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STANDARD MODEL &
BEYOND
D. P. ROY
Homi Bhabha Centre for Science Education
Tata Institute of Fundamental Research
Mumbai, India
Contents
• Basic Constituents of Matter and their Interactions
: Matter Fermions and Gauge Bosons (Std Model)
• High Energy Colliders
• Discovery of Std Model Particles at Colliders
• Higgs Mechanism : Higgs Search at LHC
• Supersymmetry : SUSY Search at LHC
• Cosmological Implications
(Natural units: ħ & c = 1 => m = mc2 , mp  1 GeV)
Basic Constituents of Matter
Mass (GeV)
Fermions (Spin = 1/2 ħ)
Leptons νe
νμ
ντ
e .0005
μ 0.1
τ 1.8
e
0
-1
Quarks
2/3
-1/3
u 0.3
d 0.3
c 1.5
s 0.5
t 175
b 5
For each Pair : Δe = 1 => Weak Int
Quarks also carry Colour Charge (C)=>Strong Int
Basic Ints (Gauge Bosons & Groups)
d
1. Strong Int (QCD) :SU(3)
q
q
g
Cq2αs / Q2
Q2
q
q
2. E.M. Int (QED) :U(1)
q
e
γ
eqee α / Q2
Q2
q
e
p
u
SU(3) => Cg => ggg Int
=> Confinement
u
u
r
d
F = Constant => V –> r
p
e
F = α/r2 => V = α/r
3. Weak Int : SU(2)
νμ
e
W
=> V = (α/r) . Exp ( -r MW )
αW / Q2-MW2
Q2
μ
νe
2 => DA = α / M 2
μ
—>
eν
ν
:
Q2
«
M
μ e
W
μ
W
W
νe
SU(2)xU(1) EW Th (GSW) =>αW=α/sin2θW4α
=> DAμ 4α/MW2 => MW=80 GeV, MZ=91GeV
•
•
•
•
p (uud), n (udd), e => All the Visible Matter
Heavier Leptons & Quarks Decay by Weak Int
They can be Observed in Accelerator or Cosmic ray
Cosmic ray Observation of μ and k (sū) in 1947
• νs are stable but very hard to Observe <= Weak Int
•
•
•
•
νe Observed in Atomic Reactor Expt in 1956
νμ in BNL PS in 1962 ( KGF Cosmic ray in 1965)
e+e- Collider : c (1974), τ (1975), b (1977), g (1979)
p-p Collider : W & Z (1983), t (1995), ντ (2000) FT
eBv = mv2/R
eB = mv/R
e+e - ( p - p) Collider
Accleration
Mode
Collision
Mode
Advantage of Collider over Fixed Target Accelerator
E
E’
E
s  2mE'
s  2E
Tevatron p-p Collider
s  21000
GeV



1TeV
E
'
Equiv
s
(2000GeV ) 2


 2000,000GeV
2m p
2 1GeV
p-p Collider vs e+e - Collider
s’
s’ ~ < xq >2 sp-p
1/6
Same s'  s p p  6 see  : ESync
s’
s’ = se e+
4 .e 2 E 4

4
3me 
s'  M Z  100GeV : s p p  600GeV , see   100GeV
CERN: p-p Coll. (ρ = 1 km), LEP-I (ρ = 5 km)
COST: ( 200 + 100) million$, 1 billion$
Precission:Tune e-e+ Energy = MZ => Higher Rate & Better Mass Res
Z events/yr : LEP-I ~ 10 6, CERN p-p Coll. ~ 10 1-2
Signal :
Clean ,
Dirty (Debris from Spectator q & g)
Past, Present & Proposed Colliders
Period
Machine
Location
70’s
SPEAR
DORIS
CESR
PEP
PETRA
Stanford e+eHamburg
Cornell
Stanford
Hamburg
80’s
90’s
TRISTAN Japan
SPPS
CERN
Beam Energy(GeV) Radius Highlight
e+epp
Tevatron
SLC
LEP-I
(LEP-II)
HERA
Fermilab p p
Stanford e+eCERN
2009
2???
3+3
5+5
8+8
18+18
22+22
30+30
300+300
125 m
charm , τ
bottom
bottom
300 m
gluon
1 km
W,Z boson
5 km
Hamburg e p
1000+1000
50+50
50+50
100+100
30+800
LHC
CERN
pp
7000+7000
5 km
ILC
???
e+e-
500+500
Top
Z
Z
W
Higgs,SUSY
kT ~ ħ/1fm~0.2 GeV
3-jets
80 GeV
91 GeV
Hard Isolated e / μ with
3 - 4 Hard jets
175 GeV
80 GeV
Godbole, Pakvasa & Roy, Phys. Rev. Lett. 50, 1539 (1983)
Gupta & Roy, Z. Phys. C39, 417 (1988)
Top pair production
Mass Problem : Higgs Mechanism
How to give mass to the SU(2) Gauge Bosons w/o breaking Gauge Sym
of the L ? For simplicity look at the U(1) Gauge Th (EM Int).
v
h
LEM
v
h
1
 (   ieA ) (   ieA )  [      (  ) ]  F F
4
*
2
*
*
F    A   A  E1..3 , B1..3
GaugeTr :   e
1
 , A  A    ( x)
e

