I LHC finishes proton-proton collisions in 2018

[dukwon]

We've had three fills with 600b. There needs to be another using 96b trains.

The timetable for the week is filled in (see below). A lot of the commissioning steps have been completed already, but there are still a few more to be done in the next couple of weeks. It's going to be solid physics from Friday afternoon and over the weekend. Optimistically, if a step in https://lpc.web.cern.ch/RampupPolicies.htm takes 4 or 5 shifts (20 hours stable beams in 3 fills), the 1200b step could start on Sunday morning. Compare this with the schedule for the year, which says 1200b on 11th May.

 

[mfb]

Stable beams with 987 bunches (96 bunches per injection). The initial luminosity was 80% the design value, and 60 collisions per bunch crossing for ATLAS/CMS have been achieved.

Luminosity statistics
ATLAS/CMS are at 0.5/fb, about 1% of the target for this year.

 

[mfb]

2300 bunches, with an initial luminosity of more than 150% the design value (~175%?). This exceeds the luminosity record for regular data-taking from last year.
0.5/fb collected in a single 14 hour long fill from midnight to 2 pm.

 

[dukwon]

The next steps are 2460b and then 2556b. I think they've abandoned the policy of 3 fills per step. I'm happy that LHCb is getting at least 400 Hz/μb, and may this last the rest of the proton run.

A combination of controlling the corrector-magnet current and adding "bumps" to both beams has dramatically reduced the spikes in losses around 16L2.

 

[dukwon]

Stable beams with 2556 bunches per beam. The intensity ramp is finished, and the machine is in full swing for physics production.

 

[mfb]

LHC Report: The LHC is full!
The peak luminosity reached 2.1*10³⁴/(cm²s), or 210% the design value, roughly the same as the record from last year and equal to the absolute luminosity record set by KEKB (with electron-positron collisions).

Apart from the usual interruptions (schedule) the focus is on getting as many collisions as possible.
An important measure of the beam focus is beta*, the smaller the better, but smaller values tend to create problems elsewhere in the accelerator. The LHC now starts with 30 cm. Later in the run, when the beam currents dropped sufficiently, this is reduced to 27 cm and then to 25 cm. Similar to the reduction in crossing angle: It cannot prevent the luminosity from decreasing over a run, but it makes it decrease slower.

Collected (integrated) luminosity:
11/fb for ATLAS and CMS (target: 60), 0.35/fb for LHC (target: 2).
~16 weeks remaining, ATLAS and CMS got 8/fb in the last two weeks, a naive extrapolation gives 64/fb extra, or about 75/fb for the whole year. The same naive extrapolation predicts 2.5/fb for LHCb. Even with some delays the goal looks realistic.

 

[alejandromeira]

Well, those experiments will show us, that there are not beyond the standard model... once again, one year plus.

 

[mfb]

We know the SM cannot be everything. It doesn't work at very high energies. The question is not "is there something new", but only "where is something new".16/fb for ATLAS and CMS, a rate of 0.5/fb in the last 10 days. Still on track for 60/fb or a bit more.

 

[alejandromeira]

We know the SM cannot be everything. It doesn't work at very high energies. The question is not "is there something new", but only "where is something new".

Yes, surely this is the truth.

I like the standard model because there are only a few number of fundamental particles, and then it's a sign of beauty.
I Would not like that the number of fundamental particles grow up like the elements of the periodic table.

But only nature has the answer, not our wishes. ; -)

 

[Islam Hassan]

We have collisions:
View attachment 223916
View attachment 223918

I can’t possibly believe that they can actually image the proton bunches! Is that what we’re seeing in the lower of the two pics or it is something else?IH

 

[mfb]

The lower image is an computer animation highlighting some detector components that saw some collision product flying through them. Other detector components are darker/more transparent. In addition some reconstructed particle tracks are marked with orange lines.

Here is a similar one, but zoomed in. I think the cones mark regions with a very high density of tracks ("jets").

 

[websterling]

Currently, as of June 12, the LHC is in Machine Development, to be followed by a short Technical Stop and a Special Physics Run before returning to luminosity production on July 4. Integrated luminosities are exceeding goals and the machine has been in stable beams ~50% of the time.

From an article on the CERN web site:

On Tuesday, 12 June, luminosity production was interrupted for a block of machine development sessions, during which no fewer than fifteen different aspects were addressed by experts. This will be followed by a four-day technical stop to perform the necessary maintenance, repairs and minor upgrades to the machine, as well as the experiments. Before resuming luminosity production on 4 July, the experiments will perform special physics runs, for which low luminosity is generally needed. Until then, the aim is to keep the luminosity production high – as I write this report, the integrated luminosity counter for ATLAS and CMS is at 23.1 fb-1, exceeding our goal of around 18 fb-1, while for LHCb, we are at 0.8 fb-1 with a goal of 0.6 fb-1.
​

These two articles present a good overview-
LHC Report: Standing strong through the storms
LHC Report: Running towards a production break

 

[websterling]

After a few minor problems, the LHC is again colliding 2556 bunches per beam. The current fill has been in stable beams for about 28 hours as of now.

