A
bstract
The production of
π
±
, K
±
, and
$$ \left(\overline{\textrm{p}}\right)\textrm{p} $$
p
¯
p
is measured in pp collisions at
$$ \sqrt{s} $$
s
= 13 TeV in different topological regions of the ...events. Particle transverse momentum (
p
T
) spectra are measured in the “toward”, “transverse”, and “away” angular regions defined with respect to the direction of the leading particle in the event. While the toward and away regions contain the fragmentation products of the near-side and away-side jets, respectively, the transverse region is dominated by particles from the Underlying Event (UE). The relative transverse activity classifier,
R
T
=
N
T
/〈
N
T
〉, is used to group events according to their UE activity, where
N
T
is the measured charged-particle multiplicity per event in the transverse region and 〈
N
T
〉 is the mean value over all the analysed events. The first measurements of identified particle
p
T
spectra as a function of
R
T
in the three topological regions are reported. It is found that the yield of high transverse momentum particles relative to the
R
T
-integrated measurement decreases with increasing
R
T
in both the toward and the away regions, indicating that the softer UE dominates particle production as
R
T
increases and validating that
R
T
can be used to control the magnitude of the UE. Conversely, the spectral shapes in the transverse region harden significantly with increasing
R
T
. This hardening follows a mass ordering, being more significant for heavier particles. Finally, it is observed that the
p
T
-differential particle ratios
$$ \left(\textrm{p}+\overline{\textrm{p}}\right)/\left({\uppi}^{+}+{\uppi}^{-}\right) $$
p
+
p
¯
/
π
+
+
π
−
and (K
+
+ K
−
)
/
(
π
+
+
π
−
) in the low UE limit (
R
T
→ 0) approach expectations from Monte Carlo generators such as PYTHIA 8 with Monash 2013 tune and EPOS LHC, where the jet-fragmentation models have been tuned to reproduce e
+
e
−
results.
Abstract
This article presents measurements of the groomed jet radius and momentum splitting fraction in pp collisions at
$$ \sqrt{s} $$
s
= 5
.
02 TeV with the ALICE detector at the Large Hadron ...Collider. Inclusive charged-particle jets are reconstructed at midrapidity using the anti-
k
T
algorithm for transverse momentum
$$ 60<{p}_{\textrm{T}}^{\textrm{ch}\;\textrm{jet}}<80 $$
60
<
p
T
ch
jet
<
80
GeV/
c
. We report results using two different grooming algorithms: soft drop and, for the first time, dynamical grooming. For each grooming algorithm, a variety of grooming settings are used in order to explore the impact of collinear radiation on these jet substructure observables. These results are compared to perturbative calculations that include resummation of large logarithms at all orders in the strong coupling constant. We find good agreement of the theoretical predictions with the data for all grooming settings considered.
Abstract
This article presents new measurements of the fragmentation properties of jets in both proton–proton (pp) and heavy-ion collisions with the ALICE experiment at the Large Hadron Collider ...(LHC). We report distributions of the fraction
z
r
of transverse momentum carried by subjets of radius
r
within jets of radius
R
. Charged-particle jets are reconstructed at midrapidity using the anti-
k
T
algorithm with jet radius
R
= 0
.
4, and subjets are reconstructed by reclustering the jet constituents using the anti-
k
T
algorithm with radii
r
= 0
.
1 and
r
= 0
.
2. In proton–proton collisions, we measure both the inclusive and leading subjet distributions. We compare these measurements to perturbative calculations at next-to-leading logarithmic accuracy, which suggest a large impact of threshold resummation and hadronization effects on the
z
r
distribution. In heavy-ion collisions, we measure the leading subjet distributions, which allow access to a region of harder jet frag- mentation than has been probed by previous measurements of jet quenching via hadron fragmentation distributions. The
z
r
distributions enable extraction of the parton-to-subjet fragmentation function and allow for tests of the universality of jet fragmentation functions in the quark–gluon plasma (QGP). We find no significant modification of
z
r
distributions in Pb–Pb compared to pp collisions. However, the distributions are also consistent with a hardening trend for
z
r
<
0
.
95, as predicted by several jet quenching models. As
z
r
→ 1 our results indicate that any such hardening effects cease, exposing qualitatively new possibilities to disentangle competing jet quenching mechanisms. By comparing our results to theoretical calculations based on an independent extraction of the parton-to-jet fragmentation function, we find consistency with the universality of jet fragmentation and no indication of factorization breaking in the QGP.
A
bstract
The first measurements of elliptic flow of
π
±
, K
±
,
$$ \textrm{p}+\overline{\textrm{p}} $$
p
+
p
¯
,
$$ {\textrm{K}}_{\textrm{S}}^0 $$
K
S
0
,
$$ \Lambda +\overline{\Lambda} $$
Λ
+
Λ
¯
,
...ϕ
,
$$ {\Xi}^{-}+{\overline{\Xi}}^{+} $$
Ξ
−
+
Ξ
¯
+
, and
$$ {\varOmega}^{-}+{\overline{\varOmega}}^{+} $$
Ω
−
+
Ω
¯
+
using multiparticle cumulants in Pb–Pb collisions at
$$ \sqrt{s_{\textrm{NN}}} $$
s
NN
= 5
.
