FORWARD SELECTRON PRODUCTION AND DETECTOR

PERFORMANCE

Bruce Schumm

University of California at Santa Cruz

SLAC LCWS05

Special Recognition: Troy Lau, UCSC senior thesis student.

THE UCSC SUSY GROUP

Past

Sharon Gerbode (now at Cornell)Heath Holguin (now a UCSC grad student)

Paul MooserAdam Pearlstein (now at Colorado State)

Present

Troy Lau (will be at ??) Ayelet Lorberbaum

Joe Rose

Particular mention: Troy Lau has done an extraordinary job as an undergraduate senior thesis student. This presentation would not be possible without his work and creativity.

Motivation

To explore the effects of limited detector resolution on our ability to measure SUSY parameters in the forward (|

cos()| > .8) region.

selectrons

LSP

SPS 1 Spectroscopy:

At Ecm = 1Tev, selectrons and neutralino are

light.

Beam/Brehm:√smin=1 √smax=1000 = .29sz = .11 (mm)

-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

13,000

14,000

15,000

16,000

SUSY: Particle cos(theta) (no cuts)

SPS1A at 1 TeVSelectrons vs. cos()

Electrons vs. cos()

Roughly ½ of statistics above |cos()| of 0.8,

but…

Energy Distribution

0

50

100

150

200

250

300

350

400

450

0 7 14

22

29

36

43

50

58

65

72

79

86

94

101

108

115

122

130

137

144

151

158

166

173

180

187

194

202

209

216

223

230

238

245

252

259

266

274

281

288

Energy GeV

Co

un

ts

• sample electron energy distribution Mselectron = 143.112 (SPS1A)

Lower Endpoint

Upper Endpoint

Electron energy distributionwith beam/bremm/ISR (.16%). No detector effects or beam energy spread.

The spectrum is weighted towards higher energy at high |cos()|, so there’s more information in the forward region than one might expect.

Previous work: Can one find the selectron signal for |

cos()|>0.8?

Dominant Backgrounds:

e+ e- e+ e- e+ e-

e+ e- e+ e-

‘STANDARD’ CUTS

• Fiducial Cut: Exactly one final-state positron and one final-state electron pair in |cos()| region of interest, each with a transverse momentum of at least 5GeV. Otherwise the event is discarded.

• Tagging Cut: No observable electron or positron in low-angle `tagging’ calorimetry (with coverage of 20mrad < < 110mrad)

• Transverse Momentum (TM) Cut: Cuts events where vector sum of transverse momentum for e+e- pair is less than 2 * 250GeV * sin (20 mrads)

‘NEW’ CUTS

• Photon Cut: TM cut eliminates four-electron background except for radiative events. Remove remaining radiative events by looking for radiated photon; i.e., if there is a photon in the tagging region with energy of 20GeV or more.

• HP Cut: Removes low-mass, t-channel-dominated ee backgrounds while preserving high-mass SUSY signal

Before H-P

After H-P

After ‘photon cut’, which eliminates the four-electron back-ground, the dominant background is ee. Manipulation of the beam polarization, combined with application of the ‘HP Cut’ reduces background to minimal levels, even in forward region.

Ignore backgrounds in detector resolution studies.

Pe- = +80%Pe+ = -50%

Pe- = +80%Pe+ = 0%

|cos| < 0.994

Standard Model Backgrounds

Fitting the Endpoints for the Selectron Mass

For now, we have done one-dimensional fits (assume 0 mass known)

Vary SUSY parameters minutely around SPS1A point so that selectron mass changes while 0 mass remains fixed.

Generate ‘infinite’ (~1000 fb-1) at each point to compare to 115 fb-1 data sample; minimize 2 vs. mselectron to find best-fit selectron mass.

Repeat for 120 independent data samples; statistics from spread around mean rather than directly from 2 contour.

