Arlington Meeting

1
Arlington Meeting
SUSY Simulation with Undergraduates at the
University of Colorado Joseph Proulx for the
Colorado Group January 10, 2003
2
The Colorado Group
James Barron, Rory Kelly, Nick Danielson, MIHAI
DIMA, Bradford Dobos, Tyler Dorland, Michael
Duckwitz, Joshua Dunn, Elizabeth Goodman, Luke
Hamilton, Anthony Johnson, Eric Jurgenson, Liron
Kopinsky, Nathan Koral, Irene Liu, Robert
Midlil, Bonna Newman, Aaron preston, Joseph
Proulx, Matthew Route, Will Ruddick, David
Staszak, Matthew Stolte, Christopher Takeuchi,
Tara Turner, Christopher Veeneman, DAVID
WAGNER, Deborah Weber, Brook Williams, Jessica
Wolfe
3
Colorado SUSY Simulations
At Snowmass 2001 the International
Collaboration generated 9 simulation points 6
SUGRA model points with high tan (?), 2 GMSB
points and 1 AMSB to determine how well they can
be determined. The tan (?) 10 is particularly
difficult because it generates a large number of
?s in the final state. This leads to a large
number of low momentum tracks which get overrun
by the large 2 photon process.
?
?
4
Colorado SUSY Simulations
?
This discussion presents the analysis of the
first point.
We discuss the selectron, sneutrino,
neutralinos, and smuon studies status.
?
5
Introduction
This discussion presents how the SUSYsignals are
observed above the background, and the observed
mass resolution after the background is
removed. The background considered is the full
complement of SUSY background, the Standard
Model WW background and 2 photon background
where the two fast electrons have an angle mrads. We have not included the background from
Beamstrahlung ?? collisions producing the
appropriate final state particles.

6
SUGRA Model Parameters
We studied the SUGRA case with the SPS1
parameters given below. The parameters were
agreed to by the International Collaboration.
M 100 GeV M 250 GeV
A -100 tan(?) 10
? 352.39 The main characteristic of
this point is due to the large value of tan (?)
which leads to final states with ?s and hence
low energy tracks.
0
1/2
7
SUSY Masses
SPS Masses


?
?
?
ISAJET
?
?
?
Baer Paige Protopopescu Tata
?
?
?
?
8
SUSY Cross Sections
SPS1 Cross Sections (fb)
ISAJET
?
Baer Paige Protopopescu Tata
?
?
9
STANDARD MODEL ?
10
Comments on 2 ? Backg.
The 2 photon background can be limited by having
a detector that tags the two high energy
electron/positron if they are emitted at an angle
greater than 20 mrad. This limits the Pt of the
two fermions in the detector namely Pt
(limit) ? 250 x 2 x .020 10 GeV In the
case when you produce 2 taus that decay into
fermions the Pt limit is larger because of the
neutrinos.
11
Pt of Background
-

Pt of the e e Vector Sum (20 mrad limit)
-



? ? ? e e (in detector)
12
Pt of the Background
-

Pt of the e e Vector Sum
-

-

-


? ? ? ? ? ? e e ? ? ? ?
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Background issues
The simulation of the background in the previous
slide does not include the 2nd order processes
shown in the next slide. Hence it is possible
that the background in the energy region near 10
GeV in the 2 lepton case or above 20 GeV in the
case of 2 taus might be larger. This needs to
be corrected.
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BACKGROUND SIMULATION

• 
  

15
Two ? Data
Data from the L3 Collaboration
16
Two ? Data

Data from the L3 Collaboration
17

More Comments on 2 ?
If we want to have a detector at angles less than
20 mrad to reduce the Pt limit and hence reduce
the background we need to contend with the large
flux from Beamstrahlung, Bremmstrahlung as shown
in the next two slides.
18
Positron Spectrum, One Side
Beam/Bremmstrahlung x-y energy deposition at 150
cm from the interaction point

19
Electron Spectrum, One Side

20
Selectron Spectrum
Positron Energy Spectrum
?

?
?
?
?
?
?
?
L L R R L R L R SUSY bkg
80 L Pol
80 R Pol
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Selectron Spectrum

• Electron Energy Spectrum

?
?
?
?
?
?
?
?
L L R R L R L R SUSY bkg
80 R Pol
80 L Pol
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Selectron Spectrum
Electron Energy Spectrum
-
-




SUSY W W ? ? ? e e ??(e e )
80 L
80 R
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Pt of the Selectron Signal
Pt
-