μ2<0
μ2>0
vev
  r  v  h( x )
 M  ev
-M2 Aμ Aμ
i ( x )
V   2 *   ( * ) 2
v   2 / 
2
<
mq = yqv
 mh    2   v   / e  M ~ 102 GeV
 vh
0
1
 vh
g2
g v WW  g v hWW
MW2
0
1
Wμ
Wμ
2 2
 vh
0
1
2
gMW
q
yq
q
yq v qq  yq hqq
mq
mq / v
Higgs couplings to Particles is Proportional to their Mass
=>Most Important Channels for Higgs Search are the
Heavy Pairs: h ( WW, ZZ, tt, bb, ττ ) & H± ( tb, τν )
τ Polarization Effect <= Roy, Phys.Lett.B459, 607 (1999)
Ferromagnetism
(Spontaneous Symmetry Breaking)
T < TC
Rotational Symmetry Broken
T > TC
Rotational Symmetry
H
, He

pe 


p pne
p 
n

uud ddu e
WZhtbeνγ
Hierarchy Problem: Supersymmetry (SUSY) Solution
How to control Higgs Mass mh ~ MW ~ 102 GeV?
1
(k 2  m 2 )
k
h
k 3dk
2
 2

k

2
(k  m )
~
h
- h
λ
Without a protecting symmetry scalar mass gets quad. div. quantum
corr.  m  ( M
;M
)
h
GUT
Plank

 

16
19
GeV
10
10
SUSY:
fermions<=>bosons
s
q, l 1/2  , g ,W , Z
~
~
q, l
0
~ ~
~
~
 , g ,W , Z
s
1
1/2
h1, 2
~
h1, 2
=> Superparticles mass ~ 10 2 GeV
s
0
1/2
R  (1)3B  L  2s
1
1
R Cons.=> Pair-prod of SP &
Stable LSP (Cold dark matter)
LSP ~:Weakly Int Massive Particle (WIMP)
M ~e ,q~  M W
=> LSP escapes detection like ν
=> Apparent imbalance of PT
(Missing-PT Signature)
Pair production of Gluinos and Squarks at LHC
=> Multi-jet plus Missing-PT Signature for SUSY
Reya & Roy, Phys. Lett. 141B, 442 (1984); Phys. Rev. Lett. 53, 881 (1984)
Conclusion
• Higgs & Superparticles are the minimal set of
missing pieces reqd. complete the picture of
particle physics (MSSM).
• LHC offers comprehensive Higgs and
Superparticle search up to MH,SUSY= 1000GeV.
• It will either complete the picture a la MSSM
or provide valuable clue for an alternative
picture : Little Higgs, Extra Dim, ETC...↓
• LSP is leading candidate for the cosmic dark
matter ~ 10 times the baryonic matter of the
Universe.
Rotation curve of nearby
dwarf spiral galaxy M33,
superimposed on its optical
image
2
v
M ( R)
G
v
2
R
R
M ( R)
R
H
, He

pe 


p pne
p 
n

uud ddu e
WZhtbeνγ
~
~
~

 


~~~~~~~
~ ~~ ~ ~ ~ ~~
WZ h t b e  