Heavy flavour spectroscopy at ATLAS, CMS and LHCb Mat Charles - PowerPoint PPT Presentation

Heavy flavour spectroscopy at ATLAS, CMS and LHCb Mat Charles (Sorbonne Université * /LPNHE) 1 * Previously Université Pierre et Marie Curie, previously Université de Paris, previously Université de France, previously Université de Paris

Topics for today • The Ξ cc++ discovery • The ongoing X(5568) mystery • Round-up of updates since La Thuile 2017 • Five new narrow Ω c0 → Ξ c+ K − states • Search for weakly decaying b-flavoured pentaquarks • Excited B c+ states • Precise measurements of χ c1 and χ c2 • A promising first look at χ b → 𝛷γ ( 𝛷 → μ + μ − ) No hope of covering all LHC spectroscopy results, sorry! 2

The Ξ cc++ (ccu) discovery 3

Ξ cc++ : Quark model • In the quark model, expect baryons with > 1 heavy quark. • Several of them should decay weakly, including: • ccu = Ξ cc++ } Ξ cc isospin doublet • ccd = Ξ cc+ ++ C Ω C=3 ccc • ccs = Ω cc++ S • ccc = Ω ccc++ I 3 • At stupidly naive 0th order, *+ *++ + ++ C=2 C=2 Ξ Ξ Ξ Ξ cc cc cc cc *+ + Ω Ω cc cc m(p) = 938 MeV m( Λ c ) = 2286 MeV *+ *++ + + ++ *0 0 + + C=1 / C=1 Σ Λ / Σ Σ Σ Σ Σ Λ Σ c c c c c c c c c => m( Ξ cc ) ~ 3.6 GeV *0 *+ 0 '0 + '+ 0 '0 + '+ / / Ξ Ξ Ξ / Ξ Ξ Ξ Ξ / Ξ Ξ Ξ c c c c c c c c c c => m( Ω ccc ) ~ 5.0 GeV *0 0 Ω Ω c c • Real calculations typically 
 - + ++ p 0 n Δ Δ Δ Δ - give 3.5 < m( Ξ cc ) < 3.7 GeV, 
 *- + *0 *+ 0 0 Σ / / Σ Σ Σ Σ Λ Λ Σ Σ C=0 C=0 - *- *0 0 Ξ Ξ Ξ Ξ τ ( Ξ cc++ ) ~ few hundred fs, 
 - + 3 + Ω P 1 J = P J = 2 2 τ ( Ξ cc++ )/ τ ( Ξ cc+ ) ~ 3 to 4 See e.g. Kiselev & Likhoded [Phys. Usp. 45, 455 (2002)], 
 Fleck & Richard [Prog. Theor. Phys. 82, 760 (1989)]. Full list of theory refs in backups. 4

Ξ cc++ : History • Longstanding experimental puzzle: observations of Ξ cc+ (ccd) claimed by SELEX in 2002, 2005 but never reproduced by other experiments. • Various oddities with SELEX result... but because production environment was unique (hyperon beam on fixed target), other results didn't formally rule it out. • Relevant points for today: 
 SELEX 8 (c) SELEX reported Events /2.5 [ MeV/c 2 ] 7 • m( Ξ cc+ ) = 3519 ± 2 MeV Ξ cc+ 6 • τ ( Ξ cc+ ) < 33 fs @ 90% CL 5 4 3 2 1 0 3.4 3.5 3.6 3.7 3.8 3.42 3.47 3.52 3.57 3.62 SELEX: PRL 89:112001 (2002) 12 + K - π + ) [ GeV/c 2 ] SELEX: PLB B628:18-24 (2005) M ( Λ c 5

Ξ cc++ : Discovery LHCb result, obtained with 2016 (Run 2) data: 2 c 180 LHCb 13 TeV Candidates per 5 MeV/ 160 Ξ ++ → Λ + c K − π + π + Data cc 140 Total 120 Signal Background 100 80 60 40 Yield: 313 ± 13 Local significance > 12 σ 20 0 3500 3600 3700 ++ m ( ) [MeV/ c 2 ] Ξ cc cand LHCb: PRL 119, 112001 (2017) 6

