"How the Universe is put to the test" – Andrei Golutvin, Ulrik Egede, CERN
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Transcript of "How the Universe is put to the test" – Andrei Golutvin, Ulrik Egede, CERN
How the Universe is put to the test
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Ulrik Egede (Imperial College London) Andrey Golutvin (Imperial College London / CERN)
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Atom of He
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Standard Model (SM) perfectly describes micro-world
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Two fundamental problems of SM in connecting micro-world (quarks and leptons) with macro-world (Universe): - Matter & (absence of) Anti-matter - Dark Matter
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Anti - matter
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Симметричны ли законы физики применительно к материи и анти-материи ???
Противоположный заряд
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Invariance properties with respect to transformations have been always important in physics
1. translations in space
2. rotations in space
3. time translations
invariance conservation
1. momentum
2. angular momentum
3. energy
Importance of symmetries in physics
Besides continuous symmetries of prime importance in high energy physics are discrete transformations • С – charge conjugation • P – space inversion • Т – time reflection 8 YAC, Moscow 2013
Beauty slightly broken symmetry
Maximal symmetry is not so interesting…
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The breaking should not be too strong, however…
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Наша Вселенная образовалась в результате слабого нарушения симметрии между материей и анти –
материей в первые моменты после Большого Взрыва
Экспериментальный факт: мы живем во Вселенной заполненной материей 11 YAC, Moscow 2013
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Попытки найти анти – вещество во Вселенной пока не увенчались успехом
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10,000,…,001 10,000,…,000
Нам повезло, потому что …
ma8ère an8ma8ère Это наш мир
А затем наступило взаимоуничтожение материи и
анти-‐материи ! 13 YAC, Moscow 2013
мы
После этого ... осталась лишь крошечная часть
образовавшегося в момент Большого Взрыва вещества
материя анти-материя
1
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В мире элементарных частиц нарушение симметрии между материей и анти-матепией хорошо известно: (CPLEAR 1999)
neutral kaon decay time distribution
anti-neutral kaon
decay time distribution
CP violation
≠
CPV is however 1010 weaker than required to explain an absence of anti-matter in our Universe ! 15 YAC, Moscow 2013
Другая фундаментальная загадка Вселенной … à travers les âges
Мы не понимаем из чего состоит 96% Вселенной 16 YAC, Moscow 2013
Major goals of LHC: - Discover a Higgs boson - Discover New Physics (Beyond the Standard Model) in order to solve failures of the SM
Use of search technologies is vital Yandex search engine has a future at the LHC !!!
with a bit of luck …
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Already now the Yandex data centre offers substantial resources
Contribution from Yandex to LHCb has been recently explicitly mentioned at the CERN Scientific Policy Committee meeting
Pledged Tier2 power
Yandex contribution ~25%
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Methodology
Исследования на Большом Адронном Коллайдере
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• Tunnel length - 27 kilometers • Depth below ground - between 50 and 175 meters
• Two colliding proton beams, 2808 bunches / beam, ~1011 protons / bunch • Four large detectors at four collision points to study physics
• Proton speed = 0.99999998 c • Proton energy: currently 4 TeV / beam or Ecm = 8 TeV Ecm ≈ 14 TeV in two years
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A few parameters of the LHC
Energy of a proton in the beam = 7 TeV = 10-‐6 J
QuesVon: why not to use mosquitos in parVcle physics?
Answer: because NAvogadro = 6.022×1023 (mol)-‐1
Energy of a mosquito is distributed among ~ 1022 nucleons.
On the other hand, total energy stored in each beam is 2808 bunches × 1011 protons/bunch × 7 TeV/proton = 360 MJ It is explosive energy of ~ 100 kg TNT or kineVc energy of “Admiral Kuznetsov” cruiser traveling at 8 knots.
It is about kineVc energy of a flying mosquito:
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How large is the LHC energy
Detectors at the LHC
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CMS
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ATLAS
Service people
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LHCb
Interaction Point
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Two strategies to search for NP: - direct search (ATLAS/CMS) - indirect search (LHCb)
- Example 1: Higgs boson
H particle(1) + particle(2) Search for the signal peak in the invariant mass of (1) and (2) M = E1E2(1 – cosθ), θ is the angle between (1) and (2) - Example 2: Super rare decay Bsµµ Precise measurement of rare decays of known particles such as Bsµµ. They are very sensitive to NP via quantum effects For both examples the use of MVA search technologies is vital ! (see Ulrik’s talk for details)
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Direct (ATLAS/CMS) vs Indirect (LHCb) search for NP
97 Indirect attack may happen to be more effective … 28 YAC, Moscow 2013
The highlight of a remarkable year 2012: Discovery of the Higgs
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A new particle: no doubt that it is there… (See talk of U. Egede for details)
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A new particle: no doubt that it is there…
By now we can establish it with a single decay channel! e.g. H à ZZ à 4l
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Another highlight of 2012: LHCb rare decay Bs µµ (see talk of U. Egede for details)!
