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.
A
bstract
The ALICE Collaboration reports a search for jet quenching effects in high-multiplicity (HM) proton-proton collisions at
s
= 13 TeV, using the semi-inclusive azimuthal-difference ...distribution ∆
φ
of charged-particle jets recoiling from a high transverse momentum (high-
p
T
,
trig
) trigger hadron. Jet quenching may broaden the ∆
φ
distribution measured in HM events compared to that in minimum bias (MB) events. The measurement employs a
p
T
,
trig
-differential observable for data-driven suppression of the contribution of multiple partonic interactions, which is the dominant background. While azimuthal broadening is indeed observed in HM compared to MB events, similar broadening for HM events is observed for simulations based on the PYTHIA 8 Monte Carlo generator, which does not incorporate jet quenching. Detailed analysis of these data and simulations show that the azimuthal broadening is due to bias of the HM selection towards events with multiple jets in the final state. The identification of this bias has implications for all jet quenching searches where selection is made on the event activity.
A
bstract
Results on the transverse spherocity dependence of light-flavor particle production (
π
, K, p,
ϕ
, K
*0
,
K
S
0
, Λ, Ξ) at midrapidity in high-multiplicity pp collisions at
s
= 13 TeV were ...obtained with the ALICE apparatus. The transverse spherocity estimator
S
O
p
T
=
1
categorizes events by their azimuthal topology. Utilizing narrow selections on
S
O
p
T
=
1
, it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The
S
O
p
T
=
1
estimator is found to effectively constrain the hardness of the events when the midrapidity (|
η
| < 0.8) estimator is used.
The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced.
The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of
S
O
p
T
=
1
.
A
bstract
Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision
s
NN
= 5
.
02 TeV and the corresponding nuclear ...modification factor
R
pPb
ch
jet
are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |
η
jet
|
<
0
.
5 from charged particles using the anti-
k
T
algorithm with resolution parameters
R
= 0
.
2, 0
.
3, and 0
.
4. The
p
T
-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10
<
p
T
,
jet
ch
<
140 GeV/
c
and 10
<
p
T
,
jet
ch
<
160 GeV/
c
, respectively, together with the nuclear modification factor
R
pPb
ch
jet
in the range 10
<
p
T
,
jet
ch
<
140 GeV/
c
. The analysis extends the
p
T
range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at
s
NN
= 5
.
02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD P
owheg
calculations with parton shower provided by P
ythia
8 as well as by J
etscape
simulations.
