D Meson

An interesting example of a particle interaction which involves the D meson was observed in a bubble chamber at SLAC in 1982 (K. Abe et al., Phys. Rev. Lett. 48,1526 (1982)). Photons at about 20 GeV were produced by Compton scattering of radiation from a YAG laser from energetic electrons from the linear accelerator. The interaction is sketched from the bubble chamber photograph. The presumption is that the photon interacted with a proton, producing the D mesons indicated. The reaction which produced these products would appear to be the following.

一个涉及D介子的粒子相互作用的例子在1982年于SLAC的泡室中被观察到（K. Abe等，Phys. Rev. Lett. 48,1526 (1982)）。通过来自YAG激光器的辐射与线性加速器中的高能电子的康普顿散射产生了约20 GeV的光子。该相互作用从泡室照片中进行了示意。假设光子与质子相互作用，产生了所示的D介子。产生这些产物的反应似乎如下所示。

The reaction can be analyzed by examining the quark content of the products, and is seen to involve the production of a charm-anticharm quark pair. From the bubble chamber tracks, it can be seen that the neutral D meson decays into two products and the positive D meson decays into three. While the specific products can not be identified with just this photograph, it is interesting to propose possibilities for this process. The decays shown below are one possibility.

该反应可以通过考察产物的夸克组成进行分析，可以看出涉及产生一个粲夸克-反粲夸克对。从泡室的轨迹可以看出，中性D介子衰变成两个产物，而正D介子衰变成三个产物。虽然仅凭这张照片无法确定具体的产物，但提出一些可能性是有趣的。下面所示的衰变是一种可能的情况。

Since the D meson is the lightest meson which contains a charm quark, it must change that charm quark to some other quark in order to decay. Transmutations of quarks occurs by the weak interaction, which changes the charm quark to a strange quark with a W particle. This weak interaction process is indicated in both of the decays above. For the particular decay proposed for the positive D meson, an up-antiup quark pair is also required.

由于D介子是包含粲夸克的最轻的介子，它必须将这个粲夸克转变为其他类型的夸克以便衰变。夸克的转变发生于弱相互作用，该作用将粲夸克转变为奇夸克，通过一个W粒子。这种弱相互作用过程在上述两种衰变中都得到了体现。对于正D介子的特定衰变过程，还需要一个上夸克-反上夸克对。

There are many possible decay processes for the D meson because it has a lot of excess mass energy. These all involve the weak interaction to change the charm quark, and the variety of W decays provide many paths for the process.

D介子有许多可能的衰变过程，因为它有较多的过剩质量能量。这些过程都涉及弱相互作用来改变粲夸克，而W衰变的多样性为这一过程提供了多种路径。

2011 reports from the Beauty detector of the Large Hadron Collider suggest that D-mesons seem to decay slightly differently from their antiparticles. The LHCb team reported a difference of about 0.8 percent - a significant difference that, if true, could herald the first "new physics" to be found at the LHC.

2011年来自大型强子对撞机上Beauty探测器的报告表明，D介子似乎与它们的反粒子在衰变方式上略有不同。LHCb团队报告了一种约0.8%的差异——如果属实，这可能标志着在LHC上发现的第一种‘新物理’。

D介子是包含粲夸克的最轻粒子，因此是研究通过弱相互作用进行夸克变换衰变的良好例子。