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What is the challenge ● Quantum Mechanics is a truly random process
● To find something rare, we just have to keep trying ● Brute force, no easy way out
A piece of grass ...
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What is the challenge
... from a lawn
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What is the challenge
Quite a big lawn in fact
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What is the challenge
● There is about 109 pieces of grass on a football pitch ● Finding one specific piece of grass here is the same as finding Bs→µµ among all B decays
● But B mesons are in fact themselves produced quite rarely
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What is the challenge Find this one ...
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What is the challenge Find this one ...
... on this one !
Where to begin ?
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Two examples
Higgs discovery in CMS
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Two examples
Higgs discovery in CMS
Bs → µµ observation in LHCb
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Higgs ● How to discover something that is only there for 10-22 seconds?
● Three tools at our hands ● Energy and mass equivalence → E = mc2
● Conservation of energy
● Conservation of momentum
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So how to find a Higgs ● Smash lots of protons together
● Look for two very energetic photons
● Add their momentum and energy together
Count how many you have
● Publish mass and get famous
m= √2E1E2(1− cos(θ))
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Easy
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Easy
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Why it isn't so easy anyway ● Smash lots of protons together
● It took 30 years to design an build the accelerator ● Look for two very energetic photons
● But each proton-proton collision may create create 20 of them ● Add their momentum and energy together
● Uncertainties mean that we do not always get the same result ● Count how many you have
● Statistical significance tricky to understand with background ● Publish mass and get famous
● That is the easy bit!
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“Seeing” the Higgs
That's it! YAC, Moscow 2013
The quantum loop ● Look for heavy particles in the decay of light particles
● This clearly violates E=mc2
● Quantum mechanics comes to the help ● Violation is OK if it only takes place for a very short time
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B→µ+µ-
Topology of decay simple ● Challenge is to keep trigger and selection efficiency high, while rejecting combinatorial background
Signal
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B→µ+µ-
Topology of decay simple ● Challenge is to keep trigger and selection efficiency high, while rejecting combinatorial background
Combinatorial background
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Many vague signatures
● Width ● Sharpness of tip ● Colour ● Humidity ● Reflectivity
Momentum Opening angle Decay time Isolation Distance of closest approach Non-pointing
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Many vague signatures ● Machine learning is the way to go
● Neural Nets ● Decision trees ● Fisher discriminants ● Support vector machines
● Implementations ● MatrixNet ● NeuroBayes ● TMVA
For all of these we need ● Training samples ● Testing samples
● From simulation so how do we know they work? YAC, Moscow 2013
Many vague signatures
Distance between the two muons
Signal simulation
Background simulation
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Many vague signatures
Momentum
Signal simulation
Background simulation
Signal simulation
Background simulation
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Boosted Decision Tree
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Bs→µµ candidates
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Bs→µµ candidates
The Bs→µµ peak
Less than 10-4 probability that this is just background
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Increase in complexity ● Bubble chamber photos
● Look at everything manually
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Increase in complexity ● Bubble chamber photos
● Look at everything manually ● Hardware triggers
● Custom built electronics to make simple fast decisions
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Increase in complexity ● Bubble chamber photos
● Look at everything manually ● Hardware triggers
● Custom built electronics to make simple fast decisions ● Software solutions
● Real time trigger farms with 20.000+ cores
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Increase in complexity ● Use of multivariate analyses at all levels to select data
● Results shown today would be impossible without it
● Reduce data rate in LHCb experiment from 30 kHz to 2 kHz
● All Higgs analyses rely on it ● Bs → µµ as illustrated
● What is the next step here? ● Collaboration with software industry may lead the way
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Understanding the Universe Observation of Higgs
● A confirmation of a 40 year quest for the Standard Model ● Discovery of Bs→µµ at predicted rate
● No observation of deviations is a different way of learning
● Nature more complex than we had anticipated ● Energy of super symmetry at higher masses ● Heavy neutrinos the way to explain the lacking antimatter and dark matter
● An experimental discovery that is not predicted ??
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Thank you
Andrey Golutvin Imperial College London / CERN
Ulrik Egede
Imperial College London
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