. the ordering principle• example: electron and neutrinoexample: electron and neutrino
3. the systematics• extending the ordering to all fermions• extending the ordering to all fermions• counting the degrees of freedom
4 i4. overview
VU lecture – World of Particles Thomas Gajdosik, FI & VU
th l te- the electrone-
ThomsonThomsonThomsonThomson
1897
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the positron (anti-matter)e+ p ( )
e-
γ
discovery
γp
nnµ
π
AndersonAndersonprediction π
DiracDirac
1897
1900-1924
1914 19321937
1947
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the neutrinoν
e-
γγp
nFermiFermiPauliPauli
nµ
ππ
e+
1897
1900-1924
1914 19321937
1947
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Reminder:Are symmetries perfect?
P violation - but maybe a CP symmetry?y y y
νν νright-handed left-handed left-handed
• there is no left-handed anti-neutrino, but there is a left-handedneutrino (and only a such-handed!)
right handedanti-neutrino
left-handedanti-neutrino
left-handedneutrino
neutrino (and only a such handed!)• obviously, this violates C-symmetry (symmetrie between matter and anti-matter)
• BUT: the combined symmetry transformation CP (exchangey y ( gmatter/anti-matter plus mirroring) works:
ν νCPCPνright-handedanti-neutrino
νleft-handed
neutrino
CPCP↔↔
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Ordering principle g p pdiscreet symmetries
• Parity P• Parity P– left handed or right handed
eL eR
• Charge Conjugation C– particle or antiparticle
νν_
particle or antiparticle
• Charge Q or Flavour 0 -1 ⅔ -⅓– possible values:
• Generationν e u d
– first – second – third e µ τ
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
cle
eR-νe eL
-
Par
tie e+e+ _
tipar
ticle eReL νe
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the protonp p
e-
γγ
RutherfordRutherford
1897
1900-1924
1914
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the neutronn the neutron
e-
γChadwickChadwick
γp
1897
1900-1924
1914 1932
VU lecture – World of Particles Thomas Gajdosik, FI & VU
partons / parton modelp p
e-
γRichard Feynman1969 γ
pn
1969
nµ
ππ
e+
νν
1900-1924
1897 1914 19471932
1937 1955
1947
1969
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
cle
eR-νe eL
- uL dL uR dR
Par
tie e+e+ _
tipar
ticle eReL νe
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the pionπ the pion
e-
γ
π
prediction discoveryγ
pnn
µPowellPowellYukawaYukawa PowellPowellYukawaYukawa
1897
1900-1924
1914
1932
1937 1947
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
cle
eR-νe eL
- uL dL uR dR
Par
tie e+e+ u
_ _d u
_ _d
tipar
ticle eReL uL dL uR dR
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
the muonµ the muon
e-
γ
µWho ordered that one? γ
pnn
k h b
Hess
spark chamber
• Hess• Anderson,
Neddermeyer
1897
1900-1924
1914
1932
1937 • Street, Stevenson
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-µL
-
Par
tie e+e+ u
_ _d u
_ _d
µR+µL
+
tipar
ticle eReL uL dL uR dR
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
RochesterΛΛ
strange particlese-
γ
KKRochester,Butler,...
ΣΣ γp
n
ΣΣ
nµ
ππ
e+
νν
1897
1900-1924
1914 1932
1937
1947 1947-...
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-µL
-
Par
ti sL sR
e e+e+ u_ _
d u_ _
d
µR+µL
+
tipar
ticle
_sL
_sR
eReL uL dL uR dR
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
antineutrino reactors:_ν
e-
γ
Clyde Cowan, Frederick Reines
γp
nnµ
ππ
e+
νν
1897
1900-1924
1914 1932
1937
1956
1955
1947
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti sL sR
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ__
sL
_sR
eReL νeuL dL uR dR
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
charm quark: J/Ψc q
e-
γγp
nnµ
πBurt Richter (SLAC), Samuel Ting (BNL) π
e+
Samuel Ting (BNL)1974
νν
1900-1924
1897 1914 19471932
1937 1955
1947
1969
1974
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti cL sL cR sR
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ_
cL_ _
sL cR_ _
sR
eReL νeuL dL uR dR
Ant
VU lecture – World of Particles Thomas Gajdosik, FI & VU
