We have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1a selectron mass reconstruction for the Silicon Detector concept. Simulating collisions at E_cm = 1 TeV, we have found that most of the information constraining the selectron mass is carried in the forward (|cos(theta)| \u3e 0.8) region. We have also found that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromise the selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2% (superconducting RF design), the detector resolution compromises the selectron mass reconstruction over the full angular region

Gerbode, Sharon J.

Holguin, Heath

Lau, Troy

Mooser, Paul

Pearlstein, Adam

Rose, Joe

Schumm, Bruce

English

arXiv

Keck Graduate Institute

Claremont Colleges
Scholarship @ Claremont
All HMC Faculty Publications and Research HMC Faculty Scholarship
3-1-2005
Selectron Mass Reconstruction and the Resolution
of the Linear Collider Detector
Sharon J. Gerbode
Harvey Mudd College
Heath Holguin
University of California - Santa Cruz
Troy Lau
University of California - Santa Cruz
Paul Mooser
University of California - Santa Cruz
Adam Pearlstein
University of California - Santa Cruz
See next page for additional authors
This Conference Proceeding is brought to you for free and open access by the HMC Faculty Scholarship at Scholarship @ Claremont. It has been
accepted for inclusion in All HMC Faculty Publications and Research by an authorized administrator of Scholarship @ Claremont. For more
information, please contact scholarship@cuc.claremont.edu.
Recommended Citation
S. J. Gerbode, H. Holguin, T. Lau, P. Moser, A. Pearlstein, J. Rose, and B. Schumm, “Selectron mass reconstruction and the resolution
of the linear collider detector,” International Linear Collider Workshop, 0214 (2005).
Authors
Sharon J. Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, and Bruce Schumm
This conference proceeding is available at Scholarship @ Claremont: http://scholarship.claremont.edu/hmc_fac_pub/775
ar
X
iv
:h
ep
-e
x/
05
07
05
3v
1 
 1
2 
Ju
l 2
00
5
SCIPP 05/05
July 2005
SELECTRON MASS RECONSTRUCTION AND THE RESOLUTION OF THE
LINEAR COLLIDER DETECTOR
SHARON GERBODE, HEATH HOLGUIN, TROY LAU, PAUL MOOSER, ADAM PEARLSTEIN, JOE ROSE,
BRUCE SCHUMM
Santa Cruz Institute for Particle Physics
University of California, Santa Cruz
We have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1a
selectron mass reconstruction for the Silicon Detector concept. Simulating collisions at Ecm = 1 TeV, we have found
that most of the information constraining the selectron mass is carried in the forward (| cos θ| ≥ 0.8) region. We have
also found that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromise
the selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2%
(superconducting RF design), the detector resolution compromises the selectron mass reconstruction over the full
angular region.
Talk presented at the 2005 International Linear Collider Workshop, Stanford University, Stanford, California, March 18-22,
2005
2005 International Linear Collider Workshop – Stanford, U.S.A.
Selectron Mass Reconstruction and the Resolution of the Linear Collider
Detector
Sharon Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, Bruce Schumm
SCIPP, University of California, Santa Cruz, CA 95064, USA
We have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1a selectron
mass reconstruction for the Silicon Detector concept. Simulating collisions at Ecm = 1 TeV, we have found that
most of the information constraining the selectron mass is carried in the forward (| cos θ| ≥ 0.8) region. We have also
found that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromise
the selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2%
(superconducting RF design), the detector resolution compromises the selectron mass reconstruction over the full
angular region.
1. INTRODUCTION
For some time, the Santa Cruz Linear Collider R&D group has been interested in exploring the requirements that