SPS1Amselectron

CHI-Squared Distribution

0

2

4

6

8

10

12

14

16

18

0.0

8.2

16

.4

24

.6

32

.8

41

.0

49

.2

57

.4

65

.6

73

.8

82

.0

90

.2

98

.4

10

6.6

11

4.8

12

3.0

13

1.2

13

9.4

14

7.6

15

5.8

16

4.0

17

2.2

18

0.4

18

8.6

19

6.8

20

5.0

21

3.2

22

1.4

22

9.6

23

7.8

24

6.0

25

4.2

26

2.4

27

0.6

27

8.8

28

7.0

Energy GeV

CH

I-S

qu

are

d

142.457

142.767

143.112 (SPS1A)Only area of significant CHI-Squared difference

Noise

Maybe a little help from here

Defining the Fit Region

Nothing, Beamspread, Smearing + Beamspread

0

50

100

150

200

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450

0 8

16

25

33

41

49

57

66

74

82

90

98

10

7

11

5

12

3

13

1

13

9

14

8

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1

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2

27

1

27

9

28

7

Energy

Co

un

ts

Nothing

Beamspread

Smearing +Beamspread

Noticeable effects from both, however smearing is much more significant

Not really an effect here

SPS1A template (high statistics) setMass of right selectron = 143.112Beamspread = .16%

CHI-Squared Distribution

0

2

4

6

8

10

12

14

16

18

Energy GeV

CH

I-S

qu

are

d

142.457

142.767

143.112 (SPS1A)

Choose fits region carefully (depending on smearing/beamspread) to avoid noise from flat region of the

spectrum.

Endpoint ranges used:Lower5.2 - 6.4 GeVUpper269.2 - 273.2 GeV (no smearing)267.8 - 274.6 GeV (smeared;

.16% beamspread)267.2 - 275.2 GeV (smeared;

1.0% beamspread)

Smeared vs. Unsmeared

0

20

40

60

80

100

120

142.2 142.4 142.6 142.8 143.0 143.2 143.4 143.6 143.8Mass GeV

CH

I-S

qu

are

d

Unsmeared

Smeared

Detector smearing does make a difference; how much?

Selectron Mass Study Scenarios

12 scenarios were considered:

Detector Resolution

Perfect (no smearing) and SDMAR01

Detector Coverage

|cos| < 0.8 and |cos| < 0.994

Beam Spread

0%, 0.16%, and 1.0%

RMS Error / Error on Error COSTHETA 0-.8

0.0730.078

0.194

0.1060.111

0.200

0.000

0.050

0.100

0.150

0.200

0.250

-0.10% 0.10% 0.30% 0.50% 0.70% 0.90% 1.10%Beamspread

RM

S E

rro

r

PERFECT

SDMAR01

First, just look in the central region (|cos| < 0.8)

Error for COSTHETA Ranges

0.0380.046

0.086

0.0730.078

0.194

0.080

0.0900.097

0.1060.111

0.200

0.000

0.050

0.100

0.150

0.200

0.250

-0.01% 0.19% 0.39% 0.59% 0.79% 0.99% 1.19%Beamspread

Err

or

PERFECT 0-1

PERFECT 0-.8

SDMAR01 0-1

SDMAR01 0-.8

Now, include the full region (|cos| < 0.994)

0.046

0.104

0.064

0.076

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

-0.10% 0.40% 0.90%

Beamspread

RM

S E

rro

r

0.078

0.089

0.113

0.128

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

-0.10% 0.10% 0.30% 0.50% 0.70% 0.90% 1.10%

Beamspread

RM

S E

rro

r

SDMAR01

NO MATERIAL

PERFECT RES-OLUTION

PERFECT RES., NO MATERIAL

|cos| < 0.8 |cos| < 0.994

Is it the point resolution, or the material?

Tentative Conclusions to Draw

1. For cold-technology beamspread (0.14%), SDMAR01 resolution has not reached the point of diminishing returns

2. Due to the stiffening of the spectrum in the forward region, there is a surprising amount of information there.

3. Detector resolution is even further from ideal in this region. If there is forward SUSY production to be measured, there is much to be gained by improving the detector

4. In the central region, point resolution is dominant. In the forward region, material may also comes into play.

5. Need to explore these conclusions further, and use studies to develop reasonable goals for forward tracking.