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

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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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