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arXiv 2411.14366hep-exnucl-ex
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质心能量 $\sqrt{s} =$ 13 TeV 的非弹性和高多重数质子-质子碰撞中的直接光子产生

Direct-photon production in inelastic and high-multiplicity proton-proton collisions at $\sqrt{s} =$ 13 TeV

ALICE Collaboration

AI总结:

首次在 $\sqrt{s} =$ 13 TeV 的非弹性和高多重数质子-质子碰撞中测量了低横向动量直接光子,发现直接光子产额随带电粒子多重数显著增加。

摘要:

在这封信中,我们首次测量了在质心能量 $\sqrt{s} =$ 13 TeV 的非弹性和高多重数质子-质子碰撞中,中心快度 $|η| < 0.8$ 范围内,横向动量为 $1 < p_{\rm T} < 6$ GeV/$c$ 的直接光子。通过拟合双电子不变质量谱,得到了包含虚光子谱中虚直接光子的比例。在零不变质量的极限下,该比例等于包含真实光子谱中真实直接光子的相对贡献。轻味中性介子衰变的贡献是使用在相同能量和相同事件类别下质子-质子碰撞的独立测量结果进行估计的。在 LHC 能量下,首次在非弹性和高多重数事件类别中观测到了低 $p_{\rm T}$ 的直接光子信号,其显著性以标准差计算分别为 3.2$σ$ 和 1.9$σ$。将非弹性 pp 碰撞中的直接光子产额与微扰 QCD 计算进行了比较。研究了积分光子产额随带电粒子多重数的函数关系,并与其他实验结果和理论计算进行了比较。结果表明,直接光子产额随带电粒子多重数显著增加。

英文摘要:

In this letter, we present the first measurement of direct photons at the transverse momentum of $ 1 < p_{\rm T} < 6$ GeV/$c$ at midrapidity $|η| < 0.8$ in inelastic and high-multiplicity proton--proton collisions at a centre-of-mass energy of $\sqrt{s} =$ 13 TeV. The fraction of virtual direct photons in the inclusive virtual photon spectrum is obtained from a fit to the dielectron invariant mass spectrum. In the limit of zero invariant mass, this fraction is equal to the relative contribution of real direct photons in the inclusive real photon spectrum. Contributions from decays of light-flavour neutral mesons are estimated using independent measurements in proton-proton collisions at the same energy and the same event class. For the first time at the LHC energies, a direct-photon signal is observed at low $p_{\rm T}$ in both inelastic and high-multiplicity event classes, with a significance of 3.2$σ$ and 1.9$σ$ in terms of standard deviations, correspondingly. The yield of direct photons in inelastic pp collisions is compared to perturbative QCD calculations. The integrated photon yield is studied as a function of charged-particle multiplicity and is compared to the results from other experiments and theoretical calculations. The results show a significant increase of direct-photon yield with charged-particle multiplicity.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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