Minutes and Summary

Main purpose of the meeting: Intensity and filling scheme for 2025, high intensity test, pO/OO/NeNe

LPC minutes 10th February

Present:

Chiara, Chris, Catrin, Paula, Rosen, Andrej, Robert, Filip, Matteo, Stephane Willocq, Anna Sfyrla, Clara Leitgeb, Giulia Negro, Lorenzo Bonechi, Manuella Vincter, Reyes Alemany Fernandez, Joanna Wanczyk, Daniele, Maciej Trzebinski, George, Kalus Monig, Ivan Amos Cali, Cedric Hernalsteens

 

Intensity and filling scheme for 2025, high intensity test, pO/OO/NeNe (Chris)

 

S8:

Paula: for plan 4, when could the switch to 5x36 be?

Chris: after ~3 weeks of running, around Whit (~1 week before TS1).

 

S9:

Catrin: how important is it to go to 1.8e11? If we can reach it within the cryo limit and 4x36 and we go up to 1.79, would this be sufficient? Is there a real push to reach 1.8? If not, we could keep the filling scheme and go up to something close to 1.8.

Matteo: 1.8 not a magic number, it is the goal of Run 3 and we just want to see if we can operate with higher intensity. If it is 1.8 or 1.75, it doesn’t really matter.

George: Just to remind that when we’re talking about intensities, we talk about ranges. When we discuss 1.6, it is in fact a range between 1.58 and 1.65 (does he mean the cryo margin here, or the range in intensity? I think the cryo range – he means the intensity – each bunch has a slightly different intensity and also each fill is a little different as we talk about the number at stable beams, so they inject more and then lose a little which varies fill-to-fill). If you assume that 167 is the margin, then you’re already running at the margin of cryo at 1.6. 

Chris: 170 includes 10 W/hc margin on the cryo side. So there is a bit of flexibility.

George: this is for the end of the year. Instead if you’re proposing a change during the physics, you might still have the recovery from the de-conditioning over YETS that you’re not running with. You might not have recovered the value of the ecloud that you had at the end of 2024. I think you are running at the limit. So increasing the intensity by 0.2, at that milestone (9th June) is meaningless and it is worth saying that we won’t do it. By choosing the 4x36, and saying that we start with the intensity of last year, which is a range of intensity that can reach up to 1.65 ppb knowing that the intensity limitations from cryo with that filling scheme is between 168 and 170 W/hc, implicitly you’re saying that if you stay with 4x36, you don’t have the possibility of an intermediate step of the intensity increase. 

Chris: the cryo people say that there is a little bit of margin. Their numbers say that we have 15 W/hc that we can play with. And the filling scheme takes only half of that (how do you know? – this is the difference between the 3x36b with 1.6 and the 4x36b with 1.6 in the table 156->164 https://indico.cern.ch/event/1469359/contributions/6233004/attachments/3001183/5292890/LHC-the-end-game.JW.Cham24.pdf ). So if we get back at the conditioning that we had at the end of last year…

George: but you have only 3 weeks of beam.

Chris: looking at last year (at the “Toroid period’), it seems that it took three fills to get where we were before. In each of the red circles, it seems we go back after three fills, after 1 week of no beam, rather than months. 

George: but we don’t know. We know that scrubbing relies on scrubbing throughout fills.

Chris: we have to wait and see. Unless we stay with 3x36, it might be that indeed we won’t be able to go very far, this is a fair statement. 

George: Going back to the table on s. 8, I thought we’d have a large gain in lumi for LHCb when going to 5x36, but I don’t see it.  

Chris: this is because they are levelled on luminosity. So they’re getting less luminosity per crossing but more collisions. They like this because they decrease the mu by spreading the luminosity over more crossings. For total lumi it is the fill length that dominates, this is why they get more with 4x36.

George: I imagine we’d get even more with 3x36

Chris: yes, the fill length becomes longer, you get more luminosity but they have higher pileup per crossing. 

George: the 3x36 for ATLAS and CMS, would it change drastically these figures? 

Chris: the lumi was 131 fb-1, I think. It is a smaller difference than from 4x36 to 5x36.