 

[websterling]

An update from CERN-

LHC Report: Back in production

 

[mfb]

Mainly quiet weeks of data-collection so far. 30/fb for ATLAS and CMS, 1.1/fb for LHCb.

The LHC accelerated electrons! Well, not on their own, but lead nuclei with a single electron still bound to them. The main goal was not collisions, it was mainly a test for a potential future use of the LHC as intense source of gamma rays. The idea: Accelerate lead ions with a single electron, shine light in the visible/UV range against their direction of motion. In the frame of the lead ions this looks like x-rays. If the energy is right, it can excite the ion. It quickly returns to the ground state, emitting x-rays again (in its rest frame). Back in the lab frame these x-rays are photons with energies of up to hundreds of MeV. While other facilities can reach the same photon energies with electrons and lasers, lead ions would provide a source millions of times brighter.

Such a bright source could be used for photon-nucleus or photon-photon collisions, as source of polarized positrons or muons, as neutron source and more.

LHC accelerates its first “atoms”
The Gamma Factory proposal for CERN

 

[Vanadium 50]

Mainly quiet weeks of data-collection so far.

Don't say that! If you do, the PS might lose 18 kV power!

Drat! The PS just lost 18 kV power.

 

[atyy]

Don't say that! If you do, the PS might lose 18 kV power!

Drat! The PS just lost 18 kV power.

Ah, so you physicists are just as superstitious as us biologists!

 

[mfb]

The discovery of the Higgs->bb decay, announced early July, got some media attention. http://press.cern/press-releases/2018/08/long-sought-decay-higgs-boson-observed.

I didn't find an updated luminosity plot for all years so I made one myself based on an older one and http://lpc.web.cern.ch/cgi-bin/plots.py?year=2018.
The black bar marks the end date (but not the final integrated luminosity!) of proton-proton collisions in 2018, afterwards we get lead-lead collisions for a few weeks.

 

[mfb]

https://home.cern/cern-people/updates/2018/09/lhc-report-final-days-run-2

ATLAS and CMS reached 53/fb. More than in 2017. Just 3/fb more to reach the overall Run 2 (2015-2018) goal of 150/fb.
LHCb reached 2/fb.

4 weeks of data-taking remaining (+1 week for special runs), ending October 27. In November we'll get lead-lead collisions.

All of 2019 and 2020 will be used for detector upgrades, Run 3 of the LHC will start in 2021.
Both LHCb and ALICE will work on major upgrades for their detectors. Starting in Run 3 LHCb will read out all of its detectors at the full rate as this information is needed to efficiently select interesting events.
ATLAS and CMS plan smaller upgrades, they will do their major upgrades 2024-2026.

 

[mfb]

Proton-proton collisions ended over night. Now we get a few days of machine development, followed by a technical stop, then lead-lead collisions from Nov 8 to Dec 2.

Final integrated luminosities are 66/fb for ATLAS and CMS, 2.5/fb for LHCb, 0.027/fb for ALICE, nicely above the expected values.

A lot of groups now can look at the full datasets and finish their analyses, we will probably get many results from searches for new physics in the next months.

 

[websterling]

Also, Long Shutdown 2 will follow the Pb-Pb collisions, so no more p-p collisions till May, 2021.

 

[dukwon]

Ion run is over. LS2 started about 2 hours ago.

 

[websterling]

This is the LHC Status Page 1 this morning- There is some humor in the comments.

 

[mfb]

From the point of view of the experiments (especially LHCb) the energy situation is a bit annoying. You want your Monte Carlo simulations to be realistic, which means they should be at the energy the accelerator will run. Probably 14 TeV, but if the magnets can't be trained enough we might end up with 13 TeV or maybe 13.5 TeV. Do you do 14 TeV simulations now and risk that they become less useful? Do you delay the production until the energy is fixed and have less time for proper phase 3 preparation? Something in between?

For searches for heavy new particles (->ATLAS, CMS) the upgrade to 14 TeV is quite useful, so it is worth trying it. I don't know how LHCb thinks about this - they mainly look for decays of lighter particles and their production rate doesn't go up that much with 14 TeV.

 

[dukwon]

We produce MC for physics analysis after the data has been taken and we know what the conditions were. There is some Run 3 MC (at 14 TeV) but it's for detector upgrade studies, not physics analysis.
Our 2017 MC productions are only just starting now

 

[mfb]

You still have to optimize the trigger and so on.

ATLAS and CMS use MC produced in advance extensively for searches - you get results faster that way. Ideally the analysis methods are essentially fixed once the data comes in and you just have to run it over data and do all the various cross checks.

 

[websterling]

Run 2 is over and Long Shutdown 2 has started. No collisions till Spring 2021.

As usual, CERN has a number of interesting summaries-

A successful conclusion to Run 2

LHC Report: Another run is over and LS2 has just begun…

Key plans for the next two years of the LHC

 

[mfb]

LHC experiments share highlights for 2018

Nothing revolutionary but still nice to see progress.