Ξ cc++ : Checks & tests • Observation confirmed with 2012 sample (crosscheck). • Lifetime significantly different from zero: observation persists when requiring (t / σ t ) > 5 • σ t varies event by event, but typical resolution ~ 40-50fs 2016 data 2012 data With lifetime cut 2 2 2 c c 180 c 70 LHCb 13 TeV Candidates per 5 MeV/ LHCb 8 TeV Candidates per 5 MeV/ 140 LHCb 13 TeV Candidates per 5 MeV/ Significance 
 160 t / > 5 σ Significance 
 60 t 120 Data Data Data >7 σ 140 >12 σ Significance 
 Total Total Total 50 100 120 Signal Signal Signal >12 σ Background Background 40 Background 100 80 80 30 60 60 20 40 40 10 20 20 0 0 3500 3600 3700 3500 3600 3700 3500 3600 3700 ++ ++ 2 ++ 2 m ( Ξ ) [MeV/ c ] m ( Ξ ) [MeV/ c ] 2 m ( Ξ ) [MeV/ c ] cc cc cand cc cand cand ± ± cc Mass: m( Ξ cc++ ) = e 3621 . 40 ± 0 . 72 (stat) ± 0 . 27 (syst) ± 0 . 14 ( Λ + /c 2 , w c ) MeV + Differs from SELEX Ξ cc+ mass by 103±2 MeV => clearly not a conventional isodoublet. LHCb: PRL 119, 112001 (2017) 7

Ξ cc++ : What's next? • Ξ cc++ lifetime measurement! Crucial to the interpretation. • Will also give a clue about Ξ cc+ lifetime. • Ξ cc++ production cross-section veil of ignorance • Confirmation at ATLAS & CMS? Belle-II? • More Ξ cc++ decay modes! Ratios of branching fractions. • Constraints on spin, parity • Ξ cc+ search • Tougher, due to shorter expected lifetime. • LHCb failed to find Ξ cc+ → Λ c+ K − π + with 0.65 fb − 1 earlier... but now have better triggers, more modes, and much more data. • Ξ cc+ properties, production relative to Ξ cc++ , etc • Ω cc+ search (tougher still) • Excited states • Lowest expected to decay electromagnetically -- tough for LHCb • Add pions, kaon... see what's out there! 8

The ongoing X(5568) mystery 9

X(5568) : The D0 observation Feb 2016: D0 reported a narrow structure in 2000 -1 D0 Run II, 10.4 fb Inclusive 2 N events / 20 MeV/c the B s0 π ± spectrum (with B s0 → J/ 𝜔 𝜚 ). 
 1500 B s0 sample (5.6k sig) Manifestly exotic b s q q resonance. 1000 500 Yield: 133±31 events 
 0 4.8 5 5.2 5.4 5.6 5.8 6 2 m ( / ) [GeV/c ] J ψ φ Significance: 6.1 σ stat, or 5.1 σ stat+sys (inc LEE) Add π ± Eff-cor yield ratio 𝜍 (X/B s0 ): 90 -1 D0 Run II, 10.4 fb X(5568) 80 (a) 2 N events / 8 MeV/c 10 < p T ( B 0 s ) < 15 GeV /c : (9 . 1 ± 2 . 6 ± 1 . 6)% DATA 70 Fit with background shape fixed Background 15 < p T ( B 0 s ) < 30 GeV /c : (8 . 2 ± 1 . 9 ± 1 . 4)% 60 Signal average : (8 . 6 ± 1 . 9 ± 1 . 4)% 50 B s0 π ± 40 This is a lot! 30 Mass and width: 20 m = 5567 . 8 ± 2 . 9 (stat) +0 . 9 − 1 . 9 (syst) MeV /c 2 10 Γ = 21 . 9 ± 6 . 4 (stat) +5 . 0 0 − 2 . 5 (syst) MeV 5.5 5.55 5.6 5.65 5.7 5.75 5.8 5.85 5.9 15 2 m 0 (B ± ) [GeV/c ] π S But then... D0: PRL 117, 022003 (2016) 10 π