George: so it means positive in all cases. With 3x36 you have even more margin to increase the intensity.

Chris: but it increases the pileup per crossing and the experiments have expressed that they want to decrease this: the statement from the experiments is that they are willing to pay a small price in decrease in integrated luminosity for a decrease in the luminosity per crossing. because the experiments prefer to pay the lumi for the pileup.

George: do we have a target pileup for ATLAS and CMS?

Chris: the target luminosity is 2.15e34, which gives the pileup in the table. 

Catrin: if we run with 3x36 like last year, we’re at 64 pileup with a 1.5% variation, if we’re at 4x36 we are at 62-62.5, with 5x36 we’d arrive at 60.

George: so you’re requesting 62 as pileup?

Catrin: initially we’ll probably level a bit lower during the intensity ramp up, but then we can see how the detector commissioning goes with the trigger commissioning, which basically sets our luminosity target. If we get 2.1e34, then the pileup will be around 62 - 62.5. 64 is if we run with 3x36. 

Chris: it is not that the experiments die with higher pileup, but the events are cleaner, and it is easier to trigger the rare events. It is a smooth behaviour.

Catrin: and we have less to read out. So overall it is a bit easier.

Chris: but it is a smooth scale.

Filip: same as Catrin said is true for CMS.

 

S10:

Catrin: if this (“Alternative is to run 8b4e in 2026 with 2.3e11”) means to run the entire 2026 with 8b4e, then the comment is no.

George: what is the fraction of the lumi test with 14 days compared to the physics time?

Chris: quite close to 20% (for pp time). 

 

S11:

Robert: for pPb, when is it the threshold to make both directions efficient? Say we lose two days for the higi lumi test, one day from Ne, then would it still be efficient?

Chris: it is still possible to do both ways, then it takes about 2 days to switch, and you need another VdM campaign. So it is about 3 days lost in total. So if you’re looking at this, then I think there are 21 days originally, we’re losing 3 (high lumi + Ne), then you’re losing 6 days in intensity ramp up plus 2 days for switch plus VdM, you’re not looking at many days per configuration. You can take the presentation from last year, to see the loss. Probably it is 20% loss in luminosity in total by doing the switch.

Catrin: do the symmetric experiment need a VdM in both directions?

Chris: yes because the luminometers see the stuff from the collisions, so all t4 experiments need a VdM campaign again. 

 

Paula: I have a concern about the fact that these full days for MD (in PbPb) could then turn into 2, then we have the 14 days of tests and we lose more from ions… sounds a quite big loss, and I am wondering about the efficiency in general. 

Chris:...even having a HI program at all?

Paula: yes.

Chris: at the moment, if 2 days are lost for the test and 1 day of NeNe, then it is the same length as 2024 and therefore it is significant and efficient. If it takes much more than that, then yes, it becomes a very short heavy ion.

Paula: yes, this was to support the request for detailed planning.

Chris: I suppose we can assume that 4 days are taken from MDs, because I suppose that some MD are done already. 

Matteo: there is no real planning yet, like I said last week. For now we just put the test in the planning, if it is accepted, we’ll work out a plan. 2 weeks is not a completely random number, but it stays a reasonable guess. 

Chris: but I expect that some contingency is already included, in case something shuts you down for 2 days.

George: the problems that you expect to arise cannot be solved in 2 days.

Matteo: this is not what he’s saying, what he means is that if you have to stop for 2 days for whatever other reason, you can still do the tests. But it depends on what you put in the planning: that you circulate for a while, that you discover that you don’t have limitations… It depends on what your goal is. If we have some stop in the planning, we’ll do a bit less, but maybe the test will still be successful.

Chris: 2 days are a kind of buffer.

George: somebody said at a certain point that we need an order of a week of running at a given intensity to understand if you’re slowly deforming something that can create a problem. Like the BSRT problem that was evolving over a week or other things. We might say that we need beams for at least some time.

Chris: this implies that you are continuously running like quite long fills for a week. Therefore the low mu suggestion has some weight behind it. If you’re trying pure 8b4e, hybrid schemes, 48 bunch schemes, 36 schemed… then you’re chopping and changing.

