1 Juan Pablo Fdez. Ramos C.I.E.M.A.T. 3/9/2014 Encanto y belleza en los quarks más pesados ( Introduction to heavy quark physics ) Buscar en google overview bottom quark physics Nowadays, all major labs have heavy quark-physics as part of their program. So, heavy quark physics must be interesting. Why is that ?

2 I- Motivation (mostly theoretical) II - Challenges (experimental)

3 Perito accidentes Su reconstrucción del suceso ¿Físico experimental de partículas = perito ?

4 Perito accidentes ¿Físico experimental de partículas = perito ? Su reconstrucción del suceso

5 Hadrons are systems bound by the strong interaction, which is described at the fundamental level by Quantum Chromodynamics (QCD). While QCD is well understood at high energy in the perturbative regime, low-energy phenomena such as the binding of quarks and gluons within hadrons are more difficult to predict. High precision measurements are most useful to test the reliability of several models and techniques, such as constituent-quark models or lattice-QCD calculations, into predicting the mass spectrum and the properties of the hadrons. “factorization”, i.e. separating long and short-distance Physics, is important for B decays, because much of the theoretical progress in the subject relies on being able to separate the short-distance physics at scales 1/mW and 1/mb which determines the quark-level process (and for which perturbation theory is a useful tool) from the complex long distance physics of hadronization. Effective field theory is a tool which makes this factorization automatic. Why study B hadrons ? ● Heavy quark hadrons are the hydrogen atom of QCD Properties: masses, lifetimes, rare-decays, CPV Precision measurements of the quark t : proof of the SM. t→b+W +, tbar → bbar+W − background on new physics searches Masses & lifetimes, rare-decays, CPV σ(ttbar), σ(single top), top mass, top charge Why top ? Look at (held in CIEMAT in April) summary for The flavour(b) physics sector provides accurate measurements of Standard Model (SM) parameters and probes the existence of new particles at energy scales well beyond the reach of direct detection

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7 At t~10 -6 s after the Big Bang, there were antiquarks for every quarks. Some time later the symmetric part annihilated into photons and neutrinos. The asymmetric part survived and turned into the Universe we live in today It all started with a tiny asymmetry CP violation is a necessary ingredient for this to have happened CP violation: matter and antimatter behave differently

8 An important quantum number in SM: flavor of quarks The three generations of quark flavor pairs are: u-d, c-s, t-b In the SM the flavor quantum number is conserved in strong and electromagnetic interactions. It can olnly be changed by charged current weak processes described by the exchange of a W+- boson To describe the different coupling strengths across the three generations the 3x3 (VCKM) matrix was introduced. So VCKM determines the coupling of W bosons to pairs of up-(u,c,t) and down-type quards (d,s,b). CP Violation accomodated by a single complex phase in the VCKM VCKM has to do with the flavor : how the flavor transitions take place

9 VCKM has a single non trivial phase. This phase violates charge-parity (CP) invariance of the theory, and in the SM is responsible for the observed CP violation in the K and B systems. CP violation then is the non-conservation of charge and parity quantum numbers Rate of Bs0Bs0  What Is what we measure? Why studying CPV on B Hadrons ? Γ(B f ) Γ(anti-B anti-f )

10  s SM  -arg[(V ts V tb * ) 2 / (V cs V cb * ) 2 ] + large CPV large small CPV small CPV CP violation phase β s in SM is predicted to be very small For a given decay, CP violation understood to come from interference between mixing and decay amplitudes The CP phase between the two decay paths appears via the factor sin(2 b s ) Bs0Bs0 Bs0Bs0 J/ Ψ  φ => sin (2 β s ) -  β s SM  - arg[(V ts V tb * ) 2 /(V cs V cb * ) 2 ] Quantum perspective

11 New Physics CPV in B s 0 Decays Under the existence of new physics... In B s 0  J/ , we would measure 2  s = (2  s SM  s NP ) ~ -  s NP Observation of large CP phase in B s 0  J/   unequivocal sign of new physics (new unknown contribution in the loop process? ) '' ' + unknown flavor structure Under the existence of new physics... In B s 0  J/ Ψφ, we would measure 2 β s = (2 ɸ s SM  ɸ s NP ) ~ - ɸ s NP Observation of large CP phase in B s 0  J/ Ψφ   unequivocal sign of new physics (new unknown contribution in the loop process? ) The objective is to probe the Standard Model, and search for physics ‘Beyond the Standard Model’.

