Baffle Design

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Baffles Design

Designing baffles from ray traces requires GEMC runs without baffles, but detectors at the baffle z positions.

Fitting trajectory paths
CLEO Baffle openings (before introduction of wedge)

We define as fixed number of blocks which expand over a radius that will accept the full angular range from the whole target. Each block then has a range in phi, which we fit shown in the figture.

Designing baffle openings

These are then considered, for each block over all baffles, to carve out an opening which does not allow particles below a momentum from making it through. There is a maximum opening which is defined from the number of sectors, along with a minimum "dead zone" which prevents photons.

First order efficiency curves

The efficiency can be estimated by considering the simple geometric arguments above, the two defining low and high momenta <math>p_{l}</math> and <math>p_{h}</math>, a maximum efficiency based on opening width (based on <math>p_{h}</math>) and number of sectors <math>n_{s}</math>, and a constant proportional to the field integral, <math>c_{Bdl}</math>.

The overall maximum efficiency is

<math>\epsilon_{max} = \frac{c_{Bdl} n_s}{2\pi p_{h}}</math>

Using one intermediate momentum <math>p_m</math> defined by

<math> p_m = \left( 1/p_{l} - 1/p_{h} \right)^{-1}</math>

there is an efficiency curve described by the piecewise function

<math> p < p_l </math>: <math>\epsilon = 0</math>
<math> p_l <p < p_m </math>: <math> \epsilon_{max} \left(1+\frac{p_h}{p_m} - \frac{p_h}{p}\right) </math>
<math> p_m < p < p_h </math>: <math> \epsilon_{max}</math>
<math> p_h < p </math>: <math> \epsilon_{max}\frac{p_h}{p}</math>


It is important to note the <math>\epsilon_{max}</math> is proportional to the field integral.

Baffle Design Results

Results for various fields, optimized with <math>p_h</math> of <math>x_{bj} = 0.55</math>.

SolidbaffleXeff.png SolidbafflePeff.png

The relative scale in efficiencies follows the relative field integrals:


Figure of Merit for baffle designs

Baffle code and file


see the "readme" file, then the note below

  • makebaf5.C_seamus is Seamus's original script which produce the "baffle_largerZ"
  • makebaf5.C_zwzhao is based on makebaf5.C_seamus, but with a few modifications listed below by Zhiwen to produce the "baffle_smallerZ_cutinner".
    • 1. the Z position for detector planes in "solout_CLEO_LD2_120d_nobaf_11GeV.root" was assumed to be 40,70,100,130,160,190cm, while they are actually 37.5,65.5,95.5,125.5,155.5,185.5cm
    • 2. The designed baffle Z is changed from 40,70,100,130,160,190cm to 40,68,96,124,152,180cm. The new Z position is to avoid overlap and leave room for GEM. There are 10cm reduction for the total baffle length in Z.
    • 3. The 1st baffle plane inner radius is fixed at 4cm. For other planes, their radius are determined by 21-36 degree polar angle acceptance from the full 40cm long target at Z=10cm.


  • baffle_largerZ_plot: files of "baffle_largerZ", produced by makebaf5.C_seamus, baffle geometry is defined in
  • baffle_largerZ_extrablock_plot: files of "baffle_largerZ_extrablock", produced by makebaf5.C_seamus with SCALE_LASTBAF = 0.20, baffle geometry is defined in
  • baffle_smallerZ_plot: files of "baffle_smallerZ", produced by makebaf5.C_zwzhao without limiting the 1st baffle plane inner radius at 4cm (which reaches about 2cm actually and create a lot radation), baffle geometry is defined in
  • baffle_smallerZ_cutinner_plot: files of "baffle_smallerZ_cutinner", produced by makebaf5.C_zwzhao, baffle geometry is defined in

For now (6/18/2013), consider "baffle_smallerZ_cutinner" as the latest baffle. The "" in SVN is actually the old BaBar baffle by Eugene. We shall update it once we finalize the baffle.

The background files with various baffles are here refer to Solid_Background#background

babarmore1 Baffles

  • Baffle parameterization [1], Rich

CLEO2 Baffles

Older Baffle Designs and Comparisons

Seamus' Baffle Comparisons

Eugene's BaBar Design in GEMC [3]
Eugene's for Other Magnets [4]
Basic New Designs [5]
New design from ray tracing [6]

Eugene's Baffles

Zhiwen's Evaluation of Eugene's Baffles in GEMC

Note: These are based on an incorrect implementation