MOTIVAZIONI PER COLLIDER ADRONICI
DOPO L’LHC: DALL’SLHC AL VLHC
G.F. Giudice
CERN
Padova, 19 Nov 2003
R. Brock (EXP Fermilab)
C. Hill (TH Fermilab)
P. Sphicas (EXP Cern)
G. Giudice (TH Cern)
1
LHC
Well-motivated energy range
• Find the Higgs
• Find the physics ultimately responsible
for EW breaking
3GF
m 
8 2 2
2
H
  SM

2m  m  m  4m  
200 GeV 
 TeV

 
2
SM
2
W
2
Z
2
H
2
t

 SM  TeV
2
2
3
300-450 MCHF (incluso 70 MCHF
di Linac4, ma senza rivelatori); 500
MCHF per SPL
~ 2 GCHF
4
A. De Roeck
5
Qual e’ il futuro dei collider
adronici dopo l’LHC?
6
VLHC Parameters
Stage 1
Stage 2
Total Circumference (km)
233
233
Center-of-Mass Energy (TeV)
40
200
Number of interaction regions
2
2
1 x 1034
2.0 x 1034
2
11.2
35.0
35.0
2.6 x 1010
5.4 x 109
Bunch Spacing (ns)
18.8
18.8
* at collision (m)
0.3
0.5
Free space in the interaction region (m)
± 20
± 30
Interactions per bunch crossing at Lpeak
21
55
Debris power per IR (kW)
6
94
Synchrotron radiation power (W/m/beam)
0.03
5.7
Average power use (MW) for collider ring
25
100
Peak luminosity (cm-2s-1)
Dipole field at collision energy (T)
Average arc bend radius (km)
Initial Number of Protons per Bunch
7
8
9
10
Stage-2 VLHC Conclusions
• The Stage 2 VLHC can reach 200 TeV and
2x1034 or more in the 233 km tunnel.
• A large-circumference ring is a great advantage for the
high-energy Stage-2 collider. A small-circumference
high-energy VLHC may not be realistic.
• There is the need for magnet and vacuum R&D
to demonstrate feasibility and to reduce cost.
– This R&D will not be easy, will not be
quick, and will not be cheap.
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VLHC Tunnel Cross Section
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13
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Underground Construction
• Three orientations
chosen to get
representative
geological samples of
sites near Fermilab.
– South site samples
many geologic strata
and the Sandwich
fault.
– One north site is flat
and goes through
many strata.
– Other north site is
15
LHC is the machine to study the scale of EW breaking
Desert, e.g. conventional susy need for precision
m < TeV
measurements after LHC
Multi-TeV linear collider?
NEW THEORY
New thresholds around 10 TeV need for energy increase
to make next step of discoveries
VLHC ?
VLHC not meant to push new-physics limits by an
order of magnitude, but to explore a well-motivated
(after some LHC discoveries) energy region
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DESERT
NON DESERT
• Connection with GUT,
strings, quantum gravity
• Low-scale string
theory,…
• Gauge-coupling
unification
• Accelerated running,
different sin2qW
• Neutrino masses
• nR in bulk
• Suppression of proton
decay and flavour
violations
• Different location of
quarks and leptons in
bulk
• Setup for cosmology
(inflation, baryogenesis)
• Low-scale inflation, EW
baryogenesis
17
NON-DESERT SCENARIOS offer good motivations
for explorations with a √s ~ 100 TeV hadron
collider
• Need to test the theory well above the EW
breaking scale
• Existence of new thresholds in the 10 TeV
region
Not a systematic review, but some examples
relevant to VLHC
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GRAVITY IN EXTRA DIMENSIONS
Fundamental scale at SM
Any short-distance scale <
SM-1 explained by geometry
M Pl  R / 2 M D1 / 2
FLAT
D  4
Arkani Hamed-Dimopoulos-Dvali
M Pl  M 5e  KR
WARPED
Randall-Sundrum
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QUANTUM GRAVITY AT LHC
G.G.- Rattazzi - Wells
Graviton emission
1
n
T
T
n
4
2
1

f   5 f 
2

Missing energy (flat)
Resonances (warped)
Contact interactions
(loop dominates over
tree if gravity is strong)
G.G. - Strumia
Higgs-radion mixing
H
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These processes are based on linearized
gravity valid at √s <<MD ~TeV
• Suitable for LHC
• VLHC can extend limits, but the
motivations are weak
VLHC can probe the region √s >>MD~TeV
(only marginal at LHC)
 independent test, crucial to verify
gravitational nature of new physics
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TRANSPLANCKIAN REGIME
 GD  
P   3 
 c 
Planck length
Schwarzschild
radius
RS 
classical limit
transplanc kian limit
1
 2
quantum-gravity scale
1  8
   3 




