LHCP conference Bologna, June 4th June 9th, 2018 Frédéric Machefert for the LHCb collaboration

Transcription

1 (In)direct Search of SUSY at LHCb LHCP conference Bologna, June 4th June 9th, 2018 Frédéric Machefert for the LHCb collaboration

2 Introduction The LHCb experiment performs complementary searches for SUSY to the general purpose detectors ATLAS and CMS Excellent vertex reconstruction Primary vertex (25 tracks) spv(z)=71mm spv(t)=13mm Excellent mass resolution 0.5% in mm Excellent particle Id muon Id 97 % for 1-3% p m misid Int. J. Mod. Phys. A 30, (2015) JINST 10 (2015) P06013 Flexible trigger readout Luminosity collected with a low pile-up Year s 8 TeV 13 TeV 13 TeV 13 TeV Number of crossings Separation 50 ns 25 ns 25 ns 25 ns Int/crossing x x x x1032 Ins. Lumi. 2

3 Scope of this talk This talk will cover Very rare decays B0 m+m- and B0s m+m- PRL 118, (2017) Search for B0 t+t- and Bs t+t- PRL 118, (2017) Radiative decay B0s fg PRL 118, (2017) Probing S+ pm+m- PRL 120, (2018) Search for B0 m+m-m+m- and B0s m+m-m+m- Search for long lived particles decaying semileptonically See talk by Flavio Archilli Very rare decays in Beauty, Charm and strange decays JHEP 03 (2017) 001 Eur. Phys. J. C 77 (2017) 224 See talk by Elena Dall Occo tomorrow afernoon 3 Search for charged stable massive particles Eur. Phys. J. C 75 (2015) 595

4 B0 m+m- and B0s m+mprl 118, (2017) In the Standard Model (SM), these processes : only occur via favour changing neutral currents are further suppressed by helicity and CKM constraints They are described by efective feld theory with the operator expansion H eff = G F α (' ) (') (' ) (' ) (' ) (') V tq V tb (C 10 O 10 +C S O S +C P O P ) 2 p C10 being the only SM contribution 4 Cs and Cp are scalar and pseudoscalar contributions which are no longer helicity suppressed The SM predictions are BR(B0s m+m-) = (3.65 ± 0.23)x10-9 BR(B0 m+m-) = (1.06 ± 0.09)x10-10 PRL 112, (2014)

5 B0 m+m- and B0s m+m Golden channel for LHCb Last update includes 3.0 (Run1) (Run 2) fb-1 data The strategy is B+ J/YK+ and B0 K+pdecays are normalisation channels The selection is based on a BDT which is trained on the MC and calibrated on the data Update: improved B h+h- rejection, ~50 % less Improved BDT and signal isolation LHCb achieved the frst «single experiment» observation of B0s m+mbr(b0s m+m-) = (3.0 ± )x10-9 at 7.8s BR(B0 m+m-) = (1.5 ± )x10-10 at 1.6s and placed the following limit on the B0 m+m- branching fraction BR(B0 m+m-) < 3.4 x at 95 % CL Those results are consistent with the SM expectations PRL 118, (2017) 5

6 B0s m+m- effective lifetime PRL 10, (2012) In the SM, only the heavy B0s mass eigenstates may decay via the B0s m+m- channel The asymmetry rate G( BsH m + m ) G(B Ls m + m ) A D G= G( BsH m + m )+G(B Ls m + m ) takes the value +1 in the SM ArXiv : ADG can be determined by measuring the efective lifetime t(m+m-). Measurement complementary to the branching ratios in the search for New Physics and permits to reduce the ambiguities 6

7 B0s m+m- effective lifetime First measurement of the efective lifetime using the Run 1 and Run 2 data (4.4 fb-1) tm m =2.04±0.44±0.05 ps Measurement is consistent with the SM prediction of ± ps Within 1.0s of ADG = +1 and 1.4s of ADG = -1 PRL 118, (2017) 7

8 B0 t+t- and B0s t+t This is a clean decay like B0(s) m+m However, helicity suppression efect highly reduced Sensitivity to NP is slightly suppressed wrt B0(s) m+m- Will provide a Lepton Flavour Violation test with B0(s) m+m- decays SM predictions are BR(B0 t+t-) = (2.22 ± 0.19)x10-9 PRL 112, (2014) BR(B0s t+t-) = (7.73 ± 0.49)x10-10 Analysis has been performed on 3fb-1 (Run 1) data using hadronic t decays BR(t± p±p±p±p±nt)=(9.31 ± 0.05) %, t- a1(1260)-nt, a1(1260)- r(770)0p- World best limit BR(B0 t+t-) < 2.1 x 10-3 at 95 % CL BR(B0s t+t-) < 6.8 x 10-3 at 95 % CL assuming no contribution from other B modes 8 PRL 118, (2017)

9 Radiative decays Radiative decays concern the b sg type transitions which are described by efective feld theory and the operator expansion 4 G F (' ) (' ) H eff = V ts V tb (C 7 O 7 +C 10 O 10 ) 2 In the SM, the photon is predominently lef-handed, the right-handed contribution being heavily suppressed by a factor ms/mb NP can enhance the right-handed contribution Related to supersymmetric partners and charged Higgs loops First observed in B+ K+p+p-g decays at LHCb PRL 112, (2014) Studied through B0 K*0l+l- decays at low q2 (=m2mm) 9 PRD (2015) JHEP 04 (2014) 064

