Discussion on triangle singularities in the Lambda(b) -> J/psi K(-)p reaction
Discussion on triangle singularities in the Lambda(b) -> J/psi K(-)p reaction
复制标题
DOI：
10.1103/physrevd.94.074039
复制
发表时间：
2016-09
影响因子：
5
通讯作者：
M. Bayar;F. Aceti;F. Guo;E. Oset
中科院分区：
文献类型：
--
作者：
M. Bayar;F. Aceti;F. Guo;E. Oset
本文详细分析了三角形环积分的奇异性，导出了一个计算物理边界上三角形奇异性的简便公式。它被应用到通过λ *-粲-质子中间态的λ（B）-> J/psi K（-）p过程。虽然绝对率的评估是不可能的，我们确定的chi（c1）和psi（2S）的所有可能的charmonia中相对最相关的状态到psi（2S）。Lambda（1890）chi（c1）p环是非常特殊的，因为它的正常阈值和三角形奇点在大约4.45 GeV处合并，在chi（c1）p处于S波的情况下，在振幅中产生狭窄而突出的峰值。我们还看到，具有相同粲偶素和其他λ * 超子的环仅从阈值奇点产生不太引人注目的峰值。对于chi（c1）p -> J/psi p和量子数3/2（-）或5/2（+）的情况，chi（c1）p中分别需要P波和D波，这会大大降低贡献的强度并平滑阈值峰值。在这种情况下，我们得出结论，奇异性不能解释所观察到的窄峰。在1/2（+），3/2（-）量子数的情况下，其中chi（c1）p -> J/psi p可以在S波中进行，Lambda（1890）chi（c1）p三角图可以发挥重要作用，尽管如果没有实验和格点QCD计算的进一步输入，两者都不能断言它们的强度。
We have analyzed the singularities of a triangle loop integral in detail and derived a formula for an easy evaluation of the triangle singularity on the physical boundary. It is applied to the Lambda(b) -> J/psi K(-)p process via Lambda*-charmonium-proton intermediate states. Although the evaluation of absolute rates is not possible, we identify the chi(c1) and the psi(2S)as the relatively most relevant states among all possible charmonia up to the psi(2S). The Lambda(1890)chi(c1)p loop is very special, as its normal threshold and triangle singularities merge at about 4.45 GeV, generating a narrow and prominent peak in the amplitude in the case that the chi(c1)p is in an S wave. We also see that loops with the same charmonium and other Lambda* hyperons produce less dramatic peaks from the threshold singularity alone. For the case of chi(c1)p -> J/psi p and quantum numbers 3/2(-) or 5/2(+), one needs P and D waves, respectively, in the chi(c1)p, which drastically reduce the strength of the contribution and smooth the threshold peak. In this case, we conclude that the singularities cannot account for the observed narrow peak. In the case of 1/2(+), 3/2(-) quantum numbers, where chi(c1)p -> J/psi p can proceed in an S wave, the Lambda(1890)chi(c1)p triangle diagram could play an important role, though neither can assert their strength without further input from experiments and lattice QCD calculations.