measuring forward selectron production places on the Linear Collider Detector. With right-handed selectron and
lightest neutralino masses of 143 and 95 GeV, respectively, Snowmass Point SPS1a produces a substantial forward
(| cos θ| ≥ 0.8|) population of electrons from selectron decay. Over the past two years, the Santa Cruz group has
developed techniques to isolate the forward selectron-decay signal from Standard-Model backgrounds, as well as
techniques to extract the selectron mass from the observed selectron-decay electron spectrum. This paper reports on
the results of those studies.
2. SIGNAL SELECTION
Backgrounds to the selectron-decay electron signal come from two primary sources: four-electron production for
which two of the final-state fermions are close in angle to the beam trajectory, and thus escape detection, and the
Z-boson fusion process e+e− → e+e−νν¯. During the course of searches for supersymmetry at LEP, several cuts were
developed to isolate potential SUSY signals from Standard Model backgrounds.
• Fiducial Region Cut: Exactly one final-state positron and one final-state electron pair must be detected in
the fiducial region. For this study, the fiducial region lies above 5 GeV in momentum, and within | cos θ| ≤ 0.8
for central-region studies, or within | cos θ| ≤ 0.994 for studies including the forward region.
• Tagging Cut: No observable electron or positron in the low-angle ‘tagging calorimetry’ (with assumed coverage
of 20mrad < θ < 110mrad).
• Transverse Momentum Cut: Cuts events for which the vector sum of the observed e+e− pair transverse
momenta is less than 500 Gev × sin(20 mrad).
For a signal region of | cos θ| ≤ 0.8, these cuts completely eliminate the four-electron background up to diagrams
with additional radiation, and sufficiently select against the eeνν process. However, as one attempts to reconstruct
the selectron decay signal beyond | cos θ| = 0.8, both the radiative four-electron background and the eeνν backgrounds
approach poles in their respective production cross sections, and begin to dominate the selectron signal. To suppress
these backgrounds to a degree appropriate for use of the forward selectron decay signal, two additional cuts were
applied.
0214
• Photon Cut: Remove event if there is an observed photon of 20 GeV or greater in either the fiducial or
tagging region.
• High-Momentum Cut: Remove even if the vector sum of the e+e− pair momenta has a magnitude of greater
than 225 GeV.
With the application of these cuts to events produced at Ecm = 1 TeV with 80% right-handed-polarized electron
beam and unpolarized positrons, it was found that Standard Model processes provided a negligible background to
the right-handed selectron signal. In addition, the application of these selection criteria did not significantly alter the
shape of the selectron-decay electron spectrum in either the central or forward region. Nevertheless, in the analysis
that follows all of the selection cuts will be applied to the selectron signal; however, Standard Model backgrounds
will be ignored from this point on. Finally, running with an 80% right-polarized electron beam, electrons from the
decay of the more massive left-handed selectron provide a diffuse background to the right-handed selectron decay
electron spectrum. This contribution was also ignored in the right-handed selectron analysis.
3. SIMULATION OF THE SELECTRON SIGNAL
The selectron signal was generated at Ecm = 1 TeV using the Snowmass point SPS1a [1] parameters m0 = 100
GeV, m1/2 = 250 GeV, A0 = −100, tanβ = 10, and sgn(µ) = +. The SPS1a specifications were implemented within
the ISAJET [2] package, and included the effects of initial state radiation, beamstrahlung (Y = 0.29), and three
different values of the fractional beam energy spread (assuming a gaussian distribution): 1.0%, 0.16%, and 0.0%.
