74 research outputs found
The present and future status of heavy neutral leptons
The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios
Measurement of the CP-violating phase ϕs in B¯s0→Ds+Ds− decays
We present a measurement of the CP-violating weak mixing phase ϕs using the decay B¯0s→D+sD−s in a data sample corresponding to 3.0 fb−1 of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint |λ|=1 to allow for the presence of CP violation in decay, yields ϕs=0.02±0.17(stat)±0.02(syst) rad, |λ|=0.91+0.18−0.15(stat)±0.02(syst). This result is consistent with the standard model expectation
Measurement of the inelastic pp cross-section at a centre-of-mass energy of √s = 7 TeV
The cross-section for inelastic proton-proton collisions, with at least one
prompt long-lived charged particle of transverse momentum pT > 0.2GeV/c in the pseudorapidity
range 2.0 > η > 4.5, is measured by the LHCb experiment at a centre-ofmass
energy of √
s = 7 TeV. The cross-section in this kinematic range is determined to
be σ
acc
inel = 55.0 ± 2.4 mb with an experimental uncertainty that is dominated by systematic
contributions. Extrapolation to the full phase space, using Pythia 6, yields
σinel = 66.9 ± 2.9 ± 4.4 mb, where the first uncertainty is experimental and the second is
due to the extrapolation
Precision luminosity measurements at LHCb
Measuring cross-sections at the LHC requires the luminosity to be determined
accurately at each centre-of-mass energy . In this paper results are
reported from the luminosity calibrations carried out at the LHC interaction
point 8 with the LHCb detector for = 2.76, 7 and 8 TeV
(proton-proton collisions) and for = 5 TeV (proton-lead
collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity
calibration methods were employed. It is observed that the beam density profile
cannot always be described by a function that is factorizable in the two
transverse coordinates. The introduction of a two-dimensional description of
the beams improves significantly the consistency of the results. For
proton-proton interactions at = 8 TeV a relative precision of the
luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43%
using beam-gas imaging, resulting in a combined precision of 1.12%. Applying
the calibration to the full data set determines the luminosity with a precision
of 1.16%. This represents the most precise luminosity measurement achieved so
far at a bunched-beam hadron collider.Comment: 100 pages, 57 figure
Study of η − η′ mixing from measurement of B (s) 0 → J/ψη(′) decay rates
A study of B and B0
s meson decays into J/ψη and J/ψη0 final states is performed
using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV,
collected by the LCHb experiment and corresponding to 3.0 fb−1
of integrated luminosity.
The decay B0 → J/ψη0
is observed for the first time. The following ratios of branching
fractions are measured:
B(B0 → J/ψη0
)
B(B0
s → J/ψη0)
= (2.28 ± 0.65 (stat) ± 0.10 (syst) ± 0.13 (fs/fd)) × 10−2
,
B(B0 → J/ψη)
B(B0
s → J/ψη)
= (1.85 ± 0.61 (stat) ± 0.09 (syst) ± 0.11 (fs/fd)) × 10−2
,
where the third uncertainty is related to the present knowledge of fs/fd, the ratio between
the probabilities for a b quark to form a B0
s or a B0 meson. The branching fraction ratios
are used to determine the parameters of η−η
0 meson mixing. In addition, the first evidence
for the decay B0
s → ψ(2S)η
0
is reported, and the relative branching fraction is measured,
B(B0
s → ψ(2S)η
0
)
B(B0
s → J/ψη0)
= (38.7 ± 9.0 (stat) ± 1.3 (syst) ± 0.9(B)) × 10−2
,
where the third uncertainty is due to the limited knowledge of the branching fractions of
J/ψ and ψ(2S) mesons
Measurement of the semileptonic asymmetry in mixing
The semileptonic asymmetry in mixing, , is measured in proton-proton collision data, corresponding to an
integrated luminosity of 3.0 fb, recorded by the LHCb experiment.
Semileptonic decays are reconstructed in the inclusive final states
and , where the meson decays into the
final state, and the meson into the
final state. The asymmetry
between the numbers of and decays is measured
as a function of the decay time of the mesons. The asymmetry is
measured to be , where the first
uncertainty is statistical and the second systematic. This is the most precise
measurement of to date and is consistent with the prediction
from the Standard Model.Comment: 10 pages, 2 figure
Measurement of the ηc(1S) production cross-section in proton–proton collisions via the decay ηc(1S) → pp¯
No abstract available
The present and future status of heavy neutral leptons
The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.Peer reviewe
Study of eta-eta ' mixing from measurement of B-(s)(0) -> J/psi eta((')) decay rates
A study of B and Bs meson decays into J/ψ η and J/ψ η′ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψ η′ is observed for the first time. The following ratios of branching fractions are measured:
B(B0→J/ψη′)B(B0s→ J/ψη′)=(2.28±0.65 (stat)±0.10 (syst)±0.13 (fs/fd))×10−2,B(B0→ J/ψη)B(B0s→ J/ψη)=(1.85±0.61 (stat)±0.09 (syst)±0.11 (fs/fd))×10−2, where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a Bs or a B0 meson. The branching fraction ratios are used to determine the parameters of η − η′ meson mixing. In addition, the first evidence for the decay Bs → ψ(2S)η′ is reported, and the relative branching fraction is measured,
B(B0s→ ψ(2S)η′)B(B0s→ J/ψη′)=(38.7±9.0 (stat)±1.3 (syst)±0.9(B))×10−2, where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons
Measurement of the inelastic pp cross-section at a centre-of-mass energy of root s=7 TeV
The cross-section for inelastic proton-proton collisions, with at least one
prompt long-lived charged particle of transverse momentum
GeV/ in the pseudorapidity range , is measured by the LHCb
experiment at a centre-of-mass energy of TeV. The cross-section in
this kinematic range is determined to be mb within the spectrometer acceptance with an experimental uncertainty
that is dominated by systematic contributions. Extrapolation to the full phase
space, using PYTHIA 6, yields mb,
where the first uncertainty is experimental and the second is due to the
extrapolation.Comment: 15 pages, 2 figure
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