    2  2 

1
 1
 GD s 
 3 
 c 


  0 : RS  P

s  M D : RS  P
1
 1
classical
gravity
same
regime
22
Non-perturbative, but calculable for
b>>RS (weak gravitational field)
b > RS
Gravitational scattering:
two-jet signal at hadron
colliders
G.G.-Rattazzi-Wells
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At b<RS, no longer calculable
Strong indications for black-hole formation
b < RS
Giddings-Thomas, Dimopoulos-Landsberg
At the LHC, limited space for transplanckian
region and quantum-gravity pollution
At the VLHC, perfect conditions
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2-jets with large Minv and Dh
Black holes
Transplanckian
VLHC
Semi-classical
approximation
QUANTUM GRAVITY
Cisplanckian
Linearized
gravity
LHC
Jets + missing ET
2-leptons
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INVESTIGATING THE THEORY OF
ELECTROWEAK BREAKING

+
H  a H Wna Bn
LEP1
10
9.7
5.6
4.6
iH D H L  L
9.2
7.3
e  e   
6.1
4.5
e   5e b   5b
4.3
3.2
6.4
5.0
9.3
12.4

H D H
2

LEP2
MFV


2
1

q L u u   q
2
H  d R d u u n q L F n
Bounds on LH
1
L 2 O
 LH
LH > 5-10 TeV
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3GF
2
 mH 
8 2 2
  SM

2
2
2
2
2mW  mZ  mH  4mt  
200 GeV 
 TeV

 
2
SM

2
SM<1 TeV, LH>5-10 TeV
“Little” hierarchy between SM and LH a
•New physics at SM is weakly interacting
•No (sizable) tree-level contributions from new
physics at SM
•Strongly-interacting physics can only occur at
scales larger than LH
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PROBLEMA DELLA GERARCHIA 
controllo delle divergenze quadratiche alla
massa dell’Higgs
SUPERSIMMETRIA:
t
mH2 =
H
~
t
+
H
~ 2 2
3GF mt2 m
t

ln ~ 2
2
mt
2
28
HIGGS AS PSEUDOGOLDSTONE BOSON

 f
2
e
iq / f
  f
  
 e :

q  q  a
Non - linearly realized symmetry
ia
h  h  a forbids m h
2
2
Gauge, Yukawa and self-interaction are large nonderivative couplings 
Violate global symmetry and introduce quadratic div.
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Arkani Hamed-Cohen-Georgi
A less ambitious programme:
LITTLE HIGGS
Explain only little hierarchy
One loop m 
2
H
GF

2
m 
2
SM
2
SM
  SM 

GF
 TeV
At SM new physics cancels one-loop power divergences
Two loops mH2 
GF2

4
4
mSM
2   
2
GF mSM
 10 TeV   LH
“Collective breaking”: many (approximate) global symmetries
preserve massless Goldstone boson
ℒ1
ℒ2
H
ℒ1 ℒ2 2
m  2

2
4 4
2
H
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Realistic models are rather elaborate
Arkani Hamed-Cohen-Georgi-Katz-Nelson-Gregoire-WackerLow-Skiba-Smith-Kaplan-Schmaltz-Terning…
Effectively, new particles at the scale f ~ SM
canceling (same-spin) SM one-loop divergences
with couplings related by symmetry
Typical spectrum:
Vectorlike charge 2/3 quark
Gauge bosons EW
triplet + singlet
Scalars (triplets ?)
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HIGGS AS EXTRA-DIM COMPONENT
OF GAUGE FIELD
AM = (A,A5),
gauge
Higgs
A5 g A5 +∂5 
forbids m2A52
Higgs/gauge unification
as graviton/photon
unification in Kaluza-Klein
Correct Higgs quantum numbers by projecting out
Csaki-Grojean-Murayama
unwanted states with orbifold
Burdman-Nomura
Yukawa couplings, quartic couplings without
reintroducing quadratic divergences
Scrucca-Serone-Silvestrini
EW BROKEN BY BOUNDARY CONDITIONS?
Csaki-GrojeanMurayama-PiloTerning
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Calculable description of EW breaking with strong dynamics
at 5-10 TeV
23 N 2
1
Unitarity  T00 
g5 s 
192 
2
g 5  g R 
96
s
M KK
2
23 N g
New realizations of technicolour theories with new elements
(extra dimensions, AdS/CFT correspondence) allowing some
calculability
“Little hierarchy” is satisfied
LHC will discover weak physics at SM
New strong-dynamics thresholds at LH within the
reach of VLHC
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P. Limon
• The most important requirement for the survival of HEP
is worldwide cooperation resulting in a global strategy
based on a visionary science roadmap.
• Sell the science, not the instruments
– Learn from the NASA strategy, in which the goals are truly
large and visionary, and the instruments are missions along
the way.
• The parameters and schedule for a VLHC will depend on
the timing and location of all other large facilities. The
global plan should recognize these couplings.
• If we ever want to build a VLHC, or any other very large
facility, we need to have a vigorous R&D program now.
– The R&D is very challenging, and the penalty for
failure will be severe.
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CONCLUSIONI
• Anni futuri cruciali per i nuovi progetti di alte energie
• La fisica fondamentale puo’ difendere con orgoglio la
sua missione
EXP
• Un grande progetto negli USA necessario per la
fisica delle particelle
• R&D sui vari fronti deve proseguire
TH
• Nuove strategie per capire la fisica della rottura EW
• In scenari “non-desert”, forti motivazioni per una
nuova scala a ~ 10 TeV  VLHC
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