Transcript An Idea for testing the composition at the ankle

Testing for
composition transitions:
An outline of a new method
(Sorry no results yet)
Summary of GAP-2009-146
Patrick Younk
Pierre Auger Collaboration Meeting
November 2009
Composition:
A reliable
inference from
shower observable
to average nuclear
mass seems
impossible.
Very Important,
Very Difficult
E=1019 eV, q = 45º
Which model do you believe?
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We must ask questions that are
more manageable.
• Differential Measurements will be the key!
• E.g., the Elongation Rate method:
d X
E.R. 
• A changing E.R. signifies a composition
•
•
max
d (log E )
transition.
But this signature can also be created by
particle physics. 
The method described here can give a more
reliable indication of a composition transition.
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The signature of a composition
transition
Xmax
50%-50%
100%
protons
proton-iron
100%
iron
Data from Conex
showers with QGSjet.
Distributions
normalized so that
their sizes are similar.
protons
iron
Nm
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The Signature
Weak Correlation
p
Strong Negative
Correlation
p + fe
Weak or Positive
Correlation
fe
• Does not depend on: <Xmax>, RMS(Xmax),
<E.R.>, or similar Nm quantities.
• Does depend on: If <Xmax(A)> greater than
<Xmax (B)>, then <Nm(A)> less than <Nm(B)>,
where A and B each refer to a group
of nuclear species.
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Quantifying the Signature
Describe shape of the
Xmax - Nm distribution
with a correlation
factor:
cov(X , N )
r
max
We assume a 20% detector resolution for Nm
We assume a 20% detector resolution for Nm
m
 ( X max ) ( N m )
r changes predictably
during a transition: a
2nd order change.
• The signature is unique.
error bars: 10-90%
quantiles for sets of
200 events.
• Detection is statistically limited.
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Some Practicalities
• Use M(1000) instead of Nm.
• Xmax and M(1000) must be normalized to
an average angle and to a central energy
for each energy bin.
• M(1000) must have a resolution of about
40%.
• Need about 200 golden events in each
energy bin. Currently >234 between 8 and
16 EeV.
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Conclusions
Photo: Mary Younk
We can determine if the
composition is
transitioning with high
certainty!
Please read GAP-2009-146
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