The energy deposited at very forward rapidities (very forward energy) is a powerful tool for characterising proton fragmentation in pp and p$-$Pb collisions. The correlation of very forward energy with particle production at midrapidity provides direct insights into the initial stages and the subsequent evolution of the collision. Furthermore, the correlation with the production of particles with large transverse momenta at midrapidity provides information complementary to the measurements of the underlying event, which are usually interpreted in the framework of models implementing centrality-dependent multiple parton interactions. Results about very forward energy, measured by the ALICE zero degree calorimeters (ZDCs), and its dependence on the activity measured at midrapidity in pp collisions at $\sqrt{s}=13$ TeV and in p$-$Pb collisions at $\sqrt{s_{\rm{NN}}}=8.16$ TeV are discussed. The measurements performed in pp collisions are compared with the expectations of three hadronic interaction event generators: PYTHIA 6 (Perugia 2011 tune), PYTHIA 8 (Monash tune), and EPOS LHC. These results provide new constraints on the validity of models in describing the beam remnants at very forward rapidities, where perturbative QCD cannot be used.
Average signal on A-side vs. C-side ZN in pp collisions at 13 TeV
Average signal on A-side vs. C-side ZP in pp collisions at 13 TeV
Pb-remnant side ZN signal normalized to MB value vs. ZN centrality percentile in p-Pb collisions at 5.02 TeV
A search for lepton-flavor-violating $Z\to e\tau$ and $Z\to\mu\tau$ decays with $pp$ collision data recorded by the ATLAS detector at the LHC is presented. This analysis uses 139 fb$^{-1}$ of Run 2 $pp$ collisions at $\sqrt{s}=13$ TeV and is combined with the results of a similar ATLAS search in the final state in which the $\tau$-lepton decays hadronically, using the same data set as well as Run 1 data. The addition of leptonically decaying $\tau$-leptons significantly improves the sensitivity reach for $Z\to\ell\tau$ decays. The $Z\to\ell\tau$ branching fractions are constrained in this analysis to $\mathcal{B}(Z\to e\tau)<7.0\times10^{-6}$ and $\mathcal{B}(Z\to \mu\tau)<7.2\times10^{-6}$ at 95% confidence level. The combination with the previously published analyses sets the strongest constraints to date: $\mathcal{B}(Z\to e\tau)<5.0\times10^{-6}$ and $\mathcal{B}(Z\to \mu\tau)<6.5\times10^{-6}$ at 95% confidence level.
The best-fit predicted and observed distributions of the combined NN output in the low-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The first and last bin include underflow and overflow events, respectively.
The best-fit predicted and observed distributions of the combined NN output in the low-$p_\text{T}$-SR for the $\mu\tau_e$ channel. The first and last bin include underflow and overflow events, respectively.
The best-fit predicted and observed distributions of the combined NN output in the high-$p_\text{T}$-SR for the $e\tau_\mu$ channel. The first and last bin include underflow and overflow events, respectively.
The production of $\phi$ mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region $2.5 < y < 4$. Measurements of the differential cross section ${\rm d}^2\sigma/{\rm d}y {\rm d}p_{\rm T}$ are presented as a function of the transverse momentum ($p_{\rm T}$) at the center-of-mass energies $\sqrt{s}=5.02$, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at $\sqrt{s}=5.02$ and 13 TeV are also studied in several rapidity intervals as a function of $p_{\rm T}$, and as a function of rapidity in three $p_{\rm T}$ intervals. A hardening of the $p_{\rm T}$-differential cross section with the collision energy is observed, while, for a given energy, $p_{\rm T}$ spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing $p_{\rm T}$. The new results, complementing the published measurements at $\sqrt{s}=2.76$ and 7 TeV, allow one to establish the energy dependence of $\phi$ meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with $p_{\rm T}$ and rapidity at all the energies.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=5.02$ TeV at forward rapidity in pp collisions.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=8$ TeV at forward rapidity in pp collisions.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=13$ TeV at forward rapidity in pp collisions.
Neutral pion ($\pi^{0}$) and $\eta$ meson production cross sections were measured up to unprecedentedly high transverse momenta ($p_{\rm T}$) in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. The mesons were reconstructed via their two-photon decay channel in the rapidity interval $-1.3< y <0.3$ in the ranges of $0.4<p_{\rm T}<200$ GeV/$c$ and $1.0<p_{\rm T}<50$ GeV/$c$, respectively. The respective nuclear modification factor ($R_{\rm pPb}$) is presented for $p_{\rm T}$ up to of 200 and 30 GeV/$c$, where the former was achieved by extending the $\pi^{0}$ measurement in pp collisions at $\sqrt{s}$ = 8 TeV using the merged cluster technique. The values of $R_{\rm pPb}$ are below unity for $p_{\rm T}<10$ GeV/$c$, while they are consistent with unity for $p_{\rm T}>10$ GeV/$c$, leaving essentially no room for final state energy loss. The new data provide strong constraints for nuclear parton distribution and fragmentation functions over a broad kinematic range and are compared to model predictions as well as previous results at $\sqrt{s_{\rm NN}}$ = 5.02 TeV.
