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]

The ROOT Team. "ROOT." ROOT. The ROOT Team, 2012. Web. 29 July 2012. <http://root.cern.ch/ drupal/>.