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NLSP :

A T L A S ________________________________________________________________________________________________ GMSB SUSY models with non-pointing photons signatures. ~. gravitino G get its mass only through gravitational interaction G is the LSP , 10 -2 < m G < 10 4 eV

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NLSP :

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  1. A T L A S________________________________________________________________________________________________ GMSB SUSY models with non-pointing photons signatures Damien Prieur

  2. ~ • gravitino G get its mass only through gravitational interaction • G is the LSP, 10-2 < mG < 104 eV • if R-parity is assumed, G is the only stable SUSY particle • all SUSY decay chains lead to the production of gravitinos ~ ~ ~ ~ NLSP : • neutralino : 01   + G • slepton : lR  l + G ~ ~ F, Mmess, N5, , tan, sign(μ) Gauge Mediated Supersymmetry Breaking (GMSB) • SUSY breaking is mediated to the visible sector via gauge interactions • Minimal GMSB model phenomenology is driven by 6 parameters  NLSP typical decay length may be macroscopic: Damien Prieur

  3. Gauge Mediated Supersymmetry Breaking (GMSB) ~ ~ 01   + G • With an intermediate lifetime, we get the following event topologies : ~ ~ χ χ 0 0 1 1 • missing ET • non pointing photons with • We consider here cases where LSP  lightest neutralino • Measuring cτ is a fair way to access to F0, a free parameter of the model • To reconstruct decay vertex : • Impact position • Photon direction  • Time of arrival tγ • From these information it is possible to determine gravitino’s directionψ: Damien Prieur

  4. Outline ~ ~ χ 0 l 1 • How to reconstruct photon direction with EM calorimeter • How to reconstruct SUSY GMSB signal and determine m and m in ATLAS original method developed byKawagoe, Kobayashi, Nojiri, Ochi (hep-ph/0309031) using a fast simulation of ATLAS detector more realistic performances parametrisation for non pointing photons • EstimateATLAS sensitivity to cτand F0 • In the following: Damien Prieur

  5. Electromagnetic calorimeter Cryostat Electromagnetic calorimeter - EndCap Electromagnetic calorimeter - Barrel Damien Prieur

  6. Reconstructing photon direction r • True direction: gen EM shower  60 GeV Middle Front  gen Layer Granularity (x) Pre-sampler 0.025 x 0.1 Front 0.003 x 0.1 Middle 0.025 x 0.025 0.05 x 0.025 Back Z 0 Damien Prieur

  7. Reconstructing photon direction r • Reconstruct  barycenter : 2 R2(2) Middle for each layer : 1,2 1 Front • Parametrisation of shower depth:R1(1) , R2(2) R1(1)  rec • Reconstructed shower direction :rec Z 0 • True direction: gen Damien Prieur

  8. EM Calorimeter angular resolution • EM calorimeter designed for pointing photons (coming from the IP - σz=5.6 cm) • resolution on polar angle θ :σθ60 mrad/E(GeV) (barrel, ||<1.4) • resolution direction : not possible because of coarse granularity • & not necessary for normal processes (σr=15 μm) • Performance for non pointing photons studied from detailed simulation (Geant3) • systematic bias with standard reconstruction algorithms • need specific corrections to improve resolution barrel • resolution parameterized and implemented in the fast simulation of ATLAS detector • used in the following study Damien Prieur

  9. Reconstruction of m and m l γ l ~ ~ l l ~ G ~ ~ χ χ 0 0 1 1 • We consider the following decay chain : • Gravitino’s energy EG is unknown, but we can determine its direction (cosψ) • Some kinematics… • El, Eγ, cosψ , cosθGl, andcosθlγ being all measured, we can compute a and b parameters for each event. • In the (a,b) plane, points should group along the line Damien Prieur

  10. Event generation and simulation Sparticules Masses (GeV) ~ χ 0 1 • Energy : EMCAL • Timing : EMCAL • Position : EMCAL • Direction : • along : EMCAL previously parametrized resolution • along φ: TRT • GMSB point G1 • 105 SUSY events generated with HERWIG (pp  sparticles 8 pb)  one year of LHC at low luminosity (13.9 fb-1) • Fast simulation for all particles • energy, position, direction and time of non pointing photons are smeared according to realistic resolutions from test-beam data or detailed simulation: barrel + end cap  Will require converted photons !!! Damien Prieur

