dL/dz and L:Results and Plans

J. Thompson, A. Roodman

SLAC

MDI Meeting - July 22, 2005

2

Introduction

• Today: Present results as shown at PAC05

• Elaborate on the details

• Lay out a “To Do” list for the future

3

Reminder

2

00

2/2

1exp

zzyx

zzL

dz

dL

2

*0,* 1

2)(

y

effyy

Ly

zzz

• Using dimuon events, we can measure:

• the z distribution of luminosity dL/dz

• the (actual) sizes of the beam spot in x and y as a function of z: L

x, Ly

• (account for resolution by measuring it in data; using estimated vertex error)

A function of z, *

y

Extract *y, z/2, z0 from fit

Extract *y, y,eff from fit

4

Assumptions

• The formulas just shown make a few assumptions:

• *y = *y,HER = *y,LER

• magnetic waists are aligned with bunch crossing point

• z0 = z0,HER = z0,LER

5

Typical dL/dz fit

• Data from June 9-25, 2004

• Error bars are shown (tiny)

• Solid curve is best fit dL/dz; dashed curve is a Gaussian with width z/2

• 2/dof = 1.3

*y = 1.62 ± 0.04 cm

z = 1.580 ± 0.004 cm

6

Typical Ly(z) fit

• Ly extracted using 2m bias correction (taken from MC), as

are all results

• Data sample: January 6-19, 2004

7

Run 4Sep

tem

ber

2003

July

200

4

A couple Ly(z)

data points missing (too high)

Questions: A true upward trend?

Source of discrepancy between methods?

8

Caution: Very correlated with *y results,

very sensitive to bias correction from MC

yLERyHERyLERyHERy ,,,,eff, 2

Run 4

9

Lx

• This measurement is done well in MC

• Are these numbers about what people expect?

Run 4

From B. Viaud, C. O’Grady, W. Kozanecki PAC05 paper:

10

Another sample: more detail Adjacent bins early in Run 4

L x

z

11

Final examples From late in Run 4 (note Lx(z) behavior)

L x

z

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To DoCategory 1: Stuff I should have already done

1. Find and fix the overall bias of 2m on Ly

2. Figure out why the Ly(z) fits to hourglass MC do not work well

3. Better toy studies – both more sophisticated and more thoroughCategory 2: Explore these results

1. Fit correlations

• ~25% between sLx and sLy

• Make sure dL/dz fits are not being affected by bunch length changes (Witold suggested cross-checks months ago….)

2. Evaluate quantitative systematics due to bias correction (in progress)

3. Crosschecks: different binning in z (done—no changes), use only slices of , redo with L

x fixed, play with resolution function, SVT misalignment

4. Try to correlate some of the results we have with changes PEP-II made over the course of Run 4

13

To Do con’t

1. Rewrite fitting code (not sexy, but would probably help a lot of things)

2. Write documentation (a BAD)

3. Change assumptions?

4. Look at Run 5 data

5. Split fits by bunch number?

6. Suggestions?

Category 3