Search for new sources of CP violation with D experiment G.Borissov - PowerPoint PPT Presentation

Seminar at University of Birmingham, 27 October 2010 Search for new sources of CP violation with DØ experiment G.Borissov Lancaster University, UK

Matter – Antimatter Asymmetry • One of major challenges of particle physics – explain the dominance of matter in our Universe • Number of particles and antiparticles produced in the Big Bang is expected to be equal = = = = t 0 • For some reason matter becomes more antimatter matter abundant in the early stages of Universe • Antimatter completely annihilated • Hence we're left only with matter today t = = = = t 1 One of conditions (A. Sakharov) required antimatter matter to explain this process – properties of particles and antiparticles must be different = = = = t today ( CP violation) antimatter matter 27/10/2010 Search for new sources of CP violation - seminar at University of 2 Birmingham

CP violation in SM • CP violation is naturally included in the standard model through the quark mixing (CKM) matrix • Many different measurements of CP violation phenomena are in excellent agreement with the SM: – All measurements are consistent with a single apex of this unitarity triangle plot 27/10/2010 Search for new sources of CP violation - seminar at University of 3 Birmingham

CP violation in SM • The SM disagrees with one experimental fact – our existence – The SM source of CP violation is not sufficient to explain the imbalance between matter and antimatter – See e.g. P. Suet, E. Sather, Phys.Rev.D51, 379-394 (1995) – Some theoretical studies claim up to 10 orders of magnitude deficit of the CP violation provided by the SM • New sources of CP violation are required to explain the • New sources of CP violation are required to explain the matter dominance Search for new sources of CP violation – an important task of current and future experiments 27/10/2010 Search for new sources of CP violation - seminar at University of 4 Birmingham

CP violation in mixing • A promising direction of the search for new sources of CP violation is the study of CP violation in mixing in the B d and B s systems q u , c , t b • This type of CP violation is described by B W W B a complex phase φ q of B q ( q=d,s ) mass matrix q q q b u , c , t ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆ = = = = = = = = − − − − − − − − ≈ ≈ ≈ ≈ ≈ ≈ ≈ ≈ 12 M M M M M M 2 2 M M q H L q ∆Γ ∆Γ ∆Γ ∆Γ = = = = Γ Γ Γ Γ − − − − Γ Γ Γ Γ ≈ ≈ ≈ ≈ Γ Γ Γ Γ φ φ φ φ 12 2 cos q L H q q                 Γ Γ Γ Γ Γ Γ Γ Γ 12 12 M M i         12 M q q q q = = = = − − − − M                         q φ φ φ φ = = = = − − − − arg q Γ Γ Γ Γ Γ Γ Γ Γ 12 * 12 * ( ) ( ) M M 2                         q         Γ Γ Γ Γ 12                 q q q q q 27/10/2010 Search for new sources of CP violation - seminar at University of 5 Birmingham

SM prediction • SM predicts very small values of φ q : + + + + φ φ φ φ SM = = = = − − − − 0 . 026 0 . 091 − − − − d 0 . 038 φ φ φ φ = = = = ± ± ± ± SM 0 . 0042 0 . 0014 s – A. Lenz, U. Nierste, J. High Energy Phys. 0706, 072 (2007) – These values are below current experimental sensitivity – These values are below current experimental sensitivity • New physics contribution can significantly change these values φ φ φ φ = = = = φ φ φ φ SM + + + + φ φ φ φ NP d d d φ φ φ φ = = = = φ φ φ φ + + + + φ φ φ φ SM NP s s s Large non-zero value of φ φ φ q would indicate φ the presence of new physics 27/10/2010 Search for new sources of CP violation - seminar at University of 6 Birmingham

Measurement of φ φ q φ φ DØ • The phase φ q can be measured in several independent ways: – Charge asymmetry of semileptonic B q decays; – Dimuon charge asymmetry; – Decay B s →J/ψφ ; – Decay B s →J/ψφ ; • DØ experiment at Fermilab performs all these measurements 27/10/2010 Search for new sources of CP violation - seminar at University of 7 Birmingham

