Abstract
The standard model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the ...electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton–proton collision data collected with the LHCb detector at CERN’s Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons.
This article presents a new bulk radiation damage model for p-type silicon for use in Synopsys Sentaurus TCAD. The model is shown to provide agreement between experiment and simulation for the ...voltage dependence of the leakage current and the charge collection efficiency, for fluences up to 8×10151MeVneq∕cm2.
Measurements of CP observables in B±→DK± and B±→Dπ± decays are presented where the D meson is reconstructed in the final states K±π∓, π±K∓, K+K−, π+π−, K±π∓π+π−, π±K∓π+π− and π+π−π+π−. This analysis ...uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb−1. Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle γ. The analysis of the four-pion D decay mode is the first of its kind.
Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb(-1) collected with the LHCb detector, seven decay modes of the B-C(+) meson into a J/psi or psi(2S) meson and ...three charged hadrons, kaons or pions, are studied. The decays B-C (+)-> (psi(2S) -> J/psi pi(+)pi(-))pi(+), B+C -> (psi(2S)pi(+)pi(-)pi(+), B+C -> J/psi K+pi(-)pi(+) and B+C -> J/K+K-K+ are observed for the first time, and evidence for the B-C (+)-> (psi(2S)K+K-pi(+), decay is found, where J/psi and psi(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different B-C(+) decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.
Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and ...mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D
D
π
mass spectrum just below the D
D
mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar Formula: see text tetraquark with a quark content of Formula: see text and spin-parity quantum numbers J
= 1
. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D
mesons is consistent with the observed D
π
mass distribution. To analyse the mass of the resonance and its coupling to the D
D system, a dedicated model is developed under the assumption of an isoscalar axial-vector Formula: see text state decaying to the D
D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the Formula: see text state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.
A
bstract
The kinematic dependences of the relative production rates,
f
Λ
b
0
/
f
d
, of
Λ
b
0
baryons and
B
0
mesons are measured using
Λ
b
0
→
Λ
c
+
π
−
and
B
¯
0
→
D
+
π
−
decays. The ...measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb
−1
at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum,
p
T
, and pseudorapidity,
η
, of the beauty hadron, in the studied kinematic region 1
.
5
< p
T
<
40 GeV
/c
and 2
< η <
5. Using a previous LHCb measurement of
f
Λ
b
0
/
f
d
in semileptonic decays, the branching fraction ℬ(
Λ
b
0
→
Λ
c
+
π
−
) = (4.30 ± 0.03
− 0.11
+ 0.12
± 0.26 ± 0.21) × 10
− 3
is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of
f
Λ
b
0
/
f
d
and the fourth is due to the b
B
¯
0
→
D
+
π
−
branching fraction. This is the most precise measurement of a
Λ
b
0
branching fraction to date.
Abstract
Long-lived particles decaying to
$${e ^\pm } {\mu ^\mp } {\nu } $$
e
±
μ
∓
ν
, with masses between 7 and
$$50 \,\text {GeV/}c^2 $$
50
GeV/
c
2
and lifetimes between 2 and
$$50 \,\text {ps} ...$$
50
ps
, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using
$$5.4 \,\text {fb} ^{-1} $$
5.4
fb
-
1
of
$$p $$
p
$$p $$
p
collisions collected with the LHCb detector at a centre-of-mass energy of
$$\sqrt{s} = 13 \,\text {TeV} $$
s
=
13
TeV
. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of
$$125 \,\text {GeV/}c^2 $$
125
GeV/
c
2
, and the charged current production from an on-shell
$$W $$
W
boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.
Observation of the decay Λb0 → ψ(2S)pπ Aidala, C. A.; Amato, S.; Andreassi, G. ...
