Run 2 of the Large Hadron Collider: Upgrades and prospects for new discoveries - AIP 2014 Congress, December 7-12, ANU, Canberra
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AIP 2014 Congress, December 7-12, ANU, Canberra
Run 2 of the Large Hadron Dr Antonio Limosani
Collider: Upgrades and University of Sydney / CERN
prospects for new discoveries
1
Recap of LHC Run 1
http://www.theage.com.au/technology/sci-tech/origin-of-
❖ September 2008 - February 2013 the-universe-revealed-20120704-21ho4.html
❖ Large Hadron Collider became the
world’s most powerful particle
accelerator and collider.
❖ Run 1 : 800 GeV to 1.36 TeV to 7 TeV to 8
TeV
❖ Highlight: Higgs Boson discovered on
July 4th, 2012 (Sooner than had been
anticipated, but still 50 years since it was
proposed)
❖ Physics beyond the Standard Model not
found
❖ Long shutdown one (LS1) Feb 2013 -
May 2015. Why?
2
LHC upgrade : Consolidate magnet interconnects
❖ Niobium-titanium superconducting
(SC) magnets to both bend and focus
proton beams
❖ Simple fault in the magnet
interconnection system brought the
LHC to a halt in September 2008
❖ Fault exposed during a magnet
“quench”
❖ Defective joint had created a small
resistive zone in a superconducting
busbar designed to carry a maximum
current of 13 kA
❖ Consolidation of the 10,170 high-
current splices between the SC
magnets
3
LHC Schedule
http://lhc-commissioning.web.cern.ch/lhc-commissioning/2015/2015-commissioning-outline.htm
❖ Collisions to occur at an energy of 13 TeV in June 2015. Run 2 will last till 2018 and deliver ~100/fb of data, 25 ns Bunch
crossing
❖ x 34 cm
Run 2 will deliver collisions at high peak luminosity 1.610 2
s 1
❖ Run 2 will deliver “10 times more Higgs Bosons” for study
4The ATLAS Detector
25 m
45 m
General purpose detector built to find the Higgs Boson amongst other things
5Insertable b-layer pixel detector
❖ Insertable b-layer (IBL) Silicon
pixel detector
❖ Inner (charged particle tracking)
detector susceptible to significant
radiation damage.
❖ IBL high radiation tolerance and
high occupancy
http://home.web.cern.ch/about/updates/2014/05/new-subdetector-atlas
6 http://iopscience.iop.org/1748-0221/9/02/C02018/pdf/1748-0221_9_02_C02018.pdfWhy an IBL ? Pile-up
Average number of simultaneous collisions is referred to as “pile-up”
Each track corresponds to a charged particle
Each track must be associated with only one vertex, namely, the point
in space where it was created in a proton collision.
7Secondary vertex reconstruction
8High Performance Computing & Software
❖ Ongoing work needed to optimise ATLAS software to keep within constraints and handle
higher data rates
❖ Several software technology updates, and up to a thousand software modules needed to be
changed
❖ Make it faster and store less data without compromising physics performance
Charged particle tracking
9Physics landscape prior to Run 2
❖ SM is a complete theory : all particles that it has
predicted have been discovered!
❖ Is it the ultimate theory of nature?
❖ Neutrino oscillations
❖ Cosmology (dark matter and matter/anti-matter
asymmetry)
❖ Numerous theory objections to the SM as well.
❖ No indication as to the scale of new physics
❖ Two possible outcomes in Run 2
❖ New particles directly produced due to the
higher energy of collisions
❖ Otherwise the long road is to undertake
125.5 GeV/c2 studies with lots and lots of data e.g. precise
H
0 measurement of the top quark Yukawa
0 coupling
Higgs boson
10The Higgs Boson grows up
❖ Measurement of rare Higgs
❖ Precision studies of leading decay modes
(uncertainties to reduce by factor 3)
production and decay modes
e.g H→Zγ, ttH, H→"" (limit)
11Are fermions and bosons related by a symmetry?
❖ Supersymmetry (SUSY) is a proposed
extension of spacetime symmetry that
relates bosons and fermions (proposed in
the 1970s)
❖ “Minimal Supersymmetric Standard
Model”predicts super partners (gluinos
and neutralinos) between 100 GeV and 1
TeV.
❖ SUSY is a framework for many theories,
parameter space is vast.
❖ Complete : mSUGRA, AMSB, GMSB
❖ Phenomenological : pMSSM: 19
Discovery (or exclusion) of weak-scale SUSY is one
parameters, GGM (gravitino)
of the highest physics priorities for the current
❖ Simplified models and future LHC
❖ Gluino/squarks production limits reached using 1-3/fb of 13 TeV data
❖ SUSY particle produced via electroweak process need large amounts of data (into run 3)
12Conclusion
❖ LHC achieved its first milestone in Run 1 (Higgs Boson discovered)
❖ LHC upgraded to reach collision energy of 13 TeV in 2015
❖ ATLAS detector, trigger and computing upgraded to deal with
higher luminosity, higher data-rates, and higher radiation levels.
