19289

2178 دكتري

دكتري

ذرات بنيادي

اصفهان : دانشگاه صنعتي اصفهان

1402

چهارده، 154ص.: مصور، جدول، نمودار

1402/12/03

كتابنامه

فيزيك

فيزيك

1402/12/19

23015609

ﺩﺭ ﺍﻳﻦ ﭘﮋﻭﻫﺶ ﻣﺎ ﺑﺎ ﺍﺳﺘﻔﺎﺩﻩ ﺍﺯ ﺩﺍﺩﻩ ﻫﺎﻱ ﺁﺷﻜﺎﺭﺳﺎﺯCMS ﺩﺭ ﺑﺮﺧﻮﺭﺩ ﺩﻫﻨﺪﻩ ﺑﺰﺭﮒ ﻫﺎﺩﺭﻭﻧﻲ(LHC) ﺩﺭ ﺳﺮﻥ(CERN) ﺑﻪ ﺩﻧﺒﺎﻝ ﻓﺮﺍﻳﻨﺪﻫﺎﻱ ﺟﺮﻳﺎﻥ ﺧﻨﺜﻲ ﺑﺎ ﺗﻐﻴﻴﺮ ﻃﻌﻢFCNC ﻛﻪ ﺷﺎﻣﻞ ﻛﻮﺍﺭﻙ ﺗﺎﭖ ﻭ ﻳﻚ ﻓﻮﺗﻮﻥ ﺑﺎﺷﺪ ﻫﺴﺘﻴﻢ. ﺩﺭ ﻣﺪﻝ ﺍﺳﺘﺎﻧﺪﺍﺭﺩ ﺫﺭﺍﺕ ﺑﻨﻴﺎﺩﻱ ﻓﺮﺍﻳﻨﺪﻫﺎﻱ FCNC ﺩﺭ ﻣﺮﺗﺒﻪ ﺩﺭﺧﺘﻲ ﻭﺟﻮﺩ ﻧﺪﺍﺭﻧﺪ ﻭ ﺩﺭﻣﺮﺗﺒﻪ ﺣﻠﻘﻪ ﺑﺸﺪﺕ ﺳﺮﻛﻮﺏ ﻣﻲ ﺷﻮﻧﺪ ﺑﻨﺎﺑﺮﺍﻳﻦ ﻧﺴﺒﺖ ﺍﻧﺸﻌﺎﺑﻲ(BR) ﺩﺭ ﻓﺮﺍﻳﻨﺪﻫﺎﻱFCNC ﻛﻮﺍﺭﻙ ﺗﺎﭖ ، )𝑡 ⟶ 𝑞𝛾(𝑞 = 𝑢,𝑐 ﺑﺴﻴﺎﺭ ﻛﻮﭼﻚ ﺍﺳﺖ ) ( . ﺍﻣﺎ ﺑﺮﺧﻲ ﻣﺪﻝ ﻫﺎﻱ ﻭﺭﺍﻱ ﻣﺪﻝ ﺍﺳﺘﺎﻧﺪﺍﺭﺩ(BSM) ﻣﻘﺎﺩﻳر ﺑﺰﺭﮔﺘﺮﻱ ﺑﺮﺍﻱ ﺍﻳﻦ ﻧﺴﺒﺖ ﺍﻧﺸﻌﺎﺑﻲFCNC )4 پيش بيني مي كنند. (. ﺩﺭ ﺍﻳﻦ ﭘﮋﻭﻫﺶ ﺩﺭ ﻧﻈﺮ ﺩﺍﺭﻳﻢ ﺍﺯ ﺗﻤﺎﻡ ﺩﺍﺩﻩ ﻫﺎﻱ ﺭﺍﻩ ﺍﻧﺪﺍﺯﻱ ﺩﻭﻡLHC ﺩﺭ ﺍﻧﺮﮊﻱ ﻣﺮﻛﺰ ﺟﺮﻡ𝑆 = 13 𝑇 𝑒𝑉 ﻭ ﺩﺭﺧﺸﻨﺪﮔﻲ ﺟﻤﻌﻲ35.86𝑓𝑏−1 ﺍﺳﺘﻔﺎﺩﻩ ﻛﻨﻴﻢ. ﺳﻴﮕﻨﺎﻝ ﻣﻮﺭﺩ ﻧﻈﺮ ﺑﺎ ﻧﻈﺮﻳﻪ مﻴﺪﺍﻥ ﻣﺆﺛﺮ ﻣﺪﻝ ﻣﻲ ﺷﻮﺩ. ﺟﻔﺖ ﺷﺪﮔﻲ ﻫﺎﻱ𝑡𝑢𝛾 ﻭ𝑡𝑐𝛾 ﺩﺭ ﻧﻈﺮ ﮔﺮﻓﺘﻪ ﺧﻮﺍﻫﺪ ﺷﺪ. ﺑﺮﺍﻱ ﺍﻳﻦ ﻣﻨﻈﻮﺭ ﺩﻭ ﻧﺎﺣﻴﻪ ﺳﻴﮕﻨﺎﻝ ﻛﻪ ﺍﺯ ﻧﻈﺮ ﺁﻣﺎﺭﻱ ﻣﺴﺘﻘﻞ ﻫﺴﺘﻨﺪ، ﺗﻌﺮﻳﻒ ﻣﻲ ﻛﻨﻴﻢ. ﺍﺯ ﺭﻭﺵ ﻫﺎﻱ ﻣﺨﺘﻠﻒ ﺩﺍﺩﻩ-ﻣﺤﻮﺭ ﺑﺮﺍﻱ ﺗﺨﻤﻴﻦ ﺳﻬﻢ ﻫﺎﻳﻲ ﺍﺯ ﭘﺲ ﺯﻣﻴﻨﻪ ﻛﻪ ﺷﺎﻣﻞ ﺭﻭﻳﺪﺍﺩ ﻫﺎﻳﻲ ﺑﺎ ﻓﻮﺗﻮﻥ ﻓﺮﻳﺒﻨﺪﻩ ﻭ ﺍﻟﻜﺘﺮﻭﻥ ﻓﺮﻳﺒﻨﺪﻩ ﻧﺎﺷﻲ ﺍﺯ ﺟﺖ ﻳﺎ ﻓﻮﺗﻮﻥ ﻓﺮﻳﺒﻨﺪﻩ ﻧﺎﺷﻲ ﺍﺯ ﺍﻟﻜﺘﺮﻭﻥ ﺑﺎﺷﺪ ﺍﺳﺘﻔﺎﺩﻩ ﺧﻮﺍﻫﻴﻢ ﻛﺮﺩ. ﻣﺎﺑﻘﻲ ﭘﺲ ﺯﻣﻴﻨﻪ ﻫﺎ ﺍﺯ ﺷﺒﻴﻪ ﺳﺎﺯﻱ ﻣﻮﻧﺖ ﻛﺎﺭﻟﻮ ﺑﺪﺳﺖ ﻣﻲ ﺁﻳﻨﺪ. ﺑﺮﺍﻱ ﺗﺼﺤﻴﺢ ﭘﺲ ﺯﻣﻴﻨﻪ ﻫﺎﻱ ﺍﺻﻠﻲ ̄𝑡𝑡𝛾 ﻭ𝑊𝛾 ﻧﻮﺍﺣﻲ ﻛﻨﺘﺮﻝ ﺗﻌﺮﻳﻒ ﻣﻲ ﻛﻨﻴﻢ. ﺑﺮﺍﻱ ﺟﺪﺍﺳﺎﺯﻱ ﺳﻴﮕﻨﺎﻝ ﺍﺯ ﭘﺲ ﺯﻣﻴﻨﻪ ﺍﺯ ﺗﺠﺰﻳﻪ ﻭ ﺗﺤﻠﻴﻞ ﭼﻨﺪ ﻣﺘﻐﻴﺮﻩ ﺍﺳﺘﻔﺎﺩﻩ ﻣﻲ ﻛﻨﻴﻢ ﺳﭙﺲ ﺑﺎ ﺍﺳﺘﻔﺎﺩﻩ ﺍﺯ ﺭﻭﺵ ﻫﺎﻱ ﺁﻣﺎﺭﻱ ﺣﺪ ﺑﺎﻻ ﺭﻭﻱ ﻧﺴﺒﺖ ﻫﺎﻱ ﺍﻧﺸﻌﺎﺑﻲ ﺑﺪﺳﺖ ﻣﻲ ﺁﻭﺭﻳﻢ.

