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NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Prague LCD Presentation
Status of SPS1 Analysisat Colorado
Uriel Nauenberg for the
Colorado Group
November 15, 2002
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
ZEUTHEN LCD PRESENTATION
Supersymmetric Particles and the
Need for Tagging in theVery Forward Direction
Uriel Nauenbergfor the
Colorado Group
November 13, 2002
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
The Colorado Group
Toshinori Abe, James Barron, Samantha Carpenter, Shenjian Chen, Eric Jurgenson, Luke Hamilton, Anthony Johnson, Liron Kopinsky, Uriel Nauenberg,
Joseph Proulx, William Ruddick, David Staszak, Chris Veeneman
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
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.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Colorado SUSY Simulations
This discussion presents the analysis of the first point.
We discuss the selectron, sneutrino, neutralinos, and smuon studies status.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
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 < 20 mrads. We have not included the background from Beamstrahlung collisions producing the appropriate final stateparticles.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SUGRA Model Parameters
We studied the SUGRA case with the SPS1 parametersgiven below. The parameters were agreed to by the International Collaboration.
M = 100 GeV M = 250 GeV A = -100 tan() = 10 = 352.39The main characteristic of this point is due to the largevalue of tan () which leads to final states with ’s andhence low energy tracks.
0 1/2
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SUSY Masses
SPS Masses
ISAJET
BaerPaige
ProtopopescuTata
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SUSY Cross Sections
SPS1 Cross Sections (fb)
ISAJET
BaerPaige
ProtopopescuTata
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
The New Result
• Selectron Mass Measurement
e e , e e , e e , e e
New MethodX 10 Resolution Improvement
eR,L
~ e± + ~10
R R L L R L L R
~ ~ ~ ~ ~ ~ ~ ~+ -_ + _ + _ + _
e L
1 e
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Background
The distribution in the next slide fairly much describes what we observe if we are looking at the final states that contain single leptons, like in the search for selectrons, sneutrinos, smuons, etc.
The large low momentum distribution is due to thelarge cross section for the 2 photon process
e + e e + e + + e + e + lepton pairwhere the 2 e’s are very forward and the lepton pairs are present in the detector.
+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
INITIAL VIEW
• All dimuons Except e e
Ecm = 750 GeVPt( from )<14 GeV
Lum = 50 fb 1
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Background issues
The simulation of the background in the previous slide does not include the 2nd order processes shown in thenext slide. Hence it is possible that the background inthe energy region above 20 GeV might be larger. This needs to be corrected.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron Spectrum
• Positron Energy Spectrum
80% L Pol 80% R Pol
L L + R R + L R + L R + SUSY bkg
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron Spectrum
Positron Energy SpectrumSUSY + W W + e e + (e e )** + -
80% L 80% R
+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron Spectrum
• Electron Energy SpectrumL L +R R +L R +L R + SUSY bkg
80% L Pol 80% R Pol
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron Spectrum
Electron Energy SpectrumSUSY + W W + e e + (e e )* * + -
80% L 80% R
+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Pt of Background
e e * * + -Pt of the e e Vector Sum+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Pt of the Background
e e * * + - + --Pt of the e e Vector Sum+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Pt of the Selectron Signal Pt
Pt of the e e Vector Sum+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron
The mass of the SUSY particles depend on observing the minimum and maximum energy of the final stateparticle. The case discussed now is the selectron andneutralino. See one of our last slides showing the equations. In the distributions before this the edgesare obscured by SUSY background channels. We usethe 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 correctedges because what background remains cancels out.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Nevertheless the low energy edge of the distribution gets degraded by the Pt cut.
Thye main background that remains is the WWe 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.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron Energy Spectrum
No Bremms Bremms
Energy Spectrum (e - e )(R-L)
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SELECTRON MASSES RESULTS
Name Input Mass Measured Mass
GeV GeV
Lum = 500 fb-1
R
L
10
e 143.00No Brem
141.57 0.80Brem 146.3 0.8
e 202.12 No Brem 201.51 0.80Brem 208.6 0.8
96.05 No Brem 95.4 4.0 Brem 99.9 3.9
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Higher Neutralinos
e e ; Z ; Zl l
2 3 0 0
30
2,10
Lum = 2000 fb1
No Strahlung With Strahlung
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SUSY Particle Masses
e + e + ; + Z ; + Z3 40 0+ _
3 1 3 2
L = 1500 fb-1
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Discussion on Neutralinos
We still need to separate the and signals Not clear that it can be done.