Semileptonic charge asymmetry 0 B 0 B X • The charge asymmetry a q sl of "wrong sign" semileptonic B 0 q ( q = d,s ) decays: + + + + − − − − Γ Γ Γ Γ 0 → → → → µ µ µ µ − − − − Γ Γ Γ Γ 0 → → → → µ µ µ µ ( B X ) ( B X ) q q q ≡ ≡ ≡ ≡ = = = = a ; q d , s sl sl + + + + − − − − Γ Γ Γ Γ Γ Γ Γ Γ → → → → → → → → µ µ µ µ µ µ µ µ + + + + + + + + + + + + Γ Γ Γ Γ Γ Γ Γ Γ → → → → → → → → µ µ µ µ µ µ µ µ − − − − 0 0 0 0 ( ( B B X X ) ) ( ( B B X X ) ) q q • This asymmetry is related with the phase φ q as: + + + + − − − − = = = = − − − − × × × × d 1 . 0 4 ∆Γ ∆Γ ∆Γ ∆Γ a ( SM ) ( 4 . 8 ) 10 − − − − q sl 1 . 2 = = = = φ φ φ φ q a tan( ) sl q ∆ ∆ ∆ ∆ M = = ± ± × × − − − − s = = ± ± × × 5 a ( SM ) ( 2 . 1 0 . 6 ) 10 q sl = = = = − − − − ± ± ± ± d a 0 . 0047 0 . 0046 • a d sl is measured by B factories : sl • a s sl is measured by DØ experiment: = = − − ± ± + + + + s = = − − ± ± 0 . 0014 a 0 . 0017 0 . 0091 − − − − sl 0 . 0015

Dimuon charge asymmetry X 0 B B q 0 B q X • Charge asymmetry of same sign dimuon pairs produced in a p p collision ++ ( N b + + + + + + + + − − − − − − − − − − − − N N N b −− ) – number of ≡ ≡ ≡ ≡ b b b same-sign µ + µ + ( µ − µ − ) A + + sl sl + + + + + + + + + + + + + + + − − − − − − − − − − − − − − − − + + + + + + + N N N N events from B→µX decay events from B→µX decay b b • Both B d and B s contribute in A b sl at Tevatron : = = = = ± ± ± ± + + + + ± ± ± ± b d s A ( 0 . 506 0 . 043 ) a ( 0 . 494 0 . 043 ) a sl sl sl B d contribution B s contribution 27/10/2010 Search for new sources of CP violation - seminar at University of 9 Birmingham

Decay B s → → J/ψ φ → → • CP violation in B s →J/ψφ decay is described by the phase φ J/ψφ • Within the SM φ J/ψφ is related to the angle β s of the ( bs ) unitarity triangle: * ~ λ λ λ λ 2 V tb V   −       * ts V V β β β β * ~ λ λ λ λ 4 ψϕ ψϕ         V ub V φ φ φ φ ψϕ ψϕ = = = = − − − − β β β β = = = = − − − = = = = − − − − ± ± ± ± J / , SM 2 2 arg tb ts 0 . 038 0 . 002 s         us s * V V         * ~ λ cb cs λ λ λ 2 V cb V cs • It can be significantly modified by the new physics contribution: φ φ ψϕ ψϕ ψϕ ψϕ = = φ φ ψϕ ψϕ ψϕ ψϕ + + φ φ φ φ J / = = φ φ J / , SM + + φ φ NP s NP is the same for φ J/ψφ and φ s φ s 27/10/2010 Search for new sources of CP violation - seminar at University of 10 Birmingham

Measuring the dimuon charge asymmetry • Experimentally, we measure two quantities: • Like-sign dimuon charge asymmetry : + + + + − − − − + + + + − − − − − − − − N N ≡ ≡ ≡ ≡ = = = = + + + + ± ± ± ± A ( 0 . 564 0 . 053 )% + + + + + + + + − − − − − − − − + + + + N N • Inclusive muon charge asymmetry : • Inclusive muon charge asymmetry : + + + + − − − − − − − − n n ≡ ≡ ≡ ≡ = = = = ± ± ± ± a ( 0 . 955 0 . 053 )% + + − − + + + + + + − − n n – N ++ , N −− – the number of events with two like-sign dimuons – n + , n − – the number of muons with given charge 27/10/2010 Search for new sources of CP violation - seminar at University of 11 Birmingham

Experimental observables and A b sl • Semileptonic B decays contribute to both A and a ; • Both A and a linearly depend on the charge asymmetry A b sl = = = = + + + + b a k A a sl bkg = = = = + + + + b A K A A sl bkg • In addition, there are detector related background • In addition, there are detector related background contributions A bkg and a bkg Our task is: • Determine the background contributions A bkg and a bkg • Find the coefficients K and k • Extract the asymmetry A b sl 27/10/2010 Search for new sources of CP violation - seminar at University of 12 Birmingham