SUSY studies at UCSC

Bruce SchummUC Santa Cruz

Victoria Linear Collider WorkshopJuly 28-31, 2004

Participants

Sharon Gerbode (Finished 2003): grad school at Cornell

Heath Holguin: will stay at UCSCPaul Mooser: job in Computer ScienceAdam Pearlstein: grad school at Colorado State

Troy Lau, J. Warren Rogers, Michael Rogers (rising seniors)

Bruce Schumm, Tim Barklow

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

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)

2003 Analysis (Gerbode)

Explored eeee backgrounds in central region

e+

e+

e-

e-

e-

e+

Divergent Backgrounds

The cross section for this process is effectivelyinfinite 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

Hard Cut-off Sample

42min Q

For this sample, a cutoff was applied to theinvariant mass (Q2) of any e+

in/e+out e-

in/e-out

combination. After exploration, chose

An additional a cutoff was applied to theinvariant mass (M) of any final-state e+e- pair. Again, after exploration, chose

4min M

Weiszacker-Williams Sample

Complementary to hard cutoff sample

Cross-section determined by integral over 42 Q

Cut of imposed on any e pair42 Q

e-

e+*

ee

Idealized Background-Generation Phase Space

Q2min

Mmin

4 GeV

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| < 0.80 (pt > 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

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

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)

2004 Analysis

Re~

100’s of backgroundevents

4e Bkgd in Extended Fiducial Region (down to 100 mrad)

Note: All plots absolutely normliazed to 10 fb-1

Hard-Cutoff W.W.

Mmin (GeV) Mmin (GeV)

10 10

5050

100100

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)

Ee (GeV) Ee (GeV)100 100200 200

50

100

50

ee and Backgrounds

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 ; ee creates visible ee final state, but with limited missing pt cut by pt

miss cut

Simulation of ee Background

10 10Mmin (GeV) Qmin (GeV)

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?