SUSY studies at UCSC

Bruce SchummUC Santa Cruz

Cornell Linear Collider WorkshopJuly 13-16, 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 upper-division physics majors at UCSC. Sharon just finished her senior thesis this year and is staying on a bit longer; other three are just getting started

Motivation

Resolution of forward trackingdegrades in nominal trackerdesigns.

SUSY endpoint measurements require high precision.Might there be information in the forward direction?Will our instrumentation be up to the task?

selectronsLSP

Right-handed selectrons at Ecm = 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 Z0 Z0 channel as well as nominal channel)

Background Simulation II

We have gotten started with eeee backgrounds

e+

e+

e-

e-

e-

e+

Background Simulation III

The cross section for this process is effectivelyinfinite

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

102 Q

For this sample, a hard cutoff was applied to theinvariant 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 102 Q

Cut of imposed on any e pair102 Q

e-

e+*

ee

Idealized Background-Generation Phase Space

Q2

Mmin

10 GeV

10 GeV

W-W Hard Cutoff

Un-simulated region

Mmin is the least of the invariant masses of all final-state e+e- pairings

SUSY-Inspired Cuts

Look at distribution of backgrounds for SUSY-like events

Define two detector regions |cos| < 0.80 (100 mrad) Tracking region (central!) ( - 20) mrad > > 20 mrad pt > Tagging region

`SUSY event’ if and only if 1 electron and 1 positron in tracking region, no additional tracks in tagging regionNote: We are doing analysis in central

region for now as we continue to ramp up our group.

SUSY-Inspired Cuts II

ee

*

< 20 mrad

If neither beam particle in e+e-e+e- event makes it into the tagging region, the event can be confused with SUSYFor such events, maximum pt carried by beam particles is

ptmax = 2*Ebeam*tag

min = 20 GeV Require pt

miss > 20 GeV for tracks in tracking region (DELPHI)

Completely eliminates e+e-e+e- process up to radiative effects

SPS1 Selectrons

Results for 10 fb-1:

Source Cross-section (fb-

1)

Events Passed

SUSY 232 695

e+e-e+e- Hard-Cut

230 0

e+e-e+e- Weisz-Willms

18,900 59

Qmin

Weiszacker-Williams Sample; 10 GeV cutoffs

Mmin

Weiszacker-Williams Sample; 10 GeV cutoffs

Simulation Phase-space

Q2

Mmin

10 GeV

10 GeV W-W

Hard Cutoff

Un-simulated region

Question:

Are events piling up against artificial kinematic cut-offs, particularly in Mmin?

Lower cut-offs to 4 GeV and se what happens!4 GeV

4 GeV

Hard-cut sample; 4 GeV cutoffs

Qmin

Weiszacker-Williams sample; 4 GeV cutoffs

Qmin

Should cut off at 4 GeV?

Weiszacker-Williams sample; 4 GeV cutoffs

Mmin

SPS1 Selectrons AgainResults for 10 fb-1:

Source Cross-section (fb-1)

Events Passed

SUSY 232 695

e+e-e+e- Hard-Cut (10 4)

230 1930 0 2

e+e-e+e- Weisz-Willms (10

4)

18,900 167,000

59 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 ee, backgrounds (full SM whizdata files?)

Start to push cos, p coverage

Tracking specifications?