❖ Run 2 will begin to move Higgs Boson studies into a precision era in
its golden decay channels and allow us to observe some rare
production and decay modes
❖ Run 2 will push back the energy frontier in accelerators further than
ever before, further probe rich SUSY phenomenology
❖ Will Run 2 reveal something beyond the Higgs Boson?
13Oct 21, 2015
❖ Flying cars, hover boards?
❖ Beyond standard model phenomena at the LHC in 2015?
14ATLAS Trigger upgrade
❖ Trigger is the system that decides
whether to save or reject a particular
event (20 MHz data rate reduced to
400 Hz)
❖ ATLAS Level 1 Topo chip. New
Topological trigger to select on
combined L1 quantities
❖ Increase overall bandwidth from 400
Hz to 1000 Hz allowing us to preserve
data where a “single lepton” has
been detected at low transverse
momentum thresholds
❖ Tracking in Hardware (FTK). See talk
by T. Kubota (Uni. of. Melbourne)
http://home.web.cern.ch/cern-people/updates/2013/12/upgrading-atlas-trigger-system
http://cds.cern.ch/record/1621660/files/ATL-DAQ-SLIDE-2013-863.pdf
15Run 1 Evidence for Higgs decay to tau-lepton pair decays
❖ Trigger upgrade will
improve prospects for
studying this channel
in run 2
❖ Evidence for this
channel in Run 1
(where CoEPP
scientists played
leading roles)
❖ Crucial direct test of
whether the Higgs
boson couples to
fermions
https://www.kaggle.com/c/higgs-boson : Higgs Boson Machine Learning Challenge
16Powering tests
http://hcc.web.cern.ch/hcc/
17Origin of neutrino masses?
❖ Tiny neutrino masses (do they interact with the Higgs boson?)
❖ Type II/III Seesaw mechanism H++ / triplet fermion (observe multi-lepton final states at
LHC)
❖ Radiative generation of masses through Zee and Zee-Babu model : k++ doubly charged
Type III
18SUSY production cross-sections
19ATLAS Collaboration
38 countries
~3500 scientists
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 20ATLAS detector
25 m
45 m
General purpose detector built to find the Higgs Boson amongst other things
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 21Beam Collisions
squeeze 100,000 million protons per bunch down to 64 microns
At design settings ~600 million collisions per second
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 22Producing data
# proton bunches Collision Brightness
# interactions per crossing
Data
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 23ATLAS detector Wedge A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 24
ATLAS Event Display A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 25
Detector Operation ATLAS records greater than 95% of the delivered data A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 26
Data throughput
ATLAS and CMS produce 1000 TeraBytes / sec
Maximum bunch crossing rate of 40 MHz, which is
required to be reduced to about 300-400 Hz by the
triggers
Permanent database is 10’s of PB
Database is distributed and shared across the globe
through the worldwide LHC grid
❖ Trigger Level 1 ( decision within 2.5 "s), Level 2 analyse regions of interest
identified in Level 1 (few thousand events saved), then Event Filter stage
(final decision)
❖ Increase L1 bandwidth from 70 kHz to 100 kHz, merge Level 2 and Event
Filter stages in Run 2
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 27Worldwide LHC Computing Grid
Global collaboration of more than 170 computing centres in 36 countries, linking up national
and international grid infrastructures.
Resources to store, distribute and analyse the ~25 Petabytes of data annually generated
Melbourne Tier 2 centre ~ 700 TB and 780 processors
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 28Re-discovery of the SM
Measure standard candles
???
Higgs
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 29Higgs Boson Decay Channels
Higgs lifetime ~ 1 zeptosecond (10-21 s)
H ! ZZ ! llll
H ! WW H!
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 30Higgs Decay Channels
The Higgs can choose from many channels in which to decay
depending on its mass
1
LHC HIGGS XS WG 2011
Higgs BR + Total Uncert
bb WW
gg
10-1
ZZ
cc
10-2
Z
10-3 100 120 140 160 180 200
MH [GeV]
Detector had to be built to be sensitive to many modes.
Dominant modes aren’t always the best.
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 31Higgs to Two Photon Decay Channel Search for two isolated photon clusters and calculate their invariant mass H! A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 32
Higgs Decay to Z boson pairs
Search for four isolated charged leptons, and calculate their invariant mass
H ! ZZ ! llll
A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 33Higgs to W boson pairs H ! W W ! l⌫l⌫ A. Limosani @ AIP 2014 LHC and ATLAS Run 2 upgrades DEC 9, 2014 SLIDE 34
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