(In)direct Search of SUSY at LHCb LHCP conference Bologna, June 4th June 9th, 2018 Frédéric Machefert for the LHCb collaboration
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, 1530022 (2015) JINST 10 (2015) P06013 Flexible trigger readout Luminosity collected with a low pile-up Year 2012 2015 2016 2017 s 8 TeV 13 TeV 13 TeV 13 TeV Number of crossings 1262 1866 2036 2332 Separation 50 ns 25 ns 25 ns 25 ns Int/crossing 1.7 1.1 1.1 1.1 4x1032 3.4x1032 3.7x1032 4.3x1032 Ins. Lumi. 2
Scope of this talk This talk will cover Very rare decays B0 m+m- and B0s m+m- PRL 118, 191801 (2017) Search for B0 t+t- and Bs t+t- PRL 118, 251802 (2017) Radiative decay B0s fg PRL 118, 021801 (2017) Probing S+ pm+m- PRL 120, 221803 (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
B0 m+m- and B0s m+mprl 118, 191801 (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, 101801 (2014)
B0 m+m- and B0s m+m Golden channel for LHCb Last update includes 3.0 (Run1) + 1.4 (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 ± 0.6+0.3-0.2)x10-9 at 7.8s BR(B0 m+m-) = (1.5 ±1.2-1.0+0.2-0.1)x10-10 at 1.6s and placed the following limit on the B0 m+m- branching fraction BR(B0 m+m-) < 3.4 x 10-10 at 95 % CL Those results are consistent with the SM expectations PRL 118, 191801 (2017) 5
B0s m+m- effective lifetime PRL 10, 041801 (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 : 1702.05498 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
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 1.610 ± 0.010 ps Within 1.0s of ADG = +1 and 1.4s of ADG = -1 PRL 118, 191801 (2017) 7
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, 101801 (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, 251802 (2017)
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, 161801 (2014) Studied through B0 K*0l+l- decays at low q2 (=m2mm) 9 PRD92 011102 (2015) JHEP 04 (2014) 064
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 = 0.047+0.029-0.025 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 = -0.98+0.46-0.52+0.23-0.20 which is consistent with the SM predictions 10 PRL 118, 021801 (2017)
S+ pm+m+ decay The HyperCP collaboration has observed the decay S+ pm+m The BR measured is BR(S+ pm+m-) = (8.6+6.6-5.4 ± 5.5) x 10-8 PRL 94 (2005) 012801 This is consistent with the SM predictions PRD 72 (2005) 074003 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) 012801 11
S+ pm+m+ decay PRL 120, 221803 (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-) = (2.2+1.8-1.3) x 10-8 13 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
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) 100001 Complementary to the S+ pm+m- decay analysis BR(B0s m+m-m+m-) =(1.83 ± 0.18)x10-8 13
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 10-10 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
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.
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
LLP decaying semileptonically Search for massive LLP decaying semileptonically into SM particles 2 approaches RPV msugra neutralino «type» mass range in 23-198 GeV/c2 Simplifed topologies less model-dependent mass range in 25-80 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) 224 17
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
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 124-309 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)
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