SLEPTON MASS RECONSTRUCTION AND

DETECTOR RESOLUTION

Bruce Schumm

University of California at Santa Cruz

ALCPG Workshop, Snowmass Colorado

August 14-28, 2005

Special Recognition: Troy Lau, UCSC senior thesis student (now at University of Michigan)

Motivation for Study

• Is there information on Slepton masses in the forward region?

• Can we detect it above backgrounds?

• Are our detectors up to the task?

In doing the study, we also found that questions can be raised about the central region.

THE UCSC SUSY GROUP

Past

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

Troy Lau (Now at Michigan) Paul Mooser (Software engineer)

Adam Pearlstein (now at Colorado State)Joe Rose

Present

Ayelet LorberbaumEric Wallace

Matthew vegas

Work accomplished by exploiting UCSC’s senior thesis requirement…

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

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)

TESLA (0.13)

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. Due to the stiffening of the spectrum in the forward region, there is a surprising amount of information there. For this scenario, most of the information on slepton masses lies in the forward (|cos| > 0.8) region.

2. For cold-technology beamspread (0.14%), SDMAR01 resolution has not reached the point of diminishing returns. The physics seems to be limited by detector resolution. Point resolution is the dominant issue.

3. Any gains that can be made in p resolution in the forward region would reap large rewards for light sleptons.