SUSY studies at UCSC Bruce Schumm UC Santa Cruz Victoria Linear Collider Workshop July 28-31, 2004

Participants Sharon Gerbode (Finished 2003): grad school at Cornell Heath Holguin: will stay at UCSC Paul Mooser: job in Computer Science Adam Pearlstein: grad school at Colorado State Troy Lau, J. Warren Rogers, Michael Rogers (rising seniors) Bruce Schumm, Tim Barklow

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 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)

2003 Analysis (Gerbode) Explored eeee backgrounds in central region e+e+ e+e+ e-e- e-e- e-e- e+e+  

Divergent Backgrounds The cross section for this process is effectively infinite since effectively m e =0  Must choose cut-offs that 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 cutoff was applied to the invariant mass (Q 2 ) of any e + in /e + out e - in /e - out combination. After exploration, chose An additional a cutoff was applied to the invariant mass (M) of any final-state e + e - pair. Again, after exploration, chose

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

Idealized Background- Generation Phase Space Q 2 min M min 4 GeV W-W Hard Cutoff Un-simulated region Sharon found these cut-offs to be safe (i.e. no pile-up at cut-off between simulated and un- simulated regions)

2003 SUSY-Inspired Cuts Look at distribution of backgrounds for SUSY-like events Define two detector regions |cos  | 5)  Fiducial region (central!) (  - 20) mrad >  > 20 mrad  Tagging region  `SUSY event’ if and only if 1 electron and 1 positron in tracking region, no additional tracks in tagging region

SUSY-Inspired Cuts II e e **  < 20 mrad If neither beam particle in e + e - e + e - event makes it into the tagging region, the event can be confused with SUSY For such events, maximum p t carried by beam particles is p t max = 2*E beam *  tag min = 20 GeV  Require p t miss > 20 GeV for tracks in tracking region (DELPHI) Completely eliminates e + e - e + e - process up to radiative effects

For 2004, we have: Explored additional backgrounds (ee,  ) & cuts Explored use of beam polarization Demonstrated we can separate from other SUSY contributions using basic cuts and beam polarization Relaxed p t cut from 5 to 0.5 GeV Extended fiducial region all the way forward (down to limit of tracking at 110 Mrad) 2004 Analysis

100’s of background events 4e Bkgd in Extended Fiducial Region (down to 100 mrad) Note: All plots absolutely normliazed to 10 fb -1 Hard-Cutoff W.W. M min (GeV)

The Photon Cut (new) Idea: if 4e background slipping through due to radiative effects, perhaps we can identify the radiated photons  Reject event if it has a  with E > 5 GeV in extended fiducial region (  > 110 mrad) E e (GeV)

ee and  Backgrounds  e-e- e e+e+ e There are a number of different ways to produce an ee final state. The neutrinos provide missing energy. The photon exchange generates a pole. ee   ;    e e creates visible ee final state, but with limited missing p t  cut by p t miss cut

Simulation of ee Background 10 M min (GeV)Q min (GeV)

SPS1 Selectrons Results for 10 fb -1 : SourceCross-section (fb -1 ) Events Passed SUSY e + e - e + e - Hard-Cut 2300 e + e - e + e - Weisz-Willms 18,90059

Q min Weiszacker-Williams Sample; 10 GeV cutoffs

M min Weiszacker-Williams Sample; 10 GeV cutoffs

Simulation Phase-space Q2Q2 M min 10 GeV W-W Hard Cutoff Un-simulated region Question: Are events piling up against artificial kinematic cut-offs, particularly in M min ?  Lower cut-offs to 4 GeV and se what happens! 4 GeV

Hard-cut sample; 4 GeV cutoffs Q min

Weiszacker-Williams sample; 4 GeV cutoffs Q min Should cut off at 4 GeV?

Weiszacker-Williams sample; 4 GeV cutoffs M min

SPS1 Selectrons Again Results for 10 fb -1 : SourceCross-section (fb -1 ) Events Passed SUSY e + e - e + e - Hard- Cut (10  4) 230   2 e + e - e + e - Weisz- Willms (10  4) 18,900  167,00059  92

Cunclusions, Outlook e + e - e + e - backgrounds seem adequately modeled (use samples with 4 GeV cut to be safe) WW samples should cut off at Q  4? Incorporate e  e ,  backgrounds (full SM whizdata files?) Start to push cos , p  coverage Tracking specifications?