Chapter 13 9.3 The Origin of Mass: the Higgs Boson. Theoretical background Experimental searches Discovery Future prospects 9.4 The Nature of the Neutrino. 9.4.1 Dirac or Majorana? 9.4.2 Neutrinoless double b decay 9.5 Beyond the Standard Model: Unification Schemes. 9.5.1 Grand Unification 9.5.2 Supersymmetry 9.5.3 Strings and things 26/05/15
F. Ould-Saada
+ Heavy ion collisions:
quark gluon plasma à see
CERN lecture
2
SU (3)C × SU (2) L ×U (1)Y
1.  Spin-­‐1-­‐gauge boson sector •  SU(3)C represents QCD –  The gauge bosons – 8 mass-­‐less colored gluons – couple only to color-­‐charged particles, quarks & gluons •  SU(2)LxU(1)Y represents EW interaction –  L indicates that SU(2) couples only to left-­‐handed particles, fermions = quarks and leptons –  Y indicates that U(1) couples to weak hypercharge –  After SSB à •  3 massive gauge bosons of WI, W+, W-­‐, Z0 •  1 mass-­‐less gauge boson of EM, γ 26/05/15
F. Ould-Saada
2.  Spin-­‐1/2-­‐fermions come in 3 families or generations –  5 multiplets per family, according to how they transform under gauge symmetries •  Particles within each multiplet are transformed into each other by gauge symmetries •  Particles in different multiplets are not –  Hypercharge assignments look rather ad-­‐hoc à beyond SM? –  In total 15 particles à 45 for 3 families! 3
SU (3)C × SU (2) L ×U (1)Y
Q = I3 +
Y
2
€
3. Spin-­‐0-­‐Higgs sector •  EW SSB •  How many Higgs bosons?
26/05/15
F. Ould-Saada
4
¡
One of main challenges in particle physics §  Understand EW symmetry breaking and origin of mass §  Solution? Existence of Scalar Higgs boson ¡
¡
¡
Motivations for Higgs Experimental search Discovery 26/05/15
F. Ould-Saada
5
The Standard Theory of Particles and Forces §  Forces are dictated by (gauge) symmetries ú
Fermions in 3! = SU(3)C*[SU(2)L*U(1)Y] à QCD + Electroweak (“=“ QED + Weak) §  Symmetries of laws do not necessarily lead to symmetries of outcomes ú  Electroweak symmetry spontaneously broken – Brout Englert Higgs mechanism ú  BEH “hides” EW symmetry, gives masses to weak gauge bosons and “approves” fermion masses, predicts couplings of particles to Higgs, and more §  Higgs boson mass is not predicted by the SM §  è Must be measured! Physics with ATLAS 26/05/15 6 ¡
Higgs coupling to massive particles predicted §  H couples very weakly to light particles, like e, µ, ν, u,d,s §  H couples more strongly to W,Z,t,b §  Coupling to fermions ~ mf §  Coupling to bosons ~ mV2 26/05/15
F. Ould-Saada
7
g Hff
M H < 2MW :
⎛ m f
= 2 gW ⎜⎜
⎝ MW
⎞
⎟⎟
⎠
H → bb → 2 − jet
2 M ) =Ο (10− 4 M )
Γ ( H →bb ) =Ο ( g Hff
H
H
M H ≥ 2 M W : H → W +W −
M H ≥ 2M Z :
H → Z 0Z 0
M H ≥ 2M t :
H → tt
26/05/15
F. Ould-Saada
8
¡
¡
Rare Higgs decay modes − H → γγ
BR ≈ 10 −3
−H →Z 0 ff
M H :110−150GeV / c2
Total width depends strongly on Higgs mass §  Note increase due to gauge boson channel opening §  Width ~mass at TeV! 26/05/15
F. Ould-Saada
9
¡
¡
Higgs boson has rich spectrum of decay modes Branching ratios depend strongly on Higgs mass 26/05/15
F. Ould-Saada
10
s ≤ 208 GeV
e + e − → H 0 Z 0 H → bb
⇒ M H > 114GeV / c 2
26/05/15
F. Ould-Saada
11
−M H < 2MW
H →bb ,τ +τ −
−M H ≥ 2MW
H →W +W − →l + l −ν lν l
−M H ≥ 2M Z
H →Z 0 Z 0 →l + l − l + l −
ATLAS, CMS optimized to search up to 1 TeV masses
26/05/15
F. Ould-Saada
13
¡
¡
¡
26/05/15
Higgs and more - F. Ould-Saada
125 GeV … a rather good compromise 4/5 production processes ≥5 decay channels 14
HàZZ*àl+l-­‐l+l-­‐ §  Understanding of “background” is important ú  Most of which is due to important physics at the Higgs and more - F. Ould-Saada
heart of the gauge structure / symmetry of electroweak interaction ú  Higgs showed up between 2 relatively busy regions! 26/05/15
15
Hàγγ 16
¡
SM successful in describing nearly all existing experimental data §  à various attempts to extend ElectroWeak unification to include QCD à Grand Unification (GUT)? Lepton-­‐Quark Symmetry §  à including Gravity in larger unification schemes? ¡
¡
¡