2 33 3 4
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Electron Sneutrinos
e + e + + -e e
+ 87.9%e
10~
e
+ e 8.8%e
1+ -
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
SUSY Cross Sections
SPS1 Cross Sections (fb)
ISAJET
BaerPaige
ProtopopescuTata
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Electron Sneutrinos
Search Procedure for Electron Sneutrinos
Plot energy distribution of e when we have only an e and
Selectron and Smuon background removedExcept for Left Selectrons, Smuons thatDecay 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
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Electron Sneutrinos
e energy spectrum for e + events No Brem Brem
80% Left Pol., Lum - 500 fb1
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Electron Sneutrinos
Energy Spectrum
This spectrum comes from decays and represents the electron background from this source.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Pt of e +
From Sneutrinos From e * *
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Selectron
Sneutrinos
Electron Sneutrinos
Energy Spectrum of e’s from e events
After Spectrum Subtraction
P=80 L
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Sneutrino Mass Results
E E low high
No Brem
Brem
4.11 .04 21.10 .09 GeV
4.22 .08 20.40 .12 GeV
Masses (GeV)M M 1
Input
No BremBrem
186.00 176.38
184.7 0.7 175.1
188.4 0.7 178.9
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
With e
Lum = 500 inv fb
* *
Total Electron Spectrum Total Muon Spectrum
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Sneutrinos
e /e - SM Energy Spectrum
Pt (e+) > 4 GeV; E (e or ) < 50 GeV
+ -
P=80 L
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Sneutrinos
e /e -- (SM+SUSY) Energy Spectrum+ -
Pt (e + ) > 4 GeV ; E (e or ) < 50 GeV
P=80 L
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Sneutrinos
Pt (e + ) > 4 GeV; E (e or ) < 50 GeV
e /e - (SM + SUSY) Energy Spectrum + -
P = 80% R
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Sneutrinos
Sneutrino production can occur via a t-channel . Hence it is sensitive to the longitudinal polarization of the electron.
The previous two slides show how the signal disappears when you have a right handed electron polarization because the coupling becomes very small in this case.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Smuons
Backgrounds
W W Decays into * * e e or
e e
e e + + -L L R R
Signal
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Smuon Backgrounds
Muon Energy versus Angle
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Smuon Background
WW Background Reduction
Remove events with energy of either muon 200 GeV
Remove events with muons in the energy vs band
Background
Rough cut at present
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Smuons
Energy SpectrumPol=80%R, Lum=500 fb-1
L
Pure Smuons Smuons+WW+Cuts
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Smuons
Energy Spectrum Pol=80%L, Lum=500 fb-1
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Beam Energy Resolution
A B + C
M = E { E (min) E (max) }A cm c c1/2
—————————{E (min) + E (max)}c c
M = M { 1 – 2[E (min) + E (max)]} c c—————————Ecm
B A1/2
(M) 0.35 (E )cm
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Conclusions
The large number of low energy events is due to the2 photon background. This can be removed by havinga detector in the very forward region that detects all tracks with angles > 20 mrad to the beam direction.Then requiring that the Pt of the tracks in the detectoradd to > 10 GeV removes this background. In the caseof the e final state the 2 s from the decay makes thislimit more diffuse. Restricting to lower than 20 mrad is useful to reduce this background. This should be an R&D effort.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
Conclusions
SUSY masses can be measure to a fraction of 1 GeV in a few cases and to about 1 GeV in the others.
The tracker should measure momenta to about 1 GeVor better. This leads to similar errors in the mass due to an uncertainty of 0.5% in the center of energy.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
More Conclusions
The selectron masses can be measured as long as the right and left selectron masses are different.
The electron sneutrino mass can measured but the 2 photon into s background affects the accuracy of the measurement.
The right smuon mass can be measured but the left smuon is obscured by the WW background.
NLC – The Next Linear Collider Project
Colorado Univ. - Boulder
More Conclusions
The neutralinos signals are seen but there are overlapping channels. We are investigating how to separate them.
We are investigating how to use the full energy spectrum to determine the masses. Looks like it will work. Very useful for decays which are not 2 body where the energy spectrum edges are not well defined.