1. Stop of 500GeV Search for Heavy Stable Charged Particles  Properties  Very Heavy : O(100 GeV/c²) or more → In general non-relativistic (See Section 3)  cτ ~ O(m) or larger → Usually, do not decay in a detector  Electric and/or strong charge  Allowed by many models beyond SM (mGMSB, Split SUSY, MSSM, and UED)  In general, long lifetime is a consequence of a quantum number conservation → e.g. : SUSY with R-parity or UED with KK-parity → Heavier states could also be quasi stable if decay phase space is small  If colored, HSCP will hadronize and form an “R-Hadron” → Fraction of gluino-balls is a relevant unknown parameter from the experimental point of view.  Main scenarios considered by the CMS collaboration are listed in this table Properties Baryons gqqq, t 1 qq Mesons gqqbar, t 1 qbar Gluino-balls gg ~ ~ ~ ~ ~ (pure neutral state)  Lepton-like HSCPs, behave like heavy muons  Cross easily the whole detector  Non-relativistic→ large ionization energy loss → long time of flight  R-Hadrons, do nuclear interactions in addition  heavy parton acts as spectator (interaction will be similar to a low energy hadron-hadron scattering)  R-Hadron does not shower in the calorimeters  Conversion to a different R-Hadron is possible → charge flipping HSCP → Non-relativistic track with High Momentum  Methods : 1.The Momentum p can be measured from track bending in inner tracker/muon system 2. The velocity β can be extracted from  The Energy loss (dE/dx) in inner tracking systems (ionization and transition radiation)  The Time of Flight in muon systems 3.The mass m can be computed from p / (βγc) 4.If m is heavier than any stable SM particle It is a candidate HSCP  Issues :  Charge flipping  Deviation from expected muon trajectory, unmatched inner tracker/muon tracks and incompatible/missing track stubs in the muon system  Neutral R-Hadronswill give no signals in the tracker/muon detectors  Neutral R-Hadrons will give no signals in the tracker/muon detectors  Main backgrounds are prompt or cosmic muons  Principle: Use muon wire detectors to measure time of flight Resistive Plate Chambers are only useful to confirm track and reject background.  Challenges : β of R-Hadron in muon system is generally lower than β at production due to energy loss. Minimum β to have inner Tracker readout in same bunch crossing is : β min ~ 0.65 Charge flipping introduce some complications Lower reconstruction efficiency than for muons Momentum measured by Stand alone Muon system is biased upward (good for triggering) Background : Cosmic muons Badly measured muons Non Relativistic Particle  Principles : HSCP id based on dE/dx estimate of a track various estimators considered including an unbinned Landau fit use Z  μμ as control sample Mass reco: β -2 ≈ k dE/dx in 0.1<βγ<0.9 region obtain k from proton sample  Challenges : Few measurements per track (~ 10 for CMS) Electronics response : saturation/cut-offs effects, readout timing  Background : Overlapping tracks SM particles in the tail of the dE/dx distribution Heavy ions from nuclear interactions  Samples : Signal : g, t 1, mGMSB τ 1, KK τ 1 : mass from 130 to 1500 GeV/c ², generated with (MadGraph), Pythia+R-hadron hadronization routines Backgrounds : all SM processes (QCD, W/Z, ttbar, bbbar + jets)  Simulation : Full Geant4 + specific routines for R-Hadron hadronic interactions  Selection : Muon Systems : p T >30 GeV Tracker : β tk 8, χ²/ndof < 5 Combined : β DT 100GeV  Mass Reconstruction : β = average (β tk,β DT ) and p = p tk  Discovery :  ~100pb -1 : mGMSB stau and low mass R-Hadron  ~ 1fb -1: gluino masses above 1TeV and for KK tau g ~ t1t1t1t1 ~ KK τ 1 ~ 1fb -1 R Mackeprang & A Rizzi : Eur.Phys.J.C50:353-362,2007 SM Muons 1fb -1 t 1 500GeV 4.6fb -1 Global  Muon trigger : Useful for most models Efficiency depends on the HSCP mass and model Very robust with respect to the P T threshold (can be increased up to ~50 GeV) mGMSB τ 1 ~ 99% UED KK τ 1 ~ 80% MSSM t 1 ~ 40% to 70% Split SUSY g ~ 60% to 95% ~ ~ ~ ~ 1. Interaction with the CMS Detector 2. Detection Techniques 4. dE/dx Techniques in Inner Tracking Detectors 5. Trigger Strategies 7. Time of Flight in Muon System 6. Offline Analysis 8. Signatures3.  Charge flipping is also a unique signature that can be used in offline analysis to confirm signal.  Jet / Missing E T : Useful for certain models (in particular for mGMSB) Less sensitive to timing/β issues Recover a part of HSCP not detected by muon system. Complementary to the muon trigger. dE/dx seeded by muon trigger :  dE/dx seeded by muon trigger : To be Investigated Background Rejection June 2008 Loïc Quertenmont Background  Tracker Calibration : estimators make the assumption that all dE/dx measurements of a tracks come from the same Landau distribution. This is not the case if the detector is not calibrated. Different response is also caused by the non linear dependence of the ionization energy loss from the path length, effects coming from saturation of the electronics, etc. A calibration procedure has been designed to equalize the response of all tracker modules. Ideal Detector 10% Miscalibrated Detector Distribution of the Most Probable Value as a function of the module thickness for an Ideal and Miscalibrated detector. The MPV comes from the fit of a Landau fit to the charge distribution normalised to the path length for each tracker module. Representation of two back to back muons with the Fast and Realistic OpenGl Displayer (FROG). All the tracker layers are well visible. CMS AN-2007/049 https://twiki.cern.ch/twiki/bin/view/CMS/FROG