Electroweak scale physics & exotic searches at LHCb

Transcription

1 Electroweak scale physics & exotic searches at LHCb Olli Lupton, on behalf of the LHCb collaboration Moriond QCD 23 March 2018 Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

2 The LHCb detector PS / ECAL / HCAL 30 MHz pp interactions 1 MHz readout Hardware Trigger (L0) MUON

3 Detector / triggering LHCb 2015 Trigger Diagram 40 MHz bunch crossing rate L0 Hardware Trigger : 1 MHz readout, high ET/PT signatures 450 khz h ± 400 khz µ/µµ Software High Level Trigger 150 khz e/γ Partial event reconstruction, select displaced tracks/vertices and dimuons Buffer events to disk, perform online detector calibration and alignment Full offline-like event selection, mixture of inclusive and exclusive triggers Flexible software trigger + new techniques in Run 2 Excellent muon ID + mass resolution over a wide p range Good jet reconstruction: 20 % energy resolution for p T > GeV/c, 65 % b-tagging eff. for 0.3 % contamination Real-time alignment & calibration 1 = offline-quality reconstruction in the trigger Event-size optimisation: only save your signal candidate 2 = smaller events, higher rates Particularly important for the physics result coming next khz (0.6 GB/s) to storage 1 LHCb, Novel real-time alignment and calibration of the LHCb detector and its performance, Nucl. Instrum. Meth. A845, (2017) 2 R. Aaij et al., Tesla: an application for real-time data analysis in High Energy Physics, Comput. Phys. 208, (2016), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

4 Dark Photons Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

5 Dark photons introduction Massive dark photon A is a dark sector portal Behaves like γ with couplings suppressed by ɛ u e c μ t γ H W τ d g Z νe s b ντ νμ axion sterile neutrino dark Higgs dark photon? 2D parameter space ( m (A ), ɛ 2) ε g e g e γ A Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

6 Dark photons experimental details Candidates / σ[m(µµ)]/ LHCb ω/ρ φ s = 13 TeV η 3 J/ψ ψ(2s) Υ(nS) This A search uses the dimuon final state 1, L = 1.6 fb 1 Flexible trigger catches soft tracks, excellent mass resolution,... Un-prescaled prompt dimuons from threshold to the Z 0! 4 prompt-like sample p T (µ) > 1 GeV, p(µ) > 20 GeV µ + µ µ ± µ ± Z 0 m(µµ) [ MeV ] 5 1 LHCb, Search for dark photons produced in 13 TeV pp collisions, Phys. Rev. Lett. 120, (2018), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

7 Dark photons experimental details [mm] 3 Data-driven γ normalisation Prompt search from 2m µ to 70 GeV/c 2 Prompt backgrounds determined with binned χ 2 IP and χ2 vtx fits Displaced search in [214, 350] MeV/c 2 At radii 5 mm, displaced background at low mass dominated by γ conversions New material veto tool developed to map VELO & veto these 1 At smaller radii heavy flavour background dominates r 20 (signed) 0 20 LHCb preliminary z [mm] Mapping the material in the LHCb vertex locator using secondary hadronic interactions, in preparation Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

8 Dark photons results No significant excess found τ (A ) [ m (A ) ɛ 2] 1 Displaced small ɛ World-best limits in.6 70 GeV/c 2 Displaced limits the first of their kind ε % CL exclusion regions on [m(a ), ε 2 ] LHCb Previous Experiments 1 1 LHCb m(a ) [ GeV ] 1 LHCb, Search for dark photons produced in 13 TeV pp collisions, Phys. Rev. Lett. 120, (2018), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

9 Dark photons future outlook Low-mass trigger efficiency significantly improved for 2017, watch this space... Expect 2 3 orders of magnitude higher dimuon statistics 1 in Run 3 Planned inclusion of dielectron channel 2 allows sensitivity below 2m µ " L n regi / / - / m(a 0 )[GeV] 1 P. Ilten et al., Proposed Inclusive Dark Photon Search at LHCb, Phys. Rev. Lett. 116, (2016), arxiv: P. Ilten, J. Thaler, M. Williams, and W. Xue, Dark photons from charm mesons at LHCb, Phys. Rev. D92, (2015), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

10 t t production Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March 2018 / 18

11 t t production introduction b ν There wasn t an LHCb talk in the top session...but we measure them too Important large-x gluon PDF constraints from top cross-sections Forward tops are particularly sensitive t t asymmetry in quark-initiated production also interesting Again: enhanced in the forward region LHC N t t anti-top top W + W l + b ν l y Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

