I’m off to Geneva for a couple of weeks. While I’m there I’ll work on the test beam for the ALICE electromagnetic calorimeter. I’ll tell you more about that in the next posts. But I thought I’d share with you the contents of my long trip survival kit:
A travel pillow, a bandana (which serves both as an eye mask and a lazy hair style), an outlet adapter, a netbook and mini-optical mouse, ear plugs, an mp3 player with a 30 hour battery, a hair brush and extra hair bands, two change purses (one for Euros, the other for Swiss Francs) and little mini-toothbrushes with toothpaste already on them. I don’t deal with sleep deprivation very well so these flights are never very fun – but they’re easier to take than flights between the US and Asia.
Tags: travel
dear Christine
I hope, you have a nice time in Geneve.
May be, you can help me. Nobody till now gave me an answer, why the luminosity of Alice in comparison to Atlas etc. is so low.
Can you find it out and inform me?
Thanks
Jochen
Hi jochen,
Alice is not built for pp-collisions, it was designed
for heavy ion collisions (lead f.e.).
Here is a thread with some hints:
http://www.lhcportal.com/Forum/viewtopic.php?f=17&t=658
I’m not sure but I believe the detector is optimized for
a lower collision rate but to “see” more “debris”/collision.
So if the time between the collisions is too short
it may simply not be ready (either the physical detector
parts, the trigger logic or the DAQ).
At least the term “pile up” would point to that behavior.
Joerg.
Hi Jochen
ATLAS and CMS are optimized to search for extremely rare processes – like production of the Higgs – which requires fast detectors and as many events as possible (high luminosity.) ALICE is optimized for bulk processes – looking at the majority of particles produced. ALICE’s primary tracking detector is a Time Projection Chamber – which is great at tracking charged particles, but is a slower detector. It is more difficult for us if the luminosity is too high because we can get another event in the detector before we have recorded the data from the last one (called pile-up.) Therefore, the luminosity is lower at ALICE – by design.
Hi Joerg
Actually ALICE does just fine with proton-proton collisions. And I have to refute some of the statements about ALICE on that forum. Clearly ALICE was ready for data and interested in proton-proton collisions – we published the first paper from the LHC!
Dear Christine
Thanks, I am relieved, that Alice is no disinvestment.
Can you explain the special results you hope to find during the runs starting in november?
Jochen
Hi Jochen
I wrote about the motivation for lead-lead collisions here:
http://blogs.uslhc.us/the-quark-gluon-plasma
The first results we’ll get will be measurements of particle multiplicities – like the early results from proton-proton collisions (http://blogs.uslhc.us/alices-second-paper) but in heavy ion collisions. This actually will give us a lot of information – early estimates for the number of particles created in a central lead-lead collision at 5.5 TeV ranged from 2000-8000.
In the first year we’ll have results that will give us information about the viscosity of the quark gluon plasma and its energy density.
And even though ATLAS and CMS were optimized for rare processes, both ATLAS and CMS have heavy ion programs and will be competing with ALICE.
Hi Christine
I’ve been following the experiments at LHC for quite some time, and must say that I really look forward to the heavy ion collisions scheduled for November (if I’m not mistaken?). What will be the maximum energy that you hope to achieve in the Pb-Pb collisions this year? I think I’ve heard 2.80TeV or something, is that correct?
Furthermore, I thought I would ask you one thing that I’ve seen mentioned on different forums on the net. Perhaps you,ve heard that some people claim that heavy ion collisions could cause a decay of our hypothetical false vacuum?
Personally I think it sounds insane, but nevertheless, what are your thoughts on those claims? Are they even based on any actual science, or are they just fringe claims with a touch of pseudoscience?
I must admit, those claims scare me quite a bit and any thoughts on it would be deeply appreciated.
Best regards
Richard
Hi Richard
The current plan is for lead-lead collisions at a center of mass energy of 2.75 TeV in November. We are really excited!
There are several claims that the LHC will do something terrible that will destroy the planet. CERN has a page debunking these rumors:
http://public.web.cern.ch/public/en/lhc/safety-en.html
And The Daily Show’s response is a personal favorite of mine:
http://www.thedailyshow.com/watch/thu-april-30-2009/large-hadron-collider
The same people claiming the LHC will destroy the world also claimed that the Relativistic Heavy Ion Collider would destroy the world when it turned on, and they were wrong then too. What they’ve done is take some of the more exotic scientific conjectures and distort them beyond recognition or any link to science. Unfortunately alarmist claims make better press than deliberated scientific discussions. Safety is boring. No newspaper will run a headline, “The LHC will be completely safe.”