For this point in SUSY parameter space, the endpoint of the selectron-decay electron energy distribution lies above
270 GeV, making the precise measurement of the endpoint energy by the tracking system somewhat challenging.
Nonetheless, the projected ∼ 1
2
% resolution of the tracking system at this energy is somewhat better than that
expected for the electromagnetic calorimetry.
The cos θ distribution of final-state electrons and positrons from the decay of right-handed selectrons is peaked
towards | cos θ| = 1.0, due to the sizeable t-channel contribution admitted by the relatively light selectron and
neutralino. Approximately half of the signal lies in the forward region, beyond | cos θ| = 0.8.
4. DETERMINATION OF THE RIGHT-HANDED SELECTRON MASS
To focus on the accuracy of the selectron mass reconstruction, it was assumed for now that the lightest neutralino
mass was known precisely from other measurements. The Santa Cruz group plans to relax this assumption in further
studies.
The selectron mass was determined by finding the best fit of the selectron energy spectrum to that of a series
of ‘template’ distributions generated with slightly varying right-handed selectron masses, but with all other aspects
of the signal generation, including beam energy spread and detector smearing effects, the same as for the data
simulation. Templates were produced for 15 right-handed selectron masses in a range of approximately ±1 GeV
about the nominal SPS1a mass of 143.11 GeV.
A total of 120 independent data sets, each corresponding to an integrated luminosity of 115 fb−1, were generated
at the nominal SPS1a mass. For each of these data sets, a χ2 was formed against each of the templates points,
according to
χ2 =
∑
i
(w ∗ ni − w ∗mi)
2
(w ∗ ni −mi)2
(1)
where the sum is over energy bins in the selectron-decay electron spectrum, ni and mi are the data and template
bin contents, respectively, and
w =
∑
i ni∑
i mi
(2)
0214
Table I: Endpoint Fit Regions
Scenario(s) Lower Endpoint χ2 Range Upper Endpoint χ2 Range
Perfect detector resolution and/or no energy spread 5.2–6.4 GeV 269.2–273.2 GeV
realistic resolution; 0.16% energy spread 5.2–6.4 GeV 267.8–274.6 GeV
realistic resolution; 1.0% energy spread 5.2–6.4 GeV 267.2–275.2 GeV
is the relative sample-size weighting factor. To minimize the statistical contributions of the template files, they were
generated with an integrated luminosity of approximately 1000 fb−1 each.
For each data set, the χ2 contour was fit with a quartic polynomial, which was then minimized to find the best-fit
selectron mass. This procedure was repeated for the 120 data sets, and the mean and root-mean-square deviation
was calculated from the distribution of best-fit right-handed selectron masses.
In forming the χ2 for each of the 120 independent data sets, it was found that the inclusion of energy-spectrum
bins not sufficiently close to the upper and lower endpoints to provide useful information on the endpoint location
introduced unacceptable scatter in the contour. Thus, for each scenario that was studied (beam energy spread,
detector model, polar angle reach), only bins near the upper and lower endpoint were used in forming the χ2. The
exact energy ranges used in the χ2 calculation depended on the scenario under study, and was determined in a
data-driven manner by examining the spectrum in the region of the endpoints in the generated data samples. Table
I shows the regions used in the forming the χ2 for the different scenarios.
4.1. Scenarios Explored
To explore the effects of detector resolution, data sets and mass templates were generated assuming perfect detector
resolution as well as that of the SDMAR01 detector. Detector resolution effects were incorporated via gaussian
smearing based on error matrices from Billior-based tracking error calculations provided by the LCDTRK program [3].
Two different ranges in | cos θ| were explored: between 0.0 and 0.8 and between 0.0 and 0.994. Finally, three different
