Hypothetical particles in physics
In
particle physics
,
W′ and Z′ bosons
(or
W-prime and Z-prime bosons
) refer to hypothetical
gauge bosons
that arise from extensions of the
electroweak symmetry
of the
Standard Model
. They are named in analogy with the Standard Model
W and Z bosons
.
Types
[
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]
Types of W′ bosons
[
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]
W′ bosons often arise in models with an extra
SU(2)
gauge group
relative to the full
Standard Model
gauge group
SU
(3)?×?SU(2)?×?
U(1)
. The extended
SU(2) × SU(2)
symmetry spontaneously breaks into the
diagonal subgroup
SU(2)
W
which corresponds to the conventional SU(2) in electroweak theory.
More generally, there could be
n
copies of SU(2), which are then broken down to a diagonal SU(2)
W
. This gives rise to
n
2
? 1
different W′
+
, W′
?
, and Z′ bosons.
Such models might arise from a
quiver diagram
, for example.
In order for the W′ bosons to couple to
weak isospin
, the extra SU(2) and the Standard Model SU(2) must mix; one copy of SU(2) must break around the
TeV
scale (to get W′ bosons with a TeV mass) leaving a second SU(2) for the Standard Model. This happens in
Little Higgs
models that contain more than one copy of SU(2). Because the W′ comes from the breaking of an SU(2), it is generically accompanied by a Z′ boson of (almost) the same mass and with couplings related to the W′ couplings.
Another model with W′ bosons but without an additional SU(2) factor is the so-called
331 model
with
The symmetry breaking chain
SU(3)
L
× U(1)
W
→ SU(2)
W
× U(1)
Y
leads to a pair of W′
±
bosons and three Z′ bosons.
W′ bosons also arise in
Kaluza?Klein
theories with SU(2) in the
bulk
.
Types of Z′ bosons
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Various models of physics
beyond the Standard Model
predict different kinds of Z′ bosons.
- Models with a new
U(1)
gauge symmetry
[
which?
]
- The Z′ is the gauge boson of the (broken) U(1) symmetry.
- E
6
models
- This type of model contains two Z′ bosons, which can mix in general.
- Pati?Salam
- In addition to a fourth leptonic "color", Pati?Salam includes a right handed weak interaction with W′ and Z′ bosons.
- Topcolor
and Top Seesaw Models of Dynamical Electroweak Symmetry Breaking
- Both these models have Z′ bosons that select the formation of particular condensates.
- Little Higgs
models
- These models typically include an enlarged gauge sector, which is broken down to the Standard Model gauge symmetry around the TeV scale. In addition to one or more Z′ bosons, these models often contain W′ bosons.
- Kaluza?Klein
models
- The Z′ boson are the excited modes of a neutral bulk gauge symmetry.
- Stueckelberg Extensions
- The Z′ boson is sourced from couplings found in
string
theories with intersecting
D-branes
(see
Stueckelberg action
).
Searches
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]
Direct searches for "wide resonance-width" models
[
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]
The following statements pertain only to "wide
resonance width
" models.
A W′-boson could be detected at hadron colliders through its decay to
lepton
plus
neutrino
or
top quark
plus
bottom quark
, after being produced in quark?antiquark
annihilation
. The
LHC
reach for W′ discovery is expected to be a few
TeV
.
Direct searches for Z′-bosons are carried out at
hadron
colliders, since these give access to the highest energies available. The search looks for high-mass dilepton
resonances
: the Z′-boson would be produced by quark?antiquark annihilation and decay to an
electron
?
positron
pair or a pair of opposite-charged
muons
. The most stringent current limits come from the
Fermilab
Tevatron
, and depend on the couplings of the Z′-boson (which control the production
cross section
); as of 2006, the
Tevatron
excludes Z′-bosons up to masses of about 800
GeV
for "typical" cross sections predicted in various models.
[2]
Direct searches for "narrow resonance-width" models
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]
Recent classes of models have emerged that naturally provide cross section signatures that fall on the edge, or slightly below the 95% confidence level limits set by the Tevatron, and hence can produce detectable cross section signals for a Z′ boson in a mass range much closer to the Z pole-mass than the "wide width" models discussed above.
These "narrow width" models which fall into this category are those that predict a Stuckelberg Z′ as well as a Z′ from a universal extra dimension (see
"The Z′ hunters' guide"
.
for links to these papers).
