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SUSY studies at UCSC
Bruce SchummUC Santa Cruz
Victoria Linear Collider WorkshopJuly 28-31, 2004
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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
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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
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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2003 Analysis (Gerbode)
Explored eeee backgrounds in central region
e+
e+
e-
e-
e-
e+
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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
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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
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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
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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)
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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
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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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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~
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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
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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 > 5 GeV in extended fiducial region ( > 110 mrad)
Ee (GeV) Ee (GeV)100 100200 200
50
100
50
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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
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Simulation of ee Background
10 10Mmin (GeV) Qmin (GeV)
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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?