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http://www.slideshare.net/worldTC Last of the Particles? Search for Higgs at LHC
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Prof. Higgs and his boson <ul><li>Peter Ware Higgs (born May 29 , 1929 ), FRSE , FRS , until recently held a personal chair in theoretical physics at the University of Edinburgh and is now an emeritus professor . </li></ul><ul><li>Higgs is best known for his 1960s proposal of broken symmetry in electroweak theory , explaining the origin of mass of elementary particles in general and of the W and Z bosons in particular. This so-called Higgs mechanism predicts the existence of a new particle, the Higgs boson . Although this particle has not turned up in accelerator experiments so far, the Higgs mechanism is generally accepted as an important ingredient in the Standard Model of particle physics . Higgs conceived of the mechanism in 1964 while walking the Cairngorms , and returned to his lab declaring he had had his "one big idea". </li></ul><ul><li>Peter Higgs has been awarded a number of prizes in recognition of his work, including the Dirac Medal and Prize for outstanding contributions to theoretical physics from the Institute of Physics , the 1997 High Energy and Particle Physics Prize by the European Physical Society , and the 2004 Wolf Prize in Physics . </li></ul><ul><li>Many others contributed to the concept – Englert, Brout, Anderson… </li></ul>Ref: Wikipedia Higgs boson is also referred as Higgs-Anderson boson (e.g. see Wikipedia)
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Mankind’s ancient question न तत सूयो भाति न चनदतारकं नेमा विदयूतॉ भानि कूतोयः यमगनिः तवमेब भानताम् अनूभाति सव॔ तसय भासा सव॔मिदम विभाति In the beginning there was no sun, neither did the moon shine, nor the stars, man made light was no where. It is Your light that lit up everything else, Every thing in this world shines from Your light Where did everything come from? What is everything made up of?
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Physicists’ latest answer The Standard Model of Particle Physics
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Names of the actors: Matter <ul><li>All of matter is made up of spin ½ particles </li></ul><ul><li>Leptons: </li></ul><ul><li>electron (e), muon( ), tau( ) (charge -1 and +1) and 3 neutrinos (charge 0) </li></ul><ul><li>Quarks: </li></ul><ul><li>Up, down, charm, strange, top, bottom </li></ul><ul><li>They have fractional charges (2/3 and -1/3)!! </li></ul>
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Names of the actors: Forces <ul><li>Forces are carried by spin 1 particles called guage bosons: </li></ul><ul><li>Electromagnetic: photon </li></ul><ul><li>Weak: W+-, Z0 </li></ul><ul><li>Strong: gluon </li></ul><ul><li>Gravitational: I don’t know – may be YOU will find out one day… </li></ul><ul><li>quarks participate in all interactions (i.e. they can exchange photon, W, Z, gluon) </li></ul><ul><li>Leptons can’t exchange gluons </li></ul>
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Feynman Diagrams This is more than just a picture !
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Without Higgs… <ul><li>Without Higgs we won’t be here because: </li></ul><ul><li>All fundamental particles will be massless, travelling at the speed of light in vacuum </li></ul><ul><li>Higgs boson – the charge less spin zero massive particle is the quantum of an all pervading Higgs field through which particles move – and interaction with this field gives them mass </li></ul>According to standard model
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How to discover new particles? <ul><li>How do we discover Higgs? </li></ul><ul><li>Good old principle : </li></ul><ul><li>Produce the particle by colliding other particles </li></ul><ul><li>Look at decay products </li></ul><ul><li>Reconstructruct invariant mass </li></ul><ul><li>Look for a peak in the invariant mass distribution </li></ul>Measure E,p, Get the mass of the original particle E1E2(1-cos(theta12)) Beware of fake products!
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Plan for finding Higgs <ul><li>What do we collide? 7 Tera electron Volt Protons </li></ul><ul><li>At what rate? Once every 25 nano seconds </li></ul><ul><li>How often do we expect to see Higgs? A few every second. </li></ul><ul><li>What will they decay to? Could be a pair of top-antitop or bottom antibottom or two photons or two Z0s… </li></ul>OK! So we just have to catch these particles and measure E,p
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parton parton Z 500 GeV 100 GeV Two partons, usually with different momenta collide and often anihilate giving rise to other particlesin the final state Beam axis Note: parton = quark, antiquark or gluon
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Of quark bondage: Jets <ul><li>There is no free quark in the world </li></ul><ul><li>Quarks and gluons, as they fly apart from each other – give birth to other quarks and gluons, eventually all these quarks and gluons combine with each other to make pions, nutrons, eta’s rho’s … known as hadrons </li></ul><ul><li>They all more or less fly in the direction of the original quark/gluon and that is JET </li></ul><ul><li>Jets are the only signatures of quarks and gluons that we can see experimentally </li></ul>Two charm quarks moving apart from each other
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Luminosity and cross section <ul><li>If I shoot 10 11 protons every 25 ns through another 10 11 protons most of them will sail through. </li></ul><ul><ul><li>how many will collide/ sec? </li></ul></ul><ul><ul><li>Out of every hundred collition how many will produce Higgs? </li></ul></ul><ul><li>Ans: no. of collisions / sec = (10 11 X 10 11 )/25ns/500sq-micron (provided the beam cross section is 500 sq-micron). </li></ul><ul><li>Sigma( ) is called reaction cross section and contains the entire physics of all possible interactions between the colliding quarks and gluons (calculated by phenomenologists) </li></ul><ul><li>The remaining terms in the formula together are called luminosity(L) </li></ul><ul><li>In general: Number of collisions/sec = L </li></ul><ul><li>(the actual formula for luminosity is somewhat more complicated, which takes into account the crossing angle of the beams, lorentz contraction of the bunches etc.) </li></ul>
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* numbers are for barrel Silicon Tracker PbWO 4 ECAL solenoid 4Tesla field data taking starts 2007 ? Startup Luminosity 2X10 33 cm -2 /s that is: 10 fb -1 per year sampling brass HCAL MUON Chambers
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