Distinguishing prompt e/ g objects from those emitted by long-lived SUSY particles

1. supersymmetry Distinguishing prompt e/g objects from those emitted by long-lived SUSY particles A Study by Nathan Readioff University of Liverpool

2. Introduction • Every existing particle has a SUSY partner with identical quantum numbers, but a spin that differs by ½ • SUSY is broken to decouple SM particle masses from SUSY masses • Gauge-mediated SUSY breaking (GMSB): • Lightest SUSY particle Gravitino • Next lightest SUSY particle Neutralino

3. Introduction • At the LHC, pairs of squarks or gluinos may be produced • These decay via a cascade of SUSY particles to a neutralino: • The neutralino will then decay into a photon and a gravitino: • The final detector state being sought is therefore:

4. Introduction • The neutralino is long-lived (lifetime 0.5ns) and so g emission delayed • Prompt e/g objects make up the background • Model all such objects as Z->ee decays • Compare Data and MC simulations to understand these

5. Note on the Data Used • Data sample is taken from: • Periods B to G • Monte Carlo sample is taken from: • mc10_7TeV.10765*.AlpgenJimmyZeeNp*_pt20.merge.NTUP_SUSY.e737_s933_s946_r2302_r2300_p601/ • In processing I have used: • GRL • Lar cleaning • Good vertex requirement • electron: egammaPID::ElectronMedium_WithTrackMatch • corrected isolation coneEtcone20<5GeV

6. Electron Selection Criteria • Cuts on Dielectron events, with reconstructed Z0 mass of ATLAS Preliminary Results

7. Comparing Data and MC • Generally, Data and MC are well-matched ATLAS Preliminary Results

8. Comparing Data and MC • Calorimeter Pointing Vector Resolution ATLAS Preliminary Results

9. Electron Cluster Time • Electrons arrive ≈0.65ns earlier than predicted ATLAS Preliminary Results

10. Electron Cluster Time – Function of Eta s2 (Negative) • End caps: Electrons arrive ≈ 1.0ns early • Barrel: Electrons arrive ≈ 0.5-0.6ns early ATLAS Preliminary Results

11. Electron Cluster Time – Function of Eta s2 (Positive) ATLAS Preliminary Results

12. Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • Barrel Region

13. Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • Barrel Region

14. Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • End Cap Region

15. Corrections to Medium Gain for Period G

16. Electron Cluster Time – Function of Eta s2 (Negative) • End caps: Electrons arrive ≈ 1.0ns early • Barrel: Electrons arrive ≈ 0.5-0.6ns early ATLAS Preliminary Results

17. Data Sets B-F • Electron Cluster Time as a function of Eta s2 (negative) ATLAS Preliminary Results

18. Data Set G • Electron Cluster Time as a function of Eta s2 (negative) ATLAS Preliminary Results

19. Data Sets B-F ATLAS Preliminary Results • Electron Cluster Time - Distribution of Energy

20. Data Set G ATLAS Preliminary Results • ElectronCluster Time - Distribution of Energy

21. eGamma Meeting • These results were presented to the eGamma group last week • At the present time, the origins of this effect are unknown • Calorimeters should be correctly time-aligned for accurate particle track reconstruction • This effect should not be observed • More work is being planned in the coming weeks to further investigate this effect...

22. In the meantime... • The cluster time MC and Data peaks can be adjusted “to work” • Consider the following data set: ATLAS Preliminary Results

23. In the meantime... • Correcting Data • Add constant to each measured Cluster Time value • Constant = difference between current peak mean values • Correcting MC • Take a set of random numbers that follow a normal distribution • TRandom::Gaus in Root • Define Random distribution with Mean = 0.0 and sigma such that MC matches Data • Sigma evaluated from: • For each MC Cluster time value, add a random number from this distribution

24. Results ATLAS Preliminary Results

25. Conclusions • Electrons are arriving earlier than predicted • Barrel: 0.4-0.6ns early (approx) • End Caps: 1.0 ns early (approx) • Within the Barrel: • Electron cluster time shifts earlier as energy increases • (≈0.3ns for 25 to 100GeV) • Indications of an energy dependence seen in data sets B-F, G, and B-G • Eta and energy dependent correction factor required • Members of the eGamma Group re investigating! • Quick-fix method for correcting cluster time outlined • Insufficient time to use this method to search for SUSY particles

26. Backup

27. Results from an Independent Study 1) The event should pass a loose EM trigger (e20, g20, ...).2) The EM cluster should have energy greater than 15GeV.3) There should be more than 70 HT TRT hits in a small delta phi window around the cluster

28. Results from an Independent Study 1) The event should pass a loose EM trigger (e20, g20, ...).2) The EM cluster should have energy greater than 15GeV.3) There should be more than 70 HT TRT hits in a small delta phi window around the cluster

29. Results from an Independent Study 1) The event should pass a loose EM trigger (e20, g20, ...).2) The EM cluster should have energy greater than 15GeV.3) There should be more than 70 HT TRT hits in a small delta phi window around the cluster

30. Results from an Independent Study 1) The event should pass a loose EM trigger (e20, g20, ...).2) The EM cluster should have energy greater than 15GeV.3) There should be more than 70 HT TRT hits in a small delta phi window around the cluster