Recent results and prospects of quark flavour physics at LHCb Marco Gersabeck (The University of Manchester) Particle Physics Seminar, Birmingham, 16/11/2016
Two roads to discovery New particles = New planets ESA/Hubble 2
Direct searches Reach limited by amount of fuel ESA/Rosetta/NAVCAM 3
Indirect searches Look for subtle deviations in known processes D. Kipping et al. ApJ 795 (2014) 25 David A. Aguilar (CfA) 4
Flavour physics: Fast-tracking discoveries • K 0 - K ̅ 0 mixing and smallness of K 0 →μ + μ - ➡ GIM mechanism predicts charm quark in 1970 • Kaon CP violation ➡ KM mechanism predicts bottom and top quarks in 1973 • Charm & bottom quarks discovered: 1974+1977 • B 0 - B ̅ 0 oscillations discovered in 1987 ➡ Requires m top > 50 GeV to deactivate GIM cancellation • Top quark discovered: 1995 5
Flavour physics: Fast-tracking discoveries Then: ARGUS, 10 5 B B ̅ decays, probing 0.1 TeV • K 0 - K ̅ 0 mixing and smallness of K 0 →μ + μ - Now: LHCb, 10 11 B B ̅ decays, probing 100 TeV ➡ GIM mechanism predicts charm quark in 1970 t • Kaon CP violation d b B 0 W W B 0 ➡ KM mechanism predicts bottom and top quarks in 1973 • Charm & bottom quarks discovered: 1974+1977 b d t • B 0 - B ̅ 0 oscillations discovered in 1987 ➡ Requires m top > 50 GeV to deactivate GIM cancellation • Top quark discovered: 1995 5
Indirect searches • Two routes to success ➡ Rare processes Small new effects can cause ‣ Rare and forbidden decays large relative changes ‣ Small asymmetries ➡ High-precision measurements of well-known processes Small new effects can cause ‣ Large asymmetries large changes w.r.t. precision of prediction ‣ Symmetry tests: e.g. lepton universality 6
Flavourful experiments High-energy proton-proton collisions → General purpose flavour experiment Fixed target rare kaon decay experiments CLEO (II) Kaon Charm/Tau Beauty Other experiments with significant Threshold production experiments flavour physics output: ATLAS, CDF, CMS, D0 7
Outline • CP violation ➡ Selected highlights of small and large asymmetries • The needles in the haystack ➡ Rare decays • A brief visit to the particle zoo ➡ Other physics areas • Future directions ➡ Upgrade programmes 8
CKM matrix • Unitary matrix combining flavour and mass eigenstates Up Charm Top d 0 V ud V us V ub d = s 0 V cd V cs V cb s b 0 V td V ts V tb b Down Strange Bottom • Unitarity relations lead to triangles in complex plane V ud V ⇤ + 1 + V td V ⇤ B d triangle ub tb = 0 V cd V ⇤ V cd V ⇤ cb cb α β γ 9
CKM matrix • Unitary matrix combining flavour and mass eigenstates Up Charm Top d 0 V ud V us V ub d = s 0 V cd V cs V cb s b 0 V td V ts V tb b Down Strange Bottom • Unitarity relations lead to triangles in complex plane V ud V ⇤ + 1 + V td V ⇤ B d triangle ub tb = 0 V cd V ⇤ V cd V ⇤ cb cb V us V ⇤ + 1 + V ts V ⇤ B s triangle ub tb = 0 V cs V ⇤ V cs V ⇤ cb cb V ud V ⇤ + 1 + V ub V ⇤ D triangle cd cb = 0 V us V ⇤ V us V ⇤ cs cs + 3 more 9
CKM and beyond Summer 2001 Summer 2011 • A decade of precision measurements 2 0 • Huge success for BaBar and Belle 0 8 10
CKM today • 2010-2020 ➡ Enter LHCb • Looking for these little ripples caused by particles beyond the standard model 11
Beauty CP violation
Measuring γ V ud V ⇤ ub V cd V ⇤ cb γ • Essentially measuring the phase of V ub • Least well measured CKM angle 0.7 excluded area has CL > 0.95 CKM f i t t e r 0.6 Summer 14 γ • Measure CP violation in 0.5 sin 2 β sol. w/ cos 2 < 0 β (excl. at CL > 0.95) 0.4 B (s) → D (s) hX decays η α 0.3 α 0.2 • CP violation requires the 0.1 β γ α 0.0 interference of two amplitudes -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 ρ • Many different methods CP violation in B - → D(K + π - π 0 ) π - ➡ Combinations of B and D decays ➡ Time-integrated and time-dependent Phys. Rev. D91 (2015) 112014 13
A multitude of methods • (0,-) → Dh (h= π ,K,K * ) decays Methods for B ➡ Observables are time-integrated ratios of rates and rate asymmetries • ADS ➡ Measure favoured B decay with doubly Cabibbo-suppressed D decay and vice versa • GLW ➡ Measure favoured/suppressed B decays with D decaying into CP eigenstate • GGSZ ➡ Measure favoured/suppressed B decays with D decaying into multi-body final state including Dalitz analysis • In addition using B s → D s K decays ➡ Need to perform time-dependent measurement of rates and asymmetries 14