12 How do we perform these measurements from the experimental point of view ? Which are the needs/challenges to make this possible ? Experimental approach

13 Basics of B Physics g g Flavor Creation (gluon fusion) b Flavor Creation (annihilation) q b q b Flavor Excitation q q b g b b Gluon Splitting g g g b ● Quarks fragment into hadrons: B c - (bc),  b (bdu),  b + (buu),  b - (bdd), Ξ b - (bsd), Ω b - (bss), B s 0 (bs), B 0 (bd), B - (bu), also B*, B**, etc ●  B hadrons decay via weak interaction and we look for their decay products. The weak decay of quarks inside hadrons depends on fundamental parameters of the SM ● High cross section  (pp  bb ) ~  b ● (vs ~ nb at the  (4s) resonance [B factories]) - b - Different experimental approaches were followed to study flavor physics. The so called B-factories produce pairs of B0/B0 and B+/B- mesons in e+e- collisions at the ϒ (4S) center of mass energy. Hadron colliders are another option...

14 B selection process of the experiment ● QCD(lighter quarks):h uge bkg to the process  (pp  bb) ● To overcome the QCD background B hadrons filtered experimentaly using selective triggers based on clear signatures: events selected by a J  ψ  oriented dimuon trigger events selected by an impact parameter based trigger (SVT) -- calorimeter  chamber  stub Central tracker Central track Measurements : Central tracking chamber: - Track momentum - Trajectory Muon chambers: - Trajectory (stub) Require : - Central track - Muon stub - Position and angle match between central track and muon stub

15 Large beauty and charm samples collected by the experiment due to the B selection!

16 Experimental results : B +, B 0 & L b mass, lifetime and ratio of lifetimes CP Violation in B s 0  J/ψφ

17 Mass measurements

18 Mass measurements Challenge : High precision mass measurements require good momentum measurement of the final state tracks. Need for excellent tracking devices with very good momentum resolution Individual track reconstruction Combination of tracks to form the b-hadron

19 b-hadrons decay in SV far from the PV b-hadron lifetimes in decays to J/ψ SVSV PVPV Challenge : measure the secondary vertex with sufficient precision Help of silicon detectors with extremely good position resolution, 60 μm strip-pitch

20 Challenge : measure the vertex with precision

21 Some help from decay topology Displaced vertices and fully reconstructed decays  We can make precision measurements… & HQE is a reliable framework… How do we model this data? B 0  J/ψK s Λ b  J/ψΛ

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25 Método de ajuste o estimación por máxima verosimilitud (MLM) Tenemos N medidas de la cantidad x {x 1, x 2, … x n }. f(x|a,b) es una función de densidad o función de probabilidad o dns. de prob. Queremos determinar los parámetros a y b. MLM: elegimos el valor de a,b que maximiza la probabilidad de obtener los valores (x i 's) que medimos. ¿Cómo funciona el MLM? La probabilidad de medir x 1 es f(x 1 | a,b )dx La probabilidad de medir x 2 es f(x 2 | a,b )dx La probabilidad de medir x n es f(x n | a,b )dx Si las medidas son independientes, la probabilidad de obtener ese conjunto de medidas es: L = f(x 1 | a,b )dx * f(x 2 | a,b )dx... f(x n | a,b )dx = f (x 1 | a,b ) * f (x 2 | a,b )... f (x n | a,b )dx n Podemos olvidarnos de los términos dx n pues se trata sólo de una constante de proporcionalidad L =Π i f(x i |a,b) Función de verosimilitud Queremos escoger el valor de los parámetros a,b que maximicen la función de verosimilitud, : δL/δα| α=α * = 0, donde α puede representar una matriz de parámetros (a,b,vida media,etc).