On 7 April 2011, the
CDF collaboration
at the Tevatron reported an excess in proton?
antiproton
collision
events
that produce a W boson accompanied by two hadronic
jets
. This could possibly be interpreted in terms of a Z′ boson.
[3]
[4]
On 2 June 2015, the
ATLAS experiment
at the LHC reported evidence for W′-bosons at significance 3.4
σ
, still too low to claim a formal discovery.
[5]
Researchers at the
CMS experiment
also independently reported signals that corroborate ATLAS's findings.
In March 2021, there were some reports to hint at the possible existence of Z′ bosons as an unexpected difference in how
beauty quarks
decay to create electrons or muons. The measurement has been made at a statistical significance of 3.1
σ
, which is well below the 5
σ
level that is conventionally considered sufficient proof of a discovery.
[6]
Z′?Y mixings
[
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]
We might have gauge
kinetic mixings
between the U(1)′ of the Z′ boson and U(1)
Y
of
hypercharge
. This mixing leads to a
tree level
modification of the
Peskin?Takeuchi parameters
.
See also
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References
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Further reading
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]
More advanced:
- Abulencia, A.; CDF Collaboration; et al. (2006). "Search for Z′ → e
+
e
?
using dielectron mass and angular distribution".
Physical Review Letters
.
96
(211801): 211801.
arXiv
:
hep-ex/0602045
.
Bibcode
:
2006PhRvL..96u1801A
.
doi
:
10.1103/PhysRevLett.96.211801
.
PMID
16803227
.
- Amini, Hassib (2003). "Radiative corrections to Higgs masses in Z′ models".
New Journal of Physics
.
5
(49): 49.
arXiv
:
hep-ph/0210086
.
Bibcode
:
2003NJPh....5...49A
.
doi
:
10.1088/1367-2630/5/1/349
.
S2CID
15264222
.
- Aoki, Mayumi; Oshimo, Noriyuki (2000). "Supersymmetric extension of the standard model with naturally stable proton".
Physical Review D
.
62
(55013): 55013.
arXiv
:
hep-ph/0003286
.
Bibcode
:
2000PhRvD..62e5013A
.
doi
:
10.1103/PhysRevD.62.055013
.
S2CID
14168936
.
- Aoki, Mayumi; Oshimo, Noriyuki (2000). "A supersymmetric model with an extra U(1) gauge symmetry".
Physical Review Letters
.
84
(23): 5269?5272.
arXiv
:
hep-ph/9907481
.
Bibcode
:
2000PhRvL..84.5269A
.
doi
:
10.1103/PhysRevLett.84.5269
.
PMID
10990921
.
S2CID
15033987
.
- Appelquist, Thomas; Dobrescu, Bogdan A.; Hopper, Adam R. (2003). "Nonexotic neutral gauge bosons".
Physical Review D
.
68
(35012): 35012.
arXiv
:
hep-ph/0212073
.
Bibcode
:
2003PhRvD..68c5012A
.
doi
:
10.1103/PhysRevD.68.035012
.
S2CID
119091245
.
- Babu, K. S.; Kolda, Christopher F.; March-Russell, John (1996). "Leptophobic U(1)s and the R
b
?R
c
crisis".
Physical Review D
.
54
(7): 4635?4647.
arXiv
:
hep-ph/9603212
.
Bibcode
:
1996PhRvD..54.4635B
.
doi
:
10.1103/PhysRevD.54.4635
.
PMID
10021145
.
S2CID
38299279
.
- Barger, Vernon D.; Whisnant, K. (1987). "Use of Z lepton asymmetry to determine mixing between Z boson and Z′ boson of E
6
superstrings".
Physical Review D
.
36
(3): 979?82.
Bibcode
:
1987PhRvD..36..979B
.
doi
:
10.1103/PhysRevD.36.979
.
PMID
9958259
.
- Barr, S.M.; Dorsner, I. (2005). "The origin of a peculiar extra U(1)".
Physical Review D
.
72
(15011): 015011.
arXiv
:
hep-ph/0503186
.
Bibcode
:
2005PhRvD..72a5011B
.
doi
:
10.1103/PhysRevD.72.015011
.
S2CID
119492913
.
- Batra, Puneet; Dobrescu, Bogdan A.; Spivak, David (2006). "Anomaly-free sets of fermions".
Journal of Mathematical Physics
.
47
(82301): 2301.
arXiv
:
hep-ph/0510181
.
