SUSY studies at UCSC

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

2. 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

3. 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?

5. selectrons LSP

6. Right-handed selectrons at Ecm = 1 TeV

7. 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 Z0 Z0 channel as well as nominal gg channel)

8. 2003 Analysis (Gerbode) Explored eeee backgrounds in central region e+ e+ e- g* e+ g* e- e-

9. Divergent Backgrounds The cross section for this process is effectively infinite since effectively me=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

10. Hard Cut-off Sample For this sample, a cutoff was applied to the invariant mass (Q2) 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

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

12. Mmin Hard Cutoff W-W 4 GeV Un-simulated region Q2min 4 GeV Idealized Background-Generation Phase Space Sharon found these cut-offs to be safe (i.e. no pile-up at cut-off between simulated and un- simulated regions)

13. Definitions of Detector Regions

14. 2003 SUSY-Inspired Cuts Look at distribution of backgrounds for SUSY-like events Define two detector regions |cosq| < 0.80 (pt > 5)  Fiducial region (central!) ( - 20) mrad > q > 20 mrad  Tagging region `SUSY event’ if and only if 1 electron and 1 positron in tracking region, no additional tracks in tagging region

15. e  < 20 mrad e * SUSY-Inspired Cuts II 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 pt carried by beam particles is ptmax = 2*Ebeam*tagmin = 20 GeV  Requireptmiss > 20 GeVfor tracks in tracking region (DELPHI) Completely eliminates e+e-e+e- process up to radiative effects

16. 2004 Analysis • 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 pt cut from 5 to 0.5 GeV • Extended fiducial region all the way forward (down to limit of tracking at 110 Mrad)

17. 4e Bkgd in Extended Fiducial Region (down to 100 mrad and pt > 0.5 GeV/c) W.W. Hard-Cutoff 100’s of background events 100 100 10 10 50 50 Mmin (GeV) Mmin (GeV) Note: All plots absolutely normalized to 10 fb-1

18. 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) 50 100 50 100 200 100 200 Ee (GeV) Ee (GeV)

19. e-  e+ e e ee and  Backgrounds 1) There are a number of different ways to produce an ee final state. The neutrinos provide missing energy. The photon exchange generates a pole. 2) ee  ;   ee creates visible ee final state, but with limited missing pt cut by ptmiss cut

20. 40 10 20 10 10 Mmin (GeV) Qmin (GeV) Simulation of ee Background Before cuts 4 Gev Hard Cutoff Sample (no problems from W-W samples) After cuts in old (non-extended) fiducial region Qmin cut seems very safe, but there may be substantial un-modeled backgrounds at low Mmin additional requirement that Me+e-> 4 GeV until further notice.

21. For 10 fb-1 (as are all plots) Signal to Background, Including Forward Events 200 100 Combined Background SUSY Eelectron (GeV) Including forward production, backgrounds (mostly ee) are substantial  Search for additional cuts

22. The H-P (Heath-Paul or High-p) Cut Apply additional `H-P’ cut: Removes low-mass, t-channel-dominated ee backgrounds while preserving high-mass SUSY signal Background (before and after H-P cut) SUSY (before and after H-P cut) 10 40 Central Extended Eelectron (GeV)

23. Use of Beam Polarization Also: can extinguish main background (ee) with RH electron and LH positron polarization For fixed integrated luminosity, the signal is higher and the background lower with positron polarization. SUSY Pe- = +80% Pe+ = -50% Pe- = +80% Pe+ = 0% 200 100 After H-P Before H-P Electron Energy (GeV)

24. Cunclusions, Outlook Selectron production can be detected over the full tracking volume Developed two additional helpful cuts: looking for photons radiated in eeee processes and cutting on momentum imbalance (`H-P’). Mmin cutoff needs to be extended down below 4 Gev for ee generation Ready at last to begin issue of addressing tracking specifications.