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
bstract
A precision measurement of the
Z
boson production cross-section at
s
= 13 TeV in the forward region is presented, using
pp
collision data collected by the LHCb detector, corresponding to an ...integrated luminosity of 5.1 fb
−
1
. The production cross-section is measured using
Z → μ
+
μ
−
events within the fiducial region defined as pseudorapidity 2
.
0
< η <
4
.
5 and transverse momentum
p
T
>
20 GeV
/c
for both muons and dimuon invariant mass 60
< M
μμ
<
120 GeV
/c
2
. The integrated cross-section is determined to be
σ
Z
→
μ
+
μ
−
=
196.4
±
0.2
±
1.6
±
3.9
pb
,
where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.
Abstract Amplitude models are constructed to describe the resonance structure of $${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$$ D0→K-π+π+π- and $${D^{0} \rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ...^{+}}$$ D0→K+π-π-π+ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 $$fb^{-1}$$ fb-1 . The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $$D^{0} \rightarrow a_1(1260)^{+} K^{-}$$ D0→a1(1260)+K- and $$D^{0} \rightarrow K_1(1270/1400)^{+} \pi ^{-}$$ D0→K1(1270/1400)+π- being prominent in $${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$$ D0→K-π+π+π- and $$D^{0}\rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ^{+}$$ D0→K+π-π-π+ , respectively. Precise measurements of the lineshape parameters and couplings of the $$a_1(1260)^{+}$$ a1(1260)+ , $$K_1(1270)^{-}$$ K1(1270)- and $$K(1460)^{-}$$ K(1460)- resonances are made, and a quasi model-independent study of the $$K(1460)^{-}$$ K(1460)- resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be $$R_{K3\pi } = 0.459\pm 0.010\,(\mathrm {stat}) \pm 0.012\,(\mathrm {syst}) \pm 0.020\,(\mathrm {model})$$ RK3π=0.459±0.010(stat)±0.012(syst)±0.020(model) , which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $$\gamma $$ γ and studies of charm mixing and $$C\!P$$ CP violation.
Long-lived particles decaying to
e
±
μ
∓
ν
, with masses between 7 and
50
GeV/
c
2
and lifetimes between 2 and
50
ps
, are searched for by looking at displaced vertices containing electrons and muons ...of opposite charges. The search is performed using
5.4
fb
-
1
of
p
p
collisions collected with the LHCb detector at a centre-of-mass energy of
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
GeV/
c
2
, and the charged current production from an on-shell
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.
A
bstract
The cross-sections of exclusive (coherent) photoproduction
J/ψ
and
ψ
(2S) mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of 5
.
02 TeV are measured ...using a data sample corresponding to an integrated luminosity of 228 ± 10 μb
−
1
, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for
J/ψ
and
ψ
(2S) mesons. The integrated cross-sections are measured to be
σ
J
/
ψ
coh
= 5
.
965
±
0
.
059
±
0
.
232
±
0
.
262 mb and
σ
ψ
2
S
coh
= 0
.
923
±
0
.
086
±
0
.
028
±
0
.
040 mb, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be
σ
ψ
2
S
coh
/
σ
J
/
ψ
coh
= 0
.
155
±
0
.
014
±
0
.
003, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.
The present white paper is submitted as part of the “Snowmass” process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy ...physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.
The Milky Way is expected to be embedded in a halo of dark matter particles, with the highest density in the central region, and decreasing density with the halo-centric radius. Dark matter might be ...indirectly detectable at Earth through a flux of stable particles generated in dark matter annihilations and peaked in the direction of the Galactic Center. We present a search for an excess flux of muon (anti-) neutrinos from dark matter annihilation in the Galactic Center using the cubic-kilometer-sized IceCube neutrino detector at the South Pole. There, the Galactic Center is always seen above the horizon. Thus, new and dedicated veto techniques against atmospheric muons are required to make the southern hemisphere accessible for IceCube. We used 319.7 live-days of data from IceCube operating in its 79-string configuration during 2010 and 2011. No neutrino excess was found and the final result is compatible with the background. We present upper limits on the self-annihilation cross-section,
σ
A
v
, for WIMP masses ranging from 30 GeV up to 10 TeV, assuming cuspy (NFW) and flat-cored (Burkert) dark matter halo profiles, reaching down to
≃
4
·
10
-
24
cm
3
s
-
1
, and
≃
2.6
·
10
-
23
cm
3
s
-
1
for the
ν
ν
¯
channel, respectively.
A
bstract
The CKM angle
γ
is determined from
CP
-violating observables measured in
B
±
→
D
K
∓
π
±
π
±
π
∓
h
±
, (
h
=
K, π
) decays, where the measurements are performed in bins of the decay ...phase-space of the
D
meson. Using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7
,
8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb
−
1
,
γ
is determined to be
γ
=
54.8
+
6.0
−
5.8
+
0.6
−
0.6
+
6.7
−
4.3
∘
,
where the first uncertainty is statistical, the second systematic and the third from the external inputs on the coherence factors and strong phases of the
D
-meson decays.
The decays
Λ
b
0
→
Λ
c
+
D
¯
(
∗
)
0
K
-
and
Λ
b
0
→
Λ
c
+
D
s
∗
-
are observed for the first time, in proton-proton collision data at
s
=
13
Te
V
, corresponding to an integrated luminosity of 5.4
...fb
-
1
collected with the LHCb detector. Their ratios of branching fractions with respect to the
Λ
b
0
→
Λ
c
+
D
s
-
mode are measured to be
B
Λ
b
0
→
Λ
c
+
D
¯
0
K
-
B
Λ
b
0
→
Λ
c
+
D
s
-
=
0.1908
-
0.0034
+
0.0036
-
0.0018
+
0.0016
±
0.0038
,
B
Λ
b
0
→
Λ
c
+
D
¯
∗
0
K
-
B
Λ
b
0
→
Λ
c
+
D
s
-
=
0.589
-
0.017
+
0.018
-
0.018
+
0.017
±
0.012
,
B
Λ
b
0
→
Λ
c
+
D
s
∗
-
B
Λ
b
0
→
Λ
c
+
D
s
-
=
1.668
±
0.022
-
0.055
+
0.061
,
where the first uncertainties are statistical, the second systematic, and the third, for the
Λ
b
0
→
Λ
c
+
D
¯
(
∗
)
0
K
-
decays, are due to the uncertainties on the branching fractions of the
D
s
-
→
K
-
K
+
π
-
and
D
¯
0
→
K
+
π
-
decay modes. The measured branching fractions probe factorization assumptions in effective theories and provide the normalization for future pentaquark searches in
Λ
b
0
→
Λ
c
+
D
¯
(
∗
)
0
K
-
decay channels.
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