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s upersymmetry. Distinguishing prompt e/ g objects from those emitted by long-lived SUSY particles. A Study by Nathan Readioff University of Liverpool. Introduction. Every existing particle has a SUSY partner with identical quantum numbers, but a spin that differs by ½
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supersymmetry Distinguishing prompt e/g objects from those emitted by long-lived SUSY particles A Study by Nathan Readioff University of Liverpool
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
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:
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
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
Electron Selection Criteria • Cuts on Dielectron events, with reconstructed Z0 mass of ATLAS Preliminary Results
Comparing Data and MC • Generally, Data and MC are well-matched ATLAS Preliminary Results
Comparing Data and MC • Calorimeter Pointing Vector Resolution ATLAS Preliminary Results
Electron Cluster Time • Electrons arrive ≈0.65ns earlier than predicted ATLAS Preliminary Results
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
Electron Cluster Time – Function of Eta s2 (Positive) ATLAS Preliminary Results
Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • Barrel Region
Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • Barrel Region
Electron Cluster Time – Distribution with Energy ATLAS Preliminary Results • End Cap Region
Corrections to Medium Gain for Period G
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
Data Sets B-F • Electron Cluster Time as a function of Eta s2 (negative) ATLAS Preliminary Results
Data Set G • Electron Cluster Time as a function of Eta s2 (negative) ATLAS Preliminary Results
Data Sets B-F ATLAS Preliminary Results • Electron Cluster Time - Distribution of Energy
Data Set G ATLAS Preliminary Results • ElectronCluster Time - Distribution of Energy
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...
In the meantime... • The cluster time MC and Data peaks can be adjusted “to work” • Consider the following data set: ATLAS Preliminary Results
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
Results ATLAS Preliminary Results
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
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
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
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
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