Study of Single Top Quark Production Using Bayesian Neural Networks With D0 Detector at the Tevatron
Abstract
Top quark, the heaviest and most intriguing among the six known quarks, can be created via two independent production mechanisms in {\pp} collisions. The primary mode, strong {\ttbar} pair production from a $gtt$$ vertex, was used by the {\d0} and CDF collaborations to establish the existence of the top quark in March 1995. The second mode is the electroweak production of a single top quark or antiquark, which has been observed recently in March 2009. Since single top quarks are produced at hadron colliders through a $$Wtb$ vertex, thereby provide a direct probe of the nature of $Wtb$ coupling and of the CabibboKobayashiMaskawa matrix element, $$V_{tb}$$. So this mechanism provides a sensitive probe for several, standard model and beyond standard model, parameters such as anomalous $Wtb$ couplings. In this thesis, we measure the cross section of the electroweak produced top quark in three different production modes, $s+t$, $$s$$ and $$t$$channels using a technique based on the Bayesian neural networks. This technique is applied for analysis of the 5.4 $$fb^{1}$$ of data collected by the {\d0} detector. From a comparison of the Bayesian neural networks discriminants between data and the signalbackground model using Bayesian statistics, the cross sections of the topmore »
 Authors:

 Panjab Univ., Chandigarh (India)
 Publication Date:
 Research Org.:
 Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
 Sponsoring Org.:
 USDOE Office of Science (SC), High Energy Physics (HEP)
 OSTI Identifier:
 1248358
 Report Number(s):
 FERMILABTHESIS201218
1186499
 DOE Contract Number:
 AC0207CH11359
 Resource Type:
 Thesis/Dissertation
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Citation Formats
Joshi, Jyoti. Study of Single Top Quark Production Using Bayesian Neural Networks With D0 Detector at the Tevatron. United States: N. p., 2012.
Web. doi:10.2172/1248358.
Joshi, Jyoti. Study of Single Top Quark Production Using Bayesian Neural Networks With D0 Detector at the Tevatron. United States. https://doi.org/10.2172/1248358
Joshi, Jyoti. Sun .
"Study of Single Top Quark Production Using Bayesian Neural Networks With D0 Detector at the Tevatron". United States. https://doi.org/10.2172/1248358. https://www.osti.gov/servlets/purl/1248358.
@article{osti_1248358,
title = {Study of Single Top Quark Production Using Bayesian Neural Networks With D0 Detector at the Tevatron},
author = {Joshi, Jyoti},
abstractNote = {Top quark, the heaviest and most intriguing among the six known quarks, can be created via two independent production mechanisms in {\pp} collisions. The primary mode, strong {\ttbar} pair production from a $gtt$ vertex, was used by the {\d0} and CDF collaborations to establish the existence of the top quark in March 1995. The second mode is the electroweak production of a single top quark or antiquark, which has been observed recently in March 2009. Since single top quarks are produced at hadron colliders through a $Wtb$ vertex, thereby provide a direct probe of the nature of $Wtb$ coupling and of the CabibboKobayashiMaskawa matrix element, $V_{tb}$. So this mechanism provides a sensitive probe for several, standard model and beyond standard model, parameters such as anomalous $Wtb$ couplings. In this thesis, we measure the cross section of the electroweak produced top quark in three different production modes, $s+t$, $s$ and $t$channels using a technique based on the Bayesian neural networks. This technique is applied for analysis of the 5.4 $fb^{1}$ of data collected by the {\d0} detector. From a comparison of the Bayesian neural networks discriminants between data and the signalbackground model using Bayesian statistics, the cross sections of the top quark produced through the electroweak mechanism have been measured as: \[\sigma(p\bar{p}→tb+X,tqb+X) = 3.11^{+0.77}_{0.71}\;\rm pb\] \[\sigma(p\bar{p}→tb+X) = 0.72^{+0.44}_{0.43}\;\rm pb\] \[\sigma(p\bar{p}→tqb+X) = 2.92^{+0.87}_{0.73}\;\rm pb\] % The $s+t$channel has a gaussian significance of $4.7\sigma$, the $s$channel $0.9\sigma$ and the $t$channel~$4.7\sigma$. The results are consistent with the standard model predictions within one standard deviation. By combining these results with the results for two other analyses (using different MVA techniques) improved results \[\sigma(p\bar{p}→tb+X,tqb+X) = 3.43^{+0.73}_{0.74}\;\rm pb\] \[\sigma(p\bar{p}→tb+X) = 0.68^{+0.38}_{0.35}\;\rm pb\] \[\sigma(p\bar{p}→tqb+X) = 2.86^{+0.69}_{0.63}\;\rm pb\] % were obtained with a significance of $5.4\sigma$, $1.8\sigma$ and $5.0\sigma$ respectively for $s+t$, $s$ and $t$channels. Using this measured cross section and constraining $0 \leq V_{tb}^2 \leq 1$, the lower limit has been calculated to be $V_{tb} > 0.79$ with 95\% confidence level (C.L.). Another measurement of $tqb$ production cross section is done using the same dataset and discriminant but without any assumption on the $tb$ production rate. From this measurement, we obtain a cross section of $2.90^{+0.59}_{0.59}$~pb for $t$channel and corresponding significance of $5.5\sigma$. In addition to the above mentioned work, a search is made for the anomalous $Wtb$ couplings in single top quark production. Within the Standard Model, the $Wtb$ vertex is purely lefthanded, and its amplitude is given by the $V_{tb}$, related to weak interaction between a top and a $b$quark. In a more general way, additional anomalous couplings such as righthanded vectorial couplings and left and righthanded tensorial couplings can also be considered. An analysis based on the Bayesian neural networks method is used to separate the signal from expected backgrounds. We find no evidence for anomalous couplings and set 95\% C.L. limits on these couplings as $V_{tb} \cdot f_{L_T}^2<0.06$, $V_{tb} \cdot f_{R_V}^2<0.93$ and $V_{tb} \cdot f_{R_T}^2<0.13$. This result represents the most stringent direct constraints on anomalous $Wtb$ interactions. This work has been done in collaboration with \d0 experiment but the analyses and results presented in this thesis are my contribution.},
doi = {10.2172/1248358},
url = {https://www.osti.gov/biblio/1248358},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2012},
month = {1}
}