Lifetime extracted from an un-binned likelihood fit, simultaneously in three variables. The likelihood function is a sum of two terms: one for signal and one for the background. How do we model this data? * Each piece is probability density function(PDF) in the three variables: reconstructed mass (m) reconstructed proper decay time (ct) reconstructed proper decay time error (  ct ) The reconstructed proper decay time error distribution La funcion L =Π i f(x i |a,b) para el caso de medida de la vida media de una partícula depende de más de una variable pero se puede factorizar en producto de funciones f que dependen de cada variable x (asumiendo que son variables independientes). El truco, está en acertar con el modelo : las funciones de densidad f o densidades de probabilidad para cada variable x. Las funciones f pueden ser a su vez combinación de varias funciones debido a la contribución de varios agentes físicos (por ejemplo, varias partículas, varios tipos de fondo, etc)....

27 How do we model this data ? Typically show recons-tructed proper decay time in log scale x es ct x es Masa f f f' f'' f f'''

28 We get the resolution model from sideband events. Los parámetros α (a,b) son la masa (media), la vida media de la particula, etc

29  0 b lifetime measurement t (  0 b ) = 1.537±0.045±0.014 ps t (  0 b )/ t (B 0 )=1.020   Theory: t ( L 0 b )/ t (B 0 ) =0.88  0.05 Some theories favour higher ratio Measurement of t (B + ), t (B 0 )& t (B + )/ t (B 0 ) t (B + )= ± 0.009± ps t (B 0 )= ± 0.010± ps t (B + )/ t (B 0 )= ± 0.009± In agreement with theoretical prediction:  t (B + )/ t (B 0 ) =(1.063  0.027) (theory) B hadron lifetimes

30 CP Violation in B s 0  J/ψφ What is what we measure? q&anti-q decays could have different properties: look at any difference in properties like decay rate, angular decomposition of the amplitude, etc between a decay and its “mirror image” resulting from C and P transformations

31 Measure Γ(B f ) - Γ(anti-B anti-f ) Γ(B s 0 J/ψφ ) [cτ] - Γ(anti-B s 0 J/ψφ ) [cτ] Γ(B s 0 J/ψφ ) [cτ] + Γ(anti-B s 0 J/ψφ ) [cτ] ~sin(2β s ) Flavor Creation (annihilation) q b q b Challenge : Determine particle/antiparticle at production (flavor tagging) Bs0Bs0  Rate of CP Violation in B s 0  J/ψφ

32 Overview of Flavor Tagging Same Side Opposite Side The final tag is the combination (properly weighted) of all the different tagging methods Output: decision (b-quark or b-quark) and the quality of that decision - b quarks generally produced in pairs at Tevatron Tag either the b quark which produces the J/ ψ ϕ (SST), or the other b quark (OST) SST is based on flavor-charge correlations, i.e. tag on the leading fragmentation track OST searches lepton (either an electron or a muon) in the other side coming from the semileptonic decay of the other B.

33 Mass: discriminate signal against background Tratamiento estadístico. Modelo y variables x: cantidades medidas que forman parte de la función de probabilidad reconstructed mass of B s 0,B s 0 and its error, decay time and its error, transversity angles, flavor tag decision, dilution D Angles: Separate CP-even from CP-odd final states Output: parámetros α (siguiente transp.) 

34 Precise measurements of φs and ΔΓs, will put severe constraints on NP in Bs mixing Large, well understood data samples from experiments ΔG s = G L – G H

35 Quién es el quark top?  La partícula elemental más masiva hasta el momento (incluído el bosón de Higgs!!). Es la contribución dominante en correcciones radiativas. m t =  0.75 GeV/c 2  la que más se acopla al bosón de Higgs. m t y m W constriñen m H  El quark top es ubicuo. Su sección eficaz es grande en el LHC ( debido al gran flujo de gluones )  Anchura  t = GeV  Medidas de precisión del quark top pueden dar info sobre ruptura de la simetría electrodébil.  O incluso nuevas partículas pue- den desintegrarse en quark tops  portal para nueva física? Masa de los quarks Quién es el quark top?  La partícula elemental más masiva hasta el momento (incluído el bosón de Higgs!!) m t =  0.75 GeV/c 2  la que más se acopla al bosón de Higgs  El quark top es ubicuo. Su sección eficaz es grande en el LHC ( debido al gran flujo de gluones )  Anchura  t = GeV  Medidas de precisión del quark top pueden dar info sobre ruptura de la simetría electrodébil.  O incluso nuevas partículas pue- den desintegrarse en quark tops  portal para nueva física? Masa de los quarks

