1. Aobo Li University of Washington
Vector Boson Scattering & Anomalous Quartic Gauge Coupling Final Presentation
Aobo Li
University of Washington

2. Outline Theory Process Future Prospection Q & A
Electroweak Symmetry Breaking
Higgs Field and VBS
Process
Madgraph & root environment
Wrtiting Proc Card
Generating Events based on different model
ROOT plot
Future Prospection
Q & A

3. Electroweak Symmetry Breaking
Goldstone Boson: Boson that appear necessarily in model exhibiting spontaneous breakdown of continuous symmetry.
At high enough temperature, Electromagnetic and weak interactions are unified(The symmetry is unbroken), all elementary particles are masless.
At a critical temperature the Higgs field become tachyonic.
Once the tachyonic field reaches its minimum potential, its quanta are no longer tachyonic, but with positive mass squared.
Higgs boson is a good example.
The tachyonic field goes through a spontaneous process called Tachyonic condensation, which grants mass to both W and Z boson.

4. EWSB

5. Higgs Field and VBS
Higgs Field: a SU(2) doublet, a complex scalar with 4 real component.
U(1) : circle group corresponding to weak hypercharge.
The gauge group for electroweak part is SU(2) × U(1). During this, three of the four scalar mixed with 3 W and Z bosons, while one remains scalar as Higgs boson.
Vector Boson scattering(quartic gauge coupling) must be attributed to this process, if not:
Unitarity is broken.
Theory become non-perturbative, require lots of correction.

6. Outline Theory Process Future Prospection Q & A
Electroweak Symmetry Breaking
Higgs Field and VBS
Process
Madgraph & root environment
Wrtiting Proc Card
Generating Events based on different model
ROOT plot
Future Prospection
Q & A

7. Madgraph & Root
Madgraph: C language based Monte Carlo generator, used to simulate particle collision process.
Root: CERN published data analysis framework, also C language based.
Our goal is to use Madgraph to generate truth events for analysis purpose, then using root to implement cut & uncertainty propagation.

8. Set up environment on Mac
Mac X OS is not C language based.
Set up C environment with X code & XQuartz.
xcode-select --install
Take care of gfortran compiler.
Install root from source(Milen’s guide)

9. Process generation
Generating particle collision process by writing Madgraph proc card.
This quarter, our goal is to simulate zajj final state process.
p p -> Z a j j
Proc cards are wiritten under different theory model.
SM,Heft, LT8

10. Generating Events
After generating process, we can proceed to events generation
Turn on Pythia parton showering.
Turn on Delphes: a detecton simulation framework for truth study.
Generating collision events for different model.

11. Standard Model
Background

12. HEFT model Higgs Effective Field Theory model.
Effective Field Theory: approximation for underline physics theory.
Include appropriate degree of freedom to describe phenomenon occurred at chosen energy/length scale, while ignoring substructures and degrees of freedom at shorter distance(higher energy scale)
Under this model, triple gauge coupling (Vector boson fusion) events are found, but no quartic gauge coupling(Vector boson scattering) events exists.

13. Vector Boson Fusion

14. Other coupling

15. Z Boson Bremsstrahlung
Braking radiation

16. LLT8 Model Generating events with dimension-8 operator on field terms.
Set dimension-8 anomalous input to amplitude 1e-12, while turn every other anomalous input off(Set amplitude to 0)
Quartic Gauge coupling(Vectro boson scattering) events starts to emerge.

17. Vector Boson Scattering

18. SLT8 NA model
LT8 model with all anomalous operator set to 0 amplitude.
Are supposed to produce background events(identical to Standard Model)

19. LT8 events

20. ROOT Analysis Writing compact root macros for data analysis purpose.
Can do a lot of things with root:
Constructing & fitting histogram
Making plot
Implementing cut
More advanced stuff.

21. ROOT Macro Reading Delphes tree by ExRootTreeReader
Loop through all events
Assigning interested object to proper type(eg particle to GenParticle, jet to Jet)
Loop through objects and filling histogram
Renormalize histogram with cross section to make the plot independent of the amount of events generated.

23. Making plot By calling macro in Mac terminal
Can either use .x Macro.C
Or .L Macro.C and call the function
Overlapping datas from 4 different event generation into single plot.
HEFT model:Green Line
LT8 model:Red Line
LT8NA model: Purple Line
Standard Model: Yellow Line

28. Outline Theory Process Future Prospection Q & A
Electroweak Symmetry Breaking
Higgs Field and VBS
Process
Madgraph & root environment
Wrtiting Proc Card
Generating Events based on different model
ROOT plot
Future Prospection
Q & A

29. What’s Next
The plots looks pretty much the same, so some event selection/cut implementation is needed
Doing more complicated analysis using root(e.g. cutflow)
Writing more advanced C code
Writing a Madgraph model
Constructing a plugin for Delphes

30. What’s Next Learning more Quantum theory
Going to Grad school!
Ingesting more Math for Theory
Reading Paper.
The fun has just start!

31. QQuestion and Answer

32. Thank You!
Have a great summer!