Constraining the CKM angle Sneha Malde University of Oxford 25 th - PowerPoint PPT Presentation

Constraining the CKM angle γ Sneha Malde University of Oxford 25 th January 2017 Sneha Malde 1

Many reasons to believe New Physics exists The maFer-anH asymmetry that is manifest in our universe is a mystery • There must be a mechanism(s) by which differences between maFer and anH- • maFer are generated. Sneha Malde 2

CP ViolaHon and New Physics • First ObservaHon of CPV in J. Cronin & V. Fitch 1964 in the Kaon system • Nobel prize awarded 1980 • Interest in CPV has conHnued to grow • Observed in B decays in 2001 • To date only observed in the quark sector, but at levels far below that required to explain the universe • There must be addiHonal sources of CPV in New Physics models Sneha Malde 3

CKM Matrix ⎛ ⎞ ⎛ ⎞ V ud V us V ub ⎛ ⎞ u d ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ← W ± → c ⎜ V cd V cs V cb ⎟ s ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ t b V td V ts V tb ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ By emission or absorpHon of a W ± boson , quarks change flavour W ± b c Sneha Malde 4

Unitarity triangle Wolfenstein parameterisaHon is commonly used where λ is the sine of the • Cabibbo angle λ≈ 0.22 The CKM matrix is unitary, and reduces to three rotaHons and one phase. • Phase gives rise to CP violaHon • ⎛ ⎞ 1 − λ 2 / 2 ⎛ ⎞ A λ 3 (1 − ρ − i η ) λ V ud V us V ub ⎜ ⎟ ⎜ ⎟ 1 − λ 2 / 2 ⎜ ⎟ A λ 2 + O ( λ 4 ) ⎜ V cd V cs V cb ⎟ = − λ ⎜ ⎟ ⎜ ⎟ A λ 3 (1 − ρ − i η ) − A λ 2 ⎜ ⎟ 1 V td V ts V tb ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ (1- λ 2 /2)( ρ , η ) Using the properHes of unitary matrices * V td * V ud α α 0 = 1 + V tb + V ub * V cd * V cd V cb V cb β β γ γ “Most open” triangle, others are possible (0,0) (1,0) Sneha Malde 5

Is the triangle a triangle? 1995 2001 2004 2006 2009 2015 Improvements in constraints on triangle apex due to both experiment and theory advances hFp://ckmfiFer.in2p3.fr Sneha Malde 6

Loop/Tree Loop processes more easily • altered by the presence of New Physics Loop Constraints on the apex • currently more stringent from loop decay measurements Largest uncertainty is on γ , a • process accessible at tree level TheoreHcally clean – uncertainty • from observable to physics Tree parameters ~10 -7 Forms a SM benchmark* • *assuming no New Physics in tree decays hFp://ckmfiFer.in2p3.fr JHEP 01 (2014) 051 PRD 92(3):033002 (2015) Sneha Malde 7

γ from indirect determinaHon The unitarity triangle is Length related raHo of B d constructed using mixing and and B s mixing sin(2 β ) measurements and lamce QCD γ = (62.7 ± 2.1) ! sin(2 β ) from B à J/ ψ K s γ γ β β (0,0) EPJC (2016) 76 197 [Blanke, Buras] (1,0) CombinaHon of all direct measurements (summer 2016) AlternaHve approach from CKM fit + 5.4 ) ! γ = (72.1 − 5.8 excluding all direct measurements of γ + 0.96 ) ! γ = (65.33 − 2.54 Reaching degree level precision from direct measurements is UncertainHes dominated by LQCD, crucial expect to reduce over the next decade hFp://ckmfiFer.in2p3.fr EPJC (2016) 76 197 Sneha Malde 8

Why is γ a key goal? • New Physics must provide a new source of CPV • γ is the least well measured parameter of the CKM triangle • Only angle easily accessible at tree-level • TheoreHcally prisHne • Provides a SM benchmark against which other measurements can be compared • With the advent of LHCb the ideal of degree level precision starts to become reality Sneha Malde 9

B à DK $ ' * γ = − arg V ud V ub & ) * V cd V cb % ( Interference possible if D 0 and D 0 decay to same final state • • Branching fracHon for favoured B decay ~10 -4 • Fully hadronic final state • Measurements will require high staHsHcs Sneha Malde 10

Interference with CP eigenstates “GLW” CP eigenstates equally accessible D 0 K - i(δ B - γ ) r B e to D 0 and D 0 Weak phase changes sign for equivalent B + diagram B - [KK] D K - r B , δ B hadronic parameters to be determined alongside γ r B ~0.1 D 0 K - Interested in the rate of observing this decay in B - vs. B + Interested in the rate of observing this decay vs. one that is not affected by interference, e.g the Cabibbo favoured decay of the D 0 Gronau & London, PLB 253 (1991) 483, Gronau & Wyler PLB 265 (1991) 172 Sneha Malde 11

Interference with CP eigenstates “GLW” D 0 K - i(δ B - γ ) r B e EquaHons simplified – B - [KK] D K - assume no D mixing For CP+ eigenstates e.g KK, ππ : D 0 K - N ( B − ) − N ( B + ) 1 N ( B − ) + N ( B + ) = A CP + = 2 r B sin( δ B )sin( γ ) R CP + N ( B → [ KK ] D K ) ×Γ ( D → K π ) 2 + 2 r N ( B → [ K π ] D K ) ×Γ ( D → KK ) = R CP + = 1 + r B cos( δ B )cos( γ ) B Sneha Malde 12

