PHYS 5326 – Lecture #21
Monday, Apr. 9, 2003
Dr. Jae Yu
•Higgs Mass Theoretical Upper Bounds
•SM Higgs Production Processes in
Hadron Colliders
•Winter 03 Experimental Results
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
1
Higgs Particles
• What are the Higgs particles we are looking for?
– Standard Model Higgs: Single neutral scalar
– MSSM Higgs: Five scalar and pseudoscalar particles
• h0, H0, H+/- and A0
– Higgs in Other Models
• What are the most distinct characteristics of
Higgs particles?
– In both SM and MSSM, the Higgs particles interact
with fermions through Yukawa coupling whose
strength mostly is set by the fermion masses.
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
2
Theoretical MH Upper Bound in SM
From the SU2xU1 L

2
v 
L  D       g d d Ld R  g u u L c u R  h.c.
2
2
2
2
2
Where, the scale v is the EWSB scale, v  1 2G  246GeV ,
and the mass of the Higgs particle and fermions are
F
M H  v 2
mf 
gfv
Wednesday, Apr. 9, 2003
2
Where  is the quartic coupling
and gf is the Yukawa coupling
PHYS 5326, Spring 2003
Jae Yu
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Theoretical MH Upper Bound in SM
While MH cannot be predicted in SM, internal consistency
and extrapolation to high energies can provide upper and
lower bounds.
Based on the general principle of t-E uncertainty, particles
become unphysical if their masses grow indefinitely. Therefore
MH must be bound to preserve the unitarity in the perturbative
regime. and the mass of the Higgs particle and fermions are
From an asymptotic expansion of a WLWL S-wave scattering, an
upper limit on MH can be obtained:
M H2  2 2
Wednesday, Apr. 9, 2003
 850GeV 
2
GF
PHYS 5326, Spring 2003
Jae Yu
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Theoretical MH Upper Bound in SM
The SM tells that there is no new physics between EWSB
scale (~1TeV) and the GUT scale (1019GeV). This can
provide a restrictive upper limit because the SM can extend
to a scale L before a new type of strong short range
interaction can occur between the fundamental particles.
From the variation of quartic Higgs coupling, , and the topHiggs Yukawa coupling, gt, with energy parameterized by
t=log(m2/v2), and requiring L to be finite, one can obtain
the Higgs mass upper bound
M
Wednesday, Apr. 9, 2003
2
H
2 2
8

v


3 log v 2 / 2
PHYS 5326, Spring 2003
Jae Yu

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Theoretical MH Upper Bound in SM
LSM
For the central mt=175GeV
Wednesday, Apr. 9, 2003
1 TeV
MH
55  M H  700GeV
1019GeV 130  M H  190GeV
PHYS 5326, Spring 2003
Jae Yu
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SM Higgs Properties
• Profiles of Higgs Particles determined by its mass
• The Yukawa coupling of Higgs to fermions set by
the fermion mass, mj, and to the electroweak
gauge bosons by their masses, MV.
g ffH 

2GF


1/ 2
gVVH  2 2GF

mf
1/ 2
M
2
V
Physical observables, the total decay width, lifetime and branching
ratio to specific final states are determined by these parameters.
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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Higgs Decay to Fermions
Higgs partial decay
width to fermions are


H f f
GF
 Nc
g ffH m 2f M H2 M H
4 2


Number of color quantum
numbers, 1 or 3
For MH=100GeV,
mb(MH2)~3GeV,
mc(MH2)~0.6GeV
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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Higgs Decay to Gauge Boson Pairs
H  VV 
 V


GF
M H3 1  4 x  12 x 2 V
16 2
Where x  M V2 / M H2 and
 V  2 or 1 for W or Z

 H  VV *

3GF2 M V4
'

M
R
(
x
)

H
V
16 3
Where  W'  1 and
 Z'  7 / 12  10 sin 2 W / 9  40 sin 4 W / 27
H   
3GF2 2
3 4
2

M
N
e
H
c t 7
3
3
128 2
2
Valid in the limit M H2  4 M W2 ,4 M t2
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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Summary of
SM Higgs
Branching
Ratio
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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Higgs Production Processes at
Hadron Colliders
Gluon fusion:
gg  H


WW, ZZ Fusion:
W W , ZZ  H
Higgs-strahlung
off W,Z:
qq  W , Z  W , Z  H
*
*
Higgs Bremsstrahlung
q q, gg  t t  H
off top:
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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Hadron Collider SM Higgs Production s
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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What do we know as of Winter 03?
LEP EWWG: http://www.cern.ch/LEPEWWG
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
114<MH<300+700 GeV
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Homework Assignment
• Study the summary SM Higgs branching ratio
plot in slide 10 and plan experimental strategies
to search for Higgs particles in the following two
scenarios
– MH=115GeV
– MH >150GeV
• Due: Wednesday, Apr. 16
Wednesday, Apr. 9, 2003
PHYS 5326, Spring 2003
Jae Yu
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