nlc – the next linear collider project colorado univ. - boulder prague lcd presentation status of...

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



ZEUTHEN LCD PRESENTATION

Supersymmetric Particles and the

Need for Tagging in theVery Forward Direction

Uriel Nauenbergfor the

Colorado Group

November 13, 2002



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



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.



Colorado SUSY Simulations

This discussion presents the analysis of the first point.

We discuss the selectron, sneutrino, neutralinos, and smuon studies status.



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.



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



SUSY Masses

SPS Masses

ISAJET

BaerPaige

ProtopopescuTata



SUSY Cross Sections

SPS1 Cross Sections (fb)

ISAJET

BaerPaige

ProtopopescuTata



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



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.

+ -



INITIAL VIEW

• All dimuons Except e e

Ecm = 750 GeVPt( from )<14 GeV

Lum = 50 fb 1



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.



BACKGROUND SIMULATION



Selectron Spectrum

• Positron Energy Spectrum

80% L Pol 80% R Pol

L L + R R + L R + L R + SUSY bkg



Selectron Spectrum

Positron Energy SpectrumSUSY + W W + e e + (e e )** + -

80% L 80% R

+ -



Selectron Spectrum

• Electron Energy SpectrumL L +R R +L R +L R + SUSY bkg

80% L Pol 80% R Pol



Selectron Spectrum

Electron Energy SpectrumSUSY + W W + e e + (e e )* * + -

80% L 80% R

+ -



Pt of Background

e e * * + -Pt of the e e Vector Sum+ -



Pt of the Background

e e * * + - + --Pt of the e e Vector Sum+ -



Pt of the Selectron Signal Pt

Pt of the e e Vector Sum+ -



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.



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.



Selectron Energy Spectrum

No Bremms Bremms

Energy Spectrum (e - e )(R-L)



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



Higher Neutralinos

e e ; Z ; Zl l

2 3 0 0

30

2,10

Lum = 2000 fb1

No Strahlung With Strahlung



SUSY Particle Masses

e + e + ; + Z ; + Z3 40 0+ _

3 1 3 2

L = 1500 fb-1



L=5000 fb-1

More on Neutralinos

3 4



Discussion on Neutralinos

We still need to separate the and signals Not clear that it can be done.

2 33 3 4



Electron Sneutrinos

e + e + + -e e

+ 87.9%e

10~

e

+ e 8.8%e

1+ -



SUSY Cross Sections

SPS1 Cross Sections (fb)

ISAJET

BaerPaige

ProtopopescuTata



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



Electron Sneutrinos

e energy spectrum for e + events No Brem Brem

80% Left Pol., Lum - 500 fb1



Electron Sneutrinos

Energy Spectrum

This spectrum comes from decays and represents the electron background from this source.



Pt of e +

From Sneutrinos From e * *



Selectron

Sneutrinos

Electron Sneutrinos

Energy Spectrum of e’s from e events

After Spectrum Subtraction

P=80 L



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



With e

Lum = 500 inv fb

* *

Total Electron Spectrum Total Muon Spectrum



Sneutrinos

e /e - SM Energy Spectrum

Pt (e+) > 4 GeV; E (e or ) < 50 GeV

+ -

P=80 L



Sneutrinos

e /e -- (SM+SUSY) Energy Spectrum+ -

Pt (e + ) > 4 GeV ; E (e or ) < 50 GeV

P=80 L



Sneutrinos

Pt (e + ) > 4 GeV; E (e or ) < 50 GeV

e /e - (SM + SUSY) Energy Spectrum + -

P = 80% R



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.



Smuons

Backgrounds

W W Decays into * * e e or

e e

e e + + -L L R R

Signal



Smuon Backgrounds

Muon Energy versus Angle



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



Smuons

Energy SpectrumPol=80%R, Lum=500 fb-1

L

Pure Smuons Smuons+WW+Cuts



Smuons

Energy Spectrum Pol=80%L, Lum=500 fb-1



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



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.



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.



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.



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.

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