Invariant differential cross section of PI0 produced in inelastic p-Pb collisions at a centre-of-mass energy per nucleon of 8.16 TeV, the uncertainty of $\sigma_\mbox{MB}$ of 1.9% is not included in the systematic error.
Invariant differential cross section of PI0 produced in inelastic pp collisions at a centre-of-mass energy of 8 TeV, the uncertainty of $\sigma_\mbox{MB}$ of 2.6% is not included in the systematic error.
Invariant differential cross section of ETA produced in inelastic p-Pb collisions at a centre-of-mass energy per nucleon of 8.16 TeV, the uncertainty of $\sigma_\mbox{MB}$ of 1.9% is not included in the systematic error.
The inclusive production of the J/$\psi$ and $\psi$(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 8.16$ TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals $-4.46 < y_{\rm cms} < -2.96$ (Pb-going direction) and $2.03 < y_{\rm cms} < 3.53$ (p-going direction), down to zero transverse momentum ($p_{\rm T}$). The J/$\psi$ and $\psi$(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 $p_{\rm T}$-differential J/$\psi$ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average $\langle p_{\rm T} \rangle$ and $\langle p^{2}_{\rm T} \rangle$ 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/$\psi$ increases from below unity in peripheral collisions to above unity in central collisions, while for the $\psi$(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 $\sqrt{s_{\rm NN}} = 5.02$ 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 $p_{\rm T}$-differential inclusive J/$\psi$ cross sections for six centrality classes at backward ($-4.46 < y_{\rm cms} < -2.96$) centre-of-mass rapidity. The first uncertainty is statistical, the second one and the third ones are the uncorrelated and correlated systematic uncertainties, respectively. The third uncertainty is fully correlated over $p_{\rm T}$.
The $p_{\rm T}$-differential inclusive J/$\psi$ cross sections for six centrality classes at forward ($2.03 < y_{\rm cms} < 3.53$) centre-of-mass rapidity. The first uncertainty is statistical, the second one and the third ones are the uncorrelated and correlated systematic uncertainties, respectively. The third uncertainty is fully correlated over $p_{\rm T}$.
The values of $\langle p_{\rm T} \rangle$ and $\langle p^{2}_{\rm T} \rangle$ for six centrality classes at backward ($-4.46 < y_{\rm cms} < -2.96$) and forward ($2.03 < y_{\rm cms} < 3.53$) centre-of-mass rapidity. The first uncertainty is statistical, the second one is the systematic uncertainty.
Measurement of Z-boson production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity $-4 < \eta_{\mu} < -2.5$ and transverse momentum $p_{\rm T}^{\mu} > 20$ GeV/$c$ in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass $60 < m^{\mu\mu} < 120$ GeV$c^2$ and rapidity $2.5 < y_{cms}^{\mu\mu} < 4$. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward ($-4.46< y_{cms}^{\mu\mu}<-2.96$) and forward ($2.03< y_{cms}^{\mu\mu}<3.53$) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a $3.4\sigma$ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.
Differential fiducial cross section in p-Pb
Integrated fiducial invariant yield in Pb-Pb
Rapidity differential fiducial invariant yield in Pb-Pb
The production of $\pi^{\pm}$, $\rm{K}^{\pm}$, $\rm{K}^{0}_{S}$, $\rm{K}^{*}(892)^{0}$, $\rm{p}$, $\phi(1020)$, $\Lambda$, $\Xi^{-}$, $\Omega^{-}$, and their antiparticles was measured in inelastic proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV at midrapidity ($|y|<0.5$) as a function of transverse momentum ($p_{\rm{T}}$) using the ALICE detector at the CERN LHC. Furthermore, the single-particle $p_{\rm{T}}$ distributions of $\rm{K}^{0}_{S}$, $\Lambda$, and $\overline{\Lambda}$ in inelastic pp collisions at $\sqrt{s}$ = 7 TeV are reported here for the first time. The $p_{\rm{T}}$ distributions are studied at midrapidity within the transverse momentum range $0\leq p_{\rm{T}}\leq20$ GeV/$c$, depending on the particle species. The $p_{\rm{T}}$ spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower $\sqrt{s}$ and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high $p_{\rm{T}}$ with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and $x_{\rm{T}}\equiv2p_{\rm{T}}/\sqrt{s}$ scaling properties of hadron production are also studied. As the collision energy increases from $\sqrt{s}$ = 7 to 13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of $\sqrt{s}$, while ratios for multi-strange hadrons indicate enhancements. The $p_{\rm{T}}$-differential cross sections of $\pi^{\pm}$, $\rm{K}^{\pm}$ and $\rm{p}$ ($\overline{\rm{p}}$) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for $\pi^{\pm}$ and $\rm{p}$ ($\overline{\rm{p}}$) at high $p_{\rm{T}}$.
