AI 中文总结
在13.6 TeV pp碰撞中测量D*+介子自旋排列，瞬发介子无自旋排列，非瞬发介子有偏差且与弱衰变预期及PYTHIA 8模拟一致，为未来重离子研究提供基线。
AI 中文摘要
本文给出了在质心能量√s = 13.6 TeV的质子-质子（pp）碰撞中，相对于螺旋度轴和产生轴，瞬发和非瞬发D*+介子自旋排列的精确测量结果，数据由大型强子对撞机（LHC）上的ALICE实验采集。自旋排列通过测量在中等快度（|y|<0.8）下D*+介子的对角自旋密度矩阵元ρ00来量化。测量分别在横动量（pT）范围3<pT<100 GeV/c（瞬发D*+介子）和3<pT<30 GeV/c（非瞬发D*+介子）内进行。对于瞬发D*+介子，测得的ρ00值在整个pT范围内与无极化预期值1/3一致，表明没有自旋排列的证据。相比之下，非瞬发D*+介子的ρ00表现出与1/3的偏差，这与弱美强子衰变的预期一致，并由耦合了EvtGen衰变包的PYTHIA 8模拟很好地描述。这些结果确认并扩展了之前的测量，为未来在重离子碰撞中研究D*+自旋排列提供了精确的基线。
英文摘要
A precise measurement of prompt and non-prompt ${\rm D}^{\rm *+}$-meson spin alignment with respect to the helicity and production axes in proton-proton (pp) collisions at $\sqrt{s} = 13.6$ TeV is presented, using data collected with the ALICE experiment at the LHC. The spin alignment is quantified by measuring the diagonal spin density matrix element $ρ_{\rm 00}$ for ${\rm D}^{\rm *+}$ mesons at midrapidity ($|y|<0.8$). The measurement is performed in the transverse-momentum ($p_{\rm T}$) range $3<p_{\rm T}<100$ GeV/$c$ for prompt ${\rm D}^{\rm *+}$ mesons and $3<p_{\rm T}<30$ GeV/$c$ for non-prompt ${\rm D}^{\rm *+}$ mesons, respectively. The measured $ρ_{\rm 00}$ values for prompt ${\rm D}^{\rm *+}$ mesons are consistent with the unpolarised expectation of $1/3$ over the entire $p_{\rm T}$ range, indicating no evidence of spin alignment. In contrast, $ρ_{\rm 00}$ of non-prompt ${\rm D}^{\rm *+}$ mesons exhibit a deviation from $1/3$, consistent with expectations from weak beauty-hadron decays and well described by PYTHIA 8 simulations coupled with the EvtGen decay package. These results confirm and extend previous measurements, providing a precise baseline for future studies of ${\rm D}^{\rm *+}$ spin alignment in heavy-ion collisions.
Comments25 pages, 7 captioned figures, 1 table, authors from page 20, submitted to Journal of High Energy Physics, figures at http://alice-publications.web.cern.ch/node/13656
