Ball Richard D, Bertone Valerio, Bonvini Marco, Carrazza Stefano, Forte Stefano, Guffanti Alberto, Hartland Nathan P, Rojo Juan, Rottoli Luca
The Higgs Centre for Theoretical Physics, University of Edinburgh, JCMB, KB, Mayfield Rd, Edinburgh, EH9 3JZ Scotland.
Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OX1 3NP UK.
Eur Phys J C Part Fields. 2016;76(11):647. doi: 10.1140/epjc/s10052-016-4469-y. Epub 2016 Nov 24.
We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the NLO calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced. We then find that the fitted charm PDF vanishes within uncertainties at a scale [Formula: see text] GeV for all [Formula: see text], independent of the value of [Formula: see text] used in the coefficient functions. We also find some evidence that the charm PDF at large [Formula: see text] and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of [Formula: see text], carrying less than [Formula: see text] of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on [Formula: see text] is reduced. The increased stability with respect to [Formula: see text] persists at high scales and is the main implication of our results for LHC phenomenology. Our results show that if the EMC data are correct, then the usual approach in which charm is perturbatively generated leads to biased results for the charm PDF, though at small this bias could be reabsorbed if the uncertainty due to the charm mass and missing higher orders were included. We show that LHC data for processes, such as high [Formula: see text] and large rapidity charm pair production and [Formula: see text] production, have the potential to confirm or disprove the implications of the EMC data.
我们给出了质子中粲夸克含量的无偏测定，其中在全局部分子分布函数（PDF）分析中，粲夸克部分子分布函数（PDF）与轻夸克和胶子在相同基础上进行参数化。这种测定依赖于在FONLL方案中对深度非弹性结构函数的NLO计算，并进行了推广以考虑大量粲夸克引发的贡献。当纳入欧洲核子研究中心（EMC）的粲夸克结构函数数据集时，拟合能很好地描述它，并且拟合的粲夸克PDF中的PDF不确定性显著降低。然后我们发现，对于所有的 ( x ) ，在 ( Q^2 ) = 20 GeV 的尺度下，拟合的粲夸克PDF在不确定性范围内消失，这与系数函数中使用的 ( \alpha_s ) 值无关。我们还发现一些证据表明，在大 ( x ) 和低尺度下的粲夸克PDF并不消失，而是有一个“内在”成分，其对尺度的依赖性非常弱，几乎与 ( \alpha_s ) 的值无关，携带的质子总动量不到1%。包含拟合的粲夸克后，所有其他PDF的不确定性仅略有增加，而这些PDF对 ( \alpha_s ) 的依赖性降低。在高尺度下，相对于 ( \alpha_s ) 的稳定性增加仍然存在，这是我们的结果对大型强子对撞机（LHC）现象学的主要影响。我们的结果表明，如果EMC数据是正确的，那么通常通过微扰产生粲夸克的方法会导致粲夸克PDF的有偏结果，不过在小 ( x ) 时，如果包括由于粲夸克质量和缺失高阶项引起的不确定性，这种偏差可能会被重新吸收。我们表明，LHC上对于诸如高 ( p_T ) 和大快度粲夸克对产生以及 ( W ) 玻色子产生等过程的数据，有可能证实或反驳EMC数据的影响。