Transverse momentum spectrum of $\pi^{+} + \pi^{-}$ measured at midrapidity ($|y|<0.5$) in inelastic pp collisions at $\sqrt{s}$ = 13 TeV. The normalization uncertainty of $\pm2.6\%$ is excluded.
Transverse momentum spectrum of $K^{+} + K^{-}$ measured at midrapidity ($|y|<0.5$) in inelastic pp collisions at $\sqrt{s}$ = 13 TeV. The normalization uncertainty of $\pm2.6\%$ is excluded.
Transverse momentum spectrum of $K^{0}_{S}$ measured at midrapidity ($|y|<0.5$) in inelastic pp collisions at $\sqrt{s}$ = 13 TeV. The normalization uncertainty of $\pm2.6\%$ is excluded.
Inclusive J/$\psi$ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/$\psi$ mesons are reconstructed at forward $(2.03 < y_{\rm cms} < 3.53)$ and backward ($-4.46 < y_{\rm cms} < -2.96$) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/$\psi$ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.
Relative yield of inclusive J/psi as a function of relative charged-particle pseudorapidity density at forward rapidity 2.03 < y_cms < 3.53 (p-going direction).
Relative yield of inclusive J/psi as a function of relative charged-particle pseudorapidity density at backward rapidity -4.46 < y_cms < -2.96 (Pb-going direction).
Mean transverse momentum of inclusive J/psi as a function of the relative charged-particle pseudorapidity density at forward rapidity 2.03 < y_cms < 3.53 (p-going direction).
Inclusive $\psi$(2S) production is measured in p-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm{NN}}}=8.16$ TeV, using the ALICE detector at the CERN LHC. The production of $\psi$(2S) is studied at forward ($2.03 < y_{\rm cms} < 3.53$) and backward ($-4.46 < y_{\rm cms} < -2.96$) centre-of-mass rapidity and for transverse momentum $p_{\rm{T}}$ $<$ 12 GeV/$c$ via the decay to muon pairs. In this paper, we report the integrated as well as the $y_{\rm cms}$- and $p_{\rm T}$-differential inclusive production cross sections. Nuclear effects on $\psi$(2S) production are studied via the determination of the nuclear modification factor that shows a strong suppression at both forward and backward centre-of-mass rapidities. Comparisons with corresponding results for inclusive J/$\psi$ show a similar suppression for the two states at forward rapidity (p-going direction), but a stronger suppression for $\psi$(2S) at backward rapidity (Pb-going direction). As a function of $p_{\rm T}$, no clear dependence of the nuclear modification factor is found. The relative size of nuclear effects on $\psi$(2S) production compared to J/$\psi$ is also studied via the double ratio of production cross sections $[\sigma_{\psi(2S)}/\sigma_{\rm{J/}\psi}]_{\rm pPb}/[\sigma_{\psi(2S)}/\sigma_{\rm{J/}\psi}]_{\rm pp}$ between p-Pb and pp collisions. The results are compared with theoretical models that include various effects related to the initial and final state of the collision system and also with previous measurements at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV.
Inclusive $\psi(2{\rm S})$ differential cross section times branching ratio as a function of $y_{\rm cms}$, in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 8.16 TeV. The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a correlated systematic uncertainty.
Inclusive $\psi(2{\rm S})$ differential cross section times branching ratio as a function of $p_{\rm T}$, at forward rapidity at $\sqrt{s_{\rm NN}}$ = 8.16 TeV .The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a correlated systematic uncertainty.
Inclusive $\psi(2{\rm S})$ differential cross section times branching ratio as a function of $p_{\rm T}$, at backward rapidity at $\sqrt{s_{\rm NN}}$ = 8.16 TeV .The first uncertainty is statistical, the second is the uncorrelated systematic, while the third one is a correlated systematic uncertainty.
The production of $\mathrm{K}^{*}(\mathrm{892})^{0}$ and $\mathrm{\phi(1020)}$ in pp collisions at $\sqrt{s}$ = 8 TeV was measured using Run 1 data collected by the ALICE collaboration at the LHC. The $p_{\rm{T}}$-differential yields d$^{\rm 2}N$/d$y$d$p_{\rm{T}}$ in the range $0 < p_{\rm{T}} < 20$ GeV/$c$ for $\rm{K}^{*0}$ and $0.4 < p_{\rm{T}} < 16$ GeV/$c$ for $\phi$ have been measured at midrapidity, $|y| < 0.5$. Moreover, improved measurements of the $\rm{K}^{*}(892)^{0}$ and $\phi(1020)$ at $\sqrt{s} = 7$TeV are presented. The collision energy dependence of $p_{\rm{T}}$ distributions, $p_{\rm{T}}$-integrated yields and particle ratios in inelastic pp collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In pp collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The $p_{\rm{T}}$-differential yields of $\rm{K}^{*0}$ and $\phi$ in pp collisions at $\sqrt{s} = 8$ TeV are compared with the expectations of different Monte Carlo event generators.
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