values of the beam energy spread were explored: ±1.0% (to allow benchmark comparisons to previous studies [4, 5]),
±0.16% (approximately that expected for the superconducting RF design), and, for comparison, 0.0%.
5. RESULTS
Figure 1 shows the root-mean-square deviation observed for the 120 independent data sets for the different scenarios
that were explored in the study (in all cases, the mean value of the fit mass was reasonably consistent with the input
vale of the right-handed selectron mass of 143.1 GeV).
For a perfect detector (no measurement uncertainty), the inclusion of the forward region provides substantial
improvement in the selectron mass measurement, independent of beam energy spread. In fact, the improvement is
better than one would expect from the factor-of-two increase in the number of signal electrons that is associated with
the inclusion of the forward region. A study of the two-dimensional frequency distribution of signal electrons as a
function of energy and the cosine of the polar angle (Figure 2) reveals that the spectrum has a greater contribution
at higher energy, where the sensitivity to the selectron mass is greatest, at high values of cos θ. Thus, in this case,
most of the information on the selectron mass (and on slepton masses in general) is in the forward region.
For large beam energy spread, it is seen that the sensitivity to the selectron mass has little dependence on the
detector resolution. For this case, the SiD design seems to be adequate to take advantage of the physics capabilities
of the accelerator. However, for smaller beam energy spread, this is not the case. For the energy spread anticipated
for the selected machine design, substantial improvement in the selectron mass determination can be achieved by
improving the detector resolution, particularly in the forward region.
0214
Figure 1: Sensitivity to the SPS1a right-handed selectron mass for 115 fb−1 of Linear Collider data at Ecm = 1000 GeV, as a
function of beam energy spread and polar angle coverage.
Figure 2: Frequency distribution of electrons from right-handed selectron decay as a function of energy and polar angle.
6. CONCLUSIONS
To examine the issue of measuring selectron masses in the forward region of the Linear Collider Detector, we
have simulated SPS1a selectron production at Ecm = 1 TeV. By developing two new selection criteria, we have
demonstrated that the selectron signal can be separated from Standard Model backgrounds through the entire
forward tracking region | cos θ| < 0.994.
Due to the stiffening of the selectron-decay electron spectrum at higher values of | cos θ|, for a light selectron
0214
most of the information on selectron mass (and slepton mass in general) comes from the forward region. For large
beam energy spread (±1.0%), we find that the SiD detector design is adequate to exploit the potential of the Linear
Collider; however, for the expected beam energy spread of the chosen cold RF technology, gains in sensitivity to
the selectron mass can be made by further improvements in momentum resolution, in both the central and forward
regions.
Acknowledgments
Although they appear as authors on this paper, one of us (Schumm) would like to acknowledge the dedication and
creativity of the other authors, who performed these studies as undergraduate physics majors at the University of
California at Santa Cruz.
References
[1] N. Ghodbane and H. Martyn, ‘Compilation of SUSY particle spectra from Snowmass 2001 benchmark models’,
hep-ph/0201233, January, 2002.
[2] F. Paige, S. Protopopescu, H. Baer, X. Tata, ‘ISAJET 7.69 A Monte Carlo Event Generator for pp , p¯p , and
e+e− Reactions’, hep-ph/0312045, December, 2003.
[3] B. Schumm, http://www.slac.stanford.edu/∼schumm/lcdtrk20011204.tar.gz
[4] M Dima et al., Phys. Rev. D65:071701,2002.
[5] K. Riles and H. Yang, physics/0506198, June, 2005.
0214


