0 baryon at LHCb The UNIVERSITY OF BIRMINGHAM SCHOOL OF PHYSICS - PowerPoint PPT Presentation

0 baryon at LHCb The Λ 𝑐 UNIVERSITY OF BIRMINGHAM SCHOOL OF PHYSICS AND ASTRONOMY SEMINAR 21/10/15 Peter Griffith University of Birmingham, UK 1

Contents • B-physics at the LHC • Heavy baryons in B-physics • The LHCb detector 0 baryon at the LHC • Understanding the Λ 𝑐 • Key measurements 0 • FCNC decays with Λ 𝑐 0 → 𝑞𝐿 − 𝜈 + 𝜈 − in detail • Λ 𝑐 • Summary University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 2

Flavour physics, SM and BSM The very successful Standard Model Hierarchy Problem ? ? Dark Matter ? Gravity ? ? Matter/antimatter asymmetry Dark Energy University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 3

LHCb |𝑊 𝑣𝑐 | measurement B-physics at LHCb: • B-physics presents many ways to test and constrain the SM • Excellent probes for New Physics & precise measurements of SM • CP measurements reconstructed decay 𝐶 → 𝑌 3872 𝐿 • FCNC observables (bs->ll etc.) • New intermediate states/particles University of Birmingham Seminar Lb baryon at LHCb Peter Griffith 4

B-physics at LHCb: • Abundant b-quark production at the LHC 𝑞 → 𝑐 • 𝜏 𝑞 𝑐X ~ 80𝜈𝑐 • ~ 100,000 𝑐 𝑐 pairs per second • 40% of heavy quark production within the acceptance of LHCb 𝑔 Λ𝑐 0 0 ′𝑡 at the LHC! (20% of b hadrons) 𝑔 𝑒 ~0.4 – plenty of Λ 𝑐 • Production fraction, 0 has half integer spin – opens the door for unique measurements • Λ 𝑐 University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 5

RICH – large The LHCb detector background rejection from PID Magnet • 4Tm • Polarity regularly VELO - high precision switched to cancel tracking and tagging systematic effects • ~4𝑛𝑛 from beam • able to reconstruct secondary vertices (B meson flight distance ~10𝑛𝑛 ) Extensive muon detection system with clean muon triggering 𝑃(1𝑛𝑛) Calorimeters • SPD • PD • ECAL • HCAL Trackers University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 6

Data taking at LHCb Atlas/CMS • Total amount of data after Run1: 3𝑔𝑐 −1 LHCb • ~1𝑔𝑐 −1 in 2011 < κ > ~2.7𝑓32 𝑑𝑛 −2 𝑡 −1 • ~2𝑔𝑐 −1 in 2012 < κ > ~4.0𝑓32 𝑑𝑛 −2 𝑡 −1 • Comparatively low • LHCb employs ‘lumi levelling’ – constant ~5 𝑙𝐼𝑨 read out rate to disk rather than high instantaneous luminosity ( 1 𝑙𝐼𝑨 originally planned ) preferred. • Some precision measurements require very well known luminosity High operational efficiency ( ~2% • PID system becomes ‘saturated’ at higher deadtime) luminosities University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 7

0 at LHCb Λ 𝑐 Interesting measurements and discoveries University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 8

0 → 𝑞𝜉𝜈 Measuring |𝑊 𝑣𝑐 | with Λ 𝑐 • Previous inclusive measurements by Babar and Belle • Large disagreement between inclusive and exclusive measurements – new particle with right-handed 0 → 𝑞𝜈 − 𝜉 𝜈 coupling? 𝑣𝑐 2 𝐶 Λ 𝑐 𝑊 𝑑𝑐 2 = 𝑆 𝐺𝐺 0 → Λ 𝑑 + 𝜈 − 𝜉 𝜈 𝑊 𝐶 Λ 𝑐 New LHCb measurement removes the need for a new particle. Where 𝑆 𝐺𝐺 is the ratio of relevant But why the initial disagreement? form factors 0 → 𝑞𝜈 − 𝜉 𝜈 candidates are Λ 𝑐 𝜗 𝑆 ~ − 0.2 Candidates with 100𝑁𝑓𝑊/𝑑 2 reconstructed using uncertainty are selected → new particle would 2 + 𝑞 ⊥ 2 + 𝑞 ⊥ m 𝑑𝑝𝑠𝑠 = 𝑛 ℎ𝜈 have ~20% coupling strength of the W boson Transverse momentum of Visible ℎ𝜈 pair mass University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 9

0 → 𝐾/𝜔𝑞𝐿 − Resonances in Λ 𝑐 0 → 𝐾/𝜔𝑞𝐿 − • Two resonances observed in Λ 𝑐 𝑸 𝒅 (𝟓𝟓𝟔𝟏) 𝑸 𝒅 (𝟓𝟒𝟗𝟏) • Consistent with pentaquark state with Mass (Me𝑊/𝑑 2 ) 44 49.8 ± 4.2 4380 ± 37 content quark cuud − 𝐾 𝑄 + 3 5 2 2 Six dimensional amplitude fit. Significance, 𝜏 12 9 Using just Λ ∗ states is not adequate. Two additional states required arXiv:1507.03414 University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 10

