1. Z path with ATLAS data 30.3. 2017 Ivan Melo
Workshop, Žilina,
Z path with ATLAS data
Ivan Melo
Z and W with CMS data
W path with ATLAS data

2. Particles of the Standard Model
Z - path
Z - path

3. Z and Higgs production (Feynman diagrams)

4. Z - path

5. Z - path

6. Transverse momentum pT
Sum of initial pT = 0
Sum of final pT = 0

7. Chýbajúca priečna hybnosť
If sum of final pT ≠ 0:
1+2+3 1 2 3
Missing pT = Missing ET = ETMiss
ETMiss > 25 GeV (asi neutríno)
ETMiss < 25 GeV (nie neutríno, skôr nedokonalosť detektora)

8. Invariantná hmotnosť

9. Invariantná hmotnosť
Signál +pozadie
Pozadie (background)

11. Z' boson Graviton (spin 2) G → e+e-, μ+μ- G → γγ G → ZZ → l+l-l+l-
a heavy partner of the Z boson and is predicted by some theories beyond the Standard Model
Graviton (spin 2)
It is expected that a hypothetical force particle, the graviton (G), is the mediator of gravity
G → e+e-, μ+μ G → γγ G → ZZ → l+l-l+l-

12. pp -> Z -> e+e-

13. e+e-

14. e+e-

17. γγ

18. γγ

21. Veľa dráh, 2 eventy naraz (pile-up)

22. kvarky (a gluóny) vidíme ako „jety“, spŕšky hadrónov

23. neutríno
Missing ET = missing pT > 25 GeV

24. To access ATLAS data (2017: no password needed!): username: ippog
ATLAS Z-path
Hypatia
1.Download Unzip it onto your Desktop To start HYPATIA:
a. Navigate to the HYPATIA folder you downloaded
b. On Windows and Mac:oDouble click on“Hypatia_7.4_Masterclass.jar”
c. On Linux: Right click on “HYPATIA_for_Linux.sh” and change permissions so that it is executable. Double-click on “HYPATIA_for_Linux.sh”
To access ATLAS data (2017: no password needed!):
username: ippog
password: mc13
Pick assigned number (1 or 2) and letter (A,B,C,....,Z)
Start with Exercise 2:

25. Analysis - Evaluate your set of 50 events (e.g. 1C)
- Make notes on your tally sheet (e.g. 1C)
- Consult cheat list for students:
Set pT cut at 5 – 10 GeV
Check tracks and physics objects
If two tracks (+- charge) point to two elmag clusters in both views – e+e- candidate
If no tracks point to two elmag clusters in both views - γγ candidate
If two tracks (+- charge) continue to muon chambers – μμ candidate
If four charged tracks (+-+-) - μμμμ, μμee, eeee candidate
Check Pixel hits >= 2 and SCT hits >= 7 to see if particles come from the same vertex
In case of converted photon candidate: check invariant mass of the (+-) double track, if
close to 0, it is photon converted to e+e-
- Enter candidate tracks as ee, μμ, γγ to see their invariant mass
- Export invariant mass table as .txt file (File – Export invariant masses)

26. How to submit results
OploT:
Click on Student For test pick January , any test city, group number and letter Upload your .txt file with invariant masses (Browse button)
If you need to delete a students upload, you can do this from the Administrator tab. Password:
username: admin
password: administrator

27. Analyzing your results
Di-lepton measurement
Compare the histograms of the electron-positron and muon-antimuon pairs.
Can you point out differences/similarities?
How often does the Z boson decay into electron-positron pairs? How often does the decay result in muon-antimuon pairs?
What did you expect? Why?
Do you notice any other particles? At which invariant masses?
What is the most probable mass of the Z boson?
Why is there not one exact value for the Z boson mass?
What could be the possible explanations of why the distribution is so wide?
Have you discovered the Z' boson?
If you think so, what is the Z' boson's mass?
Why is it useful to combine your results with those obtained by other groups?
Di-photon measurement
Do you see any sign of Higgs decaying to 2 photons, H→γγ?
If no, what could be the reasons?
In fact the full sample does contain some real Higgs candidates, even if you you have not found them!

28. Datasets: ATLAS real pp-data from 2012 at 8 TeV
Backup from 2014
Datasets: ATLAS real pp-data from 2012 at 8 TeV
Di-leptons: ~ events
- Di-electrons and di-muons from Z (mainly), Jpsi and Upsilon
fully simulated Z’ events (mass 1 TeV)
Higgs candidates: real data events corresponding to 2 fb-1
- Di-photon: events cuts as in ATLAS publication–including converted photons
- 4-leptons: 40 events cuts as in ATLAS publication
- very little background!
- almost no need to discuss ET miss!