Bibcode
:
2006JMP....47h2301B
.
doi
:
10.1063/1.2222081
.
S2CID
9830964
.
- Carena, Marcela S.; Daleo, Alejandro; Dobrescu, Bogdan A.; Tait, Tim M. P. (2004). "Z′ gauge bosons at the Tevatron".
Physical Review D
.
70
(93009): 093009.
arXiv
:
hep-ph/0408098
.
Bibcode
:
2004PhRvD..70i3009C
.
doi
:
10.1103/PhysRevD.70.093009
.
S2CID
118616267
.
- Demir, Durmus A.; Kane, Gordon L.; Wang, Ting T. (2005). "The Minimal U(1)′ extension of the MSSM".
Physical Review D
.
72
(15012): 015012.
arXiv
:
hep-ph/0503290
.
Bibcode
:
2005PhRvD..72a5012D
.
doi
:
10.1103/PhysRevD.72.015012
.
S2CID
17656689
.
- Dittmar, Michael; Nicollerat, Anne-Sylvie; Djouadi, Abdelhak (2004). "Z′ studies at the LHC: an update".
Physics Letters B
.
583
(1?2): 111?120.
arXiv
:
hep-ph/0307020
.
Bibcode
:
2004PhLB..583..111D
.
doi
:
10.1016/j.physletb.2003.09.103
.
S2CID
15749848
.
- Emam, W.; Khalil, S. (2007). "Higgs and Z′ phenomenology in
B
?
L
extension of the standard model at LHC".
European Physical Journal C
.
522
(3): 625?633.
arXiv
:
0704.1395
.
Bibcode
:
2007EPJC...52..625E
.
doi
:
10.1140/epjc/s10052-007-0411-7
.
S2CID
18985438
.
- Erler, Jens (2000). "Chiral models of weak scale supersymmetry".
Nuclear Physics B
.
586
(1): 73?91.
arXiv
:
hep-ph/0006051
.
Bibcode
:
2000NuPhB.586...73E
.
doi
:
10.1016/S0550-3213(00)00427-2
.
S2CID
16728305
.
- Everett, Lisa L.; Langacker, Paul; Plumacher, Michael; Wang, Jing (2000). "Alternative supersymmetric spectra".
Physics Letters B
.
477
(1?3): 233?241.
arXiv
:
hep-ph/0001073
.
Bibcode
:
2000PhLB..477..233E
.
doi
:
10.1016/S0370-2693(00)00187-8
.
S2CID
16294141
.
- Fajfer, S.; Singer, P. (2002). "Constraints on heavy Z′ couplings from Δ
S
= 2 B
?
→ K
?
K
?
π
+
decay".
Physical Review D
.
65
(17301): 017301.
arXiv
:
hep-ph/0110233
.
Bibcode
:
2001PhRvD..65a7301F
.
doi
:
10.1103/PhysRevD.65.017301
.
S2CID
117080415
.
- Ferroglia, A.; Lorca, A.; van der Bij, J. J. (2007). "The Z′ reconsidered".
Annalen der Physik
.
16
(7?8): 563?578.
arXiv
:
hep-ph/0611174
.
Bibcode
:
2007AnP...519..563F
.
doi
:
10.1002/andp.200710249
.
S2CID
17347199
.
- Hayreter, Alper (2007). "Dilepton signatures of family non-universal U(1)′".
Physics Letters B
.
649
(2?3): 191?196.
arXiv
:
hep-ph/0703269
.
Bibcode
:
2007PhLB..649..191H
.
doi
:
10.1016/j.physletb.2007.03.049
.
S2CID
16059648
.
- Kang, Junhai; Langacker, Paul (2005). "Z′ discovery limits for supersymmetric E
6
models".
Physical Review D
.
71
(35014): 035014.
arXiv
:
hep-ph/0412190
.
Bibcode
:
2005PhRvD..71c5014K
.
doi
:
10.1103/PhysRevD.71.035014
.
S2CID
9649745
.
- Morrissey, David E.; Wells, James D. (2006). "The tension between gauge coupling unification, the Higgs boson mass, and a gauge-breaking origin of the supersymmetric μ-term".
Physical Review D
.
74
(15008): 15008.
arXiv
:
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.
Bibcode
:
2006PhRvD..74a5008M
.
doi
:
10.1103/PhysRevD.74.015008
.
S2CID
119467594
.
External links
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