SUSY studies at UCSC

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SUSY studies at UCSC

• Bruce Schumm
• UC Santa Cruz
• Victoria Linear Collider Workshop
• July 28-31, 2004

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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
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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?
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selectrons
LSP
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Right-handed selectrons at Ecm 1 TeV
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Background Simulation
Making use of WHIZARD Monte Carlo package
Some credits

• WHIZARD due to Wolfgang Kilian
• Making use matrix elements from OMega program
  (Thorsten Ohl)
• Implementation by Tim Barklow, SLAC

Background processes characterized by final
state (e.g. ee-ee- includes Z0 Z0 channel as
well as nominal gg channel)
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2003 Analysis (Gerbode)
Explored eeee backgrounds in central region
e
e
e-
g
e
g
e-
e-
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Divergent Backgrounds
The cross section for this process is
effectively infinite since effectively me0

• 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
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Hard Cut-off Sample
For this sample, a cutoff was applied to
the invariant mass (Q2) of any ein/eout
e-in/e-out combination. After exploration, chose
An additional a cutoff was applied to
the invariant mass (M) of any final-state ee-
pair. Again, after exploration, chose
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Weiszacker-Williams Sample
Complementary to hard cutoff sample
Cross-section determined by integral over
Cut of imposed on any eg pair
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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)
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2003 SUSY-Inspired Cuts
Look at distribution of backgrounds for SUSY-like
events
Define two detector regions cosq lt 0.80
(pt gt 5) ? Fiducial region (central!) (? -
20) mrad gt q gt 20 mrad ? Tagging region
?SUSY event if and only if 1 electron and 1
positron in tracking region, no additional
tracks in tagging region
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SUSY-Inspired Cuts II
If neither beam particle in ee-ee- 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 2Ebeam?tagmin 20 GeV
? Require ptmiss gt 20 GeV for tracks in tracking
region (DELPHI)
Completely eliminates ee-ee- process up to
radiative effects
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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)

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4e Bkgd in Extended Fiducial Region (down to 100
mrad)
W.W.
Hard-Cutoff
100s of background events
100
100
10
10
50
50
Mmin (GeV)
Mmin (GeV)
Note All plots absolutely normliazed to 10 fb-1
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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 gt 5 GeV in extended fiducial region (? gt
110 mrad)
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100
50
100
100
200
200
Ee (GeV)
Ee (GeV)
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??ee and ?? Backgrounds
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
ptmiss cut
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Simulation of ee?? Background
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10
Mmin (GeV)
Qmin (GeV)
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SPS1 Selectrons
Results for 10 fb-1
Source Cross-section (fb-1) Events Passed
SUSY 232 695
ee-ee- Hard-Cut 230 0
ee-ee- Weisz-Willms 18,900 59
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Weiszacker-Williams Sample 10 GeV cutoffs
Qmin
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Weiszacker-Williams Sample 10 GeV cutoffs
Mmin
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Simulation Phase-space
Question Are events piling up against
artificial kinematic cut-offs, particularly in
Mmin? ? Lower cut-offs to 4 GeV and se what
happens!
Mmin
Hard Cutoff
W-W
10 GeV
4 GeV
Un-simulated region
4 GeV
Q2
10 GeV
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Hard-cut sample 4 GeV cutoffs
Qmin
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Weiszacker-Williams sample 4 GeV cutoffs
Should cut off at 4 GeV?
Qmin
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Weiszacker-Williams sample 4 GeV cutoffs
Mmin
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SPS1 Selectrons Again
Results for 10 fb-1
Source Cross-section (fb-1) Events Passed
SUSY 232 695
ee-ee- Hard-Cut (10 ? 4) 230 ? 1930 0 ? 2
ee-ee- Weisz-Willms (10 ? 4) 18,900 ? 167,000 59 ? 92
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Cunclusions, Outlook
ee-ee- 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?