susy studies at ucsc
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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?
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