A
bstract
The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies
s
= 380 GeV, ...1
.
5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of t
̄
tH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.
Equal amounts of matter and antimatter are predicted to have been produced in the Big Bang, but our observable Universe is clearly matter-dominated. One of the prerequisites for understanding this ...elimination of antimatter is the nonconservation of charge-parity (CP) symmetry. So far, two types of CP violation have been observed in the neutral K meson (K0) and B meson (B0) systems: CP violation involving the mixing between K0 and its antiparticle (and likewise for B0 and ), and direct CP violation in the decay of each meson. The observed effects for both types of CP violation are substantially larger for the B0 meson system. However, they are still consistent with the standard model of particle physics, which has a unique source of CP violation that is known to be too small to account for the matter-dominated Universe. Here we report that the direct CP violation in charged B±→K± 0 decay is different from that in the neutral B0 counterpart. The direct CP-violating decay rate asymmetry, (that is, the difference between the number of observed B-→K- 0 event versus B+→K+ 0 events, normalized to the sum of these events) is measured to be about +7%, with an uncertainty that is reduced by a factor of 1.7 from a previous measurement. However, the asymmetry for versus B0→K+ - is at the -10% level. Although it is susceptible to strong interaction effects that need further clarification, this large deviation in direct CP violation between charged and neutral B meson decays could be an indication of new sources of CP violation-which would help to explain the dominance of matter in the Universe.
The Compact Linear Collider (CLIC) is an option for a future
e
+
e
-
collider operating at centre-of-mass energies up to
3
TeV
, providing sensitivity to a wide range of new physics phenomena and ...precision physics measurements at the energy frontier. This paper is the first comprehensive presentation of the Higgs physics reach of CLIC operating at three energy stages:
s
=
350
GeV
, 1.4 and
3
TeV
. The initial stage of operation allows the study of Higgs boson production in Higgsstrahlung (
e
+
e
-
→
Z
H
) and
W
W
-fusion (
e
+
e
-
→
H
ν
e
ν
¯
e
), resulting in precise measurements of the production cross sections, the Higgs total decay width
Γ
H
, and model-independent determinations of the Higgs couplings. Operation at
s
>
1
TeV
provides high-statistics samples of Higgs bosons produced through
W
W
-fusion, enabling tight constraints on the Higgs boson couplings. Studies of the rarer processes
e
+
e
-
→
t
t
¯
H
and
e
+
e
-
→
H
H
ν
e
ν
¯
e
allow measurements of the top Yukawa coupling and the Higgs boson self-coupling. This paper presents detailed studies of the precision achievable with Higgs measurements at CLIC and describes the interpretation of these measurements in a global fit.
Using kaon secondary interactions in the material of the Belle detector, we search for both inclusive and exclusive production of the Θ(1540)+. We set an upper limit of 2.5% at the 90% C.L. on the ...ratio of the Θ(1540)+ to Λ(1520) inclusive production cross sections. We also search for the Θ(1540)+ as an intermediate resonance in the charge exchange reaction K+n→pKS0. We set an upper limit of ΓΘ+<0.64 MeV at the 90% C.L. for mΘ+=1.539 MeV/c2. These results are obtained from a 397 fb−1 data sample collected with the Belle detector near the ϒ(4S) resonance, at the KEKB asymmetric energy e+e− collider.
The production of J/ψ mesons in proton–proton collisions at √s = 7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/ψ production is measured as a function ...of the J/ψ transverse
momentum pT and rapidity y in the fiducial region pT ∈ 0; 14 GeV/c and y ∈ 2.0; 4.5. The differential cross-section and fraction of J/ψ from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb−1. The measured cross-sections integrated over the fiducial region are 10.52 ± 0.04 ± 1.40+1.64 −2.20 µb for prompt J/ψ production and 1.14 ± 0.01 ± 0.16 µb for J/ψ from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/ψ production cross-section is obtained assuming no J/ψ polarisation and the third error indicates the acceptance uncertainty due to this assumption.
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