Interference with flavour specific “ADS” D 0 K - i(δ B - γ ) r B e Larger interference effects as both amplitudes of similar sizes. B - [π - K + ] D K - AddiHonal two parameters r D , δ D . External inputs from charm mixing. i(δ D ) r D e D 0 K - r D ~ 0.06 N ( B − ) − N ( B + ) 1 N ( B − ) + N ( B + ) = A ADS = 2 r B r D sin( δ B + δ D )sin( γ ) R ADS N ( B ± → [ π ± K ∓ ] D K ± ) 2 + r 2 + 2 r N ( B ± → [ K ± π ∓ ] D K ± ) = R ADS = r B r D cos( δ B + δ D )cos( γ ) B D Atwood, Dunietz & Soni PRL 78 (1997) 3257, PRD 63 (2001) 036005 (ADS) Sneha Malde 13

LHCb detector RICH All except one analysis presented today come from full 2011 and 2012 datasets Sneha Malde 14

Detector performance (1) VELO: Tracking: Impact parameter resoluHon Momentum resoluHon Int. J Mod. Phys A 30 (2015) 1530022 Sneha Malde 15

Detector performance (2) Hardware trigger - hadronic trigger with high efficiency RICH detectors Low π misidenHficaHon rate Sowware trigger High kaon idenHficaHon - exploits decay topology Int. J Mod. Phys A 30 (2015) 1530022 Sneha Malde 16

Datasets 1 x -1 @ 7 TeV (2011) 2 x -1 @ 8 TeV (2012) Pile up much lower than the GPDs ~ 2 collisions per bunch crossing 0.3 x -1 @ 13 TeV (2015) 1.7 x -1 @ 13 TeV (2016) Pile up reduced to ~1 per bunch crossing Increased cross secHon Analyses today – all but one on Run 1 data - Precision measurements take effort and Hme - 2015 data only gives a modest increase. - Most “ Run 1” final results in this talk were produced in 2016 Sneha Malde 17

SelecHon All analyses shown here employ similar strategies K π B pp D collision IP π Separate the topology of interest from random combinaHons Use of mulH-variate analysis techniques. Useful variables include: Impact parameters Flight distances from primary. (B travels a ~cm) Flight distances from B – removes e.g B à K ππ backgrounds Vertex quality ParHcle ID Specific vetos against parHcular backgrounds Sneha Malde 18

B à D[K π ]h – CF control mode Difference between the two modes only the ID of the bachelor hadron Very large samples, B à DK ~ 30K B à DK PID performance à low crossfeed. B->D*h where a π 0 or photon isn’t reconstructed sits to the lew LHCb Extremely low level of combinatoric – clean environment B à D*h B à D π Control mode constrains the shapes of signal and backgrounds Control mode also used to measure LHCb the B ± producHon asymmetry. DetecHon asymmetries calibrated from other data. Results also extracted for B à D π mode, interference level expected to be ~ magnitude smaller arXiv:1603.08993 Sneha Malde 19

B à D(KK)h ) 400 0 2 c LHCb LHCb Events / ( 10 MeV/ 300 0 200 � � � � + 0 + + + B [ K K ] K B [ K K ] K � � D D 100 0 ~ 3800 B à DK 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 6000 0 LHCb LHCb 4000 0 � � � + � + + + B � [ K K ] � B � [ K K ] � D D 2000 0 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 ± m ( Dh ) [MeV/ c 2 ] KK = 0.087 ± 0.020 ± 0.008 A K StaHsHcal uncertainty dominant DescripHon of background is the leading systemaHc uncertainty arXiv:1603.08993 Sneha Malde 20

B à D( ππ )h 150 0 ) 2 ~ 1160 B à DK c LHCb LHCb Events / ( 10 MeV/ 100 0 � � � + � + + + B � [ � � ] K B � [ � � ] K D D 50 0 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 2000 0 LHCb LHCb 1500 0 1000 0 � � � + � + + + B � [ � � ] � B � [ � � ] � D D 500 0 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 ± 2 m ( Dh ) [MeV/ c ] ππ = 0.128 ± 0.037 ± 0.012 Asymmetry same direcHon as KK mode A K 5 σ Combined observaHon of CP violaHon arXiv:1603.08993 Sneha Malde 21

B à D[ π K]h ) 2 c 100 ~ 550 B à DK 0 LHCb LHCb Events / ( 10 MeV/ � � � � + + + + B � [ � K ] K B � [ � K ] K 50 0 D D 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 LHCb LHCb 400 0 � � � + � + + + B [ K ] B [ K ] � � � � � � D D 200 0 5100 5200 5300 5400 5500 5100 5200 5300 5400 5500 ± m ( Dh ) [MeV/ c 2 ] Only observed at LHCb, BF ~10 -7 -- a rare decay ObservaHon of CP violaHon in B à DK π K = − 0.403 ± 0.056 ± 0.011 8 σ A K π K = 0.100 ± 0.031 ± 0.009 CPV starts to become visible in B à D π A π 3.9 σ Combined with D à KK D à ππ significance arXiv:1603.08993 Sneha Malde 22