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The ATLAS years and the future…

Nick Ellis

EP Division, CERN, Geneva

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The Large Hadron Collider• The LHC is a new particle collider

presently under construction at CERN

• Counter rotating beams of protons will intersect inside large detector systems– ATLAS is one of two very large

“general-purpose” experimental facilities that aim to cover a wide range of physics processes

• Very high energy (7 TeV per beam)– Enough energy to produce very

massive new particles (E =mc2)

• Very high intensity (“luminosity”) – Observable rate even for very rare

processes

• Huge potential for fundamental discoveries!

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Path of the LHC (ex LEP) tunnel

CERN

Airport

Mountains

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Physics rates at LHC

• Huge total rate of pp collisions– O(109) s-1

• Searching for processes that are predicted to be extremely rare– “Discovery physics” - either

confirm theoretical predictions or find something unexpected

• Enormous experimental challenges to separate new physics from much higher-rate Standard Model backgrounds– For many studies W, Z and top

particles, major discoveries of the last two decades, represent backgrounds

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The ATLAS detector

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The ATLAS R&D years

• Some key dates … 1990 – 1994– Jul 1990 - Detector R&D Committee (“DRDC”) set up

• Initiation of many R&D projects Optical links (RD23, etc.)

– Oct 1990 - Large Hadron Collider workshop (Aachen)• Discussions on the physics and the experimental challenges at LHC

– Mar 1992 - “Towards the LHC experimental programme” (Evian) • Expressions of interest by “proto-collaborations”, including ASCOT &

EAGLE which subsequently joined forces to become ATLAS

– Oct 1992 - ATLAS Letter of Intent submitted• Between 1992 and 1994 many technical choices had to be made that shaped

the ATLAS detector review panels

– Dec 1994 - LHC project approved

– Dec 1994 - ATLAS Technical Proposal submitted• Start of approval process that concluded in December 1995 (CERN Research

Board)

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Data acquisition in ATLAS• In order to explain the significance of

John’s optical-links work, I need to make a brief digression…– Bunches of protons cross in ATLAS every

25 ns, with a total pp interaction rate of O(109) s-1 (~25 interactions per crossing)

– A 1st level trigger system selects a small fraction of the bunch-crossings that are potentially interesting for physics analysis, reducing the rate to O(105) s-1

• While the 1st level trigger is working the information from all detector channels is stored in on-detector “pipeline” memories

– Event size O(107) bits

– Events selected by the 1st level trigger are then read out over “front-end links”

• 105 s-1 107 bits = 1000 Gbits/sec

• Low power and radiation hardness needed for inner-detector readout

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Detector R&D for the LHC

• John’s involvement in R&D on optical links started in 1992– RD23: Opto-electronic Analogue Signal Transfer for the LHC detectors

• Subsequently CMS adopted this principle for their tracking detectors, so one could say that John has contributed to CMS as well as to ATLAS!

– This led into work on evaluating optical links for reading out digital information from the ATLAS semiconductor tracker

• Later on (starting 1997) John took a wider view of optical links for ATLAS as joint coordinator of the front-end links working group

– Achieving considerable commonality across detectors in their choice of link technology, etc

• As head of the Birmingham HEP group, John gave strong support and encouragement for 1st-level trigger R&D– This resulted in Birmingham’s leading position in RD27 and,

subsequently, its important role in the ATLAS LVL1 calorimeter trigger

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Optical links for the semiconductor tracker

• Birmingham has played a major role in the area around the optical links for controlling and reading out the SCT– Important work on evaluating and selecting

the on-detector components that have to be small, low-mass (X0) and non-magnetic, as well as being able to withstand radiation levels up to:

• 10 Mrad

• 2 1014 neutrons per cm2

– Radiation tests performed at CERN, RAL, NPL and PSI, and also in Birmingham

• O/E components, e.g. PIN diode

• associated ASICs

• fibres

A gamma-ray source in Birmingham has been used for tests of radiation hardness of components for the links(Early work on SEE was done using the Birmingham Dynamitron)

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Calorimeter review panels (1993-4)

• At the time of the ATLAS Letter of Intent, there remained several options for calorimeter technologies in ATLAS

• John chaired the review panels that recommended the technologies to be adopted (now being built) – End-cap electromagnetic calorimeters

• Competing designs of liquid-argon calorimeters– So-called “accordion” design recommended

– Hadronic calorimeters• Calorimeters with liquid-argon or scintillator as the active medium

– Scintillating-tile calorimeter design recommended for barrel– Liquid-argon calorimeter design recommended for end-caps

– Forward calorimeters• Calorimeters with high-pressure gas or liquid scintillator or liquid argon as the

active medium– Liquid-argon calorimeter design recommended

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ATLAS calorimeter modules

HCAL extended barrelHCAL end-cap

ECAL end-cap Forward calorimeter

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The ATLAS Collaboration Board years

• Some key dates … 1995 – 1998– 1995 – 1998 was the period in which the ATLAS detector was designed

in detail• Technical Design Reports (“TDRs”) for all detector systems were prepared

and reviewed by a peer-review committee, the LHCC

– At the same time, the sharing of responsibilities was developed for a total construction budget of 475M CHF (about £200M)

• These commitments were formalized in the Memorandum of Understanding (“MOU”) submitted for signature by the Funding Agencies in 1998

