TOP 2015: Top quarks come to Italy!

16 September 2015 | By

The annual top conference! This year we’re in Ischia, Italy. The hotel is nice, the pool is tropical and heated, but you don’t want to hear about that, you want to hear about the latest news in the Standard Model’s heaviest and coolest particle, the top quark! You won’t be disappointed.

ATLAS,ATLAS Blog,updates
The poster session, two hours in. (Image: CERN)

DAY 1:

Our keynote speaker is Michael Peskin. For those of you who have a PhD in particle physics, you already know Peskin. He wrote that textbook you fear. His talk is very good and accessible, even for an experimentalist like myself, and he gives us a very nice overview of the status of theory calculations in top physics, highlighting a few areas he’d like to see more work on.

The highlights of my day though are the ATLAS and CMS physics objects talks. Normally, these can be a little dull. However this year we have performance plots for the first time at 13 TeV, and most people are closely scrutinising the performance of both experiments. All except a guy who looks suspiciously like Game of Thrones character Joffrey Baratheon, who is sitting completely upright, eyes closed and snoring lightly.


If you’ve never been to a poster session then this is how they work: a group of students and young postdocs, eager to present their own work (a rare treat in collaborations as large as ATLAS and CMS) stand around, proudly showcasing how they managed to make powerpoint do something that it really wasn’t designed to do.

My poster (approved only hours before) gets a fair bit of attention, but not as much as I expected. Suddenly I regret not slapping a huge “New 13 TeV Results!” banner on the top of it.

After 3 hours (yes, 3 hours!) of standing by my poster I decide that everyone who wants to see it will have done by now, grab 3 (or 10) canapés and head to the laptop in the corner to cast my vote. For a brief moment I consider not voting for myself, but the moment passes and I type in my own name.

Now the speaker moves on to the precision 8 TeV results. Wait a minute? What’s going on? There are other 13 TeV results to show? What is he DOING?! Months of working on the ee and µµ cross section results and we’ve skipped past them?

DAY 2:

I sit down next to Joffrey Baratheon and smile at him politely. It’s not his fault he’s an evil king after all. We start the morning with some theory, because we’re mostly experimentalists and everyone knows our attention spans are limited if they give us wine with lunch. As with last year, the hot topic is ever more precise calculations.

Next we have a very professional talk from a very professional-looking CMS experimentalist. People who wear shirts and sensible shoes to give a plenary talk either means serious business or a terrified student giving their first conference talk. From the polished introduction on top cross-section, you can tell it’s the former.

CMS have clearly put a lot of effort in to these results (and I’m secretly relieved that I already know our results are equally impressive), and despite a spine-chillingly large luminosity uncertainty of 12%, they have achieved remarkable precision.

Finally, we’ve arrived at the talk that I’ve been waiting for: the ATLAS Run2 cross-section results.

ATLAS,ATLAS Blog,updates
A summary of the latest top anti-top cross-section measurements from ATLAS. (Image: CERN)

The speaker starts by flashing our already released cross-section in the eµ channel at 13 TeV. Even with an integrated luminosity uncertainty of 9%, it’s still a fantastic early result. We show an updated eµ result in which we measure the ratio with the Z-boson cross-section (effectively cancelling the luminosity uncertainty). People seem pretty impressed by that, as they should. Getting the top group to release results this early is hard enough, getting the standard model group to release an inclusive Z cross section is nothing short of a miracle.

Now the speaker moves on to the precision 8 TeV results. Wait a minute? What’s going on? There are other 13 TeV results to show? What is he DOING?! Months of working on the ee and µµ cross section results and we’ve skipped past them? I turn to my colleague, who led the also-skipped lepton+jets cross section analysis. His face is stoic, as is his way, but inside I know he’s ready to storm the stage with me. I begin to whisper to my boss, sat one seat ahead of me, about the injustice of it all. Somehow it’s coming out as a childish tantrum, despite sounding perfectly reasonable in my head.

… and then the speaker shows the result. My boss rolls her eyes at me and returns to her laptop, possibly rethinking my contract extension. Joffrey Baratheon scowls at the disturbance I’ve caused and I consider strangling him with his pullover.

Stay tuned for part 2! Where we learn about new single-top results, new mass measurements, and ttH!

James Howarth