Grand Unification Supersymmetry Superstrings 26/05/15
F. Ould-Saada
17
¡
Although agreement between SM and experiments is not far from being perfect §  SM contains many parameters to be determined experimentally ▪  Coupling constants, mixing angles, particle masses (fermions, gauge bosons, Higgs boson), … §  Many of such parameters have nothing to do with the symmetries of the theory §  SM leaves several questions unanswered ▪
▪
▪
▪
▪
Why are there exactly 3 independent symmetry groups? What about reducing the number of free parameters? Why are there 3 families of quarks and leptons? What is the origin of the symmetry between quarks and leptons? Are fermions composite objects? ¡
Why is electric charge quantized and proton and electron have exactly opposite charge? §  Why are quark charges fractional? ¡
¡
What is the solution to the hierarchy problem, that the EW scale is so small compared to the Planck scale? §  MW~10-­‐17 MPl? What is the solution to the fine tuning problem? §  Loop corrections involving Higgs are quadratically divergent, such that corrections to Higgs mass are many orders of magnitude larger than the mass itself! §  Unnatural fine tuning is needed, which consists in adjusting counter terms order by order in perturbation theory to cancel the divergences ¡
¡
¡
¡
17th century, Newton realized 1st unification between falling bodies and planet movements 19th century, Maxwell, in his EM theory of light, unified electricity and magnetism, on one hand, and optics on the other hand 20th century, GSW described weak force in the same formalism as EM §  One parameter, θW, relates the 2 coupling constants Towards Grand unification also including strong force? §  With Supersymmetry? ¡
Or? §  Gravity+GUT+SUSY=SuperStrings? ¡
Let us hope that time scale unit won’t be 100 years! ¡
¡
¡
Current data hint at a unification between Strong and Electroweak forces ... at much larger energies, GUT scale. GUT is a symmetry between Leptons and Quarks §  unifies strong and electroweak forces §  Requires new gauge bosons and baryon number violation SUSY unifies “matter and force particles”: “matter-­‐force duality” §  relates particles of different spins: Fermions-­‐Bosons §  introduces super-­‐partners to each SM particle §  requires 5 Higgs particles §  provides DM candidate 26/05/15 F. Ould-­‐Saada: HEPP & ATLAS GUT
...SUSY...
21 ¡
EW+QCD à grand unified theories cosθW =
MW
MZ
GU ⊃ SU(3)C ⊗ SU(2)L ⊗U(1)Y
! !"
# #
$ !##"##$
GUT
QCD
EW
e
e !
)
gU2
1
; g' =
# ? #αU ≡
≈
sin θW
cosθW " %%
→*
4π 42
#
# M ~ 1015 GeV
gs = 4πα s + X
$
g=
¡
Given the measurement uncertainties Supersymmetry or something else is needed to achieve unification at MX~1016 GeV 26/05/15
F. Ould-Saada
22
Strong
Weak
Electromagnetic
26/05/15
F. Ould-Saada: HEPP & ATLAS
23
1015 GeV
10 2 GeV
SU(5) ! !!→ SU(3)C ⊗ SU(2)L ⊗U(1)Y ! !!→ SU(3)C ⊗U(1)QED
¡
SU(5) multiplets ¡
¡
Green – SM interactions Red – SU(5) interactions mediated by X and Y gauge bosons dRred
dRgreen
dRblue
e R+
νe~
dRred
g,γ,Z
gr+g
gr+b
X-4/3red
Y-1/3red
dRgreen
gg+r
g,γ,Z
gg+b
X-4/3green Y-1/3green
dRblue
gb+r
gb+g
g,γ,Z
X-4/3blue
Y-1/3blue
e R+
X4/3red
X4/3green
X4/3blue
γ,Z
W+
νe~
Y1/3red
Y1/3green
Y1/3blue
W-
Z
¡
¡
¡
Quark fractional angles, within multiplets SU(2) doublet structure Weak mixing angle §  Z/γ mixing §  Z/γ coupling to fermions 3qd + e + 0 = 0 ⇒ q p = 2qu + qd = e
(ν e , e
−
)L , (u, d ')L : Q(ν )-Q(e)=Q(u)-Q(d)
− Qsin 2 θW ) = 0#%
∑5 QI 3
5
2
= 3 / 8 → 0.21
$ ⇒ sin θW =
2
0
∑5 Q
Z γ =0
%&
∑ Q(I
3
sin 2 θW (M Z ) ~ 0.23 ; ¡
Testing GUTs §  X,Y vertices §  à reactions where L and B violated §  à proton unstable! p → π 0 + e+ "$
# R ≡ B − ∑ Ll conserved
+
l
p → π + ν e $%
¡
(M X c 2 )4
τp ≈ 4
gU (M p c 2 )5
τ p ≈ 1030±1 yr
¡
τ(exp)>8.2x1033y SO(10)-­‐based GUTs §  More parameters, combination with supersymmetry §  Lifetimes of ~1033 for most probable pàK+ν (exp: τ>6.7x1032y) Proton decay: p à e+ π˚
Ø  To achieve lifetime limits of 1033-1034
Ø  need to control 1034 protons ...
