A
bstract
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D
0
and D
+
mesons with respect to the inclusive yield are measured as a function of the charged-particle ...multiplicity in proton-proton collisions at a centre-of-mass energy of
s
= 13 TeV with the ALICE detector at the LHC. The results are reported in intervals of transverse momentum (
p
T
) and integrated in the range 1
< p
T
<
24 GeV/
c
. The fraction of non-prompt D
0
and D
+
mesons is found to increase slightly as a function of
p
T
in all the measured multiplicity intervals, while no significant dependence on the charged-particle multiplicity is observed. In order to investigate the production and hadronisation mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour glass condensate including three-pomeron fusion.
A
bstract
The production of the W
±
bosons measured in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision
s
NN
= 8
.
16 TeV and Pb–Pb collisions at
s
NN
= 5
.
02 TeV with ALICE ...at the LHC is presented. The W
±
bosons are measured via their muonic decay channel, with the muon reconstructed in the pseudorapidity region
−
4
<
η
lab
μ
< −
2
.
5 with transverse momentum
p
T
μ
>
10 GeV
/c
. While in Pb–Pb collisions the measurements are performed in the forward (2
.
5
<
y
cms
μ
<
4) rapidity region, in p–Pb collisions, where the centre-of-mass frame is boosted with respect to the laboratory frame, the measurements are performed in the backward (
−
4
.
46
<
y
cms
μ
< −
2
.
96) and forward (2
.
03
<
y
cms
μ
<
3
.
53) rapidity regions. The W
−
and W
+
production cross sections, lepton-charge asymmetry, and nuclear modification factors are evaluated as a function of the muon rapidity. In order to study the production as a function of the p–Pb collision centrality, the production cross sections of the W
−
and W
+
bosons are combined and normalised to the average number of binary nucleon–nucleon collision 〈
N
coll
〉. In Pb–Pb collisions, the same measurements are presented as a function of the collision centrality. Study of the binary scaling of the W
±
-boson cross sections in p–Pb and Pb–Pb collisions is also reported. The results are compared with perturbative QCD calculations, with and without nuclear modifications of the Parton Distribution Functions (PDFs), as well as with available data at the LHC. Significant deviations from the theory expectations are found in the two collision systems, indicating that the measurements can provide additional constraints for the determination of nuclear PDFs and in particular of the light-quark distributions.
A
bstract
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at
s
= 13 TeV at midrapidity with the ALICE detector are presented down to a transverse ...momentum (
p
T
) of 0.2 GeV/
c
and up to
p
T
= 35 GeV/
c
, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the
p
T
range 0
.
5
< p
T
<
26 GeV/
c
at
s
NN
= 8
.
16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong
p
T
dependence is observed in pp collisions, where the yield of high-
p
T
electrons increases faster as a function of multiplicity than the one of low-
p
T
electrons. The measurement in p-Pb collisions shows no
p
T
dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations.
Abstract
In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from ...the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of
$^{3}\overline{{{\rm{He}}}$$
3
He
¯
when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of
$^{3}\overline{{{\rm{He}}}$$
3
He
¯
stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing
$^{3}\overline{{{\rm{He}}}$$
3
He
¯
momentum from 25% to 90% for cosmic-ray sources. The results indicate that
$^{3}\overline{{{\rm{He}}}$$
3
He
¯
nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation.
A
bstract
The measurement of the production of charm jets, identified by the presence of a D
0
meson in the jet constituents, is presented in proton–proton collisions at centre-of-mass energies of
s
...= 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D
0
mesons were reconstructed from their hadronic decay D
0
→ K
−
π
+
and the respective charge conjugate. Jets were reconstructed from D
0
-meson candidates and charged particles using the anti-
k
T
algorithm, in the jet transverse momentum range 5
< p
T
,
chjet
<
50 GeV/
c
, pseudorapidity |
η
jet
|
<
0
.
9 −
R
, and with the jet resolution parameters
R
= 0
.
2
,
0
.
4
,
0
.
6. The distribution of the jet momentum fraction carried by a D
0
meson along the jet axis
z
‖
ch
was measured in the range 0
.
4
<
z
‖
ch
<
1
.
0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low
p
T
,
chjet
. Measurements were also done for
R
= 0
.
3 at
s
= 5
.
02 and are shown along with their comparisons to theoretical predictions in an appendix to this paper.