• John served as the Collaboration Board chairman during this key period– 1995 Deputy CB chairman

– 1996/7 CB chairman

– 1998 Deputy CB chairman

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The Collaboration Board

• ATLAS is amongst the largest, if not the largest, scientific collaboration that has ever existed, with 150 institutes from 34 countries, and a total of about 2000 scientists and engineers

• The organization of such an enormous enterprise is very challenging and is achieved by various bodies– The Spokesman and the Executive Board, supported by Steering Groups

for each of the detector systems, are the executive side of the organization

– The Collaboration Board, in which each of the 150 institutes is represented, is the political side of the organization

• The chairman of the Collaboration Board is a key figure in ATLAS, working closely with the Spokesman and in contact almost on a daily basis

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Collaboration Board chairman

• Much of the work of the CB chair inevitably takes place behind the scenes– Work related to resources (talking to institutes and funding agencies)

• For example, John was instrumental in preparing the framework for funding construction of major items, such as the magnets, not associated with any single detector system

• This general area of the work was clearly of great importance in the period leading up to the MOU

– Helping to find solutions to all sorts of problems• Political, inter-personal, resources, differences of opinion on technical

issues, etc

• I know from the ATLAS spokesman that John’s calm and solid support during his term as CB chair was greatly appreciated

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Some other activities in the CB years

• From June 1993 until May 1996, John was the chairman of the LEP Committee (peer-review body for the LEP experiments)– During this period, LEP-I reached its full potential

• ~1.5 M Z0 events per experiment recorded in 1994, yielding a vast variety of precision measurements in electro-weak and other physics

• Numerous upgrades to the LEP detectors, e.g. improved vertex detectors that were important for B physics measurements at LEP-I and subsequently for Higgs searches at LEP-II

– It was also the time in which the machine upgrades necessary for LEP-II were made, with the addition of super-conducting RF cavities that allowed the energy to be increased above the W+W- threshold

• The first e+e- W+W- events were observed in August 1996

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The ATLAS construction years

• The construction of the ATLAS detector is well advanced, as is the associated civil engineering work– Construction of the ATLAS detector is in full swing

• Some large elements have already been delivered to CERN, for example components of the magnet systems

• Elements of the detector are being produced in industry and in the collaborating institutes around the world, including Birmingham

– The excavation of the ATLAS cavern has recently been completed • Now the cavern has to be prepared (concrete on walls, etc.) and the

infrastructure (electricity, water for cooling, support structures, etc.) has to be put in place

• Installation of the first detector elements will start in 2004

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Cryostat vessel for end-cap toroid magnet

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Work at Birmingham on the ATLAS SCT• John successfully worked to get Birmingham established as one

of the construction sites for the SCT, building up the necessary facilities in the university– The UK provides one of four “clusters” of institutes doing the construction

• Birmingham is responsible for all the hybrid construction for the UK cluster

A clean room equipped with an ultrasonic wire bonder is used to assemble hybrid circuits for the readout of the ATLAS semiconductor tracker

The assembled hybrids are tested on a water-cooled rig

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Barrel SCT prototype

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Civil engineering

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The future…

• It is anticipated that ATLAS will see its first data in 2007– Let me close with a few examples of physics that might be discovered

• The Higgs boson (or possibly several Higgs bosons)– A central element of the Standard Model (responsible for giving mass to

the fermions and to the W and Z bosons), but so far elusive• Supersymmetry

– Suggested to overcome theoretical problems with the Standard Model, but requiring the introduction of “super-partners” for each SM particle

• Extra dimensions– Recently the subject of renewed interest

» Extra dimensions possibly large if SM particles confined to 3+1 dimensional “brane”

• Or, possibly, something completely unexpected– With 7 times the energy and 50 times the luminosity of today’s most

powerful collider (TeV-II at Fermilab), the LHC is truly a discovery machine

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ATLAS physics potential

SUSY

10 d @ 1033

1 y @ 1034

Tevatron limit

4000

4000

qm~

][~ GeVmg

Extra dimensions

m

D

10 TeV

MSSM Higgs

tan

mA

Standard Model Higgs

mH 1 TeV

1 TeV

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Letter from Peter JenniDear John, With great pleasure I remember the fruitful and friendly direct collaboration with you, which I enjoyed over many years! You have taken a decisive share in steering the ATLAS Collaboration during a critical period. The two most evident occasions were as Chair of the Calorimeter Panel (1993 – 1994), preparing the difficult technology choices, and then of course the four years as Collaboration Board Chair and Deputy (1995 – 1998), covering the years when ATLAS was approved, the funding settled in the Resources Review Board with the Memorandum of Understanding and the construction actually started. The ATLAS Collaboration owes you an enormous ‘thank you’ for having led delicate decision processes to a good end, accepted by all collaborators. I was in the privileged position to benefit from your competence, integrity and human flair. Gratefully I remember your help and encouragements during your years in office at the head of the Collaboration Board. They went well beyond the normal interactions between a CB Chair and spokesperson, and indeed out-lasted your period of office. In the name of the Collaboration, but also very much personally, I wish you all the best as you pass this milestone into a new era with hopefully fewer duties and more freedom! Friendly Yours, Peter JenniSpokesperson, ATLAS Collaboration

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In conclusion, I would like In conclusion, I would like to wish John all the best for to wish John all the best for

his future retirementhis future retirement