Getting to Higgs

Finding Evidence for B: Threshold Decay Length
Data from 292 B events are in an Excel spreadsheet that looks like this table. To find the threshold decay length:

  1. Sort the data by descending decay lengths, dt.

    Run

    Event No.

    B Mass
    GeV/c2

    ptB
    GeV/c

    dt
    cm

    Velocity
    v/c

    Lab Lifetime
    sec

    Rest Lifetime
    sec

    Bin

    65160

    642324

    5.277

    7.966

    0.388

     

     

     

     

    66500

    89978

    5.274

    20.508

    0.940

     

     

     

     

    Get the data.

  2. Make a histogram of decay lengths.
    Rather than graphing all the lengths as individual points, physicists group the data. They consider the range of the data and divide it into "bins" of equal size. A histogram is a graph of the number of events in each bin vs. the bin range.

    We are looking for the smallest decay length that fits the exponential curve. This will indicate the length of the decay as detemined by that experimental run.

    Choose a bin size that you think might give good results. You may have to bin your data several times based on what the histogram looks like. If your bins are too small, the data has too many peaks and valleys. If your bins are too large, you cannot see a peak. Excel will "bin" your data for you. You should see a new page open up with two columns similar to the table on the right.

    Bin

    Frequency

    20

    3

    22

    13
       

    120

    2

    Help with data analysis.

  3. Plot frequency vs. binned decay lengths.

    How does your histogram look? Do you need to try a different size bin?

What does the data tell us?

  1. What is the threshold decay length based on these data?

  2. Could any of the Bs in your data decay outside the beam pipe (radius 2.5 cm)?

References

Assignments: Identifying B