In this study, we aim to explore neutral current flavor-changing processes (FCNC) involving the top quark and a photon using data from the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) located at CERN. In the Standard Model of particle physics, FCNC processes at tree level are absent, being highly suppressed at loop level. Consequently, the branching ratio (BR) for FCNC processes involving the top quark, 𝑡 ⟶ 𝑞𝛾(𝑞 = 𝑢,𝑐) , is predicted to be very small ( ∼ 10−14 ) . However, certain Beyond the Standard Model (BSM) theories predict larger values for this branching ratio ( ∼ 10−4 ). Our study utilizes the data from the second run of the LHC at a center-of-mass energy of √𝑆 = 13 𝑇𝑒𝑉 and an integrated luminosity of 35.86𝑓𝑏−1 . The targeted signal is modeled according to effective field theory. We consider the couplings 𝑡𝑢𝛾 and 𝑡𝑐𝛾 . For this purpose, we define two signal regions that are statistically independent. Various data-driven methods will be employed to estimate contributions from backgrounds, including events with fake photons or electrons arising from misidentified jets or misidentified electrons. The remaining backgrounds are obtained from Monte Carlo simulations. Control regions are defined to correct the main backgrounds 𝑡𝑡𝛾̄ and 𝑊𝛾 . To separate the signal from the background, a multivariate analysis will be employed, followed by statistical methods to derive upper limits on the branching ratios.

احمد شيرزاد , محسن اعتصامي

بهروز ميرزا , عبيده جعفري , سعيد پاك طينت مهدي آبادي , مجيد هاشمي