Ø  Super Kamiokande: Water Cerenkov technique
-  50 000 t of pure water (22 500 t fiducial volume)
-  readout by ½- m photomultipliers, 1000 m underground
N p = M(kg)(10 3 kg /g) N A
( ) = 2.25 × 10
10
18
7
× 10 3 × 6 × 10 23
( ) = 7.5 × 10
10
18
33
Ø After 7 years, exposure= MΔt=138 000 t yr à NpΔt=45 X 1033
Ø  Super Kamiokande: Water Cerenkov technique
π 0 → γγ
M (γγ ) = M π 0
p → e +π 0
M ( e +π 0 ) = M p
Ø  Detection efficiency: not all protons detected
Ø  efficiency ~40%
τ ≥ B( p → e+π 0 ) × 8.4 ×1033 yr
26/05/15
28
¡
MMs can be created at the time of GU SB à …, U(1) ¡
Magnetic §  charge g and mass MM huge eg = n!c ; n = 1 → g = 68.5e
¡
M X 1015
MM ~
~
~ 3×1016
αGU 0.03
Introduction of MMs into Maxwell equations §  Complete symmetry between electric and magnetic fields §  Symmetry broken by large g and MM ¡
Read §  13.1.3 Cosmology. First moment of the Universe §  13.4 Particles, Astrophysics and Cosmology §  13.6 The Big Bang and the primordial Universe ¡
See-­‐saw mechanism §  No theoretical understanding of lepton and quark mass pattern §  Neutrino masses from oscillations much lower than those of charged leptons §  Possible explanation in context of GUTs where both types of neutrinos – Majorana and Dirac – could co-­‐exist §  Mass matrix " 0
M =$
# mD
mD %
'
mM &
mD ≈ M EW ; mM ≈ MGUT
mM >> mD ⇒ λ+ ≈ mM ,
!#"#
$
very heavy neutrino
mD2
λ− ≈
mM
!#"#
$
observed neutrinos~1eV
See-­‐Saw mechanism: one mass goes up the other down! 26/05/15
F. Ould-Saada
30
¡
Introduction of new particles – sparticles -­‐ ensures cancellation in higher order diagrams ¡
¡
¡
¡
U|fermion>=|boson> U|boson>=|fermion> R-parity = (-1)2s+3B+L
R=+1 for particles
R= -1 for s-particles
If exact symmetry à particles and sparticles would have same masses SUSY must be broken! 26/05/15
F. Ould-Saada
31
¡
¡
a) SM b) SUSY ¡  SUSY (WIKIpedia)
SUSY Spectrum
Supersymmetry facing experiment: much ado (already) about nothing (yet)
Weak Scale Supersymmetry
¡
In e+e-­‐ e + e − → e~ + e~ − ⎫ + −
+ −
~ 0 χ~ 0
e
e
→
e
e
+
χ
±
±
0 ⎬
~
#"! $
~
e → e + χ ⎭
missing E/ p
e+ e− → χ~0 χ~0
e+ e− → χ~ + χ~ −
26/05/15
F. Ould-Saada
35
¡
How to incorporate Gravity? §  No successful stand-­‐alone quantum theory of Gravity ¡
¡
Replace point-­‐like particles by 1-­‐dimentional quantum strings formulated in 10 or 11 space-­‐time dimensions Superstring theories have 1 parameter – string tension §  However, we leave in 4 dimensions §  All extra dimensions have to be compactified §  Too many theories, no predictive power ... yet ¡
Higher dimensional branes in 11 dimensions §  M-­‐theories à unification of all 5 Superstring theories ¡
Operate at Planck mass-­‐scale §  Gravity ~ EW ~ QCD MP =
26/05/15
F. Ould-Saada
!c
= 1.2 × 1019 GeV / c 2
G
36
Strength
EM
gravity
r
28/05/15
F. Ould-Saada
38