Rasmus Mackeprang R-hadrons Simulation and discovery in ATLAS Participants: R. Mackeprang, D. Milstead, S. Hellman & M. Johansen

Rasmus Mackeprang Outline R-hadrons 101 Brief recap of phenomenology Atlas production Backgrounds and selection cuts Outlook

Rasmus Mackeprang R-hadrons and the like Common feature of several BSM-theories are heavy long- lived particles with SM charge. SUSY-models (long lived gluino/stop/stau) UED (KK-excitations of the gluon) Hidden Valley models (just about anything…) Heavy coloured long-lived particles hadronise SUSY: R-(parity-stable)hadrons: These hadrons consist of a light quark system (LQS) and a heavy particle. Central questions: How do these states interact in the detector? Are we going to see them in Atlas?

Rasmus Mackeprang Available Models Two models exist: Geant3 (A.C. Kraan, Eur.Phys.J.C37:91-104,2004) Model has been tested extensively on gluino-hadrons. Has been used previously in Atlas. Geant4 (R. Mackeprang & A. Rizzi, Eur.Phys.J.C50: ,2007) Physics-wise close to the Geant3 model. Some generalisations made in the physics. Obvious advantages in the move to G4. Common to the models is the fact that the R-hadrons interact exclusively through the LQS  charge may change. This presentation will deal with the Geant4 results

Rasmus Mackeprang Never say ”Obvious”… What are the advantages in moving to G4? Modular buildup of G4 facilitates the actual usage of the package in any simulation environment. Changing parts of the model is easily doable. Further parameters may be specified but otherwise it is up, up and away… # ~g # ~g rho # ~g rho # ~g Delta # ~g Delta # ~g Delta # ~g Delta # ~g rho # ~g Deltabar # ~g Deltabar # ~g Deltabar # ~g Deltabar-- ~g_rho0 # neutron # ~g_Delta- # pi0 ~g_rho+ # neutron # ~g_Delta0 # pi+ ~g_rho0 # neutron # ~g_Delta- # pi+ ~g_rho+ # proton # ~g_rho+ # proton # pi0 ~g_rho0 # proton # ~g_rho0 # proton # pi0...

Rasmus Mackeprang Disclaimer The authors would like to emphasize the fact that any similarity to actual physics, real or imagined is purely coincidental… (maybe not quite) This is a simple model of complex physics This complex physics might indeed result in vastly different phenomenologies Aim: In using a simple model that is easily applicable to varying physics scenarios we wish to make a general statement about the potential for discovery of phenomenologies containing long-lived coloured objects.

Rasmus Mackeprang Physics Case of the Day: The Gluino R-hadron The concept has its origin in (now disfavoured) GMSB models where the gluino was absolutely stable. More recent models like Split SUSY contain long-lived NLSP gluinos where the decay to the LSP is suppressed by a heavy squark For suitably high squark masses the gluino will not only have time to hadronise. It will also escape the detector before decaying.

Rasmus Mackeprang Physics model for R-hadrons Quark system interacts Gluino is ”just” a reservoir of kinetic energy Interactions are thought to be pomeron / reggeon mediated: Interactions of Figure: A.C. Kraan

Rasmus Mackeprang Cross section Assume flat xsec (12 mbarn per light quark) Assume even weights Use phase space function to ensure asymptotic limits for 2  2 vs. 2  3. Use parameterised cascade treatment already in Geant4. Figure: A.C. Kraan

Rasmus Mackeprang dE/dx Energy loss per unit length in iron: This will punch through the detector (ATLAS, that is) with 5-15 hadronic interactions in the calorimeter  heavy object punches through while changing its charge… Mackeprang & Rizzi, Eur.Phys.J.C50: ,2007

Rasmus Mackeprang Do R-hadrons look like… hadrons? Similarities are greater to muons than to hadrons One should be careful, though, to try and use the absolute normalisation of the signal to distinguish between physics scenarios.

Rasmus Mackeprang R-hadrons in ATLAS

Rasmus Mackeprang Pretty pictures! Weeeee! Yup, that looks like QCD A 10 GeV track cut does wonders One high-p t track Nothing on the other side Signal back-to-back in the muon system Just one of the number of dead give-away signatures of these beasts. Like-sign muons back to back (exclusively gluinos) Factor two in momentum measurement of b2b muons Charge flip between ID and muon system. Missing ID track / muon track found Combinations...

Rasmus Mackeprang Backgrounds! Booooooh!  We’ll be using the muon trigger, so basically our background is ”Anything with a muon”. The following samples are in play at order 1 fb -1. QCD: Sliced samples, 140 GeV/c < p t < 2240 GeV/c ( not covered yet. The cross section is… large.) TTbar filtered for one hard muon (0.8 1 fb -1 exist in an ”official” ATLAS sample. Haven’t finished my own yet) Di-boson: ZZ / WW / ZW Single boson: Z / W   /  A secret for the other PhD students: If you want something done right, do it your bloody self!

Rasmus Mackeprang Gluino Rates vs. Background Rates G l u i nomass: ( G e V = c 2 ) E ven t s: 1005 : 23 £ : 69 £ : 84 £ Events per fb -1, no cuts

Rasmus Mackeprang Gluino Rates vs. Background Rates Background events per fb -1 filtered for 150 GeV/c muons: IOW: We have a potential background of O(9k)/fb -1. QCD and ttbar samples have not yet all run through the full chain. EW b osons: WW 41 ZZ 23 WZ 12 W ! ¿º 15 W ! ¹º 638 Z ! ¿¿ 108 Z ! ¹¹ 466 QCD -s l i ces: 140 < p t < < p t < < p t < < p t < < p t 0. 1 t ¹ t 4140

Rasmus Mackeprang Naïve Selection Cuts Require a muon trigger (EF_mu6) Hard (p t > 200 GeV/c) mu track matches hard ID track of opposite charge OR Hard muon tracks back to back (cos() < -0.98) with same charge OR Hard muon track has opposite side ID track with #HT/#LT < 0.13 Events accepted per inverse femtobarn: Accepted background (excluding ttbar and low pt QCD): 57.3 events/fb -1 G l u i nomass: ( G e V = c 2 ) E ven t s: 1005 : 3 £ : 9 £ : 3 £ :

Rasmus Mackeprang So… Where to?

Rasmus Mackeprang Where to? When backgrounds are in place, start to optimize cuts, evaluate systematics from model dependence. The G4 model has parameters that can be changed. It would be nice to make a general statement on discovery potential for exotic heavy hadrons Notice how all this differs from stable stau… We’ll be looking at gluino, stops, UED and generic scenarios. Perfectly aware that we need to keep model dependence down.

Rasmus Mackeprang Th… Th… That’s all folks. OK, buckle up!