Improving γ precision • Combining LHCb measurements of B (s) → DK (*) decays • BaBar average * : 1 1-CL LHCb 0.8 ➡ (70±18)° • Belle average 0.6 * : 0.4 68.3% ➡ (73±14)° (72±7)° 0.2 • LHCb improves by factor 2 95.5% 0 50 60 70 80 90 • All based on tree decays arXiv:1611.03076 [ ] γ ° ➡ SM measurements ➡ Access to beyond SM particles through loops in γ measurements using B → hh(h) decays * CKMFitter Summer 2014 15
CP violation flavour-specific l + in mixing ν W c b B q • Look for B ̅→ l + decays q q ➡ Forbidden directly, requires B ̅→ B oscillation • Measure asymmetry of B ̅→ l + and B → l - rates ➡ CP violation in mixing • SM expectation far below current sensitivity • Can measure this separately for B d and B s mesons ➡ Separate access to A sl (B d ) & A sl (B S ) • Alternatively look for same-sign lepton pairs and compare l + l + with l - l - ➡ Measures combination of A sl (B d ) & A sl (B S ) 16
Latest results • D0 dimuon measurement differs from SM by about 3 σ 1 [%] ➡ Difficult to motivate by non-SM Standard Model sl s physics a 0 • Direct measurements of a sl (B d ) & a sl (B S ) X ν µ s 1 − D show agreement with SM D LHCb 0 µ µ • Possible differences in SM contribution − 2 X ν (*) µ LHCb D µ ν X to observables? s (*) D0 D X µ ν D − 3 D0 * BaBar D l ν • LHCb has best single measurement of BaBar ll Belle ll 4 − a sl (B d ) and a sl (B s ) − 3 − 2 − 1 0 1 d a [%] sl ➡ Latest: a sl (B s )=(0.39±0.26±0.20)% PRL 117 (2016) 061803 17
Charm CP violation V ud V ⇤ + 1 + V ub V ⇤ D triangle cd cb = 0 V us V ⇤ V us V ⇤ cs cs ~1 1 ~0.002 Hardly a triangle
Charm: hardly a triangle • Only up-type quark to form D 0 - D ̅ 0 mixing weakly decaying hadrons 1000 TeV ➡ Unique physics access Probing highest scales • Mixing → Isidori, Nir, Perez, ARNPS 60 (2010) 355 ➡ Huge cancellations ➡ Theoretically difficult Need 1000 lifetimes to see • CP violation a full D 0 - D ̅ 0 oscillation ➡ Predictions even smaller • Need highest precision → Not enough charm • Huge LHCb dataset in the universe! ➡ Blessing and a curse 19
Mixing-related CP violation • 0 → K - K + and D 0 →π - π + decays Measurements based on D • Measure asymmetries of effective lifetimes of decays to CP eigenstates: ind ➡ A Г ≈ a m y cos ϕ + x sin ϕ ≡ -a CP • Measures ability of both mass eigenstates to decay to CP eigenstate • *+ -tagged, 3 fb -1 [Preliminary, LHCb-CONF-2016-009+010] Prompt D -3 ; A Г ( ππ ) = (0.46±0.58±0.16) × 10 -3 ➡ A Г (KK) = (-0.30±0.32±0.14) × 10 • + -tagged, 3 fb -1 [JHEP 04 (2015) 043] D from semi-leptonic B decays, μ -3 ; A Г ( ππ ) = (-0.92±1.45±0.29) × 10 -3 ➡ A Г (KK) = (-1.34±0.77±0.30) × 10 (t) corr ( t ) 0 . 04 Data 0.01 LHCb Preliminary LHCb Preliminary LHCb-CONF-2016-009 CP LHCb preliminary Fit 0 . 02 A KK A Prompt signal 0 0 . 00 0.01 − − 0 . 02 2011 Up 2011 Down Unbinned − 0 . 04 0.02 LHCb-CONF-2016-010 − corr ( t ) 0 . 04 Binned LHCb preliminary t [ps] 1 2 3 0 . 02 A KK 5 0 . 00 Pull 0 − 0 . 02 2012 Up 2012 Down 5 − − 0 . 04 0 2 4 6 8 20 t/ τ D 20
The Δ a CP saga * • What is Δ a CP ? • Interplay of CP violation in decay and mixing • Individual asymmetries are expected to have opposite sign due to CKM structure * after A. Lenz @ CHARM 2013, arXiv:1311.6447 EPJC 73 (2013) 2373 21
Results • D*-tagged (2011+12 data) D 0 π s+ PRL 116 (2016) 191601 • muon-tagged (2011+12 data) D 0 μ - B JHEP 07 (2014) 014 22
Individual asymmetries a D ( π + ) a P (D * ) a raw (K - K + ) = a CP (K - K + ) + + measure want 23
Individual asymmetries a D ( π + ) a P (D * ) a raw (K - K + ) = a CP (K - K + ) + + measure want D 0 → K - π + 23
Individual asymmetries a D ( π + ) a P (D * ) a raw (K - K + ) = a CP (K - K + ) + + measure want D 0 → K - π + a D (K - π + ) 23
Individual asymmetries a D ( π + ) a P (D * ) a raw (K - K + ) = a CP (K - K + ) + + measure want D 0 → K - π + a D (K - π + ) D + → K - π + π + 23
Individual asymmetries a D ( π + ) a P (D * ) a raw (K - K + ) = a CP (K - K + ) + + measure want D 0 → K - π + a D (K - π + ) D + → K - π + π + a P (D + ), a D ( π + ) 23
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