  11. Pre-selection cuts ~ χ 0 1 • We choose lifetime cτ = 100 cm • Pre-selection cuts to limit background contribution from standard model • Full background analysis not performed •  Use cuts from I. Hinchliffe/ F.E. Paige (hep-ph/9812233 ) - require 4 jets - build an effective mass : efficiency We require : 71% + 2 leptons + 2 photons 22%  Further require non pointing photon Damien Prieur

  12. Selection of non pointing photons cuts efficiency NP  Converted NP Eγ > 30 GeV + conversion 94% Pointing  24% α > 0.2 rad 74% Δtγ > 1ns Resolution on ψ ψrec-ψtrue (mrad) • Apply cuts to select non pointing photons candidates Reconstructed angle between photon and gravitino: σψ= 60 mrad Damien Prieur

  13. Reconstruction of m and m ~ ~ l l Scatter plot - (a,b) plane ~ ~ χ χ 0 0 1 1 m = 116.8 GeV m = 161.6 GeV • For each NP photon, we select if possible an isolated lepton with pT>20 GeV to form lγ pairs • If several leptons available, we choose the one which minimizes mlγ • At this point, we end up with 300lγ pairs  linear fit : p0: 26111 p1: 13635 Input  Need more work for improving pairing 117.1 GeV 161.4 GeV Damien Prieur

  14. Reconstruction of m and m ~ l ~ χ 0 1 Input mass : 161.4 GeV Input mass : 117.1 GeV Reconstructed : 159.9 GeV Reconstructed : 115.5GeV σ : 2.1 GeV σ : 1.7 GeV • Simulation is repeated 100 times to estimate resolution on reconstructed sparticle masses • Resolution on reconstructed masses is about 2% for cτ = 100 cm Damien Prieur

  15. Reconstruction of NLSP decay vertex ~ l ~ χ 0 1 • Once we have m and m • No longer need to : - know photon’s direction along  - require a photon conversion • We minimize  once NLSP decay position is known, we can reconstruct all the decay chain • same cuts as previously, except photon conversion not required • for each NP photon, we select if possible an isolated lepton with pT>20 GeV to form lγ pairs  Reconstruct decay time of NLSP in lab. frame σtD 2 ns Damien Prieur

  16. Reconstruction of NLSP lifetime ~ χ 0 1 • Systematic bias for c > 100 cm (due to increasing amount of NLSP escaping detection) • Need to know momentum distribution to correct for bias at high c • c/c vary from 3 to 8% • make lifetime c vary from 10 up to 200 cm • fit of proper time tD/ byanexponential function • simulation reproduced 100 times to estimate sensitivity on fitted values • in this case we need lot of statistics  10 fb-1 is not enough, use 100 fb-1 instead (1 year @ high lumi) c/c 8% 3% Damien Prieur

  17. Summary • A realistic angular resolution parameterization for non pointing photons implemented in a fast simulation of ATLAS detector • Resolution on reconstructed masses for NLSP and slepton masses about 2% • Resolution on NLSP lifetime below 8% for c between 10 and 200 cm for c = 100 cm • Can determine SUSY fundamental breaking scale F0 with 4% precision • Can extend accessible crange using statistical method • Systematics and acceptance need to be carefully studied with a detailed simulation of ATLAS : • - Effects on direction reconstruction of pile-up, underlying events • - Description of EM showers • - Contributions from background Damien Prieur

  18. Damien Prieur

  19. EM calorimeter granularity Front layer Readout electrode (barrel) Middle layer =0.8 =0 Back layer =1.4 Pre sampler Layer Granularity (x) Pre-sampler 0.025 x 0.1 Front 0.003 x 0.1 Middle 0.025 x 0.025 0.05 x 0.025 Back r  Damien Prieur

  20. Reconstruction of NLSP lifetime l γ l ~ ~ l l ~ G ~ ~ χ χ 0 0 1 1 • Having m and m , we are able to reconstruct the slepton decay chain • No longer need to : - know photon’s direction along  - require a photon conversion inside the inner detector - photon impact position - photon polar angle • we measure : • few relations : • we minimize Calorimeter Damien Prieur

  21. Production of sleptons p ~ G ~ ~ ~ l l l ~ ~ ~ q g q p  ~ ~ ~ ~ χ χ χ χ 0 0 0 0 p 2 1 2 2 q l q l p p l q p l Damien Prieur

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