Tek Lepton Kanalında Standart Model Ardalan Analizi

Yıl 2023, , 37 - 42, 01.03.2023

Buğra Yıldız , Muge Boz

https://doi.org/10.35414/akufemubid.1182938

Öz

Protonlar temel parçacık olmadıkları için, proton-proton çarpışmalarında büyük bir ardalan üretirler. Dolayısıyla, süpersimetri arayışlarında ana problem, süpersimetrik sinyalleri bu Standart Model ardalanından ayırmaktır. Bu nedenle, kapsamlı bir ardalan analizi, süpersimetri arayışları yönünde bilgi edinebilmek için önemli hale gelir. Tek lepton kanalı, Standart Model ardalanının elde edildiği etkin süreçlerden biridir. Bu çalışmada, çeşitli olaylardan oluşan ardalan üretilmiş, homojen ve temiz bir ardalan oluşabilmesi için temel seçimler ve kesimler uygulanmıştır. Öte yandan, dedektörde iz bırakmadan kaçabilen parçacıkları tespit edebilmek için, kayıp enine enerjinin büyüklüğü ve tüm enine momentumlarım skaler toplamı oldukça önemlidir. Bu nedenle, gerekli tüm histogramlar çizilmiştir. Ardalan, büyük ölçüde W-bozonları + jetleri ve top kuark-antikuark + jetlerinden oluşmakla birlikte, neredeyse tüm enerji bölgelerinde en fazla katkı, W+jetlerinden gelmektedir. Ancak çok sayıda jet üreten çarpışmalar için top kuark-antikuark + jetleri daha baskın hale gelmektedir. Çalışmanın son adımı ise, potansiyel süpersimetri sinyallerinin izolasyonu için ek seçimler ve kesimlerin uygulanmasıdır.

Anahtar Kelimeler

Süpersimetri, Standart Model, Tek lepton kanalı, Analiz

Standard Model Background Analysis for Single Lepton Channel

Öz

Since protons are not fundamental particles, they produce very large backgrounds in proton-proton collisions. Therefore, in supersymmetry searches, the main challenge is to differentiate supersymmetric signals from Standard Model background. Hence, extensive background analysis becomes an important probe to obtain information in the direction of supersymmetry searches. Among the variety of signatures in this direction, single lepton channel is one of the effective processes in which Standard Model background is obtained. In this work, starting from the generation of background emerging from various events, basic selections and cuts have been applied to obtain a homogenous and a clean sample. On the other hand, the magnitude of missing transverse energy and scalar sum of all transverse momentums are crucial to detect particles that can escape without leaving trace in the detector. Therefore, all necessary histograms have been plotted. Emerging the leading backgrounds from W-bosons + jets and top quark-antiquark + jets events, almost all energy regions, it is seen that W+jets have greater contribution to background. However, for the collisions that produce high number of jets top quark-antiquark + jets become more dominant. Final step of the work is the application of additional selections and cuts for the isolation of potential supersymmetry signals.

