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.
The production of the
η
c
(
1
S
)
state in proton-proton collisions is probed via its decay to the
p
p
¯
final state with the LHCb detector, in the rapidity range
2.0
<
y
<
4.5
and in the meson ...transverse-momentum range
p
T
>
6.5
GeV
/
c
. The cross-section for prompt production of
η
c
(
1
S
)
mesons relative to the prompt
J
/
ψ
cross-section is measured, for the first time, to be
σ
η
c
(
1
S
)
/
σ
J
/
ψ
=
1.74
±
0.29
±
0.28
±
0
.
18
B
at a centre-of-mass energy
s
=
7
TeV
using data corresponding to an integrated luminosity of 0.7 fb
-
1
, and
σ
η
c
(
1
S
)
/
σ
J
/
ψ
=
1.60
±
0.29
±
0.25
±
0
.
17
B
at
s
=
8
TeV
using 2.0 fb
-
1
. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the
η
c
(
1
S
)
and
J
/
ψ
decays to the
p
p
¯
final state. In addition, the inclusive branching fraction of
b
-hadron decays into
η
c
(
1
S
)
mesons is measured, for the first time, to be
B
(
b
→
η
c
X
)
=
(
4.88
±
0.64
±
0.29
±
0
.
67
B
)
×
10
-
3
, where the third uncertainty includes also the uncertainty on the
J
/
ψ
inclusive branching fraction from
b
-hadron decays. The difference between the
J
/
ψ
and
η
c
(
1
S
)
meson masses is determined to be
114.7
±
1.5
±
0.1
MeV
/
c
2
.
Photodissociation of interstellar N2 Li, X.; Heays, A. N.; Visser, R. ...
Astronomy and astrophysics (Berlin),
07/2013, Letnik:
555
Journal Article
Recenzirano
Odprti dostop
Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly ...studied. The partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. Aims. The aim of this work is to gain a better understanding of the interstellar N2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. Methods. We used an approach similar to that adopted for CO in which we simulated the full high-resolution line-by-line absorption + dissociation spectrum of N2 over the relevant 912–1000 Å wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schrödinger equation. The simulated N2 spectra were compared with the absorption spectra of H2, H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk. Results. The unattenuated photodissociation rate in the Draine (1978, ApJS, 36, 595) radiation field assuming an N2 excitation temperature of 50 K is 1.65 × 10-10 s-1, with an uncertainty of only 10%. Most of the photodissociation occurs through bands in the 957–980 Å range. The N2 rate depends slightly on the temperature through the variation of predissociation probabilities with rotational quantum number for some bands. Shielding functions are provided for a range of H2 and H column densities, with H2 being much more effective than H in reducing the N2 rate inside a cloud. Shielding by CO is not effective. The new rates are 28% lower than the previously recommended values. Nevertheless, diffuse cloud models still fail to reproduce the possible detection of interstellar N2 except for unusually high densities and/or low incident UV radiation fields. The transition of N → N2 occurs at nearly the same depth into a cloud as that of C+ → C → CO. The orders-of-magnitude lower N2 photodissociation rates in clouds exposed to black-body radiation fields of only 4000 K can qualitatively explain the lack of active nitrogen chemistry observed in the inner disks around cool stars. Conclusions. Accurate photodissociation rates for N2 as a function of depth into a cloud are now available that can be applied to a wide variety of astrophysical environments.
Many patients undergoing rhinoplasty can benefit from chin augmentation, yielding a more balanced appearance. Preoperative facial analysis identifies patients with retrusive chins and suggests ...optimal chin position. Current profile analysis methods depend on subnasale position (Legan's angle) or require estimation of bony landmarks from soft-tissue photographs (Goode's alar crease perpendicular, Gonzalez-Ulloa's zero meridian, and Merrifield's Z-angle). We describe a technique for determining ideal chin position using soft-tissue landmarks. We compare this technique with Legan's, Goode's, Gonzalez-Ulloa's, and Merrifield's techniques in 35 women and conclude that this method provides accurate and rapid determination of ideal chin position.
A search for rare B → Dμ+μ− decays Alessio, F.; Aliouche, Z.; Artamonov, A. ...
The journal of high energy physics,
02/2024, Letnik:
2024, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
A search for rare
B → Dμ
+
μ
−
decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb
−
1
. No ...significant signals are observed in the non-resonant
μ
+
μ
−
modes, and upper limits of
B
B
0
→
D
¯
0
μ
+
μ
−
<
5.1
×
10
−
8
,
B
B
+
→
D
s
+
μ
+
μ
−
<
3.2
×
10
−
8
,
B
B
s
0
→
D
¯
0
μ
+
μ
−
<
1.6
×
10
−
7
and
f
c
/
f
u
·
B
B
c
+
→
D
s
+
μ
+
μ
−
<
9.6
×
10
−
8
are set at the 95 % confidence level, where
f
c
and
f
u
are the fragmentation fractions of a
B
meson with a
c
and
u
quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a
J/ψ → μ
+
μ
−
decay. The branching fraction of
B
c
+
→
D
s
+
J
/
ψ
multiplied by the fragmentation-fraction ratio is measured to be
f
c
f
u
·
B
B
c
+
→
D
s
+
J
/
ψ
=
1.63
±
0.15
±
0.13
×
10
−
5
,
where the first uncertainty is statistical and the second systematic.
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.
We report four narrow peaks in the Ξb0K− mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1 recorded ...by the LHCb experiment. Referring to these states by their mass, the mass values are mΩb(6316)−=6315.64±0.31±0.07±0.50 MeV, mΩb(6330)−=6330.30±0.28±0.07±0.50 MeV, mΩb(6340)−=6339.71±0.26±0.05±0.50 MeV, mΩb(6350)−=6349.88±0.35±0.05±0.50 MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξb0 mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be ΓΩb(6316)−<2.8 MeV, ΓΩb(6330)−<3.1 MeV and ΓΩb(6340)−<1.5 MeV. The natural width of the Ωb(6350)− peak is 1.4−0.8+1.0±0.1 MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ωb(6316)− and Ωb(6330)− peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ωb− resonances.
Abstract
Successive atmospheric river (AR) events—known as AR families—can result in prolonged and elevated hydrological impacts relative to single ARs due to the lack of recovery time between ...periods of precipitation. Despite the outsized societal impacts that often stem from AR families, the large-scale environments and mechanisms associated with these compound events remain poorly understood. In this work, a new reanalysis-based 39-yr catalog of 248 AR family events affecting California between 1981 and 2019 is introduced. Nearly all (94%) of the interannual variability in AR frequency is driven by AR family versus single events. Using
k
-means clustering on the 500-hPa geopotential height field, six distinct clusters of large-scale patterns associated with AR families are identified. Two clusters are of particular interest due to their strong relationship with phases of El Niño–Southern Oscillation (ENSO). One of these clusters is characterized by a strong ridge in the Bering Sea and Rossby wave propagation, most frequently occurs during La Niña and neutral ENSO years, and is associated with the highest cluster-average precipitation across California. The other cluster, characterized by a zonal elongation of lower geopotential heights across the Pacific basin and an extended North Pacific jet, most frequently occurs during El Niño years and is associated with lower cluster-average precipitation across California but with a longer duration. In contrast, single AR events do not show obvious clustering of spatial patterns. This difference suggests that the potential predictability of AR families may be enhanced relative to single AR events, especially on subseasonal to seasonal time scales.
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