higgs - page 26

1964 of the long-lived neutral kaon’s decay to two pions
( KL → pp) 187 showed that even CP was not conserved. In
1973, Kobayashi and Maskawa ~KM!144 proposed that CP
violation in the neutral kaon system could be explained in a
model with three families of quarks. The quarks of the third
family, now denoted by b for bottom and t for top, were
subsequently discovered in 1977188,189 and 1994,190–195 re-
spectively. Popular articles on these discoveries include one
by Lederman110 and Liss and Tipton.129
An alternative theory of CP violation in the kaon system,
proposed by Wolfenstein,196 involved a ‘‘superweak’’ CP-
violating interaction mixing K 0 and K¯0, which would lead to
identical CP violation in K L→ p1 p2 and KL → p0 p0. The
discovery that this was not so ~see Refs. 197, 198 for the
most recent published results, which are continually being
updated in conference reports! disproved the superweak
theory and displayed a ‘‘direct’’ form of CP violation with
magnitude consistent with that predicted by the KM theory.
Decays of hadrons containing b quarks are further ground
for testing the KM hypothesis and for displaying evidence
for new physics beyond this ‘‘standard model’’ of CP viola-
tion. A meson containing a b¯ quark will be known generi-
cally as a B meson. Electron-positron colliders have been
constructed at SLAC ~Stanford, CA! 199 and KEK ~Tsukuba,
Japan! 200 expressly to study B mesons; others at DESY
~Hamburg, Germany! and Cornell ~Ithaca, NY!201 were for-
tunate in having just the right energy to produce B mesons in
pairs. The BaBar detector at SLAC and the Belle detector at
KEK have already produced a series of major results on B
decays and CP violation.202,203 Studies of particles contain-
ing b quarks also are expected to be an important part of the
physics program at the Fermilab Tevatron204 and the CERN
Large Hadron Collider ~ LHC!.205
187. ‘‘Evidence for the 2 p Decay of the K 2
0 Meson,’’ J. H. Christenson, J.
W. Cronin, V. L. Fitch, and R. Turlay, Phys. Rev. Lett. 13, 138–140
~1964!. ~I!
188. ‘‘Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV
Proton–Nucleus Collisions,’’ S. W. Herb et al., Phys. Rev. Lett. 39,
252–255 ~1977!. ~I!
189. ‘‘Observation of Structure in the Y Region,’’ W. R. Innes et al., Phys.
Rev. Lett. 39, 1240–1242, 1640~E! ~1977!. ~I!
190. ‘‘Evidence for Top Quark Production in p¯ p Collisions at As 51.8
TeV,’’ CDF Collaboration, F. Abe et al., Phys. Rev. D 50, 2966–3026
~1994!. ~I!
191. ‘‘Evidence for Top Quark Production in p¯ p Collisions at As 51.8
TeV,’’ CDF Collaboration, F. Abe et al., Phys. Rev. Lett. 73, 225–231
~1994!. ~I!
192. ‘‘Observation of Top Quark Production in p¯ p Collisions,’’ CDF Col-
laboration, F. Abe et al., Phys. Rev. Lett. 74, 2626–2631 ~1995!. ~I!
193. ‘‘Search for the Top Quark in pp¯ Collisions at As 51.8 TeV,’’ D0
Collaboration, S. Abachi et al., Phys. Rev. Lett. 72, 2138–2142
~1994!. ~I!
194. ‘‘Search for High Mass Top Quark Production in pp¯ Collisions at
As 51.8 TeV,’’ D0 Collaboration, S. Abachi et al., Phys. Rev. Lett.
74, 2422–2426 ~1995!. ~I!
195. ‘‘Observation of the Top Quark,’’ D0 Collaboration, S. Abachi et al.,
Phys. Rev. Lett. 74, 2632–2637 ~1995!. ~I!
196. ‘‘Violation of CP Invariance and the Possibility of Very Weak Inter-
actions,’’ L. Wolfenstein, Phys. Rev. Lett. 13, 562–564 ~1964!. ~I!
197. ‘‘Observation of Direct CP Violation in K S, L → pp Decays,’’ Fermi-
lab KTeV Collaboration, A. Alavi-Harati et al., Phys. Rev. Lett. 83,
22–27 ~1999!. ~I! For a more recent reference see ‘‘Measurements of
Direct CP Violation, CPT Symmetry, and Other Parameters in the
Neutral Kaon System,’’ A. Alavi-Harati et al., preprint hep-ex/
0208007, submitted to Phys. Rev. D. ~I!
