UK news from CERN Issue 9: 20 November 2012 In this issue:
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Action stations at ATLAS – preparing for the upgrade
Industry meets the buyer – engineering contracts up to £30M up for grabs
What’s next for particle physics – BBC Radio 4 goes beyond the Higgs
People news – Celebrating Sir Chris Llewellyn-Smith FRS
Dates for the diary
Action stations at ATLAS
As LS1, the first long shutdown approaches,
ATLAS engineers and physicists are on
standby, ready to start the first of several major
upgrades to their experiment. With the amount
of work to be done, the schedule is tight.
The ATLAS
experiment
© CERN
SemiConductor Tracker (SCT)
The SCT is a silicon strip detector that is one of
the tracking detectors at the heart of ATLAS. It
is made of more than 4,000 modules that are
tiled over four concentric barrels around the
beam pipe and nine discs on each of the end
caps.
Working on
the ATLAS
SCT barrel
© CERN
It is designed to reconstruct the trajectories of
charged particles that are the debris that
emerge from proton-proton collisions at 14TeV.
“From these particle trajectories, we can reconstruct what happened in the most
interesting collisions and look for rare physics
processes,” explains project leader Steve
McMahon from STFC Rutherford Appleton
Laboratory (RAL). “But there are a lot of these
charged particles produced - one billion every
second - and the detector has to be able to sort
the wheat from the chaff.”
From conception to first operation took around
20 years; the SCT was designed, developed
and built in more than 40 institutes from 15
countries on four continents. The barrel (central
section) was assembled at RAL and the
University of Oxford, and the end caps were
assembled by the University of Liverpool and
Nikhef (Netherlands). Once installed,
commissioning the SCT took three years, but
those painstaking checks and calibrations have
paid off – the performance of the tracker has
consistently exceeded expectations.
During the first long shutdown in 2013-2014, a
new silicon pixel layer will be installed around a
new smaller beam-pipe to get even closer to the
collision point at the LHC. This Insertable Blayer (IBL) helps spot the production of very
short-lived particles, such as B-hadrons, but has
to be very radiation hard. Silicon sensor
technologies worked on by the Universities of
Glasgow, Liverpool and Manchester help to
ensure the required radiation survival.
Written and edited by Stephanie Hills, STFC Communications and Innovation Officer @ CERN Stephanie.hills@stfc.ac.uk or Stephanie.hills@cern.ch Page 1 “One of the interesting things about silicon detectors like the SCT is that to mitigate the
worst effects of radiation damage caused by the
proximity of the SCT to the LHC beamline, the
detector needs to be kept below 0°C all the
time,” says Steve, “and this will include much of the time during the long shutdown. So, while
other operations teams are getting a wellearned rest in 2013 and 2014, we have to keep
a close eye on the detector with regular ‘health checks’ in the form of calibrations.”
The SCT is enabling a long stream of graduate
students to learn about how silicon technology
works and extend the body of knowledge on
these devices. Even now the successor to the
SCT is being designed in universities around the
world, and planning is already in hand for the
installation of a new detector after 2022.
Trigger and Data Acquisition System (TDAQ)
So how do you sort the wheat from the chaff?
And how can you be sure that you haven’t missed something of interest in the data that
you’re rejecting? The answer is a sophisticated three level Trigger system and Data Acquisition
System (DAQ) designed to select which events
should be recorded for future analysis and
which will be ignored.
Steve Hillier (University of Birmingham) is Level1 Calorimeter Trigger Deputy Coordinator, “The Level-1 Trigger sees every collision, but within
two millionths of a second the specialised
electronics have to decide which events to keep
or reject. The selection rate is approximately
one in 1000.”
Steve’s part of the Level-1 Trigger (designed,
built and installed by the University of
Birmingham, Queen Mary University of London
and STFC Rutherford Appleton Laboratory)
identifies electrons, photons, jets and missing
energy. 56 Cluster Processing Modules are
equipped with 30 different programmable chips
to identify the collisions of interest. Another part
of the Level-1 Trigger identifies muons.
The Level-2 and 3 Triggers comprise a
computing farm of commercial PCs.