tau lepton: ττ p
e-
γMartin Perl (SLAC LBL) γ
pn
(SLAC-LBL)1975
nµ
ππ
e+
νν
19751900-1924
1897 1914 19471932
1937 1955
1947
1969
1974
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti cL sL cR sR
τR-τL
-
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ_
cL_ _
sL cR_ _
sR
eReL νeuL dL uR dR
Ant
τR+τL
+
VU lecture – World of Particles Thomas Gajdosik, FI & VU
bottom quarkb q
e-
γγp
nnµ
ππ
e+
νE288 (Fermilab)1977
ν
19751900-1924
1897 1914 19471932
1937 1955
1947
1969
1974 1977
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti cL sL cR sR
τR-τL
- bL bR
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ_
cL_ _
sL cR_ _
sR
eReL νeuL dL uR dR
Ant
τR+τL
+_bL
_bR
VU lecture – World of Particles Thomas Gajdosik, FI & VU
top quarktCDF D0p q
e-
γ
CDF, D0 (Fermilab)1995 γ
pnn
µππ
e+
νν
19751900-1924
1897 1914 19471932
1937 1955
19951947
19831969
1974 1977
1979
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti cL sL cR sR
τR-τL
- tL bL tR bR
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ_
cL_ _
sL cR_ _
sR
eReL νeuL dL uR dR
Ant
τR+τL
+ tL
_ _bL tR
_ _bR
VU lecture – World of Particles Thomas Gajdosik, FI & VU
tau neutrino: ντντ
e-
γ
DONUT (Fermilab)2000 γ
pn
2000
nµ
ππ
e+
νν
19751900-1924
1897 1914 19471932
1937 1955
19951947
19831969
1974 1977
20001979
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νe eL
- uL dL uR dR
µR-νµ µL
-
Par
ti cL sL cR sR
τR-ντ τL
- tL bL tR bR
e e+e+ _u_ _
d u_ _
d
µR+µL
+
tipar
ticle
νµ_
cL_ _
sL cR_ _
sR
eReL νeuL dL uR dR
Ant
τR+τL
+ ντ_
tL
_ _bL tR
_ _bR
VU lecture – World of Particles Thomas Gajdosik, FI & VU
neutrino oscillations: νe ↔ νµ↔ ντνx
• solve the “solar neutrino puzzle”
µ
solve the solar neutrino puzzleneutrinos have a tiny mass
there exist also right-handed neutrinos
• but they have:
no charge, no hypercharge, and no color
no interaction except the mass termno interaction, except the mass-term
their existence does not change the Standard Model!
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: Fermions
RightLeft
--cle
eR-νeReL
- uL dL uR dRνe
µR-νµRµL
-
Par
ti cL sL cR sR
τR-ντRτL
- tL bL tR bR
νµ
ντ
e e+e+_u_ _
d u_ _
d_
µR+µL
+
tipar
ticle
νµR_
cL_ _
sL cR_ _
sR
eReLνeR uL dL uR dR
νµ_νe
Ant
τR+τL
+ντR_
tL
_ _bL tR
_ _bRντ
_
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model:Particles of the Standard Model: Gauge Bosons
1. Gauge Theory (wop-sm2.pdf)
2. screening in QED2. screening in QED• Vacuum polarization• running coupling constantrunning coupling constant
3. anti-screening in QCD• asymptotic freedom• asymptotic freedom• confinement
4 i t b4. massive vector bosons
VU lecture – World of Particles Thomas Gajdosik, FI & VU
screeningscreening• the effective charge of an electrong
in dielectric media is reduced by dielectric molecules surrounding the charge
• the same happens in the vacuum: ppif one looks at the charge with sufficient energy to see virtual electron-positron pairs:
Vacuum polarization!Vacuum polarization!
VU lecture – World of Particles Thomas Gajdosik, FI & VU
screeningscreening• the energy dependence of the gy p
effective charge in the vacuumdue to Vacuum polarizationis described by the
running coupling:running coupling:
VU lecture – World of Particles Thomas Gajdosik, FI & VU
anti screeninganti-screening• the self couplings in QCDp g
have the opposite effect for the color charges:
• the closer one looks, the weaker the charges seem to gbecome:
asymptotic freedom!asymptotic freedom!
VU lecture – World of Particles Thomas Gajdosik, FI & VU
anti screeninganti-screening• but that also means:
th l th• the lower the energy becomes, the strongerthe charges seem to be!the charges seem to be!
• when we try to separate color charges, we havecolor charges, we have no problems at high energies colliders
• but at low energies, the force is strong enough, g , g g ,that the potential (= force * distance) can createa quark-antiquark pair, that restores color neutrality
color confinement!