198. ‘‘A Precise Measurement of the Direct CP Violation Parameter Re
( e8 / e),’’ CERN NA48 Collaboration, A. Lai et al., Eur. Phys. J. C
22, 231–254 ~2001!. ~I! For a more recent reference see ‘‘A Precision
Measurement of Direct CP Violation in the Decay of Neutral Kaons
Into Two Pions,’’ J. R. Batley et al., Phys. Lett. B 544, 97–112
~2002!. ~I!
199. ‘‘The First Year of the BaBar Experiment at PEP-II,’’ BaBar Collabo-
ration, B. Aubert et al., SLAC report SLAC-PUB-8539, contributed
to 30th International Conference on High-Energy Physics ~ICHEP
2000!, Osaka, Japan, 27 Jul–2 Aug 2000, e-Print Archive: hep-ex/
0012042. ~I!
200. ‘‘KEKB Performance,’’ Belle Collaboration, presented by A. E.
Bondar at Beauty-2000: 7th International Conference on B-Physics at
Hadron Machines, Sea of Galilee, Kibbutz Maagan, Israel, 13–18
Sept. 2000, Nucl. Instr. Meth. A 462, 139–145 ~2001!. ~I!
201. ‘‘Review of Results from CESR and DORIS,’’ E. I. Shibata, in Be-
yond the Standard Model: Proceedings, Ames, IA, Nov. 18–22,
1988, edited by B.-L. Young ~World Scientific, Singapore, 1988!, pp.
38–59. ~I!
202. ‘‘Measurement of the CP-violating Asymmetry Amplitude sin(2 b),’’
BaBar Collaboration, B. Aubert et al., Phys. Rev. Lett. 89, 201802
~2002!. ~I!
203. ‘‘An Improved Measurement of Mixing-Induced CP Violation in the
Neutral B Meson System,’’ Belle Collaboration, K. Abe et al., Phys.
Rev. D 66, 071102 ~R ! ~2002!. ~I!
204. ‘‘B physics at the Tevatron: Run II and Beyond,’’ K. Anikeev et al.,
proceedings of workshops at Fermilab, 23–25 Sept. 1999 and 24–26
Feb. 2000, Fermilab preprint FERMILAB-PUB-01-197, hep-ph/
0201071 ~unpublished!. ~I!
205. ‘‘The LHCb Project,’’ A. Schopper, Acta Phys. Pol. B32, 1769–1775
~2001!. ~I!’’
G. Dynamics of heavy quarks
With the discovery of the charmed ~ Sec. IX E! and beauty
~Sec. IX F! quarks, a whole new laboratory emerged for the
study of QCD. A bound state of a heavy quark and its anti-
quark, cc¯ or bb¯ , is known as quarkonium, in analogy with
positronium, the bound state of a positron and an electron.
~The top quark lives too short a time for t t¯ bound states to be
of much interest, though one can study some effects of the
binding.! Quarkonium states have been extensively
studied,50,51,53,54 with their spectroscopy and decays provid-
ing useful information on QCD at various distance scales.
The states of light quarks bound to a single heavy quark
have their own regularities. They are analogous to atoms in
which the light quarks and gluons represent the ‘‘electronic’’
degrees of freedom, while the heavy quarks represent the
nuclei. Thus, certain properties of these states are related in
the same way that, for example, properties of hydrogen and
deuterium are related. This ‘‘heavy quark symmetry’’55 has
provided very useful guides to the properties of hadrons con-
taining charm and beauty quarks, and permits more precise
determinations of underlying weak couplings ~such as ele-
ments of the Cabibbo–Koyayashi–Maskawa @CKM# matrix!.
H. Higgs boson„s…
An unbroken SU~2! ^ U~1! theory involving the photon
would require all fields to have zero mass, whereas the W 6
and Z are massive. The symmetry-breaking that generates W
and Z masses must not destroy the renormalizability of the
theory. The Higgs mechanism achieves this goal at the price
of introducing an additional degree of freedom correponding
to a physical particle, the Higgs particle, which is the subject
of intense searches.32,120,206,207 Current 95% c.l. limits on a
311 311 Am. J. Phys., Vol. 71, No. 4, April 2003 Jonathan L. Rosner