Search for the doubly charmed baryon Ξcc Alexander, M.; Alves, A. A.; Baryshnikov, F. ...
Science China. Physics, mechanics & astronomy,
02/2020, Letnik:
63, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A search for the doubly charmed baryon
Ξ
c
c
+
is performed through its decay to the
Λ
c
+
K
−
π
+
final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass ...energies of 7, 8 and 13 TeV. The data correspond to a total integrated luminosity of 9 fb
−1
. No significant signal is observed in the mass range from 3.4 to 3.8 GeV/
c
2
. Upper limits are set at 95% credibility level on the ratio of the
Ξ
c
c
+
production cross-section times the branching fraction to that of
Λ
c
+
and
Ξ
c
c
+
+
baryons. The limits are determined as functions of the
Ξ
c
c
+
mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/
c
.
A measurement of
D
0
meson production by the LHCb experiment in its fixed-target configuration is presented. The production of
D
0
mesons is studied with a beam of 2.5
Te
V
protons colliding on a ...gaseous neon target at rest, corresponding to a nucleon–nucleon centre-of-mass energy of
s
NN
=
68.5
Ge
V
. The sum of the
D
0
and
D
¯
0
production cross-section in
p
Ne
collisions in the centre-of-mass rapidity range
y
⋆
∈
-
2.29
,
0
is found to be
σ
D
0
y
⋆
∈
-
2.29
,
0
=
48.2
±
0.3
±
4.5
μ
b
/
nucleon
where the first uncertainty is statistical and the second is systematic. The
D
0
-
D
¯
0
production asymmetry is also evaluated and suggests a trend towards negative values at large negative
y
⋆
. The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including 1
%
intrinsic charm and 10
%
recombination contributions better describe the data than the other models considered.
Silicon on insulator (SOI) substrates offer a promising platform for monolithic high energy physics detectors with integrated read-out electronics and pixel diodes. This paper describes the ...fabrication and characterisation of specially-configured SOI substrates using improved bonded wafer ion split and grind/polish technologies. The crucial interface between the high resistivity handle silicon and the SOI buried oxide has been characterised using both pixel diodes and circular geometry MOS transistors. Pixel diode breakdown voltages were typically greater than 100
V and average leakage current densities at 70
V were only 55
nA/cm
2. MOS transistors subjected to 24
GeV proton irradiation showed an increased SOI buried oxide trapped charge of only 3.45
×
10
11
cm
−2 for a dose of 2.7
Mrad.
A
bstract
The production cross-section of
J/ψ
pairs in proton-proton collisions at a centre-of-mass energy of
s
= 13 TeV is measured using a data sample corresponding to an integrated luminosity of 4
....
2 fb
−
1
collected by the LHCb experiment. The measurement is performed with both
J/ψ
mesons in the transverse momentum range 0
< p
T
<
14 GeV/
c
and rapidity range 2
.
0
< y <
4
.
5. The cross-section of this process is measured to be 16
.
36 ± 0
.
28 (stat) ± 0
.
88 (syst) nb. The contributions from single-parton scattering and double-parton scattering are separated based on the dependence of the cross-section on the absolute rapidity difference ∆
y
between the two
J/ψ
mesons. The effective cross-section of double-parton scattering is measured to be
σ
eff
= 13
.
1
±
1
.
8 (stat)
±
2
.
3 (syst) mb. The distribution of the azimuthal angle
ϕ
CS
of one of the
J/ψ
mesons in the Collins-Soper frame and the
p
T
-spectrum of the
J/ψ
pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of ⟨cos 2
ϕ
CS
⟩ and ⟨cos 4
ϕ
CS
⟩ are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.
The LHCb detector has undergone a major upgrade for LHC Run 3. This Upgrade I detector facilitates operation at higher luminosity and utilises full-detector information at the LHC collision rate, ...critically including the use of vertex information. A new vertex locator system, the VELO Upgrade, has been constructed. The core element of the new VELO are the double-sided pixelated hybrid silicon detector modules which operate in vacuum close to the LHC beam in a high radiation environment. The construction and quality assurance tests of these modules are described in this paper. The modules incorporate 200 \mum thick, n-on-p silicon sensors bump-bonded to 130 \nm technology ASICs. These are attached with high precision to a silicon microchannel substrate that uses evaporative CO\(_2\) cooling. The ASICs are controlled and read out with flexible printed circuits that are glued to the substrate and wire-bonded to the chips. The mechanical support of the module is given by a carbon fibre plate, two carbon fibre rods and an aluminium plate. The sensor attachment was achieved with an average precision of 21 \(\mathrm{\mu m}\), more than 99.5\% of all pixels are fully functional, and a thermal figure of merit of 3 \mathrm{Kcm^{2}W^{-1}}$ was achieved. The production of the modules was successfully completed in 2021, with the final assembly and installation completed in time for data taking in 2022.
