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Geoffrey Fatin
Mentors:
Dr. Robert Harr
Dr. Kalanand Mishra
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
http://arxiv.org/pdf/0911.0438v1.pdf
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
http://root.cern.ch/drupal/
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
http://www.kit.edu/index.php
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)
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
http://www.hep.lu.se/staff/eerola/relativitet.pdf http://en.wikipedia.org/wiki/Pseudorapidity
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
Photon Observables
Lepton Observables
Peak at around 40GeV: boosted W bosons are rare, so this peak should be near half of the W boson mass (80.4GeV)
Other Plots of Interest
∆ϕ Between Particles
Important for discerning how the interaction proceeds from the primary vertex and how to reconstruct events
∆ϕ ( 𝑊+ ,𝑊− )
W bosons produced back-to-back with low energy photons
Distribution is more even when photons are energetic
∆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
∆ϕ ( 𝑊+, 𝑣𝑙+ )
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
∆ϕ ( 𝑊+, 𝑙+ )
Similar to neutrino plot, but peak has been shifted toward zero
This is an artifact of the lepton pT cut
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
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
Effects of PDF Sets (Continued) PDF Set Total Cross Section (All
Channels) (fb)
MSTW2008 3.539fb
MSTW2008nlo90cl 3.979fb
MSTW2008nnlo90cl 3.999fb
MRST2004qed 3.905fb
CTEQ6L1 3.454fb
cteq66 3.813fb
CT10 3.880fb
CT10w 3.906fb
NNPDF23_as_nlo_0119 3.950fb
NNPDF23_as_nnlo_0119 3.935fb
Mean Value 3.836fb
Standard Deviation ±0.178fb
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%
http://lh5.ggpht.com/_4ruQ7t4zrFA/SnwlbPdMWmI/AAAAAAAADH8/2v1_nLM_G0Y/LHC_hall_1.jpg
𝑊+𝑊−𝑊+,𝑊−𝑊+𝑊−, & 𝑊+𝑊−𝑍0 Events: 8TeV
Process Total Cross Section (All Channels) (fb)
𝑊+𝑊−𝑊+ → 𝑙1+𝑣𝑙1𝑙2
−𝑣 𝑙2𝑙3+𝑣𝑙3
Average Over 3 PDF Sets 0.7695 fb
Standard Deviation ±0.0367 fb
𝑊−𝑊+𝑊− → 𝑙1−𝑣 𝑙1𝑙2
+𝑣𝑙2𝑙3−𝑣 𝑙3
Average Over 3 PDF Sets 0.4063 fb
Standard Deviation ±0.0308 fb
𝑊+𝑊−𝑍0 → 𝑙1+𝑣𝑙1𝑙2
−𝑣 𝑙2𝑙3+𝑙3
−
Average Over 3 PDF Sets 0.1344 fb
Standard Deviation ±0.0080 fb
𝑊+𝑊−𝑊+,𝑊−𝑊+𝑊−, & 𝑊+𝑊−𝑍0 Events: 13TeV
Process Total Cross Section (All Channels) (fb)
𝑊+𝑊−𝑊+ → 𝑙1+𝑣𝑙1𝑙2
−𝑣 𝑙2𝑙3+𝑣𝑙3
78% increase
Average Over 3 PDF Sets 1.3721 fb
Standard Deviation ±0.0860 fb
𝑊−𝑊+𝑊− → 𝑙1−𝑣 𝑙1𝑙2
+𝑣𝑙2𝑙3−𝑣 𝑙3
103% increase
Average Over 3 PDF Sets 0.8242 fb
Standard Deviation ±0.0641 fb
𝑊+𝑊−𝑍0 → 𝑙1+𝑣𝑙1𝑙2
−𝑣 𝑙2𝑙3+𝑙3
−
100% increase
Average Over 3 PDF Sets 0.2687 fb
Standard Deviation ±0.0171 fb
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 80-100% with a 60% 𝑠 increase
Directions for Further Research
Simulate events at NLO (Powheg and MC@NLO)
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
Works Consulted V. Hankele and D. Zeppenfeld, Phys. Let. B661:103-108 (2008) [arXiv:0712.3544v3]
F. Campanario, V. Hankele, C. Oleari, S. Prestel, D. Zeppenfeld, Phys. Rev. D78: 094012 (2008) [arXiv:0809.0790]
G. Bozzi, F. Campanario, V. Hankele, and D. Zeppenfeld, Phys. Rev. D81:094030 (2010) [arXiv:0911.0438]
G. Bozzi, F. Campanario, M. Rauch, H. Rzehak, D. Zeppenfeld, Phys. Lett. B696:380-385 (2011) [arXiv:1011.2206]
G. Bozzi, F. Campanario, M. Rauch, D. Zeppenfeld, Phys. Rev. D83:114035 (2011) [arXiv:1103.4613]
G. Bozzi, F. Campanario, M. Rauch, D. Zeppenfeld, Phys. Rev. D84:074028 (2011) [arXiv:1107.3149]
Green, Dan. “Triple V-W+W+Photon?”, 23 July. 2012. Web. 29 July 2012. https://indico.cern.ch/getFile.py/access?contribId=1&resId=1&materialId=slides&confId=201498
Whalley, Mike, and Andy Buckley. "The Les Houches Accord PDF Interface." LHAPDF - Hepforge. N.p., n.d. Web. 29 July 2012. <http://lhapdf.hepforge.org/>.
VBFNLO - A parton level Monte Carlo for processes with electroweak bosons. Karlsruhe Institute of Technology, n.d. Web. 29 July 2012. <http://www-itp.particle.uni-karlsruhe.de/~vbfnloweb/ wiki/doku.php?id=overview>.
K. Arnold, J. Bellm, G. Bozzi, et al, (2012) [arXiv:1107.4038v2]
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