Pt of the e e Vector Sum
24
Selectron
The mass of the SUSY particles depend on
observing the minimum and maximum energy of the
final state particle. The case discussed now is
the selectron and neutralino. See one of our
last slides showing the equations. In the
distributions before this the edges are obscured
by SUSY background channels. We use the large
differences in the Pt distributions of some of
the large background to remove it. In the next
slide where we take differences we get the
correct edges because what background remains
cancels out.
25
Nevertheless the low energy edge of the
distribution gets degraded by the Pt cut. The
main background that remains is the WW?e e ? ?
which is mostly removed by demanding that neither
electron be more that 200 GeV, The remaining
background is cancelled by taking the difference
since the electron and positron energy spectrum
of WW decays is the same.
26
Selectron Energy Spectrum
?
?
Energy Spectrum (e - e )(R-L)
Bremms
No Bremms
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Mass Fits

• Mass Fit Results

Particle Input Mass (GeV) Fitted Mass (GeV)

e 142.96 143.12 0.23
R

e 202.07 202.27 0.11
L
0
?
? 95.70 95.72 0.12
1
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Electron Sneutrinos
?
?
-

e e ? ? ?
e
e
?

0
? ? ? ? 87.9
e
e
1
?
?
-

? ? ? e 8.8
e
1
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SUSY Cross Sections
SPS1 Cross Sections (fb)
ISAJET
Baer Paige Protopopescu Tata
?
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Electron Sneutrinos
Search Procedure for Electron Sneutrinos
?
Plot energy distribution of e when we have
only an e and ?
Selectron and Smuon background removed Except
for Left Selectrons, Smuons that Decay into a
Neutrino and Chargino and Chargino decays into
Staus or Taus. Only ? ? ? ? ? and e e ?
W W remain
?
?


Use ? energy spectrum to remove e background
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Electron Sneutrinos
?
e energy spectrum for e ? events
No Brem
Brem
?1
80 Left Pol., Lum - 500 fb
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Electron Sneutrinos
? Energy Spectrum
This spectrum comes from ? decays and represents
the electron background from this source.
33
Electron Sneutrinos
Energy Spectrum of es from e? events
After ? Spectrum Subtraction
Sneutrinos
P80? L
Selectron
34

Add 2 ? Background
Now we add the 2 photon background from taus
decaying into an e and ?..
35
With ? ? ?? ???e????


Lum 500 inv fb
Total Electron Spectrum
Total Muon Spectrum
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Pt of e ?

From ? ? ????e?????

From Sneutrinos
37
Sneutrinos
-

e /e -- (SMSUSY) ? Energy Spectrum
Pt (e ?) 4 GeV E (e or ?)
P80? L
38
Sneutrino Mass Results
E E
low
high
No Brem
21.10 ? .09
GeV
4.11 ? .04
20.40 ? .12
GeV
4.22 ? .08
Brem
Masses (GeV)
?
?
M
M
?
?
?
1
186.00
176.38
Input
175.1 ? 0.7
184.7 ? 0.7
No Brem
178.9 ? 0.7
188.4 ? 0.7
Brem
39
Sneutrinos
-

e /e - (SM SUSY) ? Energy Spectrum
Pt (e ?) 4 GeV E (e or ?)
P 80 R
40
Sneutrinos
Sneutrino production can occur via a t-channel .
Hence it is sensitive to the longitudinal
polarization of the electron. The previous slide
shows how the signal disappears when you have
right-handed electron polarization, because the
coupling becomes very small in this case.
41
Smuons
-
?
?
?
?

e e ? ? ? ? ?
L
R
L
R
Signal
?
?
? ?
Backgrounds
W W Decays into ?


? ? ? ? ?
?
?
e e ? ? ? or ? ?
?
?
e e ? ? ?
?
?
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Smuon Background
WW Background Reduction
?Remove events with energy of either
muon ? 200 GeV

? WW?? ? ????? Background
? Rough cut at present
43
Smuons
? Energy Spectrum
-1
Pol80R, Lum500 fb
SmuonsWWCuts
Pure Smuons
?
?
L
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Higher Neutralinos
_
?
?

0
0
e e ? ? ? ? ? ? Z
? ? ? Z
3
4
3
1
3
2
-1
L 1500 fb
45
Higher Neutralinos
?
?
? ?
3
4
-1
L5000 fb
46
Discussion on Neutralinos
?
?
?
?
We still need to separate the ? ? and ? ?
signals Not clear that it can be done.
?
3
4
2
3
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