fulltext

DOI 10.1393/ncc/i2013-11451-4

Colloquia_{: IFAE 2012}

IL NUOVO CIMENTO Vol. 36 C, N. 1 _{Gennaio-Febbraio 2013}

Study of three-body charmless decays at LHCb

R. Cardinale

Department of Physics, University of Genova and INFN - Genova, Italy CERN - Geneva, Switzerland

ricevuto il 31 Agosto 2012

Summary. — Charmless three-body B decays are of interest to measure CP asymmetry and also to search for possible new physics Beyond the Standard Model. Three-body baryonic decays offer the possibility to study intermediate resonances. The study performed at LHCb and the results obtained using the 2010 35 pb−1data sample are presented.

PACS 13.25 – Decays of bottom mesons.

1. – Measurements of the relative branching fractions of the B+_{→ p¯pK}+_decay

channel including charmonium contributions

The measurements of the branching fractions of the B+ → p¯pK+, of the charmless

component (Mp ¯p < 2.85 GeV/c2) and of the charmonium contribution ηc: B(B+ →

ηcK+)× B(ηc → p¯p) with respect to the J/ψ: BJ/ψ=B(B+→ J/ψK+)× B(J/ψ → p¯p) have been performed. The measurement relies only on the ratios of events and efficiencies

with respect to the reference mode J/ψ: BR(mode)_BR

J/ψ =

Nmode

NJ/ψ ×

J/ψ

mode. The efficiencies have

been determined using simulated events and the efficiency variation in the Mp ¯p range

has been corrected for. Since the final state for all the considered channels is the same, most of the systematic uncertainties cancel in the ratio. The selection uses a multivariate technique based on topological variables and on the particle identification information provided by the RICH detectors. The selected events are reported in fig. 1. The obtained branching fractions [1] are compatible with B-factories measurements but are statistically limited:

B(B±_{→ η}

cK±)× B(ηc → p¯p)/BJ/ψ= 0.71± 0.20stat± 0.07syst B(B±_{→ p¯pK}±₎

Mp ¯p<2.85 GeV/c2/BJ/ψ= 2.21± 0.41stat± 0.24syst

B(B±_{→ p¯pK}±₎

all/BJ/ψ= 4.6± 0.6stat± 0.5syst.

c

260 R. CARDINALE ) 2 K) (MeV/c p M(p 5100 5200 5300 5400 2 Events/10 MeV/c 0 20 40 60 Preliminary LHCb -1 L=36 pb =7 TeV s 18 ± N(B) = 225 2 1.4) MeV/c ± M(B) = (5278.7 2 1.3) MeV/c ± (B) = (16.7 σ ) 2 ) (MeV/c p M(p 2700 2800 2900 3000 3100 3200 3300 2 Events/10 MeV/c 0 5 10 15 20 25 _PreliminaryLHCb -1 L=36 pb =7 TeV s 7.4 ± ) = 48.3 ψ N(J/ 7.7 ± ) = 34.3 c η N( 2 1.3) MeV/c ± ) = (3095 ψ M(J/ 2 6) MeV/c ± ) = (2976 c η M( 2 13) MeV/c ± )= (35.2 c η ( Γ 2 1.14) MeV/c ± = (8.28 σ

Fig. 1. – All B selected events (left) and p¯p events (right).

The 2011 available statistics, about 1 fb−1of data collected in 2011, a factor 10 more with

respect to B-factories, allows to perform more precise measurements of the branching

fractions and to study more rare charmonium contributions (ηc(2S), X(3872), . . .) that

have never been measured before.

2. – Relative branching ratio measurements of B+ → K+K+K− and B+ →

p¯pK+ _{to B}+ _{→ K}+_π+_π−

Exploiting the topological similarities, a cut based inclusive selection has been used for all the considered channels (fig. 2). The measurement [2] is based on the ratio:

B(B+_{→ h}+_h−_h+₎ B(B+_{→ K}+_π+_π−₎ = Nhhh NKππ × acc Kππ acc hhh ×reco&selKππ reco&sel hhh × trigger Kππ trigger_hhh × P ID Kππ P ID hhh

The efficiency ratios have been estimated using simulated events except for the PID estimated using control samples. Acceptance, reconstruction, trigger and PID efficiency systematics have been evaluated. The obtained results are compatible with PDG values:

B(B+_{→ K}+_K+_K−_)/B(B+_{→ K}+_π+_π−_{) = 0.52± 0.03} stat± 0.01syst B(B+_{→ p¯pK}+_)/B(B+_{→ K}+_π+_π−_{) = 0.19± 0.02} stat± 0.02syst ] 2 [MeV/c KKK M 5100 5200 5300 5400 2

Number of Entries / 10 MeV/c ₀

20 40 60 80 100 120 140 160 ] 2 [MeV/c KKK M 5100 5200 5300 5400 2

Number of Entries / 10 MeV/c ₀

20 40 60 80 100 120 140 160 Preliminary LHCb = 610 +- 29 evts B N signal combinatorics ) KK 0 π (K *+ K → B

STUDY OF THREE-BODY CHARMLESS DECAYS AT LHCb 261

3. – Search of CP violation in B+→ K+π+π− and B+→ K+K+K−

The ACP(B+→ K+π+π−) e ACP(B+→ K+K+K−) can be measured in the Dalitz

Plot using the “Mirandizing” method [3] using 2011 data sample extracting the produc-tion and the detector asymmetry from control channels.

REFERENCES

[1] LHCb-CONF-2011-058. [2] LHCb-CONF-2011-059.