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首页> 外文期刊>Physical review, D >Study on ηc2(ηb2) electromagnetic decay into double photons
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Study on ηc2(ηb2) electromagnetic decay into double photons

机译：将ηc2（ηb2）电磁衰减分成双光子的研究

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Within the framework of nonrelativistic QCD factorization formalism, we compute the helicity amplitude as well as the decay width of η Q 2 ( Q = c , b ) electromagnetic decay into two photons up to next-to-next-to-leading order in α s expansion. For the first time, we verify the validity of nonrelativistic QCD factorization for the D -wave quarkonium decay at next-to-next-to-leading order. We find that the O ( α s ) and O ( α s 2 ) corrections to the helicity amplitude are negative and moderate, nevertheless both corrections combine to suppress the leading-order prediction for the decay width significantly. By approximating the total decay width of η Q 2 as the sum of those for the hadronic decay and the electric E 1 transition, we obtain the branching ratios Br ( η c 2 → 2 γ ) ≈ 5 × 10 ? 6 and Br ( η b 2 → 2 γ ) ≈ 4 × 10 ? 7 . To explore the potential measurement on η Q 2 , we further evaluate the production cross section of η Q 2 at LHCb at the lowest order in α s expansion. With the kinematic constraint on the longitudinal rapidity 4.5 > y > 2 and transverse momentum P T > ( 2 – 4 ) m Q for η Q 2 , we find the cross section can reach 2–50?nb for η c 2 , and 1–22?pb for η b 2 . Considering the integrated luminosity L = 10 ? ? fb ? 1 at s = 7 , 13?TeV, we estimate that there are several hundreds events of p p → η c 2 → 2 γ . Since the background is relatively clean, it is promising to reconstruct η c 2 through its electromagnetic decay. On the other hand, due to the small branching ratio and production cross section, it is quite challenging to detect η b 2 → 2 γ at LHCb.
机译：在非素描QCD分解形式主义的框架内，我们计算肝脏幅度以及ηq2（q = c，b）电磁衰减的衰减宽度，进入两个光子，直到α的下一点到前导顺序S扩张。我们首次验证了在接下来的下一对特的秩序下对D -Wave Quarkonium衰减的非筛选QCD分解的有效性。我们发现O（αs）和o（αs 2）校正对肝脏幅度是负的和中等的，但两种校正都相结合，以显着抑制衰减宽度的前导阶预测。通过近似ηq2的总衰减宽度作为辐射衰减和电气e 1转变的总和，我们获得了分支比Br（ηc2→2γ）≈5×10？ 6和Br（ηb2→2γ）≈4×10？ 7。为了探讨ηQ2的电位测量，我们进一步在αS膨胀中的最低阶数在LHCB处进一步评估ηQ2的生产横截面。随着纵向快速性的运动约束4.5> Y> 2和横向动量Pt>（2 - 4）M q对于ηq2，我们发现横截面可以达到2-50°C 2，1- 22？ηb 2 pb 2。考虑到集成亮度L = 10？还FB？ 1在S = 7,13？TEV，我们估计有几百个P P→ηc2→2γ事件。由于背景相对清洁，因此希望通过其电磁衰减重建ηc2。另一方面，由于分支比和生产横截面小，在LHCB处检测ηb2→2γ是非常具有挑战性的。

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