Measurements with doubly-charmed hadrons Daniel Vieira University - PowerPoint PPT Presentation

Measurements with doubly-charmed hadrons Daniel Vieira University of Chinese Academy of Sciences On behalf of LHCb collaboration 9th International Workshop on Charm Physics 22/05/2018 � 1 � 1

Outline Introduction LHCb Experimental status Ξ cc++ observation Lifetime measurement Prospects and conclusion � 2

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 interactions to J P = 1/2 + (J P = 1/2 + and J P = 3/2 + ) Each has a doubly charmed SU(3) triplet J P = 1/2 + baryons decay weakly to other ( Ξ cc++ (ccu), Ξ cc+ (ccd) and Ω cc+ (ccs)) flavours � 3

Ξ cc++ - Mass https://indico.cern.ch/event/632400/ Theoretical predictions of Ξ cc++ mass are 3.5-3.7 GeV/c 2 and expected to be close to Ξ cc+ [1-6] � 4

Ξ cc++ - Lifetime Ξ cc++ (ps) Ξ cc+ (ps) Reference Ω cc+ (ps) Karliner, Rosner, 2014 0.185 0.053 Kiselev, Likhoded, 0.430 +/- 0.100 0.110 +/- 0.010 Onishchenko, 1998 Kiselev, Likhoded, 2002 0.460 +/- 0.050 0.160 +/- 0.050 0.270 +/- 0.060 Guberina, Melic, 
 1.050 0.200 0.300 Stefancic, 1998 Chang, Li, Li, Wang, 2007 0.670 0.250 0.210 Large ambiguity in theoretical predictions [7-12] W-exchange � 5

SELEX experiment Ξ cc+ measurement PRL 97, 162001 (2006) 15.9 events 5.62 events Observed Ξ cc+ → Λ c+ K - π + and Ξ cc+ → pD + K - decays Short lifetime: 𝞄 Ξ cc+ < 33 fs @90% CL Large production: exceeding theoretical predictions by orders of magnitude Mass (combined): 3518.7 ± 1.7 MeV � 6

Other Ξ cc+ searches Results not confirmed by other experiments (Focus, BaBar, Belle and LHCb) Belle SELEX Ξ cc+ PRL 97, 162001 (2006) JHEP 12 (2013) 090 � 7

LHCb Good momentum resolution: p/ δ p ≈ 0.5% - 1% (5-200 GeV) Good vertex resolution: IP resolution ≈ 20 µm Particle identification: 𝜗 ( 𝐿 → 𝐿 ) ~95%, Mis-ID 𝜗 ( 𝜌 → 𝐿 ) ~5% � 8

LHCb L0 hardware trigger: looks for transverse energy signatures Software high level trigger: near real time alignment and calibration in trigger � 9

LHCb Run I: 1.0 fb -1 at 7 TeV (2011) + 2.0 fb -1 at 8 TeV (2012) Run II: 0.3 fb -1 (2015) + 1.7 fb -1 (2016) + 1.7 fb -1 (2017) at 13 TeV � 10

Ξ cc++ → Λ c+ K - π + π + Most promising channel for observation [13] See talk in parallel session tomorrow by Prof. Yu 
 https://indico.inp.nsk.su/event/10/session/7/ contribution/29 Lifetime measurement 
 important to confirm weakly decaying nature � 11

Dataset, reconstruction and selection 2016 data (1.7fb -1 ) Signal kinematical distributions taken from MC Background distributions taken from wrong-sign 
 Ξ cc++ → Λ c+ K - π + π - samples First reconstruct Λ c+ → pK - π + , then combine with K - π + π + � 12

Dataset, reconstruction and selection Selection is performed in three steps: Trigger (dedicated trigger line): Kinematical constraints, PID, track and vertex quality Preselection: Ghost probability, kinematical constraints, vertex and PV refit quality MVA: Kinematical constraints and Vertex refit quality � 13

Mass fit PRL 119 (2017) 112001 𝑛 ( Ξ cc++ ) = 𝑛 ( Λ c+ 𝐿 - 𝜌 + ) − 𝑛 ( Λ c+ ) + cc = 3621 . 40 ± 0 . 72( stat ) ± 0 . 27( syst ) ± 0 . 14( Λ c ) MeV m Ξ ++ Mass value consistent with theoretical range of predictions! Not consistent with Ξ cc+ SELEX measurement [M LHCb ( Ξ cc++ ) - M SELEX ( Ξ cc+ ) = 103 ± 2 MeV ] Local significance > 12 𝜏 Signal yield: 313 ± 33 � 14