02 TeV are resented. Results obtained with two- (
v
2
{2}) and four-particle cumulants (
v
2
{4}) are shown as a function of transverse momentum,
p
T
, for various collision centrality intervals. Combining the data for both
v
2
{2} and
v
2
{4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous
p
T
-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low
p
T
and the approximate scaling with the number of constituent quarks at intermediate
p
T
, are similarly present in the four-particle correlations and the combinations of
v
2
{2} and
v
2
{4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide
p
T
range.
Measurement of the Λ hyperon lifetime Aglieri Rinella, G.; Al-Turany, M.; Aleksandrov, D. ...
Physical review. D,
08/2023, Letnik:
108, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb-Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV with ALICE. The Λ and $\bar{Λ}$ hyperons are ...reconstructed at midrapidity using their two-body weak decay channel Λ→p+π- and $\bar{Λ}$→$\bar{p}$+π+. The measured value of the Λ lifetime is τΛ=261.07±0.37(stat.)±0.72(syst.) ps. The relative difference between the lifetime of Λ and $\bar{Λ}$, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value (τΛ-τ$\bar{Λ}$)/τΛ=0.0013±0.0028(stat.)±0.0021(syst.) is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τΛ and τ$\bar{Λ}$ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.
The pseudorapidity density of charged particles with minimum transverse momentum (pT) thresholds of 0.15, 0.5, 1, and 2 GeV/c is measured in pp collisions at the center of mass energies of √s=5.02 ...and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity (η) within ±0.8 and pT larger than the corresponding threshold. In addition, measurements without pT-thresholds are performed for inelastic and nonsingle-diffractive events as well as for inelastic events with at least one charged particle having |η|<1 in pp collisions at √s=5.02 TeV for the first time at the LHC. These measurements are compared to the pythia 6, pythia 8, and epos-lhc models. In general, the models describe the η dependence of particle production well. However, discrepancies are observed for the highest transverse momentum threshold (pT>2 GeV/c), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at √s=13 TeV.
The interactions of kaons (K) and antikaons (
K
¯
) with few nucleons (N) were studied so far using kaonic atom data and measurements of kaon production and interaction yields in nuclei. Some details ...of the three-body KNN and
K
¯
NN dynamics are still not well understood, mainly due to the overlap with multi-nucleon interactions in nuclei. An alternative method to probe the dynamics of three-body systems with kaons is to study the final state interaction within triplet of particles emitted in pp collisions at the Large Hadron Collider, which are free from effects due to the presence of bound nucleons. This Letter reports the first femtoscopic study of p–p–K
+
and p–p–K
-
correlations measured in high-multiplicity pp collisions at
s
= 13 TeV by the ALICE Collaboration. The analysis shows that the measured p–p–K
+
and p–p–K
-
correlation functions can be interpreted in terms of pairwise interactions in the triplets, indicating that the dynamics of such systems is dominated by the two-body interactions without significant contributions from three-body effects or bound states.
A
bstract
The production of J/
ψ
is measured as a function of charged-particle multiplicity at forward rapidity in proton-proton (pp) collisions at center-of-mass energies
$$ \sqrt{s} $$
s
= 5.02 and ...13 TeV. The J/
ψ
mesons are reconstructed via their decay into dimuons in the rapidity interval (2.5
< y <
4.0), whereas the charged-particle multiplicity density (d
N
ch
/
d
η
) is measured at midrapidity (
|η| <
1). The production rate as a function of multiplicity is reported as the ratio of the yield in a given multiplicity interval to the multiplicity-integrated one. This observable shows a linear increase with charged-particle multiplicity normalized to the corresponding average value for inelastic events (d
N
ch
/d
η
/〈d
N
ch
/d
η
〉), at both the colliding energies. Measurements are compared with available ALICE results at midrapidity and theoretical model calculations. First measurement of the mean transverse momentum (〈
p
T
〉) of J/
ψ
in pp collisions exhibits an increasing trend as a function of d
N
ch
/d
η
/〈d
N
ch
/d
η
〉 showing a saturation towards high charged-particle multiplicities.
A
bstract
A measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at
$$ \sqrt{s_{\mathrm{NN}}} $$
s
NN
= 5
.
02 TeV, using data collected with the ALICE ...detector at the LHC. The jets were reconstructed in the central rapidity region
|η| <
0
.
5 from charged particles using the anti-
k
T
algorithm with resolution parameter
R
= 0
.
4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The
p
T
-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10
≤ p
T
,
ch jet
≤
100 GeV/
c
, together with the nuclear modification factor,
$$ {R}_{\mathrm{pPb}}^{\mathrm{b}-\mathrm{jet}} $$
R
pPb
b
−
jet
. The analysis thus extends the lower
p
T
limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at
$$ \sqrt{s_{\mathrm{NN}}} $$
s
NN
= 5
.
02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation.
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