We propose a novel method to measure flavor oscillations and charge-parity ( C P ) violation in charm mixing. The approach applies to multibody charm decays, such as D0 → K0Sπ+π−, and avoids the need ...for a fit of the decay amplitudes while suppressing biases due to nonuniform signal reconstruction efficiencies as functions of phase space and decay time. Data are partitioned in decay-time and Dalitz-plot regions (bins). The Dalitz-plot bins are symmetric with respect to the principal bisector and chosen to ensure nearly constant values of the strong interaction phases in each. The ratios of signal yields observed in each symmetric bin pair are fit as functions of decay time, using independent auxiliary measurements of the strong interaction phases as constraints, to determine the relevant physics parameters. Simulation shows a 35% improvement in sensitivity to the normalized charm-eigenstate mass difference with respect to existing model-independent methods. In addition, we introduce a parametrization of oscillation and CP-violation effects in charm mixing that has attractive statistical properties and may find wider applicability.
Several methods exist to measure CP violation observables related to the CKM unitarity triangle angle γ using B meson decays. These observables are different for every B meson decay considered, ...although the information they contain on γ is encoded in a similar way for all of them. This paper describes a strategy for a simultaneous measurement of γ using several B meson decays that takes into account possible correlations between them based on the methodologies described in J. Garra Ticó, arXiv:1804.05597. Sensitivity studies demonstrate that the simultaneous analysis of several B meson decay modes results in smaller uncertainties and improved statistical behavior compared to a combination of standalone measurements.
A
bstract
The
ϒ
(1
S
)
μ
+
μ
−
invariant-mass distribution is investigated for a possible exotic meson state composed of two
b
quarks and two
b
¯
quarks,
X
b
b
¯
b
b
¯
. The analysis is based on a ...data sample of
pp
collisions recorded with the LHCb detector at centre-of-mass energies
s
=
7
, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb
−1
. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the
X
b
b
¯
b
b
¯
state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range 2
.
0
,
5
.
0, and the
X
b
b
¯
b
b
¯
state has rapidity in the range 2
.
0
,
4
.
5 and transverse momentum less than 15 GeV/
c
.
A
bstract
Measurements are reported of the central exclusive production of
J/ψ
and
ψ
(2
S
) mesons in
pp
collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced ...compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2
.
0
< η <
4
.
5, are measured to be
σ
J
/
ψ
→
μ
+
μ
−
=
435
±
18
±
11
±
17
p
b
σ
ψ
2
S
→
μ
+
μ
−
=
11.1
±
1.1
±
0.3
±
0.4
p
b
.
The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.
A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding ...to integrated luminosities of 1 and 2
fb
-
1
, respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80
GeV
/
c
2
and lifetimes from 5 to 100
ps
are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23–198 GeV/
c
2
range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.
A search is presented for long-lived particles with a mass between 25 and 50
GeV
/
c
2
and a lifetime between 2 and 500 ps, using proton–proton collision data corresponding to an integrated ...luminosity of 2.0
fb
-
1
, collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125
GeV
/
c
2
Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.
A
bstract
The production of
B
±
mesons is studied in pp collisions at centre-of-mass energies of 7 and 13 TeV, using
B
±
→
J
/
ψ K
±
decays and data samples corresponding to 1.0 fb
−1
and 0.3 fb
−1
, ...respectively. The production cross-sections summed over both charges and integrated over the transverse momentum range 0 <
p
T
< 40 GeV/
c
and the rapidity range 2.0 <
y
< 4.5 are measured to be
σ
pp
→
B
±
X
,
s
=
7
T
e
V
=
43.0
±
0.2
±
2.5
±
1.7
μ
b
,
σ
pp
→
B
±
X
,
s
=
13
T
e
V
=
86.6
±
0.5
±
5.4
±
3.4
μ
b
,
where the first uncertainties are statistical, the second are systematic, and the third are due to the limited knowledge of the
B
±
→
J
/
ψ K
±
branching fraction. The ratio of the cross-section at 13 TeV to that at 7 TeV is determined to be 2.02 ± 0.02 (stat) ± 0.12 (syst). Differential cross-sections are also reported as functions of
p
T
and
y
. All results are in agreement with theoretical calculations based on the state-of-art fixed next-to-leading order quantum chromodynamics.
A
bstract
The production cross-sections of
ϒ
(1
S
),
ϒ
(2
S
) and
ϒ
(3
S
) mesons in proton-proton collisions at
s
=
13
TeV are measured with a data sample corresponding to an integrated luminosity ...of 277 ± 11 pb
−1
recorded by the LHCb experiment in 2015. The
ϒ
mesons are reconstructed in the decay mode
ϒ
→
μ
+
μ
−
. The differential production cross-sections times the dimuon branching fractions are measured as a function of the
ϒ
transverse momentum,
p
T
, and rapidity,
y
, over the range 0
< p
T
<
30 GeV
/c
and 2
.
0
< y <
4
.
5. The ratios of the cross-sections with respect to the LHCb measurement at
s
=
8
TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.
A
bstract
Forward top quark pair production is studied in
pp
collisions in the
μeb
final state using a data sample corresponding to an integrated luminosity of 1.93 fb
−1
collected with the LHCb ...experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted Δ
R
, between the two leptons must be larger than 0.1. The
b
-jet axis is required to be separated from both leptons by a Δ
R
of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be
σ
t
t
¯
=
126
±
19
stat
±
16
syst
±
5
lumi
f
b
where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction.
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