36 c) Diagrama dominante en Tevatron (pp) LHC a,b) Diagramas dominantes en LHC (pp) Modo de producción predominante: pares tt (int. fuerte)  W+ b W- b q q  t t ud e - ν e __ gg ~85% ~15% qq ~10% ~90%

37 Modo de producción no predominante: t (int. debil) Establecido y medido por Tevatron y LHC  = 42 pb  s = 7 TeV Establecido y medido por CMS en 2014  = 8.1 pb  s = 7 TeV Establecido y medido por D0 (Tevatron) en 2013  = 3.2 pb  s = 7 TeV t channel s channel W-associated channel

38 Desintegración del quark top Estados finales: siempre 2 quarks b  jets según desintegración de W: tt  bb l + l -  di-leptónico tt  bb qq’ l  leptónico + jets tt  bb qq’ q’’q’’’ hadrónico Prácticamente (  99.8%) t  Wb (V tb  0.998) t  W + b t  W - b Tiempo de vida media muy corto (  5  s)  se desintegra antes de hadronizar W es real (no es un propagador) W  l  (l=e, ,  ) BR: (10.80± 0.09)% por leptón W  qq’ BR: (67.60± 0.27)% -- Proceso creación pares t anti-t

39 Reconstrucción (identificación) tt Objetos (partículas) reconstruidos Leptones (e, ,  ) aislados (sin actividad alrededor) Jets b-jets : etiquetado (b-tagging) Energía faltante : MET Trigger Pile-up: superposición colisiones ¿Qué es b-tagging? Identificación de jets (b-jets) originados en el proceso de hadronización de un quark b o antiquark antib. Se explota para la indentificación las propiedades que distinguen al quark b de los demás Masa del b-quark 4.18 GeV mayor que para c-,light-quark. τ B > resto hadrones. Multiplicidad trazas en b-jet~ 5

40 Fondos irreducibles Fondos instrumentales Debido a mala reconstrucción de objetos ( falsa MET, falsos e, μ, mistag b )

41 Medidas sobre el quark top Necesitamos medir : Top mass and width Top spin Top charge Top couplings, to W, Z, γ,G and H. Distributions of produced top quarks, (information about partons, search for resonances).Combination of production and decay observables is crucial to constrain the Wtb couplings. New searches Parámetros fundamentales del SM

42 Sección eficaz de producción t anti-t Cuántos quark tops se producen requiere : *gran precisión y conocimiento de calibración de detectores *gran control de otros procesos del ME que tengan una signatura similar: fondos ; estudio previo de bosones W, Z, nos asegura estos 2 puntos (leptones, fakes…) *se calcula en cada unos de los tres modos de desintegración finales: hadrónico, leptones+jets, dileptónico *Luminosidad: dado por acelerador *Factores corrección: Aceptancia (espacio fases), eficiencia, BR tener en cuenta posibles candidatos de otros procesos exóticos (nueva física) en la muestra

43 Secciones eficaces a  s = 7,8 TeV Medidas dominadas por incertidumbres sistemáticas  LHC es una factoría de top quarks Buen acuerdo datos -predicciones teóricas del SM

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46 Very rich heavy flavour program, examples: - heavy baryons - precision lifetimes of all B hadrons - CPV Conclusions Top will be exquisitely studied at the LHC Provide extreme QCD tests & contraints on new physics Top decays before it has time to hadronize; no top mesons. Top production is perturbatively calculable because of the large mass of the top. Single top production rate are substantial and give sensitivity to V tb. Associated production of vector bosons Z,H, gamma, jet will give information about the top couplings. EWQCD New Physics top

