Fri·Mar 24, 2023Friday·March 24, 2023

1. 01*

   Disentangling centrality bias and final-state effects in the production of high-$p_T$ ${\pi }^0$ using direct $\gamma$ in $d$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV

   N.J. Abdulameer · U. Acharya · C. Aidala · Y. Akiba · M. Alfred · K. Aoki · N. Apadula · C. Ayuso · V. Babintsev · K.N. Barish · S. Bathe · A. Bazilevsky and 267 other authors

   PHENIX presents a simultaneous measurement of the production of direct $\gamma$ and ${\pi }^0$ in $d$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=200$ GeV over a $p_T$ range of 7.5 to 18 GeV/$c$ for different event samples selected by event activity, i.e. charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor $R_{d\mathrm{Au},\mathrm{EXP}}^{{\gamma }^{\mathrm{dir}}}$ is $0.925\pm 0.023(\mathrm{stat})\pm 0.15^{(\mathrm{scale})}$, consistent with unity for minimum-bias (MB) $d$$+$Au events. For event classes with moderate event activity, $R_{d\mathrm{Au},\mathrm{EXP}}^{{\gamma }^{\mathrm{dir}}}$ is consistent with the MB value within 5\% uncertainty. These results confirm that the previously observed enhancement of high-$p_T$ ${\pi }^0$ production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5\% of events with the highest event activity, $R_{d\mathrm{Au},\mathrm{EXP}}^{{\gamma }^{\mathrm{dir}}}$ is suppressed by 20\% relative to the MB value with a significance of $4.5\sigma$, which may be due to final-state effects.

   nucl-exPRL(2025)·43 citations
2. 02*

   Characterization of the breakup channel in the asymmetric systems ${}^{40,48}$Ca+${}^{12}$C at 25 and 40 MeV/nucleon

   S.Piantelli🇮🇹 · G.Casini🇮🇹 · P.Ottanelli🇮🇹 · L.Baldesi🇮🇹 · S.Barlini🇮🇹 · B.Borderie🇫🇷 · R.Bougault🇫🇷 · A.Camaiani🇧🇪 · A.Chbihi🇫🇷 · C.Ciampi🇮🇹 · J.A.Duenas🇪🇸 · D.Fabris🇮🇹 and 27 other authors

   An analysis of the asymmetric reactions ${}^{40,48}$Ca+${}^{12}$C at 25 and 40 MeV/nucleon is presented. Data have been collected with six modules of the FAZIA array. The analysis is focused on the breakup channel of sources produced in dissipative collisions, partially corresponding to incomplete fusion processes. The study has been performed both on detected fragments and on some resonances reconstructed by means of particle-fragment correlations, with a focus on the evolution of the breakup channel with the beam energy and the neutron content of the system, looking in particular at the relative velocity between the breakup fragments. Results show that also Carbon fragments reconstructed by means of particle correlations can be in large part interpreted as the light partner of a scission.

   nucl-exPRC(2023)·9 citations
3. 03*

   Measurement of the angle between jet axes in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   This letter presents the first measurement of the angle between different jet axes (denoted as $\Delta R$) in Pb$-$Pb collisions. The measurement is carried out in the 0$-$10% most-central events at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Jets are assembled by clustering charged particles at midrapidity using the anti-$k_{\mathrm{T}}$ algorithm with resolution parameters $R=0.2$ and $0.4$ and transverse momenta in the intervals $40<p_{\mathrm{T}}^{\mathrm{chjet}}<140$ GeV/$c$ and $80<p_{\mathrm{T}}^{\mathrm{chjet}}<140$ GeV/$c$, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark$-$gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP shows that the observed narrowing of the Pb$-$Pb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements discard intra-jet $p_{\mathrm{T}}$ broadening as described in a model calculation with the BDMPS formalism as the main mechanism of energy loss in the QGP. The data are sensitive to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.