The journal of high energy physics,
08/2018, Letnik:
2018, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
The Cabibbo-suppressed decay Λ
b
0
→ ψ(2S)pπ
−
is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and ...1.9 fb
−1
of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ
+
μ
−
final state. The branching fraction with respect to that of the Λ
b
0
→ ψ(2S)pK
−
decay mode is measured to be
ℬ
Λ
b
0
→
ψ
2
S
p
π
−
ℬ
Λ
b
0
→
ψ
2
S
p
K
−
=
11.4
±
1.3
±
0.2
%
,
where the first uncertainty is statistical and the second is systematic. The ψ(2S)p and ψ(2S)π
−
mass spectra are investigated and no evidence for exotic resonances is found.
Abstract
Using a data sample corresponding to an integrated luminosity of 2.0
$$\, \text {fb} ^{-1}$$
fb
-
1
, collected by the LHCb experiment, the production of the
$${\eta _{c}} (1S)$$
η
c
(
1
S
)
...state in proton–proton collisions at a centre-of-mass energy of
$$\sqrt{s} =13$$
s
=
13
$$\, \text {TeV}$$
TeV
is studied in the rapidity range
$$2.0< y < 4.5$$
2.0
<
y
<
4.5
and in the transverse momentum range
$$6.5< p_{\mathrm {T}} < 14.0 \, \text {GeV} $$
6.5
<
p
T
<
14.0
GeV
. The cross-section for prompt production of
$${\eta _{c}} (1S)$$
η
c
(
1
S
)
mesons relative to that of the
$${J /\psi }$$
J
/
ψ
meson is measured using the
$$p $$
p
$$\overline{{p}}$$
p
¯
decay mode and is found to be
$${\sigma _{{\eta _{c}} (1S)}/\sigma _{{{J /\psi }}} = 1.69 \pm 0.15 \pm 0.10 \pm 0.18}$$
σ
η
c
(
1
S
)
/
σ
J
/
ψ
=
1.69
±
0.15
±
0.10
±
0.18
. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the
$${{J /\psi }} \!\rightarrow {p} {\overline{{p}}} $$
J
/
ψ
→
p
p
¯
and
$${\eta _{c}} \!\rightarrow {p} {\overline{{p}}} $$
η
c
→
p
p
¯
decays. The prompt
$${\eta _{c}} (1S)$$
η
c
(
1
S
)
production cross-section is determined to be
$${\sigma _{{\eta _{c}} (1S)} = 1.26 \pm 0.11\pm 0.08\pm 0.14 \,\upmu \text {b}}$$
σ
η
c
(
1
S
)
=
1.26
±
0.11
±
0.08
±
0.14
μ
b
, where the last uncertainty includes that on the
$${J /\psi }$$
J
/
ψ
meson cross-section. The ratio of the branching fractions of
$$b $$
b
-hadron decays to the
$${\eta _{c}} (1S)$$
η
c
(
1
S
)
and
$${J /\psi }$$
J
/
ψ
states is measured to be
$${{\mathcal {B}} _{{b} \!\rightarrow {\eta _{c}} X}/{\mathcal {B}} _{{b} \!\rightarrow {{J /\psi }} X} = 0.48 \pm 0.03 \pm 0.03 \pm 0.05}$$
B
b
→
η
c
X
/
B
b
→
J
/
ψ
X
=
0.48
±
0.03
±
0.03
±
0.05
, where the last uncertainty is due to those on the branching fractions of the
$${{J /\psi }} \!\rightarrow {p} {\overline{{p}}} $$
J
/
ψ
→
p
p
¯
and
$${\eta _{c}} \!\rightarrow {p} {\overline{{p}}} $$
η
c
→
p
p
¯
decays. The difference between the
$${J /\psi }$$
J
/
ψ
and
$${\eta _{c}} (1S)$$
η
c
(
1
S
)
masses is also determined to be
$$113.0 \pm 0.7 \pm 0.1 \, \text {MeV} $$
113.0
±
0.7
±
0.1
MeV
, which is the most precise single measurement of this quantity to date.
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