0 polarisation Measurement of the Λ 𝑐 Decay amplitudes • First of its kind at a hadron collider 0 → J/𝜔Λ decays • Uses Λ 𝑐 1 1 2 particle into spin 1 and • Decay of a spin 2 particles Transverse polarisation parameter Angular analysis performed on all Angular distributions three angles to downstream Transverse production polarisation: 0.06 ± 0.07 ± 0.02 long Appears to be small (O(10%) or less) • Not so favourable for studying photon helicity in 0 → Λ𝛿 and Λ 𝑐 0 → Λ ∗ 𝛿 decays if small ☹ Λ 𝑐 arXiv:1302.5578 University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 11

0 lifetime measurement 𝛭 𝑐 0 → 𝐾/𝜔𝑞𝐿 − • Lifetime measured with 𝛭 𝑐 decays • Relative to 𝐶 0 → 𝐾/𝜔𝜌 + 𝐿 − lifetime • 1𝑔𝑐 −1 of data 0 and 𝐶 0 Acceptance ratio of Λ 𝑐 0 and 𝐶 0 Decay time distributions for Λ 𝑐 Unprecedented precision dominates world average arXiv:1509.00292 𝑀𝐼𝐷𝑐 = 𝜐 Λ 𝑐 0 1.482 ± 0.018 ± 0.012 ps University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 12

Rare Decays at LHCb 𝜈 − 𝑐 𝑡 𝑐 • FCNC’s can occur through 𝑡 𝜈 + loops • Highly suppressed • Sensitive to new physics e.g. 𝜈 + 𝜈 − additional diagrams from new An effective field theory is employed BSM particles in loops 𝑡 𝑐 𝑡 𝑐 • Numerous observables – many very sensitive to NP 𝜈 + 𝜈 − 𝜈 + 𝜈 − • LHCb ideal for studying rare FCNC decays of mesons and baryons, e.g. 𝑐 → 𝑡 All Wilson coefficients • High resolution tracking Operators calculable (local interaction terms) Wilson coefficients → predictive • High performance PID NP can be seen in • Muon signals ‘clean’ at LHCb deviations of Wilson coefficients University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 13

0 → Λ 𝜈 + 𝜈 − Branching ratio measurement Λ 𝑐 LHCb-PAPER-2013-025 • Previously measured at CDF • No signal observed at low 𝑟 2 at either CDF or LHCb but results consistent with SM • Now updated to 3𝑔𝑐 −1 , with angular analysis University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 14

0 → 𝛭 𝜈 + 𝜈 − 3𝑔𝑐 −1 update 𝛭 𝑐 BR as a function of 𝑟 2 • First evidence of the signal at low 𝑟 2 ! (3 𝜏 ) • Slight deviation from SM predictions – similar to other 𝑐 → 𝑡𝑚𝑚 measurements • Forward backward asymmetries measured Leptonic 𝐵 𝐺𝐶 Hadronic 𝐵 𝐺𝐶 arXiv:1503.07138 University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 15

0 → 𝑞𝐿 − 𝜈 + 𝜈 − Λ 𝑐 Branching fraction measurement University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 16

0 → 𝑞𝐿 − 𝜈 + 𝜈 − 0 → 𝑞𝐿 − 𝜈 + 𝜈 − Non-resonant Λ 𝑐 Λ 𝑐 • Rare FCNC decay through excited states 0 → Λ ∗ (1520)𝜈 + 𝜈 − • Likely dominated by Λ 𝑐 • 𝑛(𝑞𝐿 − ) structure known All variables blinded in 𝟏 • ‘Unobserved’ mass region of the 𝚳 𝐜 0 → 𝐾/𝜔 → 𝜈 + 𝜈 − 𝑞𝐿 − 𝑛(𝑞𝐿 − ) in Λ 𝑐 • Very limited theoretical knowledge Branching fraction predictions (in units of 10e6) for SCA (SM1) and MCN (SM2) models. (a and b without and with LD charmonium contributions respectively) arXiv:1108.6129 SUSY Wilson coefficients from M. J. Aslam, Y.-M. Wang and C.-D. Lu, Phys. Rev. D 78, 114032 (2008) University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 17

0 → 𝑞𝐿 − 𝜈 + 𝜈 − branching fraction measurement 𝛭 𝑐 0 → 𝐾/𝜔𝑞𝐿 − • Measured relative to Λ 𝑐 • Simpler calculation No clean separation DATA of Λ ∗ (1520) • Cancellation of systematic effects MC • Lack of theoretical and experimental knowledge • → Lots of ‘correcting’ to be done 0 → 𝐾/𝜔𝑞𝐿 − 𝑛(𝑞𝐿 − ) in Λ 𝑐 MC is produced with only phase- space kinematics ‘Typical’ differential decay rate ( 𝐶 0 → Dimuon mass squared Experimentally motivated model 0 → 𝑞𝐿 − 𝜈 + 𝜈 − MC 𝐿 ∗0 𝜈 + 𝜈 − ) as function of dimuon mass Λ 𝑐 for decay structure would need squared full amplitude analysis University of Birmingham 21/10/15 Lb baryon at LHCb Peter Griffith 18