Testing of Level-1
Calorimeter Trigger
Cluster Processor
Module at Birmingham
© CERN
The Level-2 Trigger takes an average of four
hundredths of a second to reduce the number of
events from 75,000 to 6000 per second further
by applying a more detailed filter in which the
event must satisfy several specific criteria, for
example, a signal in the calorimeter compatible
with that electron and spatially consistent with a
track identified in the SCT.
The Level-3 Trigger further reduces the data
using a yet more complex filter in an average of
four seconds. After this stage, around 400
events per second are recorded at CERN’s Tier0 Data Centre and then disseminated to the
Tier-1 data hubs around the world including the
STFC Rutherford Appleton Laboratory.
“The filtering implements the scientific goals agreed by the ATLAS collaboration,” explains Chris Bee (CPPM Marseille and Deputy
Trigger/DAQ Project Leader. “Each filter or trigger imposes a set of criteria on events. Only
events satisfying these criteria are passed to the
next filter. Triggers can be changed to meet new
science goals. New ideas have to be approved
by the collaboration to make sure that they will
deliver ‘good physics’ and then evaluated for
their technical feasibility. Once approved, new
triggers undergo very rigorous testing before
they can be applied.” With so much data being rejected, how can the
physicists be sure that they have captured the
right data?
David Francis (CERN and Trigger/DAQ Project
Leader) is responsible for the DAQ and works
closely with Chris: “ATLAS was never intended to capture the data generated by every collision.
The Standard Model and other models that
Page 2 Written and edited by Stephanie Hills, STFC Communications and Innovation Officer @ CERN Stephanie.hills@stfc.ac.uk or Stephanie.hills@cern.ch ATLAS studies, tell us that in many cases the
physics we want to study (including new
physics) can be characterised by relatively
simple objects that individually we understand
well, such as electrons and muons with a lot of
energy. In turn sophisticated and detailed
computer simulation of the ATLAS detector tells
us what signals these objects generate in the
ATLAS detector. These are the signals and
combination of signals that the three level
trigger is designed to capture. Without this
selection, even with today’s computing technology, analysis and management of the
data would be insurmountable. The DAQ is the
glue that holds the experiment together. It is a
large distributed computing system used to
orchestrate the capture of data from the
detector; it moves the data between the three
different stages of the Trigger and finally to
storage - eight full DVDs worth of data every
minute!”
The LHC is already outperforming expectations
and contingencies built in to ATLAS technology
have been reached. The planned increase in
luminosity in 2015 will enable higher collision
rates - more data require more efficient decision
making.
During LS1, the Level-1 Trigger will be
upgraded to perform spatial correlations
between signals and therefore make more
precise decisions about keeping or rejecting
data. This will enable the Level-2 and 3
Triggers to continue working at similar data
thresholds. But this is not a long-term solution
and, like Steve McMahon, the Trigger and DAQ
teams are focused on future major upgrades.
Phil Allport of University of Liverpool is the
Upgrade Coordinator for ATLAS. He is already
spending far more of his time at CERN than he
had anticipated. “Planning for LS1, which starts early in 2013, LS2 (three years after the LHC
resumes in 2015), and LS3 (early in the next
decade) keeps us all very busy. For the UK, the
largest upgrade programmes are upgrading the
Trigger throughout this period and replacing the
whole inner tracking detector with a vast, finer
segmented, radiation-hard silicon array at LS3.
However, there are many aspects of software,
computing, physics preparations etc which will
need to evolve significantly over these
timescales and other major parts of the
experiment are undergoing major upgrades
which impact on us all.”
“History shows that we should anticipate a long programme at the LHC,” says Phil, “For example, the Tevatron collider in the US
operated from 1986 to 2011, much longer than
predicted. By 2022 the LHC will have exceeded
its original design lifespan. We’ll be upgrading with technologies that simply didn’t exist when the experiment was first proposed, to explore
the frontiers of physics in ever greater detail.”
For David, this is opening up new frontiers, “Our ambitions are getting bigger and we’re having to anticipate capabilities for the unknown.”
