The multiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies
s
=
5.02
, 7 and 13 TeV measured by ALICE is reported. The ...analysis relies on track segments measured in the midrapidity range (
|
η
|
<
1.5
). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval
|
η
|
<
1
. The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The study of the production of nuclei and antinuclei in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic ...collisions. In this paper, the production of protons, deuterons and
3
He
and their charge conjugates at midrapidity is studied as a function of the charged-particle multiplicity in inelastic pp collisions at
s
=
5.02
TeV using the ALICE detector. Within the uncertainties, the yields of nuclei in pp collisions at
s
=
5.02
TeV are compatible with those in pp collisions at different energies and to those in p–Pb collisions when compared at similar multiplicities. The measurements are compared with the expectations of coalescence and Statistical Hadronisation Models. The results suggest a common formation mechanism behind the production of light nuclei in hadronic interactions and confirm that they do not depend on the collision energy but on the number of produced particles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Angular correlations of heavy-flavour and charged particles in high-energy proton–proton collisions are sensitive to the production mechanisms of heavy quarks and to their fragmentation as well as ...hadronisation processes. The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in proton–proton collisions at a centre-of-mass energy of
s
=
13
TeV with the ALICE detector is reported, considering
D
0
,
D
+
, and
D
∗
+
mesons in the transverse-momentum interval
3
<
p
T
<
36
GeV/
c
at midrapidity (
|
y
|
<
0.5
), and charged particles with
p
T
>
0.3
GeV/
c
and pseudorapidity
|
η
|
<
0.8
. This measurement has an improved precision and provides an extended transverse-momentum coverage compared to previous ALICE measurements at lower energies. The study is also performed as a function of the charged-particle multiplicity, showing no modifications of the correlation function with multiplicity within uncertainties. The properties and the transverse-momentum evolution of the near- and away-side correlation peaks are studied and compared with predictions from various Monte Carlo event generators. Among those considered, PYTHIA8 and POWHEG+PYTHIA8 provide the best description of the measured observables. The obtained results can provide guidance on tuning the generators.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at
s
= 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-(∆
η
∼ 0) and ...long-range (1
.
6
<
|∆
η
|
<
1
.
8) in pseudorapidity are extracted on the near-side (∆
φ
∼ 0). They are reported as a function of transverse momentum (
p
T
) in the range 1
< p
T
<
4 GeV/
c
. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-
p
T
leading particles or jets for varying
p
T
thresholds. The results demonstrate that the long-range “ridge” yield, possibly related to the collective behavior of the system, is present in events with high-
p
T
processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the
p
T
dependency, while overestimating the event-scale dependency.
A
bstract
Measurements of elliptic (
v
2
) and triangular (
v
3
) flow coefficients of
π
±
, K
±
, p+
p
¯
,
K
S
0
, and Λ+
Λ
¯
obtained with the scalar product method in Xe-Xe collisions at
s
NN
= 5
....
44 TeV are presented. The results are obtained in the rapidity range |
y
|
<
0
.
5 and reported as a function of transverse momentum,
p
T
, for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for
p
T
<
3 GeV/
c
, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3
< p
T
<
8 GeV/
c
). The magnitude of the baryon
v
2
is larger than that of mesons up to
p
T
= 6 GeV/
c
. The centrality dependence of the shape evolution of the
p
T
-differential
v
2
is studied for the various hadron species. The
v
2
coefficients of
π
±
, K
±
, and p+
p
¯
are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for
p
T
<
1 GeV/
c
. A comparison with
v
n
measurements in the corresponding centrality intervals in Pb-Pb collisions at
s
NN
= 5
.
02 TeV yields an enhanced
v
2
in central collisions and diminished value in semicentral collisions.
Understanding the role of parton mass and Casimir color factors in the quantum chromodynamics parton shower represents an important step in characterizing the emission properties of heavy quarks. ...Recent experimental advances in jet substructure techniques have provided the opportunity to isolate and characterize gluon emissions from heavy quarks. In this Letter, the first direct experimental constraint on the charm-quark splitting function is presented, obtained via the measurement of the groomed shared momentum fraction of the first splitting in charm jets, tagged by a reconstructed D^{0} meson. The measurement is made in proton-proton collisions at sqrts=13 TeV, in the low jet transverse-momentum interval of 15≤p_{T}^{jet ch}<30 GeV/c where the emission properties are sensitive to parton mass effects. In addition, the opening angle of the first perturbative emission of the charm quark, as well as the number of perturbative emissions it undergoes, is reported. Comparisons to measurements of an inclusive-jet sample show a steeper splitting function for charm quarks compared with gluons and light quarks. Charm quarks also undergo fewer perturbative emissions in the parton shower, with a reduced probability of large-angle emissions.
A
bstract
The inclusive production of the J/
ψ
and
ψ
(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair
s
NN
= 8
.
16 TeV at ...the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals
−
4
.
46
< y
cms
< −
2
.
96 (Pb-going direction) and 2
.
03
< y
cms
<
3
.
53 (p-going direction), down to zero transverse momentum (
p
T
). The J/
ψ
and
ψ
(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The
p
T
-differential J/
ψ
production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈
p
T
〉 and
p
T
2
values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/
ψ
increases from below unity in peripheral collisions to above unity in central collisions, while for the
ψ
(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at
s
NN
= 5
.
02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.
The production of K∗(892)0and ϕ(1020)resonances has been measured in p-Pb collisions at √sNN = 8.16 TeV using the ALICE detector. Resonances are reconstructed via their hadronic decay channels in the ...rapidity interval −0.5 < y < 0 and the transverse momentum spectra are measured for various multiplicity classes up to pT = 20 GeV/c for K∗(892)0and pT = 16 GeV/c for ϕ(1020). The pT-integrated yields and mean transverse momenta are reported and compared with previous results in pp, p-Pb and Pb-Pb collisions. The xT scaling for K∗(892)0and ϕ(1020)resonance production is newly tested in p-Pb collisions and found to hold in the high-pT region at Large Hadron Collider energies. The nuclear modification factors (RpPb) as a function of pT for K*0 and ϕ at √sNN = 8.16 TeV are presented along with the new RpPb measurements of K*0, ϕ, Ξ, and Ω at √sNN = 5.02 TeV. At intermediate pT (2–8 GeV/c), RpPb of Ξ, Ω show a Cronin-like enhancement, while K*0 and ϕ show no or little nuclear modification. At high pT (>8 GeV/c), the RpPb values of all hadrons are consistent with unity within uncertainties. The RpPb of K∗(892)0and ϕ(1020)at √sNN = 8.16 and 5.02 TeV show no significant energy dependence.
We report on the inclusive
J
/
ψ
production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy
s
=
13
TeV. The
J
/
ψ
mesons are ...reconstructed in the
e
+
e
-
decay channel and the measurements are performed at midrapidity (
|
y
|
<
0.9
) in the transverse-momentum interval
0
<
p
T
<
40
GeV/
c
, using a minimum-bias data sample corresponding to an integrated luminosity
L
int
=
32.2
nb
-
1
and an Electromagnetic Calorimeter triggered data sample with
L
int
=
8.3
pb
-
1
. The
p
T
-integrated
J
/
ψ
production cross section at midrapidity, computed using the minimum-bias data sample, is
d
σ
/
d
y
|
y
=
0
=
8.97
±
0.24
(
stat
)
±
0.48
(
syst
)
±
0.15
(
lumi
)
μ
b
. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and
p
T
-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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