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SUSY studies at UCSC
Bruce SchummUC Santa Cruz
Cornell Linear Collider WorkshopJuly 13-16, 2003
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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
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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?
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selectronsLSP
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Right-handed selectrons at Ecm = 1 TeV
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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)
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Background Simulation II
We have gotten started with eeee backgrounds
e+
e+
e-
e-
e-
e+
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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
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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
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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
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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
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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.
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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
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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
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Qmin
Weiszacker-Williams Sample; 10 GeV cutoffs
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Mmin
Weiszacker-Williams Sample; 10 GeV cutoffs
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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
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Hard-cut sample; 4 GeV cutoffs
Qmin
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Weiszacker-Williams sample; 4 GeV cutoffs
Qmin
Should cut off at 4 GeV?
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Weiszacker-Williams sample; 4 GeV cutoffs
Mmin
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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
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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?