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1. Particle production as a function of charged-particle flattenicity in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevD.111.012010  

   Acharya, S; Adamová, D; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; et al (January 2025, Physical Review D)

   This paper reports the first measurement of the transverse momentum ( $p_{\mathrm{T}}$ ) spectra of primary charged pions, kaons, (anti)protons, and unidentified particles as a function of the charged-particle flattenicity in pp collisions at $\sqrt{s}=13\mathrm{TeV}$ . Flattenicity is a novel event shape observable that is measured in the pseudorapidity intervals covered by the V0 detector, $2.8<\eta <5.1$ and $-3.7<\eta <-1.7$ . According to QCD-inspired phenomenological models, it shows sensitivity to multiparton interactions and is less affected by biases toward larger $p_{\mathrm{T}}$ due to local multiplicity fluctuations in the V0 acceptance than multiplicity. The analysis is performed in minimum-bias (MB) as well as in high-multiplicity events up to $p_{\mathrm{T}}=20\mathrm{GeV}/c$ . The event selection requires at least one charged particle produced in the pseudorapidity interval $\left|\eta \right|<1$ . The measured $p_{\mathrm{T}}$ distributions, average $p_{\mathrm{T}}$ , kaon-to-pion and proton-to-pion particle ratios, presented in this paper, are compared to model calculations using 8 based on color strings and EPOS LHC. The modification of the $p_{\mathrm{T}}$ -spectral shapes in low-flattenicity events that have large event activity with respect to those measured in MB events develops a pronounced peak at intermediate $p_{\mathrm{T}}$ ( $2<p_{\mathrm{T}}<8\mathrm{GeV}/c$ ), and approaches the vicinity of unity at higher $p_{\mathrm{T}}$ . The results are qualitatively described by , and they show different behavior than those measured as a function of charged-particle multiplicity based on the V0M estimator. © 2025 CERN, for the ALICE Collaboration2025CERN 

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2. $D^0$ -meson-tagged jet axes difference in proton-proton collisions at $\sqrt{s}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/nt4q-7t77  

   Acharya, S; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; et al (November 2025, Physical Review D)

   Heavy-flavor quarks produced in proton-proton (pp) collisions provide a unique opportunity to investigate the evolution of quark-initiated parton showers from initial hard scatterings to final-state hadrons. By examining jets that contain heavy-flavor hadrons, this study explores the effects of both perturbative and nonperturbative QCD on jet formation and structure. The angular differences between various jet axes, $\mathrm{\Delta }{R}_{\mathrm{axis}}$ , offer insight into the radiation patterns and fragmentation of charm quarks. The first measurement of $D^0$ -tagged jet axes differences in pp collisions at $\sqrt{s}=5.02\mathrm{TeV}$ by the ALICE experiment at the LHC is presented for jets with transverse momentum $p_{\mathrm{T}}^{\text{ch jet}}\ge 10\mathrm{GeV}/c$ and $D^0$ mesons with $p_{\mathrm{T}}^{{\mathrm{D}}^0}\ge 5\mathrm{GeV}/c$ . In this $D^0$ -meson-tagged jet measurement, three jet axis definitions, each with different sensitivities to soft, wide-angle radiation, are used: the standard axis, soft drop groomed axis, and winner-takes-all axis. Measurements of the radial distributions of $D^0$ mesons with respect to the jet axes, $\mathrm{\Delta }{R}_{\mathrm{axis}\text{−}{\mathrm{D}}^0}$ , are reported, along with the angle, $\mathrm{\Delta }{R}_{\mathrm{axis}}$ , between the three jet axes. The $D^0$ meson emerges as the leading particle in these jets, closely aligning with the winner-takes-all axis and diverging from the standard jet axis. The results also examine how varying the sensitivity to soft radiation with grooming influences the orientation of the soft drop jet axis and uncover that charm-jet structure is more likely to survive grooming when the soft drop axis is further from the $D^0$ direction, providing further evidence of the dead-cone effect recently measured by ALICE. 