47 Reconstrucción cinemática t anti-t Reconstrucción es compleja, no existe pico de masa (como en Z). Existen partículas (ν, ¿materia oscura?) que escapan indetectadas Aplicar conservación mom. en plano ⊥ productos finales de colisión Se realizan todas las posibles permutaciones de asignación de jets/partículas a cada rama (top) Ajuste de las medidas disponibles, maximizando la probabilidad de la desintegración y la cinemática resultante:  2 Sólo el caso hadrónico es resoluble totalmente (dentro de incertidumbre sistemáticas de medidas y calibraciones) En el resto, asunción de ciertas igualdades, en cada rama de desintegración: m W, m t, m t1 =m t2, m W1 =m W2

48 ● Time evolution of B s flavor eigenstates from Schrödinger equation: Neutral B s system Experimentally accessible ● The magnitude of the box diagram gives the oscillation frequency  m s = m H - m L ≈ 2|M 12 | ;  m s =  0.12 ps -1 (CDF) ● Diagonalize mass and decay matrices → obtain mass eigenstates (mixture of flavor eigenstates) ● Mass eigenstates have different decay widths (lifetimes)  =  L –  H ≈ 2|  12 | cos  s ; DG = 0.08  0.06 ps -1 (CDF) [part of this analysis] ● The phase of the diagram gives the complex number q/p = e -i  s where  s = arg (-M 12 / G 12 ) [ CP-violating phase] ● Mass eigenstates have different decay widths (lifetimes)  ΔG s = G L – G H ≈ 2|G 12 | cos  s ; DG = 0.08  0.06 ps -1 ● The magnitude of the box diagram gives the oscillation frequency Δ m s = m H - m L ≈ 2|M 12 | ; Δ m s =  0.12 ps -1 ● Diagonalize mass and decay matrices → obtain mass eigenstates (mixture of flavor eigenstates) ● Diagonalize mass and decay matrices → obtain mass eigenstates (mixture of flavor eigenstates) ● Diagonalize mass and decay matrices → obtain mass eigenstates (mixture of flavor eigenstates) ● Time evolution of B s flavor eigenstates from Schrödinger equation: Neutral Bs system

49 Collider sigma (pb) Tevatron 7.26 LHC LHC LHC

50 Secciones eficaces diferenciales Mejor descripción con NNLO que NLO, en dileptones y semileptónico Resultados acordes con SM Junto con mW permitió poner límites indirectos a mH Masa del quark top Spin del quark top y sus correlaciones

51 Identificación de jets (b-jets) originados en el proceso de hadronización de un quark b o antiquark bbar puede ser más o menos eficiente según el algoritmo de identificación que se use. Hay que calcular es eficiencia. Se calcula el cociente entre la eficiencia medida en datos / eficiencia MC B-Tagging Efficiency

52 Se calcula el cociente entre la eficiencia medida en datos / eficiencia MC

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54 b-hadrons Lifetime: largely determined by charged weak decay of b quark Interactions of quarks inside hadrons change these lifetimes by up to about 10%. In  B+ /  B0 =  0.027, In  Lb /  B0 = 0.88  0.05 HQE predicts   (B u )>  (B d ) ~  (B s ) >  (L b )>>  (B c ) Why b-hadron lifetimes ? ● The measurement of lifetimes (and ratios) can be used to evaluate deviations from the naive spectator quark model : b quark decays like free “particle” => all B hadron lifetimes are equal ● In reality QCD => lifetimes of B hadrons study the interplay between strong and weak interaction

55 Results φ s = 0.07 ± 0.09 (stat) ± 0.01(syst) rad ΔΓ s = ± (stat) ± (syst) ps -1 SM: φ s ≈ -2β s = ± rad, ΔΓ s = ± ps -1 ΔG s = G L – G H

56 Peak at 0 comes from prompt J/ ψ (main source: Drell Yan) Long lived tail is mostly our B s 0  J/ ψ ϕ Signal B s 0 Lifetime Reconstruction - l l q q p p - B s 0 travels ~ 450  m before decaying into J/ Ψφ Properties of decay depend on decay time, CP at decay, and initial flavor of B s 0 / B s 0

57 Overview of fit Single event likelihood decomposed and factorized in: : probability distribution functions (PDFs) for signal : PDFs for background f s : signal fraction (fit parameter) Single event likelihood decomposed and factorized in: