Please find the answers to the referee reports

Report on JINST 015T 1109

Date: December 16, 2009

Author(s): CMS Collaboration

Title: Fine Synchronization of the CMS Muon Drift-Tube Local Trigger using Co

REPORT JINST

Received: 2009-11-26 06:54:45.0

The article requires some minor revision prior to acceptance, according to

the following remarks made by the referee:

Referee report

General comments

Throughout the paper the reference [8,9] are extensively cited but the to

studies are exactly orthogonal. In the reference [9], in fact the method for the ﬁne synchronization relies

of the ﬁnding of the maximum of the ratio ’number of HL/ number of HH’

which represent the worst phase due to the problem of using absolute eﬃ-

ciency in a changing luminosity environment as LHC collision will be. Here instead is used the ratio of ’number of HH / number of triggers’ due to the fact the the cosmic rate is stable. Why it is not clear cited the fact that the change of LHC scenario has pushed in this direction?

R. The method presented in reference 9 is not orthogonal to the method presented here.

In Reference 9 it was point out that the use of the ratio ’number of HL/ number of HH’

allows to be independent on the possible variation of beam conditions in the different runs necessary for performing the scan.

In the method of Reference 9 we could have used the ratio ’number of HH/ number of (HH+HL+LL+H)’ that is the

' number of HH/ number of total DTLTt ’ .

Here, as stated already in the introduction, making advantage of the fact that with the DT drift time signals we measure the time of tracks, and of the fact that cosmic rays have a flat distribution, we showed that

we could perform the measurement of the efficiency distribution as function of TTCrx delays of all chambers before LHC start_up.

With LHC data we have only to identify tracks from pp in the Muon Barrel Detector and measure their time position.

Obviously the new method has a larger advantage with the lower luminosity in the first phases of LHC operations but that was not the reason of the new method ; the main reason is the simplicity.

Another general remark. There is no mention to the global alignment

strategy. it is important to understand the impact of the ﬁne alignment on

the global trigger eﬃciency. At page 14 it is clearly stated the the expected

global alignment will be of the order of 3 BX with an overall eﬃciency of

∼80 %. So just relaxing the request on the track quality (HL) in the trigger

will achieve the same level of eﬃciency. I agree that if one can correct should

do it, but then this is relevant only after the global alignment is within 1 BX.

R.

The global alignment strategy is reported only shortly in the text since it is discussed in another paper; anyway we had measured with great accuracy the alignment with cosmic rays ( as explained in the “Performance of the CMS Level-1 Trigger during Commissioning with Cosmic Rays” (http://arxiv.org/abs/0911.5422). For LHC, taking into account the Time of Flight from tracks from IP we are confident that we could have a coarse synchronization alignment within 1-2 Bxs.

The reported range of three BX s is due to the fact that we can measure accurately the time if we have not more then ~3 Bxs latency spread.

On the other side the Fine synchronization is an aspect specific of the data and the trigger electronics of each chamber; the coarse instead is related to the relative synchronization of the different chambers and it is performed checking the DTLTs at the input of the DTTF which correlates the DTLTs of different chambers. Because of that the fine synchronization is not related to the coarse synchronization ( while the coarse is related to the fine).

The importance of having the best possible quality with the maximum efficiency is due from one side to the fact that in each chamber only two DTLTs can come out and they are chosen depending on the quality; from the other side the DTTF starts checking global tracks from the DTLTs with higher quality.

Section 2

• caption of ﬁgure 2:

OK perhaps it would be worth to mention the reference in the caption

and the fact that this is taken with external scintillator trigger

• page 3

the phrase:“This structure is intrinsic to the BTI” please clarify

OK the meaning the phrase:“Since this plateau has a width of 10∼15 ns, we need a

∼ 1 ns” from the picture the plateau is less than 10 ns, in fact in

reference [9] it is clear stated ∼8 ns. perhaps would be better to

say ∼10 ns. Moreover would be worth to mention that the track

time resolution is ∼ 2 ns.

• caption of ﬁgure 3:

Modified If you are phase aligned with leading edge don’t you risk to in-

crease the marginality? I would imagine that you align with the

other edge in the middle of the clock to make it less sensible to

the jitter due to diﬀerent eﬀects that contribute. But this is not

what shown on the ﬁgure. Also the speciﬁcation “As will be seen,

this value is similar for all chambers.” here seems not relevant

without specifying why as you will do later.

Section 3

• in the second paragraph and also the foot note could be better

Reference added understood if the coarse BX alignment strategy would have be

explained somewhere.

• ﬁgure 4

You don’t need to put the whole scan. perhaps just 3-4 are enough

and in case you can then avoid to specify the jump of BC due to

the change in latency.

We think that to have the full scan shown is more complete even if the data had the change of BX

Yes • ﬁgure 5

is not easy correlate with the value in ﬁgure 4. If I understood

correctly the entry in the plot are equal av×25 ns

• page 8 - ﬁrst paragraph

Not essential. Sentence removed the phrase “The distribution after the delay adjustment is nar-

rower.” is trivial as it is evident from the plot.

Section 4

• page 4 - ﬁrst paragraph after title

Not essential. Sentence removed the phrase “The result, i.e. the optimal phase, is an intrinsic

property of each chamber and is independent of the actual value

of the TTCrx delay.” is obscure.

• ﬁgure 7

I like this picture because makes clear why you need to use the

HH quality and that the ﬁgure 1 is the folding of this in 25 ns.

Why not use this since the beginning and later cite the measure

at test beam?

Cwe prefer to start with what was known ( result of the many runs of the scan of test beam with muon always at the same BX and triggered by scintillator ) and present after the results of the cosmic that is fix delay and different track time wrt the clock .

• ﬁgure 8 – caption ( figure 9 ..I suppose)

Corrected “No result is shown for a few chambers for which a high voltage

channel was disconnected, or for which the trigger primitives were

not read out.” can be “Some chambers are missing because they

could not be read-out or they have the HV disconnected”

• ﬁgure 10 - caption

Comment included the double peak should be comment also here not only in the text.

Section 5

• here once again I would expected a comment about the general

Comment included alignment (BX level and ﬁne one).

• ﬁgure 12

I don’t understand the information of this ﬁgure. The range are

forced to 25 ns and the shape are obviously diﬀerent.

The 25 ns range is just the range with entries ; is not forced. Comments have been added in the text.

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