利用緊湊渺子線圈探討質子質子對撞實驗中單光子加上三個噴流事例的雙部分子散射現象

Abstract

在大強子對撞機實驗中,同時間在同一粒子對撞中產生多組反應的機率是不可忽略的。這些額外的反應隨著對撞時的質心能量的增加,其發生的機率也隨之增 加,並且變得能夠辨識,甚至於影響分析那些來自主要對撞反應的物理現象。我們探討質心能量為七兆電子伏特的質子質子對撞實驗中單光子加上三個噴流事例的雙部分子散射現象。其中實驗數據是在二零一零年由大強子對撞機實驗的緊湊 渺子線圈偵測器所收集而來,數據的總有效照度約為三十六 皮靶負一次方。藉由分析緊湊秒子線圈偵測器所得數據,並加以重組數據資訊及篩選事例, 我們測量出質子質子對撞後末狀態為一個光子加上三個噴流的事例截面可能性為一百二十四點九 皮靶,統計誤差約為八點九 皮靶,系統誤差約為二十二點六 皮靶。同時 我們也探討了事例中, 光子和三個噴流的空間分布以及橫向動量平衡等有利於觀察雙部分子散射現像的物理量,而藉由蒙地卡羅法來模擬預測且和實際數據作比 對, 使我們了解各種物理模型正確性並對其加以修正。

The probability of having more than one interaction per collision is non-negligible at the LHC. These additional interactions might reach a hard scale comparable to the primary scattering and become experimentally distinguishable at high energies. Distributions sensitive to double parton scattering are investigated in the photon + 3 jets final state in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected by the CMS experiment at the LHC with an integrated luminosity of 36 pb−1 in 2010. The cross section σ for a final state with a photon and a jet of transverse momentum pT > 75 GeV together with 2 jets of pT > 20 GeV, where the photon and jets are within the fiducial volume of the CMS detector, is measured to be 124.9 ± 8.9 (stat.) ± 22.6 (syst.) pb. The differential cross sections are measured as a function of the difference in azimuthal angles and the transverse momentum balance between the photon-jet pair and the di-jet pair. Further it is investigated whether additional contributions from double par- ton scattering can improve the agreement between the measured data and the Monte Carlo predictions.