George: 3x36 is ruled out for high lumi. 

Chris: but you have 72 potential… if you’re trying different things all the time, we cannot do the low mu. 

Filip: we can do like a mix, change for some days, and then to look at stability, keep the same configuration (filling scheme…) and during those days we could do the low mu physics. 

George: if we do 8b4e scheme, we can run for all the 14 days. 

Chris: I am assuming you are not going to ramp on day 1 for the full 8b4e scheme.

George: during MD we should have covered quite some part of the injection. Left only with the heating, quickly filling the machine. The plan needs to be populated. Most likely we’ll accumulate all exotic MDs at the end. 4 days from MD is a fair figure for MD studies. Important is that the test is ruled from the experiments point of view in 2025. 

Chris: at least from ATLAS. We are waiting for a statement for CMS. 

Filip: but for the last 2 weeks you could go to 8b4e, no?

George: in 2026?

Filip: yes, for the last two weeks, not the beginning of the year.

George: the point is that if we want to really see if we arrive at the point of breaking something, we need to put the maximum load that we have, which we don’t have with 8b4e. 

Matteo: but if you want to go to top energy, you have no choice. 

George: This is a limit only to protect the dump.

Filip: but this is not a strong argument for the last 2 weeks.

George: that is why it is put in the last 2 weeks. It’s like going beyond all the real limitation of the machine with 1.8

Matteo: every time we discussed to do this at top energy, we never discussed doing this at low beta. Just to be clear. So far we wanted to ramp it up and keep it there. We have not discussed to go to 60 cm. But everything can be discussed.

Filip/Chris: no need to squeeze so much, 1.5 m would be ok.

Robert: so if we run 10 days with pp low mu, does it mean that we still need to take the 2 days from PbPb, or can we take everything from pp?

Chris: no response :-). But we can also run at 8.9 and get some reference data. If you want to do commission of optics at this energy, to take the pPb reference. Which could also be useful to take pPb at top energy. But maybe it is not ideal.

 

S12:

Paula: the ½ day of MD for collimation, does it have to be in working hours?

Chris: it can be during the night.

 

S14: 

Chris: can we agree to move on when the target is reached?

Lorenzo: yes, agreed.

 

S18:

Robert: we also discussed to run at lower energy in OO, which implies that we need to run longer to reach the target. Is this then scenario A?

Chris: we’re already assuming that we’ll run at lower energy, and this might be too slow and take longer. Roderik is trying to work on the estimates, the projections will be shown at the next LBOC meeting. From informal work by him, it looks tight for OO, but he’s optimistic that the pO will be done in the right time and maybe we manage to advance the program a little bit on that side (so it balances).

Robert: what about the commissioning time?

Chris: this is not mentioned.Some of this is kind of floating commissioning time, so we hope that is can slot in when we are waiting for a checklist to be completed, during the intensity ramp up for example, when they spend the morning on the hw side checking the output of the different things. So I did not explicitly mention where the additional commissioning time would come from. I hope it is kind of floating stuff that can be done at any time because it is safe beam, then we can find some slots when it can be done efficiently. But for now it is unclear.

 

S17:

Paula: when are the injection tests for NeNe happening?

Chris: week 15, which is the 2nd week of april. When they do the test, they’ll check the contamination and how much time it takes to switch the source. If they find that it takes too long, it will probably be discarded. They hope it’ll take under 6 hours.

Paula: I know that we’re waiting for Roderik’s projections, so probably the following week we’ll know more, right?

Chris: yes, in the LPC meeting of 24th.

 

S15:

Reyes: for pO, option B, very last bullet, you say you allow 3 extra days: do you mean on top of the 8 days?

Chris: in case we cannot capture the O beam, or we cannot transfer it to the LHC, or if the bkg is too high in the experiments are we’re unable to take the data… Something whose implication is that we cannot do the physics program. Then we’ll try to fix the issue for a maximum of 3 days. Then we’ll have to go back to the management, what happened. So yes, if magically after 2.9 days we fix the problem, this would mean to prolong by 3 days, and the physics program would last three more days than allocated now.

