An official website of the United States government
Abstract The interaction between pions and nucleons plays a crucial role in hadron physics. It represents a fundamental building block of the low-energy QCD dynamics and is subject to several resonance excitations. This work studies the$$\text {p--}\uppi ^{\pm }$$ dynamics using femtoscopic correlations in high-multiplicity pp collisions at$$\sqrt{s} = 13$$ TeV measured by ALICE at the LHC. As the final-state interaction between protons and pions is well constrained by scattering experiments and the study of pionic hydrogen, the results give access to information on the particle-emitting source in pp collisions using the femtoscopy methods. The scaling of the source size of primordial protons and pions against their pair transverse mass is extracted. The results are compared with the source sizes studied with p–p,$$\text {p--K}^+$$ , and$$\uppi ^\pm $$ –$$\uppi ^\pm $$ pairs by ALICE in the same collision system and are found to be in agreement for the different particle pairs. This reinforces recent findings by ALICE of a common emission source for all hadron-pairs in pp collisions at LHC energies. Furthermore, the$$\text {p--p--}\uppi ^{\pm }$$ systems are studied using three-particle femtoscopy in pp collisions at$$\sqrt{s} = 13$$ TeV. The presence of three-body effects is analyzed utilizing the cumulant expansion method. In this formalism, the known two-body interactions are subtracted in order to isolate the three-body effects. For both,$$\text {p--p--}\uppi ^{+}$$ and$$\text {p--p--}\uppi ^{-}$$ , a non-zero cumulant is found, indicating effects beyond pairwise interactions. These results give information on the coupling of the pion to multiple nucleons.
more »
« less
Common femtoscopic hadron-emission source in pp collisions at the LHC
Abstract The femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose–Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at$$\sqrt{s}~=~13$$ TeV from charged$$\uppi $$ –$$\uppi $$ correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of$$\textrm{K}$$ –$$\textrm{p}$$ pairs. The size of the primordial source is evaluated as a function of the transverse mass ($$m_{\textrm{T}}$$ ) of the pairs, leading to the observation of a common scaling for both$$\uppi $$ –$$\uppi $$ and$$\textrm{K}$$ –$$\textrm{p}$$ , suggesting a collective effect. Further, the present results are compatible with the$$m_{\textrm{T}}$$ scaling of the$$\textrm{p}$$ –$$\textrm{p}$$ and p$$-\Lambda $$ primordial source measured by ALICE in high multiplicity pp collisions, providing additional evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron–hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles.
more »
« less
- PAR ID:
- 10599243
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- The European Physical Journal C
- Volume:
- 85
- Issue:
- 2
- ISSN:
- 1434-6052
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The transverse momentum spectra and integrated yields of anti-$$\Sigma $$ hyperons ($$\overline{\Sigma }^{\pm } $$ ) have been measured in$$\text {pp}$$ and$$\text {p}{-}\text {Pb}$$ collisions at$$\sqrt{s_{\textrm{NN}}}=5.02$$ TeV with the ALICE experiment. Measurements are performed via the newly accessed decay channel$$\overline{\Sigma }^{\pm } \!\!\rightarrow \mathrm{\overline{n}} \pi ^{\pm }$$ . A new method of antineutron reconstruction with the PHOS electromagnetic spectrometer is developed and applied to this analysis. The$$p_{\textrm{T}}$$ spectra of$$\overline{\Sigma }^{\pm } $$ are measured in the range$$0.5<3$$ GeV/$$c$$ and compared to predictions of the PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4 models. The EPOS LHC and EPOS4 models provide the best descriptions of the measured spectra both in$$\text {pp}$$ and$$\text {p}{-}\text {Pb}$$ collisions, while models which do not account for multiparton interactions provide a considerably worse description at high$$p_{\textrm{T}}$$ . The total yields of$$\overline{\Sigma }^{\pm } $$ in both$$\text {pp}$$ and$$\text {p}{-}\text {Pb}$$ collisions are compared to predictions of the Thermal-FIST model and dynamical models PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4. All models reproduce the total yields in both colliding systems within uncertainties. The nuclear modification factors$$R_\textrm{pPb}$$ for both$$\overline{\Sigma }^{+} $$ and$$\overline{\Sigma }^{-} $$ are evaluated and compared to those of protons,$$\Lambda $$ and$$\Xi $$ hyperons, and predictions of EPOS LHC and EPOS4 models. No deviations of$$R_\textrm{pPb}$$ for$$\overline{\Sigma }^{\pm } $$ from the model predictions or measurements for other hadrons are found within uncertainties.more » « less