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3. Observation of Medium-Induced Yield Enhancement and Acoplanarity Broadening of Low- $p_{\mathrm{T}}$ Jets from Measurements in $pp$ and Central Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.133.022301  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (July 2024, Physical Review Letters)

   The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high $p_{\mathrm{T}}$ ) hadron trigger in proton-proton and central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ . A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter $R=0.2$ , 0.4, and 0.5 in the range $7<p_{\mathrm{T},\text{jet}}<140\mathrm{GeV}/c$ and trigger-recoil jet azimuthal separation $\pi /2<\mathrm{\Delta }\phi <\pi$ . The measurements exhibit a marked medium-induced jet yield enhancement at low $p_{\mathrm{T}}$ and at large azimuthal deviation from $\mathrm{\Delta }\phi \sim \pi$ . The enhancement is characterized by its dependence on $\mathrm{\Delta }\phi$ , which has a slope that differs from zero by $4.7\sigma$ . Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation. © 2024 CERN, for the ALICE Collaboration2024CERN 

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4. Search for Quasiparticle Scattering in the Quark-Gluon Plasma with Jet Splittings in $pp$ and Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.135.031901  

   Acharya, S; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; et al (July 2025, Physical Review Letters)

   The ALICE Collaboration reports measurements of the large relative transverse momentum ( $k_T$ ) component of jet substructure in $pp$ and Pb-Pb collisions at center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ . Enhancement in the yield of such large- $k_{\mathrm{T}}$ emissions in head-on Pb-Pb collisions is predicted to arise from partonic scattering with quasiparticles of the quark-gluon plasma. The analysis utilizes charged-particle jets reconstructed by the anti- $k_{\mathrm{T}}$ algorithm with resolution parameter $R=0.2$ in the transverse-momentum interval $60<p_{\mathrm{T},\mathrm{ch},\mathrm{jet}}<80\mathrm{GeV}/c$ . The soft drop and dynamical grooming algorithms are used to identify high transverse momentum splittings in the jet shower. Comparison of measurements in Pb-Pb and $pp$ collisions shows medium-induced narrowing, corresponding to yield suppression of high- $k_T$ splittings, in contrast to the expectation of yield enhancement due to quasiparticle scattering. The measurements are compared to theoretical model calculations incorporating jet modification due to jet-medium interactions (“jet quenching”), both with and without quasiparticle scattering effects. These measurements provide new insight into the underlying mechanisms and theoretical modeling of jet quenching. 

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5. Measurements of $\mathrm{\Upsilon }$ states production in $p+p$ collisions at $\sqrt{s}=500\mathrm{GeV}$ with STAR: Cross sections, ratios, and multiplicity dependence

   https://doi.org/10.1103/bsyx-qtjp  

   Aboona, B E; Adam, J; Adamczyk, L; Aggarwal, I; Aggarwal, M M; Ahammed, Z; Alshammri, A K; Aschenauer, E C; Aslam, S; Atchison, J; et al (August 2025, Physical Review D)

   We report measurements of $\mathrm{\Upsilon }\left(1S\right)$ , $\mathrm{\Upsilon }\left(2S\right)$ and $\mathrm{\Upsilon }\left(3S\right)$ production in $p+p$ collisions at $\sqrt{s}=500\mathrm{GeV}$ by the STAR experiment in year 2011, corresponding to an integrated luminosity ${\mathcal{L}}_{\mathrm{int}}=13{\mathrm{pb}}^{-1}$ . The results provide precise cross sections, transverse momentum ( $p_{\mathrm{T}}$ ) and rapidity ( $y$ ) spectra, as well as cross section ratios for $p_{\mathrm{T}}<10\mathrm{GeV}/\mathrm{c}$ and $\left|y\right|<1$ . The dependence of the $\mathrm{\Upsilon }$ yield on charged particle multiplicity has also been measured, offering new insights into the mechanisms of quarkonium production. The data are compared to various theoretical models: the color evaporation model (CEM) accurately describes the $\mathrm{\Upsilon }\left(1S\right)$ production, while the color glass $\mathrm{condensate}+\text{nonrelativistic}$ quantum chromodynamics ( $\mathrm{CGC}+\mathrm{NRQCD}$ ) model overestimates the data, particularly at low $p_{\mathrm{T}}$ . Conversely, the color singlet model (CSM) underestimates the rapidity dependence. These discrepancies highlight the need for further development in understanding the production dynamics of heavy quarkonia in high-energy hadronic collisions. The trend in the multiplicity dependence is consistent with CGC/saturation and string percolation models or $\mathrm{\Upsilon }$ production happening in multiple parton interactions modeled by 8. 

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