X(5568) : Not seen at LHCb Aug 2016: LHCb tries to confirm peak, finds Candidates / (5 MeV) 900 0 Claimed X(5568) state LHCb p ( B ) > 5 GeV s 800 T Combinatorial 700 nothing despite larger B s0 sample, extra mode. 600 500 LHCb } 400 300 Candidates / (3 MeV) 200 6000 LHCb 100 B s0 → D s − π + 5000 0 Pull 4 2 4000 0 − 2 − 4 3000 106k B s0 5550 5600 5650 5700 5750 5800 5850 5900 5950 6000 0 2000 m(B ) (MeV) π ± s 1000 Candidates / (5 MeV) Add π ± , try 0 Claimed X(5568) state LHCb p ( B ) > 10 GeV s 0 T 250 Combinatorial 5300 5350 5400 5450 5500 5550 5600 - m(D + ) (MeV) π 200 s various p T 150 Candidates / (3 MeV) 12000 100 cuts... B s0 → J/ 𝜔 𝜚 10000 50 8000 0 Pull 6000 4 2 0 4000 − 2 − 4 5550 5600 5650 5700 5750 5800 5850 5900 5950 6000 2000 0 m(B ) (MeV) π ± s 0 5200 5250 5300 5350 5400 5450 5500 Candidates / (5 MeV) 90 0 Claimed X(5568) state LHCb p ( B ) > 15 GeV m(J/ ) (MeV) ψ φ s 80 T Combinatorial Upper limits set on (X/Bs) cor. yield ratio: 70 60 50 40 ⇢ LHCb ( p T ( B 0 s ) > 5 GeV) < 0 . 011 (0 . 012) , 30 X 20 ⇢ LHCb ( p T ( B 0 at 90% (95%) CL 10 s ) > 10 GeV) < 0 . 021 (0 . 024) , 0 X Pull 4 2 ⇢ LHCb ( p T ( B 0 0 s ) > 15 GeV) < 0 . 018 (0 . 020) . − 2 − 4 X 5550 5600 5650 5700 5750 5800 5850 5900 5950 6000 ... vs (8.6 ± 1.9 ± 1.4)% at D0 (but different environment) 0 m(B ) (MeV) π ± s And then... LHCb: PRL 117, 152003 (2016) 11

X(5568) : Nor at CMS 17 Dec 2017: CMS tries to confirm CMS -1 19.7 fb (8 TeV) Candidates / 5 MeV (a) peak, also finds nothing. 800 600 0 p (B ) > 10 GeV -1 CMS 19.7 fb (8 TeV) s T 10000 Candidates / 5 MeV Data N = 49 277 278 ± 400 0 B Data s Fit = 5366.54 0.06 MeV µ ± 49k B s0 0 B Signal s Fit 8000 σ = 8.03 ± 0.18 MeV 1 Background σ = 18.6 ± 0.5 MeV 200 2 Add π ± , try f = 0.47 0.02 ± B s0 → J/ 𝜔 K + K − 6000 various p T Pull 5.5 5.6 5.7 5.8 5.9 2 4000 0 − 2 cuts... 5.5 5.6 5.7 5.8 5.9 0 2000 Δ M (B ± ) [GeV] π s 5.2 5.3 5.4 5.5 + − CMS -1 M(J/ K K ) [GeV] ψ 19.7 fb (8 TeV) Candidates / 5 MeV (b) → 600 r X < 1.1% at 95% CL for p T ( B 0 s ) > 10 GeV and 0 p (B ) > 15 GeV 400 s T r X < 1.0% at 95% CL for p T ( B 0 s ) > 15 GeV. Data Fit 200 ... vs (8.6 ± 1.9 ± 1.4)% at D0, but again Pull 5.5 5.6 5.7 5.8 5.9 2 0 different production environment. 2 − 5.5 5.6 5.7 5.8 5.9 0 Δ M (B ± ) [GeV] π s And just 10 days later... CMS: arXiv:1712.06144 (submitted to PRL) 12

X(5568) : Nor at CDF 120 2 27 Dec 2017: CDF searches, finds Scaling D0 results to CDF... c Candidates per 5 MeV/ 100 nothing, sets UL. 80 2 60 c Candidates per 5 MeV/ 800 B s0 → J/ 𝜔 𝜚 40 3.6k B s0 600 20 Add π ± ... 400 0 200 5.5 5.6 5.7 5.8 5.9 0 2 M(B ± ) GeV/ c π 0 s 5.2 5.275 5.35 5.425 5.5 120 2 2 M(J/ ) GeV/ c ψ φ c Candidates per 5 MeV/ 100 0 B signal region s Limit on corrected yield ratio: 80 60 𝜍 (X/Bs) < 6.7% at 95% CL 40 0 B sideband regions s ... vs (8.6 ± 1.9 ± 1.4)% at D0. 
 20 NB same environment 0 5.5 5.6 5.7 5.8 5.9 0 2 ± GeV/ c M(B ) π s And then just two days later... CDF: arXiv:1712.09620 13