A
bstract
The associated production of prompt
J/ψ
and
Υ
mesons in
pp
collisions at a centre-of-mass energy of
s
= 13 TeV is studied using LHCb data, corresponding to an integrated luminosity of 4 fb
...−
1
. The measurement is performed for
J/ψ
(
Υ
) mesons with a transverse momentum
p
T
<
10 (30) GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. In this kinematic range, the cross-section of the associated production of prompt
J/ψ
and
Υ
(1
S
) mesons is measured to be 133 ± 22 ± 7 ± 3 pb, with a significance of 7
.
9
σ
, and that of prompt
J/ψ
and
Υ
(2
S
) mesons to be 76 ± 21 ± 4 ± 7 pb, with a significance of 4
.
9
σ
. The first uncertainty is statistical, the second systematic, and the third due to uncertainties on the used branching fractions. This is the first observation of the associated production of
J/ψ
and
Υ
(1
S
) in proton-proton collisions. Differential cross-sections are measured as functions of variables that are sensitive to kinematic correlations between the
J/ψ
and
Υ
(1
S
) mesons. The effective cross-sections of the associated production of prompt
J/ψ
and
Υ
mesons are obtained and found to be compatible with measurements using other particle productions.
A
bstract
Four decay modes of the
B
c
+
meson into a
J/ψ
meson and multiple charged kaons or pions are studied using proton-proton collision data, collected with the LHCb detector at centre-of-mass ...energies of 7, 8, and 13 TeV and corresponding to an integrated luminosity of 9 fb
−
1
. The decay
B
c
+
→ J/ψK
+
K
−
π
+
π
+
π
−
is observed for the first time, and evidence for the
B
c
+
→ J/ψ
4
π
+
3
π
−
decay is found. The decay
B
c
+
→ J/ψ
3
π
+
2
π
−
is observed and the previous observation of the
B
c
+
→ ψ
(2
S
)
π
+
π
+
π
−
decay is confirmed using the
ψ
(2
S
) →
J/ψπ
+
π
−
decay mode. Ratios of the branching fractions of these four
B
c
+
decay channels are measured.
A
bstract
A comprehensive study of the local and nonlocal amplitudes contributing to the decay
B
0
→
K
*0
(→
K
+
π
−
)
μ
+
μ
−
is performed by analysing the phase-space distribution of the decay ...products. The analysis is based on
pp
collision data corresponding to an integrated luminosity of 8.4 fb
−
1
collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient
C
9
, responsible for vector dimuon currents, exhibits a 2.1
σ
deviation from the Standard Model expectation. The Wilson Coefficients
C
10
,
C
9
′
and
C
10
′
are all in better agreement than
C
9
with the Standard Model and the global significance is at the level of 1.5
σ
. The model used also accounts for nonlocal contributions from
B
0
→ K
*0
τ
+
τ
−
→ μ
+
μ
−
rescattering, resulting in the first direct measurement of the
bsττ
vector effective-coupling
C
9
τ
.
A
bstract
A first search for the lepton-flavour violating decays
B
0
→
K
*0
τ
±
μ
∓
is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb ...detector at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018, corresponding to an integrated luminosity of 9 fb
−
1
. No significant signal is observed, and upper limits on the branching fractions are determined to be
B
B
0
→
K
∗
0
τ
+
μ
−
<
1.0
1.2
×
10
−
5
and
B
B
0
→
K
∗
0
τ
−
μ
+
<
8.2
9.8
×
10
−
6
at the 90% (95%) confidence level.
A
bstract
A search for
CP
violation in
D
0
→
K
S
0
K
+
π
−
and
D
0
→
K
S
0
K
−
π
+
decays is reported. The search is performed using an unbinned model-independent method known as the energy test that ...probes local
CP
violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5
.
4 fb
−
1
collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of
s
= 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the
D
0
→
K
S
0
K
−
π
+
and
D
0
→
K
S
0
K
+
π
−
modes, respectively. The method is validated using
D
0
→
K
−
π
+
π
−
π
+
and
D
0
→
K
S
0
π
+
π
−
decays, where
CP
-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with
CP
symmetry in both the
D
0
→
K
S
0
K
−
π
+
and the
D
0
→
K
S
0
K
+
π
−
decays, with
p
-values for the hypothesis of no
CP
violation of 70% and 66%, respectively.
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