susy studies at ucsc
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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?
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