Se Search for Dark Matter produc uced in n as associat ation with a a Higgs bo boson at at LHC by Reham Mohamed Aly PhD student Physics Department – Bari University Tutor Prof. /Nicola De Filippis Polittecnico and INFN, Bari Corso di Dottorato XXXIII Ciclo
Introduction Particle physics is the study of what everything is made of ? What is the nature of our Universe made of ? This study is called Elementary particle Physics or sometimes High Energy Physics (HEP). Elementary particle is a particle not known to have substructure. 2
04/07/2012 the Higgs boson has been found ! 3
Shortcomings of SM Ø Gravity: It does not construct a theory of gravity similar to those for the other forces. It does not tell us anything about the forth fundamental force, gravity. Ø Unified Problem:The Standard Model does not offer a unified description of all the fundamental forces. Ø Why do we observe matter and almost no antimatter if we believe there is a symmetry between the two in the universe? What happened to antimatter after Big Bang? Ø Fermion generations: why are there exactly three generations of leptons and quarks? Ø Dark matter& Dark energy: No candidate in SM. 4
Universe Composition Ø Cosmology Observations indicate that: Ø 4% of universe is Visible Matter (SM) Ø 23% of universe is Dark Matter (DM) Ø 73% of universe is Dark Energy Ø “The great majority our universe is unseen & visible stars, galaxies and clusters account for 4% of the universe.” Ø Dark matter is a hypothetical type of matter distinct from ordinary matter such as protons, neutrons and electrons. Ø The name refers to the fact that it does not emit or interact with electromagnetic radiation. 5
Candidate dark matter particle Properties: Ø Long Lived (old) Ø Non relativistic particles (Slow) Ø No electric or color charge Ø Very Weakly Interacting with standard model particles Ø Subject to gravity No such particle exists in the SM There are several candidates fulfill these requirements for Dark Matter Hot & Dark: Ultra-relativistic velocity Ø neutrinos Warm & Dark: Very high velocity Ø sterile neutrinos & gravitons. Cold & Dark: moving slowly Ø Weakly interacting massive particles (WIMP) 6
Dark Matter production DM SM DM DM SM DM DM SM SM SM SM DM Experiments search for Experiments look for Produce DM particles by the SM products from nuclear recoil produced colliding SM particles at DM annihilation. when a DM particle collide high energy. Appear as with an atomic nucleus of a “Missing Energy” target. 7
Search for DM @ LHC Ø Dark matter search at LHC has been performed with various Mono-X + Missing Et signatures (Where X = W, Z, jet, H or γ ) Ø Here X could be emitted directly from a quark as ISR or as a part of new effective vertex coupling DM to SM Ø Unlike W, Z, jets or γ , Higgs ISR is highly suppressed -> mono-Higgs Signal could be probe directly the structure of the effective DM SM coupling. Ø Experimental Signature : MET + 4l from Higgs decay 8
Mono-H Model Simplified Model A new massive particle (Z’,S,A 0 ) mediates DM-H interaction arXiv:1312.2592 arXiv:1402.7074 Ø Scalar mediator Ø PesudoScalar A 0 mediator Ø Vector Z’ mediator 9
DM search at LHC Ø Signature: Ø 4l + MET Ø Based on Standard Model H-> ZZ-> 4l analysis Ø Channels: 4e, 4 µ and 2e2 µ µ + ΜΕΤ final state Ø We will study the leptons (e, µ ) reconstruction algorithm and MET . Ø Data : Will use 2017 data collected by CMS Ø Background Ø Irreducible: ZH, Z → νν and H → ZZ → 4l or Z → ll and H → ZZ → 2l2ν (MC) Ø Reducible: - Non-resonant ZZ → 4l + MET -Others: Z+jets, WZ+jets, ttbar (data) Ø We need to study the discrimination of the background from our signal. 10
DM search at LHC Ø Signal Ø M A0 = 300 - 800 GeV with step 100 Ø M x = (1 – 10 -50 – 150 – 500 - 1000)GeV Ø M Z’ from 600 to 2500 with step 200 Ø M Z’ (10 – 100 - 200 – 1000 – 2000 - 10000) GeV Ø We need to put an upper limit on the DM mass using 2017 data plus 2016 data. 11
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Evidence of existence of DM v Galaxy clusters Ø In 1933, Fritz Zwicky studied the nearest large galaxy cluster “ Coma Galaxy Cluster ” . Ø In this study he estimated how much mass in the cluster based on the motions of galaxies in the cluster, then he compared to the estimated mass from Luminous matter. Ø He concluded that the cluster had about 400 times more mass than was visually observable. Ø There should be some a lot of ‘ Missing Matter- Dark matter ’ 14
Evidence of existence of DM v Rotational curves of galaxies Ø About 47 years later Vera Rubin was observing the rotational curves of galaxies“orbital speeds of stars in the galaxy versus radial distance from the galaxy center” Ø She measured where you go further and further away, the velocity of dust and stars remain high. Ø Her conclusion is to assume that there is a halo of invisible matter (Dark Matter) surrounded the galaxy. 15
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Evidence of existence of DM v Gravitational lensing Ø When a massive objects (such as a cluster of galaxies) lying between a more distant source and an observer should act as a lens to bend the light from this source. The more massive an object, the more lensing is observed. Ø What observed is a distortion of background galaxies into arcs when their light passes through such a gravitational lens. Ø By measuring the distortion => the geometry and the mass of the cluster can be obtained, scientists have been able to map the distribution of dark matter around the galaxy cluster. 17
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