Anahtar Kelimeler

Supersymmetry, Standart Model, Single lepton channel, Analysis

Kaynakça

• Alves, D. et al., 2012. Simplified models for LHC new physics searches. Journal of Physics G: Nuclear and Particle Physics, 39, 105005. doi.org/10.1088/0954-3899/39/10/105005.
• Alwall, J., Schuster, P. C. and Toro, N., 2009. Simplified models for a first characterization of new physics at the LHC. Physical Review D, 79, 075020. doi.org/10.1103/PhysRevD.79.075020.
• Alwall, J., Herquet, M., Maltoni, F., Mattelaer, O. and Stelzer, T., 2011. MadGraph 5: Going Beyond. Journal of High Energy Physics, 128, 1-40. doi.org/10.1007/JHEP06(2011)128.
• ATLAS Collaboration, 2012. Further search for supersymmetry at sqrt{s} = 7 TeV in final states with jets, missing transverse momentum and isolated leptons with the ATLAS detector. Physical Review D, 86, 092002. doi.org/10.1103/PhysRevD.86.092002.
• ATLAS Collaboration, 2014. Search for strong production of supersymmetric particles in final states with missing transverse momentum and at least three b-jets at sqrt{s} = 8 TeV proton-proton collisions with the ATLAS detector. Journal of High Energy Physics, 24, 1-53. doi.org/10.1007/JHEP10(2014)024.
• ATLAS Collaboration, 2015. Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at sqrt{s}=8 TeV with the ATLAS detector. Journal of High Energy Physics, 116, 1-75. doi.org/10.1007/JHEP04(2015)116.
• ATLAS Collaboration, 2016. Search for pair production of gluinos decaying via stop and sbottom in events with b-jets and large missing transverse momentum in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector. Physical Review D, 94, 032003. doi.org/10.1103/PhysRevD.94.032003.
• Brun, R. and Rademakers, F., 1997. ROOT An Object Oriented Data Analysis Framework. Nuclear Instruments and Methods in Physics Research A, 389, 81-86. doi.org/ 10.1016/S0168-9002(97)00048-X.
• Chatrchyan, S. et al., May. 2013. Search for supersymmetry in pp collisions at sqrt{s} = 7 TeV in events with a single lepton, jets, and missing transverse momentum. The European Physical Journal C, 73, 2404-2445. doi.org/10.1140/epjc/s10052-013-2404-z.
• Chatrchyan, S. et al., Sep. 2013. Interpretation of searches for supersymmetry with simplified models. Physical Review D, 88, 052017. doi.org/10.1103/PhysRevD.88.052017.
• CMS Collaboration, 2013. Search for supersymmetry in final states with a single lepton, b-quark jets, and missing transverse energy in proton-proton collisions at sqrt{s} = 7 TeV. Physical Review D, 87, 052006. doi.org/10.1103/PhysRevD.87.052006.
• CMS Collaboration, 2013. Search for supersymmetry in pp collisions at sqrt(s) = 8 TeV in events with a single lepton, large jet multiplicity, and multiple b jets. Physics Letters B, 733, 328-353. doi.org/10.1016/j.physletb.2014.04.023.
• CMS Collaboration, 2016. Search for supersymmetry in pp collisions at sqrt(s) = 13 TeV in the single-lepton final state using the sum of masses of large-radius jets. Journal of High Energy Physics, 122, 1-49. doi.org/10.1007/JHEP08(2016)122.
• Dimopoulos, S., Raby, S. and Wilczek, F., 1981 Supersymmetry and the scale of unification. Physical Review D, 24, 1681–1683. doi.org/10.1103/PhysRevD.24.1681.
• Farrar, G. R. and Fayet, P., 1978. Phenomenology of the production, decay, and detection of new hadronic states associated with supersymmetry. Physics Letters B, 76, 575–579. doi.org/10.1016/0370-2693(78)90858-4.
• Fayet, P., 1975. Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino. Nuclear Physics B, 90, 104–124. doi.org/10.1016/0550-3213(75)90636-7.
• Golfand, Y. A. and Likhtman, E. P., 1971. Extension of the algebra of Poincare ́ group generators and violation of P invariance. JETP Letters, 13, 323-326.
• Hooft, G.’t. et al., 1980. Recent Developments in Gauge Theories. NATO Advanced Study Institutes Series B. 59, 135-157.
• Khachatryan, V. et al., 2017. Search for supersymmetry in events with one lepton and multiple jets in proton-proton collisions at, sqrt{s} = 13 TeV. Physical Review D, 95, 012011. doi.org/10.1103/PhysRevD.95.012011.
• Neveu A. and Schwarz, J. H., 1971. Factorizable dual model of pions. Nuclear Physics B, 31, 86–112. doi.org/10.1016/0550-3213(71)90448-2.
• Nilles, H. P., 1984. Supersymmetry, supergravity and particle physics. Physics Reports, 110, 1–162. doi.org/10.1016/0370-1573(84)90008-5.
• Ramond, P., 1971. Dual Theory for Free Fermions. Physical Review D, 3, 2415–2418. doi.org/10.1103/PhysRevD.3.2415.
• The NNPDF Collaboration et al., 2014. Parton distributions for the LHC Run II. Journal of High Energy Physics, 40, 1-148. doi.org/10.1007/JHEP04(2015)040.
• Yildiz, B., 2016. Supersymmetry searches in the single lepton channel at CMS experiment. Ph.D. Thesis, Institute of Science and Technology, Hacettepe University, 99.