Reyes: do the experiment know or have a feeling about the contamination of O in the Ne beam that is allowed?

Chris: I suspect that they have to go back to the ion groups and this might take some time. Because then there will be NeNe, NeO, OO and you’ll get a mix of the three. It’ll get some time. Do you have an idea of the level of contamination?

Reyes: we don’t know yet, maybe in the meeting this week it will be discussed, but it will be more of a guess. 

Chris: maybe 10% is unacceptable, or 20% is unacceptable…?

Reyes: after the meeting we might know what is the contamination that is expected. A feeling should be there this week, but it will be a guess.

Chris: a ballpark will be useful. After that meeting, we’ll mail the experiments contacts with the expectations, then we’ll come back to you.

Reyes: On 21st Feb I am giving a presentation at the IEFC and I will be asked to have an official position from the experiments for the NeNe run. Do you think that by the 21st Feb you will have a kind of official position?

Chris: probably not by the 21st, You might need to say something like on S18, and I can prepare a statement.

Reyes: Ok. I find it reasonable what you state, that whether to do NeNe depends on OO. It might also be a good thing to get more papers with NeNe than with more lumi for pp. 

Catrin: it depends on many delays, and  on how much lumi we lose for pp. 

 

S19

Filip: concerning the “updated desire for CMS”: the 0.8 is always what was used for the yellow report, where it was mentioned 0.5 because this is the used lumi (recorded), while 0.8 is delivered. 

Chris: 0.5 is what is written in the yellow report by all 4 experiments.

Filip: but that is recorded. This is what the CMS HI says.

 

S19:

Paula: you wrote that the physics case for lower energy is very strong. Is there a simple distillation of this?

Chris: the presentation at the Opportunities workshop, there is a presentation by someone from ATLAS. I will send the reference (from later exchange, here for completeness: Slides 18 on-wards of [https://indico.cern.ch/event/975877/timetable/#28-atlas-contribution](https://indico.cern.ch/event/975877/timetable/#28-atlas-contribution) explain why a pp reference at the same energy is very important to ATLAS (and in general - note CMS also wants this, so does ALICE if it doesn't take too much time). The alternative is to extrapolate from other datasets -- this solves the energy dependence but doesn't allow for the efficient cancellation of systematic uncertainties (more important in jet measurements than tracks). In the same meeting the ALICE speaker shows that such an extrapolation can work well [https://indico.cern.ch/event/975877/timetable/#27-alice-goals-and-projections](https://indico.cern.ch/event/975877/timetable/#27-alice-goals-and-projections) Both are using similar variables in this case (not jets). (There are recordings of both talks)).

 

Stephane: back to the question of intensities: the integrated lumi difference is not very small, but what about stabilities, robustness, and risk factors? Of course it is hard to quantify… But at the end of the day you want the highest luminosity and maybe the other factors are more important than the 2% increase in one area only. 

Chris: I agree, availability is the most important. What could impact availability? Pushing the intensity has the risk of hitting cryogenic limits, and you lose in that sense. But also the change in the filling scheme, that is why I say that 5x36 is a larger perturbation compared to 2024. This could also lead to a problem in the injectors. Both could decrease the availability but in a way that cannot be predicted. People are generally happy that 1.7 won’t cause significant availability issues, but 1.8 they are less confident about. So maybe 3x36 at 1.8 is probably a bit riskier. But it hasn’t been expressed that going to 5x36 is a bigger/riskier perturbation. Obviously, doing something similar to last year that works well makes sense, but we also know that if we have more collisions then we keep the intensity low, that’s quite safe. It is a bit difficult in this phase space to know where the best availability would come from. And all the integrated numbers are very similar.

Stephane: yes, I’d suggest keeping this in mind.

Chris: sure, we’ll do, but it is just unclear whether it is better to not change, to change one thing or the other. 

 

Paula: I have a much precise question about the intensity ramp-up. We’d expect as previously the list of steps as defined by the MPP to be the 3/12/75/100/800… so on, and two fills going to the full process like last year?

