Geoffrey Fatin. Mentors: Dr. Robert Harr Dr. Kalanand Mishra

Transcription

1 Geoffrey Fatin Mentors: Dr. Robert Harr Dr. Kalanand Mishra

2 Basic Overview The standard model predicts single, double, and triple vector boson production Single vector boson production: common Double vector boson production: rare, but observed Triple vector boson production: very rare, never observed experimentally yet

3 Struggles with Programming Consistently presented with new languages to use: C++ ROOT Fortran 77 Python Issues with VBFNLO, configuration with ROOT and LHAPDF were also causes for lost time

4 VBFNLO: Vector Boson Fusion at Next Leading Order Monte Carlo Generator with limited capabilities at NLO Can simulate events involving gluon fusion, vector boson fusion, double and triple vector boson production, and more

5 The W + W γ Process Conservative choice for a process to study: Higher cross section than WWW or WWZ processes Lower background due to fully leptonic decays Still, there are issues: Cross section is still small: 4 fb with lepton and photon cuts at 20GeV (~10 events in 5 fb 1 of data) Cross section is further reduced by photon pt cuts (2.7% efficiency in moving the cut from 0.1GeV to 20GeV)

6 Variables Studied Rapidity, energy, pt, and azimuthal angles of final state particles and W+W- pair Difference in azimuthal angles between various particles All cross sections ( ds ) in this presentation are in units of femtobarns

7 Normalizations Used The plots created were normalized to one of the following: Cross section of one channel (for W+W-γ there are 4 channels, which correspond to different final state leptons) A percentage based scale to purely compare the shapes of distributions

8 Photon Observables

9

10 Lepton Observables

11 Peak at around 40GeV: boosted W bosons are rare, so this peak should be near half of the W boson mass (80.4GeV)

12 Other Plots of Interest

13 ϕ Between Particles Important for discerning how the interaction proceeds from the primary vertex and how to reconstruct events

14 ϕ ( W +, W ) W bosons produced back-to-back with low energy photons Distribution is more even when photons are energetic

15 ϕ ( W +, γ ) Photon and one of the W bosons are produced at rest (back-to-back) when photon is highly energetic Slight increase at small angles for very energetic photons

16 ϕ ( W +, v l + ) Peak at a small but nonzero angle that decreases slightly with higher photon pt cuts More neutrinos produced at small angles to W boson momentum vector

17 ϕ ( W +, l + ) Similar to neutrino plot, but peak has been shifted toward zero This is an artifact of the lepton pt cut

18 PDF Sets Different PDF (Particle Distribution Function) sets were used to test for built in error of modeling the W+W-γ process Each PDF set models the interaction differently. There are numerous unknowns that can vary, such as the actual energy of a collision and the properties of interacting partons

19 Effects of PDF Sets Significant error can be seen Shapes are nearly identical The PDF sets that resulted in minimum and maximum total cross sections are shown to the right

20 Effects of PDF Sets (Continued) PDF Set MSTW2008 MSTW2008nlo90cl MSTW2008nnlo90cl MRST2004qed CTEQ6L1 cteq66 CT10 CT10w NNPDF23_as_nlo_0119 NNPDF23_as_nnlo_0119 Mean Value Standard Deviation Total Cross Section (All Channels) (fb) 3.539fb 3.979fb 3.999fb 3.905fb 3.454fb 3.813fb 3.880fb 3.906fb 3.950fb 3.935fb 3.836fb ±0.178fb

21 Effects of a Change in s LHC will soon be upgraded to 14TeV (conservatively, it will only attain 13TeV center of mass energy) Cross sections of the W+W-γ event were calculated at 8TeV and 13TeV Cross sections for W+W- γ increased by roughly 80% M_G0Y/LHC_hall_1.jpg

22 W + W W +, W W + W, & W + W Z 0 Events: 8TeV Process W + W W + l 1 + v l1 l 2 v l 2 l 3 + v l3 W W + W l 1 v l 1 l 2 + v l2 l 3 v l 3 W + W Z 0 l 1 + v l1 l 2 v l 2 l 3 + l 3 Average Over 3 PDF Sets Standard Deviation Average Over 3 PDF Sets Standard Deviation Average Over 3 PDF Sets Standard Deviation Total Cross Section (All Channels) (fb) fb ± fb fb ± fb fb ± fb

23 W + W W +, W W + W, & W + W Z 0 Events: 13TeV Process W + W W + l 1 + v l1 l 2 v l 2 l 3 + v l3 78% increase W W + W l 1 v l 1 l 2 + v l2 l 3 v l 3 103% increase W + W Z 0 l 1 + v l1 l 2 v l 2 l 3 + l 3 100% increase Average Over 3 PDF Sets Standard Deviation Average Over 3 PDF Sets Standard Deviation Average Over 3 PDF Sets Standard Deviation Total Cross Section (All Channels) (fb) fb ± fb fb ± fb fb ± fb

24 Conclusions W+W-γ events are rare, but could be observed soon with recent data collection at the LHC (~10 events) PDF Set Error 5% W+W-W+, W-W+W- and W+W-Z events are much rarer, even with smaller lepton pt cuts than W+W-γ Cross sections of all of the above events increase between % with a 60% s increase

25 Directions for Further Research Simulate events at NLO (Powheg and More extensive research of other quartic coupling events such as triple W boson production or W+W-Z Investigation of the effects of different MET cuts

26 Works Consulted V. Hankele and D. Zeppenfeld, Phys. Let. B661: (2008) [arxiv: v3] F. Campanario, V. Hankele, C. Oleari, S. Prestel, D. Zeppenfeld, Phys. Rev. D78: (2008) [arxiv: ] G. Bozzi, F. Campanario, V. Hankele, and D. Zeppenfeld, Phys. Rev. D81: (2010) [arxiv: ] G. Bozzi, F. Campanario, M. Rauch, H. Rzehak, D. Zeppenfeld, Phys. Lett. B696: (2011) [arxiv: ] G. Bozzi, F. Campanario, M. Rauch, D. Zeppenfeld, Phys. Rev. D83: (2011) [arxiv: ] G. Bozzi, F. Campanario, M. Rauch, D. Zeppenfeld, Phys. Rev. D84: (2011) [arxiv: ] Green, Dan. Triple V-W+W+Photon?, 23 July Web. 29 July Whalley, Mike, and Andy Buckley. "The Les Houches Accord PDF Interface." LHAPDF - Hepforge. N.p., n.d. Web. 29 July < VBFNLO - A parton level Monte Carlo for processes with electroweak bosons. Karlsruhe Institute of Technology, n.d. Web. 29 July < wiki/doku.php?id=overview>. K. Arnold, J. Bellm, G. Bozzi, et al, (2012) [arxiv: v2] The ROOT Team. "ROOT." ROOT. The ROOT Team, Web. 29 July < drupal/>.