10 Radiative B0s fg decay Photon polarisation measured through time-dependent decay rate G B + B (t ) e s s Gs t D Gs t D Gs t D [cosh ( 2 ) A sinh ( 2 )] where AD is related to lef and right handed amplitudes and therefore C7 In the SM: AD = B0s f(k+k-)g decays analysed on 3fb-1 data (Run 1) using the control channel B0 K*0(K+p-)g First measurement sensitive to the polarisation of the photon produced by the B0s decay AD = which is consistent with the SM predictions 10 PRL 118, (2017)

11 S+ pm+m+ decay The HyperCP collaboration has observed the decay S+ pm+m The BR measured is BR(S+ pm+m-) = ( ± 5.5) x 10-8 PRL 94 (2005) This is consistent with the SM predictions PRD 72 (2005) The observed events (3) had a similar di-muon mass Could be due to the fact that the decay proceeds via a resonance X 0 S+ p+x0(m+m-) PRL 94 (2005)

12 S+ pm+m+ decay PRL 120, (2018) The decay S+ pm+m- has been confmed by LHCb with 3fb-1 data (Run 1) The BR measured is BR(S+ pm+m-) = ( ) x events have been observed leaded to a signifcance of 4.1s However no evidence for a di-muon resonance at 214MeV/c2 (1.6 ± 1.9 events) 12

13 B0 m+m-m+m- and B0s m+m-m+m The decay channels B0 m+m-m+m- and B0s m+m-m+m- are strongly suppressed in the SM PLB 556 (2003) 169 Decay can proceed either through resonant and non-resonant modes NP is expected to enhance the decay rates up to ~10-4 MSSM allows B0(s) P(m+m-)S(m+m-) where S and P are sgoldstino particles BR(B0s m+m-m+m-) =3.5x10-11 Chin. Phys. C 40 (2016) Complementary to the S+ pm+m- decay analysis BR(B0s m+m-m+m-) =(1.83 ± 0.18)x

14 B0 m+m-m+m- and B0s m+m-m+m A frst analysis has been performed with 2fb-1. Since, update with 3fb-1 improved selection (multivariate classifer) usage of a new normalisation mode JHEP 03 (2017) 001 No event observed, but the upper limit is improved BR(B0 m+m-m+m-) < 6.9 x 10-8 BR(B0s m+m-m+m-) < 2.5 x 10-9 BR(B0 S(m+m-)P(m+m-)) < 6.0 x BR(B0s S(m+m-)P(m+m-)) < 2.2 x 10-9 with the assumptions ms=2.6gev/c2, mp=214.3mev/c2 for the second set of limits 14

15 Long lived particles at LHCb They can be produced either in B / D decays or in pp collisions Signature Displaced dileptons Light bosons from b s Majorana neutrino Displaced jets LLP jet jet LLP m+jets Background Constrain the reconstructed B mass Constrains on the vertices 15 VELO RF box at ~ 5mm from the beam <5mm bkg from heavy favour >5mm bkg from material int.

16 VELO map to reduce the background Knowledge of the VELO permits to drastically reduce the background in LLP search 16 A p-value is assigned to the hypothesis that a secondary vertex originates from material interaction

17 LLP decaying semileptonically Search for massive LLP decaying semileptonically into SM particles 2 approaches RPV msugra neutralino «type» mass range in GeV/c2 Simplifed topologies less model-dependent mass range in GeV/c2 Uses the Run 1 dataset (3fb-1) Trigger on m + displaced vertex Mh0 in [50, 130] GeV/c2 Lifetime range : 5-100ps Use the muon isolation (Em/Etracks cone R=0.3) Main background is bb Radial position of the vertex Eur. Phys. J. C 77 (2017)

18 LLP decaying semileptonically The signal yield obtained from a simultaneous ft of the LLP candidate mass in 2 regions «signal region» high isolation «background region» Background region Signal region low isolation 18 Signal yields compatible with zero Eur. Phys. J. C 77 (2017) 224

19 Charged Massive Stable particles Search for CMSP correspond to the signature of stau pairs predicted by the mgmsb model Looked at in a range of GeV/c2 In the Run 1 data sample (3fb-1) Look for the absence of signal in the RICH or small radiation angle Eur. Phys. J. C 75 (2015) 595 Stau would interact only weakly and behave like heavy muons 19 Detection time window for muons limits sensitivity to b>0.8 The main background is muon pair production (Drell-Yan)

20 Summary First experiment single measurement of B0s m+m- BR from Run 1 and 2 data Excess of B0 m+m- decays confrmed See related talk by Flavio Archilli Very rare decays in Beauty, Charm and strange decays Feasibility of B0s m+m- efective lifetime measurement Limits placed on Bs t+t- Measurement of photon polarisation in Bs decays Confrmations of S+ pm+m- decays and searches for B0 m+m-m+m- and B0s m+m-m+m- Search for long lived particles in semileptonical decay modes (other modes also looked at) Search for charged massive stable particles 20 See talk by Elena Dall Occo tomorrow afernoon