Chris: yes, obviously the filling scheme will be different since it will depend on how many bunches will have in the train, but we’ll have the same steps.

 

CMS (Filip):

 

S2:

Filip: if and when splashed and SB at injection energy would be nice to know, when possible, and when we can do the PPS beam based alignment. 

Chris: about the splashes: I don’t know, but there is a suggestion for the handshake on 21st March (with a Friday as backup).

Matteo: for the last bullet (Beam Based Alignment), we’ll let you know. For the splashes, this depends on you, because they are not needed by us. Splashes at P2 and P8 come from free when we start injecting, but dedicated splashes in ATLAS and CMS we’ll only do if you want it, and stable beams at injection as well. For the PPS, does it mean that the work is completed? Because I’ve seen in the planning that this is expected till mid March.

Filip: as far as I understood, one of the two vacuum went down last week, this week the other one, then the backout should be done in 1 week. Order at the end of next week, it should be done. We are in advance because the rotation went well. But please double check with the LHC experts from vacuum. 

Robert: did you say that there will be SB at injection?

Filip: on request.

Matteo: if you want it. It takes some time off our schedule, but if you want it, yes.

Filip: we’re not particularly asking for it, but if someone wants it,we will happily take it.

Andrej: What is the overhead?

Matteo: It depends on what you want: if you want three bunches, it should be a shift or two. It is not a big deal for us, it is not something that we need to do, but we can. 

Paula: what date would it be?

Matteo: fairly early, approx 1 week after we start. Maybe this is not the ideal moment, and we should see, but we can do it as early as after one week.

 

S3:

Chris: for the high lumi test, you prefer to wait till the end of 2026?

Filip: if there is the risk of breaking anything, then we should wait. If they want to play with a few bunches in 2025, it is fine, the full machine is the problem.

ATLAS (Catrin):

S2:

Catrin: is it possible to do a test for the lumi quality flags? This is something we changed following this one day when we stopped providing luminosity but we were still giving collisions, and then I got a panic call for the cryo of the triplet. This is something we’d like to test. Whom should we contact?

Matteo: Michi. To relax you: we have a workaround, and we don’t have to rely anymore on your data only. We now have a more robust system. But it is good to test, so check with Michi, to see with all the other activities.

Catrin: it could be done during the handshake test.

 

Catrin: how likely is it that after the transfer line test, planned for a Thursday, you keep the beam in?

Matteo: It very much depends on how the rest progresses. But I’d be not surprised if we have beam also on Friday. We can try to put the transfer line test a bit earlier, and if you’re ready then you can have the beam. 

 

S5:

Matteo: we might find some synergy to combine the high mu request with an MD.

 

Matteo: x-angle plane scan for ATLAS ZDC easy to arrange

 

S6:

Chris: lumi program is quite long. 

Klaus: for the VdM, this is what we estimate for the request, even if long. We can shorten it if we decrease the precision on the luminosity.

 

Chris: you don’t need LSC for OO because it is the same optics as PbPb, but if we’re at a different energy, is that still the case? And potentially a different squeeze which we might not do (and stay at 1 m)? 

Catrin: but we’re running at 0.5 m right?

Chris: this would take additional commissioning, so it depends if it is worth it or not. 

Catrin: that would need to be discussed.

Klaus: actually we need a LSC anyway because it is a new beam. We’re planning to have a short one for the 5%. It will be short because we don’t need the linearity but we need the slope.

Catrin: I will add it. 

 

Giulia: isolated bunches fill: was it 1/week last year?

Catrin: no, it was every few months. This is probably the same frequency for this year.

Giulia/Filip: and we liked it, we’d keep it as last year.

 

ALICE (Robert):

 

Robert: does the machine prefer a polarity for OO and pO? We don’t have a preference. We’d just like to not change between pp and pO/OO.

Matteo: we don’t have a preference either.

 

LHCb (Paula):

 

No comment.

 

AOB:

 

Chris: Discussion on Wed morning with Joachim and spokespeople. The high intensity test will also be mentioned, in case you have comments, let me know.