STAR Muon Telescope Detector development

["Zetong Li" <li_vefree AT m.scnu.edu.cn>]

Hi Rongrong,

Thanks for your reply with great patience. It really helps a lot. I want to confirm if my understanding is correct: We use the vpd-mom events for centrality calibration, and in peripheral collisions where the vpd-mom efficiency is low, we apply event weight corrections. In the offline analysis, we simulate the vpd-mon trigger using |Vz - Vz^VPD| < 5 cm. Is this similar to how we require our triggered electrons to have pt greater than 3.5 GeV/c and adc0 > 300 in the offline analysis to simulate our BHT2 triggered electrons, and apply the same cuts to the electrons in the MC samples to estimate our trigger efficiency?

Additionally, I have another question: When we calibrate Centrality using MC samples, should the MC samples be produced similarly to the embedding samples to simulate the real detector environment, or should it be slightly simpler compared to our embedding Upsilon samples?

Lastly, I would like to argue that there seems to be a slight difference between multiplying refmult by a coefficient and directly adding or subtracting a value related to other variables. If we multiply refmult by a coefficient, it slightly changes the variance when we flatten the mean, whereas simply adding or subtracting a value from refmult seems not to.

Again, thank you for your detailed explanation. Hope you have a nice weekend.

Best regards

Zetong

 

------------------ Original ------------------

From:  "Ma, Rongrong"<marr AT bnl.gov>;

Date:  Fri, Aug 30, 2024 09:58 PM

To:  "star-mudet-l"<star-mudet-l AT lists.bnl.gov>;

Subject:  Re: [[Star-mudet-l] ] MTD local meeting 08/28/2024 10:00 am BNL time

 

Hello Zetong

We do not expect BHT2 plus vertex cuts to overlap with vpd-mon plus vertex cut. BHT2 requires the presence of a high tower, i.e. a BEMC tower with energy deposition above a certain threshold, in the event, which is usually generated by some hard process (in your case a Upsilon meson). Since hard processes are more likely to occur in central collisions than in peripheral collisions, BHT2 has a strong bias towards central collisions. In other words, if you plot RefMult distribution for BHT2 event, you will see that it is skewed towards to large values compared to the vpd-mon events.

For centrality calibration, one needs to use an unbiased or minimum-biased sample, not the BHT2 sample with a biased RefMult distribution, such that the true RefMult distribution is measured (modulo trigger inefficiency for low RefMult events, which is usually corrected for via event weights). This is why vpd-mon events were used for centrality calibration. To select good events, a |Vz - Vz^VPD| < 5 cm cut was applied. Then the question is can one apply such centrality calibration to BHT2 events? Actually, in principle one can not since BHT2 does not require vpd-mon conditions. Therefore, the possible small bias, even though it is minimal, introduced by vpd-mon trigger is not necessarily present for BHT2 trigger. To resolve this inconsistency, one can require vpd-mon conditions for BHT2 trigger by hand in offline analysis. This is why on slide 8, Te-Chuan has "nVpdHitsEast > 0" and "nVpdHitsWest > 0" on top of BHT2 trigger since these two conditions can mimic vpd-mon trigger requirements. Then on slide 9, he shows that after applying |Vz - Vz^VPD| < 5 cm cut on BHT2 events, the additional requirements of "nVpdHitsEast > 0" and "nVpdHitsWest > 0" do not reject any further events. This is understandable since to have a good Vz^VPD value that satisfies the 5 cm cut, one needs to have hits in both east and west VPD, which automatically satisfies "nVpdHitsEast > 0" and "nVpdHitsWest > 0".

I do not think there is a fundamental difference between multiplication and addition for correction. One can easily convert one operation to the other. As long as you can flatten the distribution (refMult vs. Vz or nSigamE vs. eta), you can choose either operation.

Best

Rongrong

On Aug 30, 2024, at 3:33 AM, Zetong Li <li_vefree AT m.scnu.edu.cn> wrote:

Hi Rongrong,

Thank you for your help. This slide answered a question I have ever had regarding how do we get the two curves used to reject pile-up events on the refMult vs nBtofMatched plot. However, I still don’t fully understand the slides. On the page 2, we see that the trigger we required is vpd-mon, while in our analysis, we use the BHT2 trigger. On the ninth slide, it shows that after applying the vertex cuts, the additional trigger requirements have 100% efficiency in both Ru+Ru and Zr+Zr collisions, but this doesn’t seem to indicate that the events triggered by vpd-mon plus applying vertex cuts can fully cover those triggered by BHT2 plus vertex cuts, which means that the events triggered by BHT2 plus vertex cuts are not completely the same as those triggered by vpd-mon plus vertex cuts. Am I correct and is that OK? Or does this have a minimal impact on our final results?

Additionally, When we correct the refMult for the impact of ZDC rates and Vz, we chose to multiply the refMult by a coefficient rather than adding or subtracting a value. Is this because the influence of zdcrates and Vz on the measurement of refMult is multiplicable? If so, in our nSigmaE correction, should we directly subtract a value related to eta or do the same thing like the refmult correction?

Best regards

Zetong

 

 

------------------ Original ------------------

From:  "Ma, Rongrong"<marr AT bnl.gov>;

Date:  Thu, Aug 29, 2024 03:29 AM

To:  "Zetong Li"<li_vefree AT m.scnu.edu.cn>;

Cc:  "STAR Muon Telescope Detector development"<star-mudet-l AT lists.bnl.gov>;

Subject:  Re: [[Star-mudet-l] ] MTD local meeting 08/28/2024 10:00 am BNL time

 

Hello Zetong

I found this presentation from Te-Chuan about centrality calibration for |vz| < 100 cm: https://drupal.star.bnl.gov/STAR/system/files/TeChuan_IsobarHT_20230301.pdf. See slide 2. Indeed, he used |vz - vz_VPD| < 5 cm cut for the centrality calibration, so I think you need to use the same.

Best

Rongrong

On Aug 26, 2024, at 1:43 PM, Ma, Rongrong <marr AT bnl.gov> wrote:

Hello All

We will have our weekly MTD local meeting at 10:00 am BNL time this Wednesday. Talk to you then.

Thanks!

Best regards

Rongrong

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