Selectron Mass Reconstruction and the Resolution of the Linear Collider Detector

Scholarship@Claremont

Claremont CollegesScholarship @ ClaremontAll HMC Faculty Publications and Research HMC Faculty Scholarship3-1-2005Selectron Mass Reconstruction and the Resolutionof the Linear Collider DetectorSharon J. GerbodeHarvey Mudd CollegeHeath HolguinUniversity of California - Santa CruzTroy LauUniversity of California - Santa CruzPaul MooserUniversity of California - Santa CruzAdam PearlsteinUniversity of California - Santa CruzSee next page for additional authorsThis Conference Proceeding is brought to you for free and open access by the HMC Faculty Scholarship at Scholarship @ Claremont. It has beenaccepted for inclusion in All HMC Faculty Publications and Research by an authorized administrator of Scholarship @ Claremont. For moreinformation, please contact scholarship@cuc.claremont.edu.Recommended CitationS. J. Gerbode, H. Holguin, T. Lau, P. Moser, A. Pearlstein, J. Rose, and B. Schumm, “Selectron mass reconstruction and the resolutionof the linear collider detector,” International Linear Collider Workshop, 0214 (2005).AuthorsSharon J. Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, and Bruce SchummThis conference proceeding is available at Scholarship @ Claremont: http://scholarship.claremont.edu/hmc_fac_pub/775arXiv:hep-ex/0507053v1  12 Jul 2005SCIPP 05/05July 2005SELECTRON MASS RECONSTRUCTION AND THE RESOLUTION OF THELINEAR COLLIDER DETECTORSHARON GERBODE, HEATH HOLGUIN, TROY LAU, PAUL MOOSER, ADAM PEARLSTEIN, JOE ROSE,BRUCE SCHUMMSanta Cruz Institute for Particle PhysicsUniversity of California, Santa CruzWe have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1aselectron mass reconstruction for the Silicon Detector concept. Simulating collisions at Ecm = 1 TeV, we have foundthat most of the information constraining the selectron mass is carried in the forward (| cos θ| ≥ 0.8) region. We havealso found that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromisethe selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2%(superconducting RF design), the detector resolution compromises the selectron mass reconstruction over the fullangular region.Talk presented at the 2005 International Linear Collider Workshop, Stanford University, Stanford, California, March 18-22,20052005 International Linear Collider Workshop – Stanford, U.S.A.Selectron Mass Reconstruction and the Resolution of the Linear ColliderDetectorSharon Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, Bruce SchummSCIPP, University of California, Santa Cruz, CA 95064, USAWe have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1a selectronmass reconstruction for the Silicon Detector concept. Simulating collisions at Ecm = 1 TeV, we have found thatmost of the information constraining the selectron mass is carried in the forward (| cos θ| ≥ 0.8) region. We have alsofound that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromisethe selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2%(superconducting RF design), the detector resolution compromises the selectron mass reconstruction over the fullangular region.1. INTRODUCTIONFor some time, the Santa Cruz Linear Collider R&D group has been interested in exploring the requirements thatmeasuring forward selectron production places on the Linear Collider Detector. With right-handed selectron andlightest neutralino masses of 143 and 95 GeV, respectively, Snowmass Point SPS1a produces a substantial forward(| cos θ| ≥ 0.8|) population of electrons from selectron decay. Over the past two years, the Santa Cruz group hasdeveloped techniques to isolate the forward selectron-decay signal from Standard-Model backgrounds, as well astechniques to extract the selectron mass from the observed selectron-decay electron spectrum. This paper reports onthe results of those studies.2. SIGNAL SELECTIONBackgrounds to the selectron-decay electron signal come from two primary sources: four-electron production forwhich two of the final-state fermions are close in angle to the beam trajectory, and thus escape detection, and theZ-boson fusion process e+e− → e+e−νν¯. During the course of searches for supersymmetry at LEP, several cuts weredeveloped to isolate potential SUSY signals from Standard Model backgrounds.• Fiducial Region Cut: Exactly one final-state positron and one final-state electron pair must be detected inthe fiducial region. For this study, the fiducial region lies above 5 GeV in momentum, and within | cos θ| ≤ 0.8for central-region studies, or within | cos θ| ≤ 0.994 for studies including the forward region.• Tagging Cut: No observable electron or positron in the low-angle ‘tagging calorimetry’ (with assumed coverageof 20mrad < θ < 110mrad).