Results are reported from an amplitude analysis of the B+ → D+D− K+ decay. The analysis is carried out using LHCb proton-proton collision data taken at √s = 7, 8, and 13 TeV, corresponding to a total ...integrated luminosity of 9 fb−1. In order to obtain a good description of the data, it is found to be necessary to include new spin-0 and spin-1 resonances in the D−K+ channel with masses around 2.9 GeV/c2, and a new spin-0 charmonium resonance in proximity to the spin-2 χc2(3930) state.
Abstract
Conventional, hadronic matter consists of baryons and mesons made of three quarks and a quark–antiquark pair, respectively
1,2
. Here, we report the observation of a hadronic state ...containing four quarks in the Large Hadron Collider beauty experiment. This so-called tetraquark contains two charm quarks, a
$$\overline{{{u}}}$$
u
¯
and a
$$\overline{{{d}}}$$
d
¯
quark. This exotic state has a mass of approximately 3,875 MeV and manifests as a narrow peak in the mass spectrum of
D
0
D
0
π
+
mesons just below the
D
*+
D
0
mass threshold. The near-threshold mass together with the narrow width reveals the resonance nature of the state.
Display omitted
Using proton-proton collision data at centre-of-mass energies of s=7,8 and 13TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated ...luminosity of 9fb-1, the invariant mass spectrum of J/ψ pairs is studied. A narrow structure around 6.9GeV/c2 matching the lineshape of a resonance and a broad structure just above twice the J/ψ mass are observed. The deviation of the data from nonresonant J/ψ-pair production is above five standard deviations in the mass region between 6.2 and 7.4GeV/c2, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit-Wigner lineshape.
Measurement of the W boson mass Ackernley, T.; Balagura, V.; Belyaev, I. ...
The journal of high energy physics,
2022, Letnik:
2022, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
The
W
boson mass is measured using proton-proton collision data at
s
= 13 TeV corresponding to an integrated luminosity of 1.7 fb
−
1
recorded during 2016 by the LHCb experiment. With a ...simultaneous fit of the muon
q/p
T
distribution of a sample of
W
→
μν
decays and the
ϕ
*
distribution of a sample of
Z
→
μμ
decays the
W
boson mass is determined to be
m
w
=
80354
±
23
stat
±
10
exp
±
17
theory
±
9
PDF
MeV
,
where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.
A
bstract
A combination of measurements sensitive to the
CP
violation angle
γ
of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between
...D
0
and
D
¯
0
mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN’s Large Hadron Collider, are combined for the first time. This method provides an improvement on the precision of the charm mixing parameter
y
by a factor of two with respect to the current world average. The charm mixing parameters are determined to be
x
=
0.400
−
0.053
+
0.052
%
and
y
=
0.630
−
0.030
+
0.033
%
. The angle
γ
is found to be
γ
=
65.4
−
4.2
+
3.8
°
and is the most precise determination from a single experiment.
A measurement of mixing and C P violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding ...to an integrated luminosity of 5.4 fb−1. A total of 30.6 million D0 → K0S π+ π− decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be xCP = 3.97 ± 0.46 ( stat ) ± 0.29 (syst) × 10−3 and yCP = 4.59 ± 1.20 (stat) ± 0.85 (syst) × 10-3, respectively. The C P -violating parameters are measured as Δx = −0.27 ± 0.18 (stat) ± 0.01 (syst) × 10−3 and Δy = 0.20 ± 0.36 (stat) ± 0.13 (syst ) × 10−3. This is the first observation of a nonzero mass difference in the D0 meson system, with a significance exceeding seven standard deviations. The data are consistent with C P symmetry and improve existing constraints on the associated parameters.
Events containing a Z boson and a charm jet are studied for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of 6 ...fb^{-1} collected at a center-of-mass energy of 13 TeV with the LHCb detector. In events with a Z boson and a jet, the fraction of charm jets is determined in intervals of Z-boson rapidity in the range 2.0<y(Z)<4.5. A sizable enhancement is observed in the forwardmost y(Z) interval, which could be indicative of a valencelike intrinsic-charm component in the proton wave function.
Searches for low-mass dimuon resonances Alexander, M.; Alves, A. A.; Bedeschi, F. ...
The journal of high energy physics,
10/2020, Letnik:
2020, Številka:
10
Journal Article
Recenzirano
Odprti dostop
A
bstract
Searches are performed for a low-mass dimuon resonance,
X
, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample corresponding to an integrated ...luminosity of 5.1 fb
−
1
and collected with the LHCb detector. The
X
bosons can either decay promptly or displaced from the proton-proton collision, where in both cases the requirements placed on the event and the assumptions made about the production mechanisms are kept as minimal as possible. The searches for promptly decaying
X
bosons explore the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible
X
widths considered above 20 GeV. The searches for displaced
X → μ
+
μ
−
decays consider masses up to 3 GeV. None of the searches finds evidence for a signal and 90% confidence-level exclusion limits are placed on the
X → μ
+
μ
−
cross sections, each with minimal model dependence. In addition, these results are used to place world-leading constraints on GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios.
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