A subset of IPP
Canada group has read your paper "The Underlying Event in Hard
Interactions at the Tevatron ppbar Collider". We would like to thank you
for doing this important study. Following please find our general and specific
comments.
Thanks.
General Comments:
_________________
1. It
would be very useful if you better motivate this study
by rewriting the introduction in a more coherent way. Your study
looks at the effects of different physical phenomena as a
package, and it can not make a clear distinction between these
effects. Although we appreciate the fact that it would be
unrealistic to expect that one can make such distinction, we
believe that it would help if you comment on this in the
introduction, so the reader do not see this study as purely
technical.
A: I re-wrote the abstract to try to provide some more motivation for the measurement presented in the paper and to make the study seem less of just a technical exercise. I believe the introduction itself already presents a fairly clear case of what we are measuring and why.
2. Although
the study of the interjet soft gluon radiation is
important, unfortunately we do not know a way to be able to
specifically look at these effects (using data) and they have
not been discussed in this paper either. Can you explain if you
know of any method to study this effect and if yes could you
include it in the introduction too? If this is only to say that
these effects are also included in the underlying event that
you study here, maybe you do not want to emphasise on it as
much as you do now. In other words, the way the introduction is
written right now, it seems this is one of the main motivations
for your study, even though you do not make any conclusions
about this effect.
A: Interjet radiation can be studied precisely by the manner
outlined in the paper; looking at the energy contained in regions away from the two main hard
jets and comparing the measurements to Monte Carlo predictions. Our conclusion
was that both Herwig and Pythia agree with the data qualitatively, with the
Herwig agreement being better. This indicates that the approximate description
of this radiation contained in the Monte Carlos is reasonable.
3. We
are confused about your choice of vertex quality for the MB
study. What do you mean by "all vertices" and "high
quality
vertex"? How does the "medium quality vertex",
defined on page
5, fit with the two? We didn't find any explanation on why and
how the two different MB samples are defined.
A: I donıt know of a quantitative way of defining a class 12 vertex for a non-CDF user. In the paper, a ³high quality vertex² is defined as corresponding to a high track multiplicity and a ³medium quality vertex² to a lower track multiplicity. I added the words for the latter that it results from a beam-beam interaction rather than a beam-gas interaction. Is this specific enough? I would welcome a better wording.
Specific comments:
__________________
Abstract
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1. It
is not customary to include references in abstracts.
A: I removed the references from the abstract and put them in the introduction.
Page 3
2. You mention that this
study is complementary to your previous analysis, however the way it reads now,
the previous study seems very similar to the current one. It would be useful if
you add a few sentences to explain how the two differ?
A: Rickıs analysis looked at charged particle jets from 0.5 to 50 GeV/c at 1800 GeV. This analysis looks at the data samples used to define CDFıs high ET jet analyses at 630 and 1800 GeV, i.e. starting at 40 GeV/c at 1800 and 20 GeV/c at 630 GeV. Thus, there is little overlap with Rick. We also specifically look at min bias events. I added a sentence in the paper to the effect that these jet samples are specifically the high ET jet samples.
3. What
is the region in which you define your random cone for the MB events? A few
different |eta| regions have been specified ( for
example <0.7 on page 3 and <0.5 on page 7).
A: Thanks. I corrected the wording on p. 3 to say <0.5.
Page 4
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5. At
the end of the first paragraph, you say,"At both energies...the highest
energy jet is within the central rapidity region,
|eta|<0.5". We believe you choose the centroid of the
highest
energy jet to be within |eta|<0.5. Please clarify it.
A: You are correct. I changed the wording to say centroid.
Page 5
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6. Line
12: "...is evaluated by increasing these cuts..." we suggest
you use "loosening the requirements" instead of
"increasing the
cuts". The term "increasing the cuts" makes one
think that this is
a more stringent cut than what was used before.
A: Done.
7. Line
17, you write,"For all the measurements in this paper, the
statistical and systematic errors have been added in
quadrature".
This is not the case for quite a few cases (specifically in
Tables). We suggest you remove this sentence and add necessary
explanations for different measurements.
A: Done.
8. Line
20, "At 1800 GeV" -
"At sqrt(s) of 1800 GeV"
A: Done.
Page 6
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9. When
you say, " by decreasing the regularization scale of the
transverse momentum spectrum...", is there a significant
physics
which motivates this specific change? or is it just one of the few
parameters that one has to play with? It would be nice to add a
few
sentence to explain the physics motivation of it, if it is the
former.
A: I added a sentence explaining that such a decrease causes the double parton scattering component to be less hard, leading to a better agreement with the data.
Page 7
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10. We do
not understand the comment about the effects due to large angle soft gluon
emission, starting on page 6 continuing on page 7, "The effects due
to...to the energy in the cones is large". The
first part seems obvious while the second part seems to contradict
the first part. Could you explain?
A: We want the momentum in the cones to be larger than a few GeV/c so as to reduce the contribution from the soft underlying event. We want to build up a logarithm (log[p_T^jet/(p_T^max+p_T^min)]} so as to make the effect from the radiation appreciable. I added a few more descriptive words to the text.
11. Line 8,
"...the simulations than in the data." - "...the
simulations compared to the data."
A: Done.
Page 8
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12. When
you require a high quality vertex for your MB events, you get a value of 0.57
GeV on average per cone, while you get 0.36 GeV for "all vertices".
For P_{T}^{90,min} in jet events, you get 0.45 GeV,
and argue it is somewhat in the middle. However, you select jet
events with 1 high quality vertex, can you explain why the result
for P_{T}^{90,min} does not compare more closely to the high
quality vertex MB events? Is it because of underlying event energy
fluctuations (within one event) and the fact that if you use the
minimum cone you tend to select the part of underlying events
which fluctuates low?
A: Yes, thatıs at least part of the explanation. I donıt think
we want to draw a more specific conclusion in this paper.
Page 11
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13. We did
not find a single value being mentioned for the average
P_{T}^{90,max/min} in 1800 GeV (we have different values based on
jet Et), although single values were mentioned for sqrt(s) of 630
GeV and were compared to the ones at sqrt(s) of 1800 GeV. We
believe these single values are the average of the average Pts for
all jet Ets. It would be appropriate to mention them somewhere in
the paper (for example Table I?)
A: It is the average of all of the jet ET bins. On p. 11, we want to specifically compare the results at 1800 and 630 GeV. I donıt think there is a need to list the values elsewhere.
Page 15
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13. Just a
reminder about Acknowledgement...
A: Oops. Thanks.
Figures
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14. Could
you explain which point/line style corresponds to which
sample in the captions as well?
A: Wonıt that be a bit unwieldy? The legends in the figures should make the descriptions clear, right?
15.For the sake of comparison, it would be nice if you use the
same
binning and axes limit for figures 6 and 10. The way they are
right now could be confusing.
Can you center the axis titles?
A: Making changes to the figures at this point is going to be extremely difficult. The student who did the analysis has left physics.
We hope you find these comments useful,
Shabnaz Pashapour (for IPP Canada group)
Thanks for your careful reading.