• Transverse Momentum Cut: Cuts events for which the vector sum of the observed e+e− pair transversemomenta is less than 500 Gev × sin(20 mrad).For a signal region of | cos θ| ≤ 0.8, these cuts completely eliminate the four-electron background up to diagramswith additional radiation, and sufficiently select against the eeνν process. However, as one attempts to reconstructthe selectron decay signal beyond | cos θ| = 0.8, both the radiative four-electron background and the eeνν backgroundsapproach poles in their respective production cross sections, and begin to dominate the selectron signal. To suppressthese backgrounds to a degree appropriate for use of the forward selectron decay signal, two additional cuts wereapplied.0214• Photon Cut: Remove event if there is an observed photon of 20 GeV or greater in either the fiducial ortagging region.• High-Momentum Cut: Remove even if the vector sum of the e+e− pair momenta has a magnitude of greaterthan 225 GeV.With the application of these cuts to events produced at Ecm = 1 TeV with 80% right-handed-polarized electronbeam and unpolarized positrons, it was found that Standard Model processes provided a negligible background tothe right-handed selectron signal. In addition, the application of these selection criteria did not significantly alter theshape of the selectron-decay electron spectrum in either the central or forward region. Nevertheless, in the analysisthat follows all of the selection cuts will be applied to the selectron signal; however, Standard Model backgroundswill be ignored from this point on. Finally, running with an 80% right-polarized electron beam, electrons from thedecay of the more massive left-handed selectron provide a diffuse background to the right-handed selectron decayelectron spectrum. This contribution was also ignored in the right-handed selectron analysis.3. SIMULATION OF THE SELECTRON SIGNALThe selectron signal was generated at Ecm = 1 TeV using the Snowmass point SPS1a [1] parameters m0 = 100GeV, m1/2 = 250 GeV, A0 = −100, tanβ = 10, and sgn(µ) = +. The SPS1a specifications were implemented withinthe ISAJET [2] package, and included the effects of initial state radiation, beamstrahlung (Y = 0.29), and threedifferent values of the fractional beam energy spread (assuming a gaussian distribution): 1.0%, 0.16%, and 0.0%.For this point in SUSY parameter space, the endpoint of the selectron-decay electron energy distribution lies above270 GeV, making the precise measurement of the endpoint energy by the tracking system somewhat challenging.Nonetheless, the projected ∼ 12% resolution of the tracking system at this energy is somewhat better than thatexpected for the electromagnetic calorimetry.The cos θ distribution of final-state electrons and positrons from the decay of right-handed selectrons is peakedtowards | cos θ| = 1.0, due to the sizeable t-channel contribution admitted by the relatively light selectron andneutralino. Approximately half of the signal lies in the forward region, beyond | cos θ| = 0.8.4. DETERMINATION OF THE RIGHT-HANDED SELECTRON MASSTo focus on the accuracy of the selectron mass reconstruction, it was assumed for now that the lightest neutralinomass was known precisely from other measurements. The Santa Cruz group plans to relax this assumption in furtherstudies.The selectron mass was determined by finding the best fit of the selectron energy spectrum to that of a seriesof ‘template’ distributions generated with slightly varying right-handed selectron masses, but with all other aspectsof the signal generation, including beam energy spread and detector smearing effects, the same as for the datasimulation. Templates were produced for 15 right-handed selectron masses in a range of approximately ±1 GeVabout the nominal SPS1a mass of 143.11 GeV.A total of 120 independent data sets, each corresponding to an integrated luminosity of 115 fb−1, were generatedat the nominal SPS1a mass. For each of these data sets, a χ2 was formed against each of the templates points,according toχ2 =∑i(w ∗ ni − w ∗mi)2(w ∗ ni −mi)2(1)where the sum is over energy bins in the selectron-decay electron spectrum, ni and mi are the data and templatebin contents, respectively, andw =∑i ni∑i mi(2)0214Table I: Endpoint Fit RegionsScenario(s) Lower Endpoint χ2 Range Upper Endpoint χ2 RangePerfect detector resolution and/or no energy spread 5.2–6.4 GeV 269.2–273.2 GeVrealistic resolution; 0.16% energy spread 5.2–6.4 GeV 267.8–274.6 GeVrealistic resolution; 1.0% energy spread 5.2–6.4 GeV 267.2–275.2 GeVis the relative sample-size weighting factor. To minimize the statistical contributions of the template files, they weregenerated with an integrated luminosity of approximately 1000 fb−1 each.For each data set, the χ2 contour was fit with a quartic polynomial, which was then minimized to find the best-fitselectron mass. This procedure was repeated for the 120 data sets, and the mean and root-mean-square deviationwas calculated from the distribution of best-fit right-handed selectron masses.In forming the χ2 for each of the 120 independent data sets, it was found that the inclusion of energy-spectrumbins not sufficiently close to the upper and lower endpoints to provide useful information on the endpoint locationintroduced unacceptable scatter in the contour. Thus, for each