Industry meets the buyer
Mechanical and civil engineering companies in
the UK will have the opportunity to learn more
about international science organisations
including CERN at an event designed to help
them win contracts up to £30M.
The Meet the Buyer event on 21 November has
been organised by STFC and UKTI.
International science projects and organisations
in which the UK is a member will give
presentations detailing their mechanical and civil
engineering requirements. Representatives
from the companies will then have the
opportunity to discuss their capabilities in ‘oneto-one’ meetings with procurement and technical specialists from the projects.
The UK has a better record in winning CERN
contracts in the 10-750K CHF range but it is still
only reaching approximately 50% of the target
level. The personal contacts created at Meet
the Buyer events can make all the difference,
particularly as CERN procurement procedures
vary according to the size of the contract – a full
tender process is used for contracts over 200K
CHF, but at the other end of the scale, CERN
purchasers or staff can place orders direct with
companies for up to 10K CHF.
Current civil engineering opportunities at CERN
include constructing new buildings and
Page 3 Written and edited by Stephanie Hills, STFC Communications and Innovation Officer @ CERN Stephanie.hills@stfc.ac.uk or Stephanie.hills@cern.ch laboratories, renovating existing buildings, air
conditioning and ventilation. Mechanical
opportunities include contactless optical
measurements, ultra high vacuum and ultraprecision machining.
Structural repair and refurbishment contractors,
Concrete Repairs Limited (CRL) has recently
won a €1.3M contract to clean and repair the
exteriors of CERN buildings. The contract
covers surface cleaning using high pressure
water jetting and abrasive blasting, and concrete
repairs including applying coatings to improve
the protection for steel reinforcements.
“This is our first time working with CERN,” says Kevin Jones of CRL, “and we’re enjoying it. There have been a few teething problems along
the way, but it has been a useful learning
process and we believe that this will pay
dividends when we want to apply for future
contracts. We would certainly like to continue
working with CERN.”
The STFC website provides details on CERN
tender opportunities and any UK companies
wishing to engage with large-scale science
facilities can join the Innovations Club.
What’s next for particle physics?
BBC Radio 4’s Frontiers programme has been at
CERN to interview
scientists about the next
challenges in particle physics.
Presenter Tracey Logan visited LHCb with Tara
Shears (Liverpool) to learn more about the
imbalance between matter and antimatter.
Other interviewees on the programme include
CERN Director General, Rolf Heuer, John Ellis,
Jon Butterworth (UCL), Gavin Davies (Imperial),
and Ben Allanach (Cambridge).
You can listen again to the programme on the
Radio 4 web site.
People news
Sir Chris Llewellyn-Smith
FRS
On 20 November, CERN is
hosting a symposium to
celebrate the 70th birthday of
former Director General Sir
Chris Llewellyn-Smith and his
considerable contribution to
theoretical and experimental physics. During
his time as DG, the LHC was approved and
work started.
The CERN symposium will cover key elements
of Chris’ career in physics including updates on the LHC, fusion energy, theoretical physics and
SESAME, the project to build a synchrotron light
source in the Middle East (Chris is President of
the SESAME Council).
Speakers will include the current DG of CERN,
Rolf Heuer, Lyn Evans (project leader for the
LHC and now leading development work for the
proposed CLIC and ILC linear colliders), John
Ellis (CERN and King’s College London), Steve Cowley (Culham Centre for Fusion Energy) and
Chris Allsopp (Oxford Institute for ENERGY
Studies). How to subscribe To subscribe to (or unsubscribe from) UK News
from CERN, please contact jill.little@stfc.ac.uk.
Back issues of UK News from CERN are
available from the archive.
Diary dates
LHC on Tour at Welsh Senedd – 27 Nov-2 Dec
CERN Council – 10-13 December
Brits@CERN meeting – 13 December (5pm)
LHC shutdown – mid February 2013
CERN Industry open day – 27 September 2013
CERN public open day – 29 September 2013
Page 4 Written and edited by Stephanie Hills, STFC Communications and Innovation Officer @ CERN Stephanie.hills@stfc.ac.uk or Stephanie.hills@cern.ch