The elliptic flow
(
v
2
)
of
D
0
mesons from beauty-hadron decays (non-prompt
D
0
)
was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair
s
NN
=
5.02
TeV ...with the ALICE detector at the LHC. The
D
0
mesons were reconstructed at midrapidity
(
|
y
|
<
0.8
)
from their hadronic decay
D
0
→
K
-
π
+
, in the transverse momentum interval
2
<
p
T
<
12
GeV/
c
. The result indicates a positive
v
2
for non-prompt
D
0
mesons with a significance of 2.7
σ
. The non-prompt
D
0
-meson
v
2
is lower than that of prompt non-strange D mesons with 3.2
σ
significance in
2
<
p
T
<
8
GeV
/
c
, and compatible with the
v
2
of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties.
The multiplicity dependence of jet production in pp collisions at the centre-of-mass energy of
s
=
13
TeV
is studied for the first time. Jets are reconstructed from charged particles using the anti-
...k
T
algorithm with resolution parameters
R
varying from 0.2 to 0.7. The jets are measured in the pseudorapidity range
|
η
jet
|
<
0.9
-
R
and in the transverse momentum range
5
<
p
T
,
jet
ch
<
140
GeV
/
c
. The multiplicity intervals are categorised by the ALICE forward detector V0. The
p
T
differential cross section of charged-particle jets are compared to leading order (LO) and next-to-leading order (NLO) perturbative quantum chromodynamics (pQCD) calculations. It is found that the data are better described by the NLO calculation, although the NLO prediction overestimates the jet cross section below
20
GeV
/
c
. The cross section ratios for different
R
are also measured and compared to model calculations. These measurements provide insights into the angular dependence of jet fragmentation. The jet yield increases with increasing self-normalised charged-particle multiplicity. This increase shows only a weak dependence on jet transverse momentum and resolution parameter at the highest multiplicity. While such behaviour is qualitatively described by the present version of PYTHIA, quantitative description may require implementing new mechanisms for multi-particle production in hadronic collisions.
The transverse-momentum
(
p
T
)
spectra of K
∗
(
892
)
0
and
ϕ
(
1020
)
measured with the ALICE detector up to
p
T
= 16 GeV/
c
in the rapidity range
-
1.2
<
y
<
0.3
,
in p–Pb collisions at the ...center-of-mass energy per nucleon–nucleon collision
s
NN
=
5.02
TeV are presented as a function of charged particle multiplicity and rapidity. The measured
p
T
distributions show a dependence on both multiplicity and rapidity at low
p
T
whereas no significant dependence is observed at high
p
T
. A rapidity dependence is observed in the
p
T
-integrated yield (d
N
/d
y
), whereas the mean transverse momentum
⟨
p
T
⟩
shows a flat behavior as a function of rapidity. The rapidity asymmetry (
Y
asym
) at low
p
T
(< 5 GeV/
c
) is more significant for higher multiplicity classes. At high
p
T
, no significant rapidity asymmetry is observed in any of the multiplicity classes. Both K
∗
(
892
)
0
and
ϕ
(
1020
)
show similar
Y
asym
. The nuclear modification factor
(
Q
CP
)
as a function of
p
T
shows a Cronin-like enhancement at intermediate
p
T
, which is more prominent at higher rapidities (Pb-going direction) and in higher multiplicity classes. At high
p
T
(> 5 GeV/
c
), the
Q
CP
values are greater than unity and no significant rapidity dependence is observed.
A
bstract
Measurements of charged-particle production in pp, p–Pb, and Pb–Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined ...event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum
p
T
trig
in the range 8
<
p
T
trig
<
15 GeV
/c
. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier,
R
T
=
N
ch
T
/
N
ch
T
, is used to group events according to their UE activity, where
N
ch
T
is the charged-particle multiplicity per event in the transverse region and
N
ch
T
is the mean value over the whole analysed sample. The energy dependence of the
R
T
distributions in pp collisions at
s
= 2
.
76, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle
p
T
spectra as a function of
R
T
in the three azimuthal regions in pp, p–Pb, and Pb–Pb collisions at
s
NN
= 5
.
02 TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p–Pb).
A
bstract
The Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics ...of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision
s
NN
= 5
.
02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic (
v
2
) and triangular (
v
3
) flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope
r
3
Norm
is found to be larger than zero and to have a magnitude similar to
r
2
Norm
, thus pointing to a large background contribution for these measurements. Furthermore,
r
2
Norm
can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW (
f
CMW
) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for
f
CMW
, and in the 10–60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level.