VU lecture – World of Particles Thomas Gajdosik, FI & VU
color confinementcolor confinement• low energy states have to be color neutralgy
we can only observe color neutral particles
• the strong force hides inside the nucleons
the nuclear force is more like a• the nuclear force is more like a van der Waals force:
– mediated by mesons (quark – antiquark pairs)
• Baryons and Mesons are color singletsBaryons and Mesons are color singlets
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model:
first hint for
massive vector bosons• first hint for
neutral currents: G llGargamelle Bubble chamber,1973
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model:
W and Z bosons
massive vector bosons• W- and Z-bosons
detected in 1983b UA1 d UA2by UA1 and UA2
W+W- event in Aleph (LEP)
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: W- and Z-bosons
precision studies by LEP:by LEP:
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model: W- and Z-bosons
precision studies by LEP:
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Particles of the Standard Model:Particles of the Standard Model: Higgs Boson
1. Why a Higgs Boson?2. The Higgs mechanism2. The Higgs mechanism
• … again formulas … …
3 Systematics:3. Systematics:• counting the degrees of freedom
4 E i t l id4. Experimental evidence• how it is seen• exclusion / hints
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Why a Higgs Boson ?• The Standard Model is a chiral theory
it is described with massless fermion fieldsit is described with massless fermion fields• Gauge Symmetry enforces
massless vector bosonsmassless vector bosons• But we have
i f i l t d k• massive fermions: leptons and quarks• massive vector bosons: W± and Z0
• Solution: the Higgs mechanism
VU lecture – World of Particles Thomas Gajdosik, FI & VU
The Higgs mechanism
• Ingredients:• a scalar field • continuous symmetries = gauge symmetries• vacuum
• Result:• the symmetry is spontaneously brokeny y y• the scalar field develops a vacuum expectation
value (vev)• other fields can acquire masses due to the vev
VU lecture – World of Particles Thomas Gajdosik, FI & VU
symmetry breakingy y g
example: chess
• the rules of chess are in principle• the rules of chess are in principleabsolutely symmetric for both players
• i.e. the rules how the pieces move arethe same for black and whitethe same for black and white
but:
• symmetry is broken at the beginning• symmetry is broken at the beginning,due to the initial setup of the pieces
• therefore, e.g. a bishop never canchange the color of the field it ischange the color of the field it isstanding on
VU lecture – World of Particles Thomas Gajdosik, FI & VU
symmetry breaking
In the standard model, the particle‘s masses are an effect of symmetry breaking:
y y gthe origin of mass
• originally, all particles are massless • but there is an additional interaction with the so-called Higgs-field• if there were no Higgs-field, the interaction would have no effect• however due to a spontaneous symmetry breaking the whole universe• however, due to a spontaneous symmetry breaking, the whole universe is filled with a non-zero Higgs-field
• the interaction with this omni-present field produces what we know as mass of particles
energy hot universe(shortly after big bang)
particles are massless
Higgs-field0
cold universe(condensed into anasymmetric state)
particles get a mass
spontaneous symmetry breaking
gg
VU lecture – World of Particles Thomas Gajdosik, FI & VU
degrees of freedom:degrees of freedom: (only SU(2) x U(1) bosons)
massive theorymassless theory
1 complex scalar 4 1 real scalar field 11 pdoublet 4
4 massless gauge 8
1 (Higgs) 1
1 massless gauge 24 g gboson (B, Wi) 8
0 massiv gauge 0
1 g gboson (photon) 2
3 massiv gauge 90 g gbosons 0
12
3 g gbosons (W±,Z0) 9
1212 12
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Production at LEP:Production at LEP: Higgs production cross section :Higgs-strahlung:
Higgs fusion:Higgs-fusion:
VU lecture – World of Particles Thomas Gajdosik, FI & VU
Production at LEP:Production at LEP: Higgs branching ratio :Higgs branching ratio :
seen in the decay to:
• bottom quarks
b-tagged jets
• tau leptons
reconstructed τ
IF the m > 161 GeVIF the mH > 161 GeV• W-pair
• Z-boson pair
VU lecture – World of Particles Thomas Gajdosik, FI & VU
exclusion by LEP I & II:exclusion by LEP I & II:
comparison between an
expected (calculated)
distribution and the
measured distribution of
events
← measured mass distribution
VU lecture – World of Particles Thomas Gajdosik, FI & VU
exclusion by LEP I & II:exclusion by LEP I & II: statistically better
evaluated by a likelihood ratio Q:
comparison between the
distribution, depending
on a “test mass” and theon a test mass and the
measured distribution of
events
VU lecture – World of Particles Thomas Gajdosik, FI & VU
exclusion by LEP I & II:exclusion by LEP I & II: then one compares the likelihood oflikelihood of signal+background, measured in confidence levels CLs+b with thelevels CLs+b, with the likelihood of only backgroundand defines the signal as
CL CL / CLCLs = CLs+b / CLb
exclusion of the signal is given if g
CLs < 0.05
LEP excludes a 114.4 GeV Higgs boson at 95% CL
VU lecture – World of Particles Thomas Gajdosik, FI & VU
exclusion by Tevatron:exclusion by Tevatron:
VU lecture – World of Particles Thomas Gajdosik, FI & VU
hints:hints:electroweak
precision measurementsprecision measurements
precise measurements ll th i ithallow the comparison with
precise calculations:
but all loop calculations depend on the masses of the particles in the loop!the particles in the loop!
sensitivity to particles,th t ld t t bthat could not yet beproduced!
VU lecture – World of Particles Thomas Gajdosik, FI & VU
hints:hints:blueband-plot:
• giving the most probable value for the mass of thethe mass of the Higgs boson from electro-weak precision measurements:
• the most probable value is already excluded by direct non-observation.