SUSY in the Forward Region Bruce Schumm UC Santa Cruz ECFA/DESY Linear Collider Workshop April 1-4, 2003

Participants Sharon Gerbode, Heath Holguin, Paul Mooser, Adam Pearlstein, Bruce Schumm (all UCSC), with substantial help from Tim Barklow at SLAC Sharon, Heath, Paul, and Adam are senior physics majors at UCSC. Sharon is writing her senior thesis this year; other three are just getting started

Motivation Resolution of forward tracking degrades in nominal tracker designs. SUSY endpoint measurements require high precision. Might there be information in the forward direction? Will our instrumentation be up to the task?

selectrons LSP

Right-handed selectrons at E cm = 1 TeV

Background Simulation I Making use of WHIZARD Monte Carlo package Some credits: WHIZARD due to Wolfgang Kilian Making use matrix elements from O’Mega program (Thorsten Ohl) Implementation by Tim Barklow, SLAC Background processes characterized by final state (e.g. e + e - e + e - includes Z 0 Z 0 channel as well as nominal  channel)

Background Simulation II We are beginning with eeee backgrounds for now e+e+ e+e+ e-e- e-e- e-e- e+e+  

Background Simulation III The cross section for this process is effectively infinite  Must choose cut-offs which are guided by experi- mental constraints. This can be tricky, and there is a risk that a dom- inant background will go unmodelled N.B. Background simulations done by Tim Barklow

Hard Cut-off Sample For this sample, a hard cutoff was applied to the invariant mass of any e + in /e + out e - in /e - out or final- state e + e - pair In the absence of any feedback, Tim chose a cut- off of

Weiszacker-Williams Sample Complementary to hard cutoff sample Cross-section determined by integral over Cut of imposed on any e  pair Photon virtuality always set to   e-e- e+e+

SUSY-Inspired Cuts Look a distribution of backgrounds for SUSY-like events  Define `fiducial region’ *) |cos  | <.995 (100 mrad) *) p t > p cut (p cut = 0.2 and 5.0 GeV/c)  `SUSY event’ if and only if 1 electron and 1 positron in fiducial region

 (mrad) Hard cut-off component; SUSY cuts use p cut = 0.2

 (mrad) Weiszacker-Williams component; SUSY cuts use p cut = 0.2

p t (GeV/c)  (mrad) Hard cut-off; p cut = 0.2 Hard cut-off; p cut = 5.0

p t (GeV/c)  (mrad) Weiszacker-Williams p cut = 0.2 GeV/c Weiszacker-Williams p cut = 5.0 GeV/c

3-D Back-to-Back Cut Require two `SUSY’ leptons to be back-to-back (cos  < -.96) Hard-cut sample; lowest-  track Weiszacker-Williams sample; all tracks

2D Back-to-Back Cut Two `SUSY’ leptons back-to-back in axial projection Hard-cut sample Weiszacker- Williams sample

Up and Coming… Tim Barklow has now generated hard cut-off sample with cut-off of Weiszacker-Williams background has been modified by Tim Barklow to retain photon virtuality in final-state kinematics Must explore properties of these two background samples, plus e e sample Will check central-region analysis (Sharon) in addition to consideration of forward region (new students)