scenario that was studied (beam energy spread,detector model, polar angle reach), only bins near the upper and lower endpoint were used in forming the χ2. Theexact energy ranges used in the χ2 calculation depended on the scenario under study, and was determined in adata-driven manner by examining the spectrum in the region of the endpoints in the generated data samples. TableI shows the regions used in the forming the χ2 for the different scenarios.4.1. Scenarios ExploredTo explore the effects of detector resolution, data sets and mass templates were generated assuming perfect detectorresolution as well as that of the SDMAR01 detector. Detector resolution effects were incorporated via gaussiansmearing based on error matrices from Billior-based tracking error calculations provided by the LCDTRK program [3].Two different ranges in | cos θ| were explored: between 0.0 and 0.8 and between 0.0 and 0.994. Finally, three differentvalues of the beam energy spread were explored: ±1.0% (to allow benchmark comparisons to previous studies [4, 5]),±0.16% (approximately that expected for the superconducting RF design), and, for comparison, 0.0%.5. RESULTSFigure 1 shows the root-mean-square deviation observed for the 120 independent data sets for the different scenariosthat were explored in the study (in all cases, the mean value of the fit mass was reasonably consistent with the inputvale of the right-handed selectron mass of 143.1 GeV).For a perfect detector (no measurement uncertainty), the inclusion of the forward region provides substantialimprovement in the selectron mass measurement, independent of beam energy spread. In fact, the improvement isbetter than one would expect from the factor-of-two increase in the number of signal electrons that is associated withthe inclusion of the forward region. A study of the two-dimensional frequency distribution of signal electrons as afunction of energy and the cosine of the polar angle (Figure 2) reveals that the spectrum has a greater contributionat higher energy, where the sensitivity to the selectron mass is greatest, at high values of cos θ. Thus, in this case,most of the information on the selectron mass (and on slepton masses in general) is in the forward region.For large beam energy spread, it is seen that the sensitivity to the selectron mass has little dependence on thedetector resolution. For this case, the SiD design seems to be adequate to take advantage of the physics capabilitiesof the accelerator. However, for smaller beam energy spread, this is not the case. For the energy spread anticipatedfor the selected machine design, substantial improvement in the selectron mass determination can be achieved byimproving the detector resolution, particularly in the forward region.0214Figure 1: Sensitivity to the SPS1a right-handed selectron mass for 115 fb−1 of Linear Collider data at Ecm = 1000 GeV, as afunction of beam energy spread and polar angle coverage.Figure 2: Frequency distribution of electrons from right-handed selectron decay as a function of energy and polar angle.6. CONCLUSIONSTo examine the issue of measuring selectron masses in the forward region of the Linear Collider Detector, wehave simulated SPS1a selectron production at Ecm = 1 TeV. By developing two new selection criteria, we havedemonstrated that the selectron signal can be separated from Standard Model backgrounds through the entireforward tracking region | cos θ| < 0.994.Due to the stiffening of the selectron-decay electron spectrum at higher values of | cos θ|, for a light selectron0214most of the information on selectron mass (and slepton mass in general) comes from the forward region. For largebeam energy spread (±1.0%), we find that the SiD detector design is adequate to exploit the potential of the LinearCollider; however, for the expected beam energy spread of the chosen cold RF technology, gains in sensitivity tothe selectron mass can be made by further improvements in momentum resolution, in both the central and forwardregions.AcknowledgmentsAlthough they appear as authors on this paper, one of us (Schumm) would like to acknowledge the dedication andcreativity of the other authors, who performed these studies as undergraduate physics majors at the University ofCalifornia at Santa Cruz.References[1] N. Ghodbane and H. Martyn, ‘Compilation of SUSY particle spectra from Snowmass 2001 benchmark models’,hep-ph/0201233, January, 2002.[2] F. Paige, S. Protopopescu, H. Baer, X. Tata, ‘ISAJET 7.69 A Monte Carlo Event Generator for pp , p¯p , ande+e− Reactions’, hep-ph/0312045, December, 2003.[3] B. Schumm, http://www.slac.stanford.edu/∼schumm/lcdtrk20011204.tar.gz[4] M Dima et al., Phys. Rev. D65:071701,2002.[5] K. Riles and H. Yang, physics/0506198, June, 2005.0214

https://scholarship.claremont.edu/cgi/viewcontent.cgi?article=1782&amp;context=hmc_fac_pub

Selectron Mass Reconstruction and the Resolution of the Linear Collider Detector

Abstract

Similar works

Full text

Available Versions

Keck Graduate Institute

Scholarship@Claremont