-
Abstract The elliptic flow$$(v_2)$$ of$${\textrm{D}}^{0}$$ mesons from beauty-hadron decays (non-prompt$${\textrm{D}}^{0})$$ was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair$$\sqrt{s_{\textrm{NN}}} = 5.02$$ TeV with the ALICE detector at the LHC. The$${\textrm{D}}^{0}$$ mesons were reconstructed at midrapidity$$(|y|<0.8)$$ from their hadronic decay$$\mathrm {D^0 \rightarrow K^-\uppi ^+}$$ , in the transverse momentum interval$$2< p_{\textrm{T}} < 12$$ GeV/c. The result indicates a positive$$v_2$$ for non-prompt$${{\textrm{D}}^{0}}$$ mesons with a significance of 2.7$$\sigma $$ . The non-prompt$${{\textrm{D}}^{0}}$$ -meson$$v_2$$ is lower than that of prompt non-strange D mesons with 3.2$$\sigma $$ significance in$$2< p_\textrm{T} < 8~\textrm{GeV}/c$$ , and compatible with the$$v_2$$ of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties.more » « less
-
Abstract Event-by-event fluctuations of the event-wise mean transverse momentum,$$\langle p_{\textrm{T}}\rangle $$ , of charged particles produced in proton–proton (pp) collisions at$$\sqrt{s}$$ = 5.02 TeV, Xe–Xe collisions at$$\sqrt{s_{\textrm{NN}}}$$ = 5.44 TeV, and Pb–Pb collisions at$$\sqrt{s_{\textrm{NN}}}$$ = 5.02 TeV are studied using the ALICE detector based on the integral correlator$$\langle \!\langle \Delta p_\textrm{T}\Delta p_\textrm{T}\rangle \!\rangle $$ . The correlator strength is found to decrease monotonically with increasing produced charged-particle multiplicity measured at midrapidity in all three systems. In Xe–Xe and Pb–Pb collisions, the multiplicity dependence of the correlator deviates significantly from a simple power-law scaling as well as from the predictions of the HIJING and AMPT models. The observed deviation from power-law scaling is expected from transverse radial flow in semicentral to central Xe–Xe and Pb–Pb collisions. In pp collisions, the correlation strength is also studied by classifying the events based on the transverse spherocity,$$S_0$$ , of the particle production at midrapidity, used as a proxy for the presence of a pronounced back-to-back jet topology. Low-spherocity (jetty) events feature a larger correlation strength than those with high spherocity (isotropic). The strength and multiplicity dependence of jetty and isotropic events are well reproduced by calculations with the PYTHIA 8 and EPOS LHC models.more » « less
-
Abstract This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p–Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p–Pb collisions at centre-of-mass energies per nucleon pair of$$\sqrt{s_{\text {NN}}}={5.02}\,\textrm{TeV}$$ and 8.16 TeV, as well as in pp collisions at$$\sqrt{s}={5.02}\,\textrm{TeV}$$ and 8 TeV. The cross section is obtained at midrapidity$$(|y|<0.7)$$ using a charged-track based isolation momentum$$p_\textrm{T}^{\text {iso,~ch}}<{1.5}\,\textrm{GeV}/c$$ in a cone with radius$$R=0.4$$ . The data for both collision systems are well reproduced by perturbative QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor$$R_{\text {pA}}$$ for both collision energies is consistent with unity for$$p_{\textrm{T}}$$ $$>{20}\,\textrm{GeV}/c$$ . However, deviations from unity ($$R_\textrm{pA}<1$$ ) of up to 20% are observed for$$p_{\textrm{T}}$$ $$<{20}\,\textrm{GeV}/c$$ with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision. The suppression increases with decreasing$$p_{\textrm{T}}$$ with a significance of$$2.3\upsigma $$ for a non-zero slope and yields$$R_{\textrm{pA}}<1$$ with a significance of$$1.8\upsigma $$ at$$\sqrt{s_{\textrm{NN}}}={8.16}\,\textrm{TeV}$$ for$$p_{\textrm{T}}$$ $$<{20}\,\textrm{GeV}/c$$ . In addition, a significance of$$1.1\upsigma $$ is observed for$$R_{\textrm{pA}}<1$$ at the lower collision energy$$\sqrt{s_{\textrm{NN}}}={5.02}\,\textrm{TeV}$$ for$$p_{\textrm{T}} < {14}\,\textrm{GeV}/c$$ . The magnitude and shape of the suppression are consistent with pQCD predictions at NLO using nPDFs that incorporate nuclear shadowing effects in the Pb nucleus.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1140/epjc/s10052-025-13793-y