   nucl-exhep-exPRC(2026)·26 citations
4. 04*

   Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p$-$Pb collisions

   ALICE Collaboration

   Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at $\sqrt{s}=13$ TeV at midrapidity with the ALICE detector are presented down to a transverse momentum ($p_{\mathrm{T}}$) of 0.2 GeV$/c$ and up to $p_{\mathrm{T}}=35$ 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 $p_{\mathrm{T}}$ range $0.5<p_{\mathrm{T}}<26$ GeV$/c$ at $\sqrt{s_{\mathrm{NN}}}=8.16$ 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 $p_{\mathrm{T}}$ dependence is observed in pp collisions, where the yield of high-$p_{\mathrm{T}}$ electrons increases faster as a function of multiplicity than the one of low-$p_{\mathrm{T}}$ electrons. The measurement in p$-$Pb collisions shows no $p_{\mathrm{T}}$ 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.

   nucl-exhep-exJHEP(2023)·15 citations
5. 05*

   Measurements of inclusive J/$\psi$ production at midrapidity and forward rapidity in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The measurements of the inclusive J/$\psi$ yield at midrapidity ($\left|y\right|<0.9$) and forward rapidity (2.5 $<y<$ 4) in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC are reported. The inclusive J/$\psi$ production yields and nuclear modification factors, $R_{\mathrm{AA}}$, are measured as a function of the collision centrality, J/$\psi$ transverse momentum ($p_{\mathrm{T}}$), and rapidity. The J/$\psi$ average transverse momentum and squared transverse momentum ($⟨p_{\mathrm{T}}⟩$ and $⟨p_{\mathrm{T}}^2⟩$) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb$-$Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the $p_{\mathrm{T}}$ coverage. The $p_{\mathrm{T}}$-integrated $R_{\mathrm{AA}}$ shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The $p_{\mathrm{T}}$-differential $R_{\mathrm{AA}}$ shows a strong suppression at high $p_{\mathrm{T}}$ with less suppression at low $p_{\mathrm{T}}$ where it reaches a larger value at midrapidity compared to forward rapidity. The ratio of the $p_{\mathrm{T}}$-integrated yields of J/$\psi$ to those of D${}^0$ mesons is reported for the first time for the central and semicentral event classes at midrapidity. Model calculations implementing charmonium production via the coalescence of charm quarks and antiquarks during the fireball evolution (transport models) or in a statistical approach with thermal weights are in good agreement with the data at low $p_{\mathrm{T}}$. At higher $p_{\mathrm{T}}$, the data are well described by transport models and a model based on energy loss in the strongly-interacting medium produced in nuclear collisions at the LHC.

   nucl-exhep-exPLB(2024)·71 citations
6. 06*

   Higher-order correlations between different moments of two flow amplitudes in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   The correlations between different moments of two flow amplitudes, extracted with the recently developed asymmetric cumulants, are measured in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV recorded by the ALICE detector at the CERN Large Hadron Collider. The magnitudes of the measured observables show a dependence on the different moments as well as on the collision centrality, indicating the presence of non-linear response in all even moments up to the eighth. Furthermore, the higher-order asymmetric cumulants show different signatures than the symmetric and lower-order asymmetric cumulants. Comparisons with state-of-the-art event generators using two different parametrizations obtained from Bayesian optimization show differences between data and simulations in many of the studied observables, indicating a need for further tuning of the models behind those event generators. These results provide new and independent constraints on the initial conditions and transport properties of the system created in heavy-ion collisions.

   nucl-exhep-exPRC(2023)·14 citations
7. 07*

   Study of the p$-$p$-$K${}^{+}$ and p$-$p$-$K${}^{-}$ dynamics using the femtoscopy technique

   ALICE Collaboration

   The interactions of kaons (K) and antikaons ($\overline{\mathrm{K}}$) 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 $\overline{\mathrm{K}}$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 $\sqrt{s}$ = 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.

   nucl-exhep-exEPJA(2023)·18 citations
8. 08*

   Transparency of the $\gamma (n,p){\pi }^{-}$ reaction in nuclei

   Swapan Das🇮🇳

   The transparency of the hadrons produced in the $\gamma (n,p){\pi }^{-}$ reaction in nuclei is calculated using the Glauber model modified by including the Fermi motion of the nucleon in the nucleus. Since the calculated results underestimates the measured transparency for ${}^4$He nucleus, the Glauber model is further modified by incorporating the short-range correlation of the nucleon and the color transparency of the hadron in the nucleus. The nuclear transparency of the $\gamma (n,p){\pi }^{-}$ reaction is calculated for ${\theta }_{{\pi }^{-}}$(c.m.) = 50${}^{\circ }$, 70${}^{\circ }$ and 90${}^{\circ }$. The calculated results are compared with the data reported for ${}^4$He nucleus.

   ↳ nucl-thnucl-exPRC(2023)·3 citations
9. 09*

   Measurement of inclusive J/$\psi$ pair production cross section in pp collisions at $\sqrt{s}=13$ TeV

   ALICE Collaboration

   The production cross section of inclusive J/$\psi$ pairs in pp collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV is measured with ALICE. The measurement is performed for J/$\psi$ in the rapidity interval $2.5<y<4.0$ and for transverse momentum $p_{\mathrm{T}}>0$. The production cross section of inclusive J/$\psi$ pairs is reported to be $10.3\pm 2.3(stat.)\pm 1.3(syst.)$ nb in this kinematic interval. The contribution from non-prompt J/$\psi$ (i.e. originated from beauty-hadron decays) to the inclusive sample is evaluated. The effective double-parton scattering cross section is computed, neglecting the single-parton scattering contribution.

   ↳ hep-exnucl-exPRC(2023)·11 citations
10. 10*

    "Ultima Ratio": Simulating wide-range X-ray scattering and diffraction

    Brian R. Pauw · Sofya Laskina · Aakash Naik🇺🇸 · Glen J. Smales · Janine George · Ingo Breßler · Philipp Benner

    We demonstrate a strategy for simulating wide-range X-ray scattering patterns, which spans the small- and wide scattering angles as well as the scattering angles typically used for Pair Distribution Function (PDF) analysis. Such simulated patterns can be used to test holistic analysis models, and, since the diffraction intensity is on the same scale as the scattering intensity, may offer a novel pathway for determining the degree of crystallinity. The "Ultima Ratio" strategy is demonstrated on a 64-nm Metal Organic Framework (MOF) particle, calculated from Q < 0.01 1/nm up to Q < 150 1/nm, with a resolution of 0.16 Angstrom. The computations exploit a modified 3D Fast Fourier Transform (3D-FFT), whose modifications enable the transformations of matrices at least up to 8000^3 voxels in size. Multiple of these modified 3D-FFTs are combined to improve the low-Q behaviour. The resulting curve is compared to a wide-range scattering pattern measured on a polydisperse MOF powder. While computationally intensive, the approach is expected to be useful for simulating scattering from a wide range of realistic, complex structures, from (poly-)crystalline particles to hierarchical, multicomponent structures such as viruses and catalysts.

    ↳ cond-mat.mtrl-scihep-exnucl-exphysics.comp-ph+10 citations
11. 11*

    Data-driven precision determination of the material budget in ALICE

    ALICE Collaboration

    The knowledge of the material budget with a high precision is fundamental for measurements of direct photon production using the photon conversion method due to its direct impact on the total systematic uncertainty. Moreover, it influences many aspects of the charged-particle reconstruction performance. In this article, two procedures to determine data-driven corrections to the material-budget description in ALICE simulation software are developed. One is based on the precise knowledge of the gas composition in the Time Projection Chamber. The other is based on the robustness of the ratio between the produced number of photons and charged particles, to a large extent due to the approximate isospin symmetry in the number of produced neutral and charged pions. Both methods are applied to ALICE data allowing for a reduction of the overall material budget systematic uncertainty from 4.5% down to 2.5%. Using these methods, a locally correct material budget is also achieved. The two proposed methods are generic and can be applied to any experiment in a similar fashion.

    ↳ physics.ins-dethep-exnucl-exJINST(2023)·19 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.