12 Z t t production p T (l, j) > 20 which GeV final state? cross section [pb] Inclusive tt Many final states to choose from 1 Some perks at LHCb: low pile-up, excellent vertex resolution, unique η range Tevatron combined 96 TeV (L ATLAS+CMS Preliminary Nov 20 7 yield purity CMS dilepton l jets 5 02 TeV (L = 27 4 pb ATLAS eµ 7 TeV (L = 4 6 fb LHCtop WG CMS eµ 7 TeV (L = 5 fb ATLAS eµ 8 TeV (L = 20 2 fb CMS eµ 8 TeV (L = 9 7 fb lblhc combined final eµ 8 TeV (L = state 3 fb LHCtop WG is most statistically accessible at LHCb in Run 1 ATLAS eµ 3 TeV (L = 3 2 fb CMS eµ 3 TeV (L = 2 2 fb Downsides too: small acceptance, low L, no E ATLAS ee/µµ 3 TeV (L = 85 pb ATLAS l jets 3 TeV (L = 85 pb T miss... CMS l jets 3 TeV (L = 2 2 fb CMS all jets 3 TeV (L = 2 53 fb 900 Prelim nary will contain largest background Limited component acceptance, partial reconstruction attractive NNLO NNLL (pp) does not differentiate between cross-section single top and boost topatpair LHCb at 13 vs. 8 TeV NNLO NNLL (pp) NNPDF3 0, m = 72 5 GeV, α (M ) = 0 8 ± New channels are feasible in Run 2 data! s [TeV] a number of final states inaccessible in Run 1 arry University of Liverpool 8 8 fb Czakon, Fiedler, Mitov, PRL 0 (20 3) s [TeV 1 R. Gauld, Measuring top quark production asymmetries at LHCb, LHCb-PUB (June 2013) 2 LHCb, First observation of top quark production in the forward region, Phys. Rev. Lett. 115, (2015), arxiv: LHCb, Measurement of the t t, W + b b and W + c c production cross sections in pp collisions at s = 8 TeV, Phys. Lett. B767, 1 (2017) Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

13 t t production experimental details Hot off the press 1, LHCb has measured the t t cross-section in the µeb final state L = 2 fb s = 13 TeV High purity: 2 nd l ± suppresses W + b b, opposite-flavour leptons suppress Z 0 + b b Lepton p T > 20 GeV/c, 2.0 < η < 4.5, prompt, isolated SV-tagged jet with loose selection R(l ±, b) > 0.5, R(µ ±, e ) > 0.1 Events / (30 GeV) LHCb, s = 13 TeV data tt Wt Z+jets QCD M(eµb) [GeV] 44 candidates selected 1 LHCb, Measurement of forward top pair production in the dilepton channel in pp collisions at s = 13 TeV, arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

14 t t production results LHCb s = 13 TeV data POWHEG amc@nlo Statistically dominated σ(pp tt µebx) [fb] Systematics dominated by b-jet tagging Cross-section in fiducial region: σ t t = N N bkg F res L ɛ = 126 ± 19 (stat) ± 16 (syst) ± 5 (lumi) fb Results compared to amcatnlo (Madspin) and POWHEG. Pythia parton shower Compatible with SM predictions (@ NLO) 1 LHCb, Measurement of forward top pair production in the dilepton channel in pp collisions at s = 13 TeV, arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

15 Finally... Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

16 Brief highlights: Observation of Z 0 b b First measurement in the forward region & important validation of jets and b-tagging 1 6σ observation using L = 2 fb 8 TeV b-jets with p T > 20 GeV/c, 2.2 < η < rd balancing jet required to help control QCD background MVA defines signal/control regions using 4 kinematic variables of the 3-jet system Measured cross-section compatible with amcatnlo prediction Candidates / (3.75 GeV) LHCb 8 TeV Signal Region Z Data Total uncertainty Dijet Mass [GeV] 1 LHCb, First observation of forward Z b b production in pp collisions at s = 8 TeV, Phys. Lett. B776, 430 (2017), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

17 Brief highlights: Dimuon resonances near Υ(nS) g g φ µ t, b µ + New scalars can be produced in ggf, many LHC searches already performed 1 m φ GeV/c 2 region hard to probe with γγ, ττ...use µµ to look near Υ(nS) No signal 2, 1 st limits in GeV/c 2, competitive with CMS elsewhere More details shown last week 3 Candidates/37.1 MeV Pulls LHCb Preliminary L = 3.0 fb 1 s = 7, 8 TeV Fit PDF Υ(nS) Background pp φ (50 pb) Data m(µµ) [GeV] 1 U. Haisch, J. F. Kamenik, A. Malinauskas, and M. Spira, Collider constraints on light pseudoscalars, arxiv: LHCb, Search for a dimuon resonance in the Υ mass region, LHCb-PAPER , in preparation 3 M. Borsato, Moriond EW 2018, η Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March 2018 Υ 17 / 18

18 Conclusions Had to focus on the most recent results in this short talk Interesting new EW-scale physics and exotic results coming out Looking forward to continuing to exploit our unique coverage :-) (LHCb isn t just a flavour physics experiment!) Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

19 Backup Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

20 Dark photons prompt spectrum with selection Candidates / σ[m(µ + µ )]/ LHCb s = 13 TeV 3 isolation applied 4 prompt-like sample p T (µ) > 1 GeV, p(µ) > 20 GeV prompt µ + µ µ Q µ Q hh + hµ Q m(µ + µ ) [ MeV ] 5 1 LHCb, Search for dark photons produced in 13 TeV pp collisions, Phys. Rev. Lett. 120, (2018), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

21 Dark photons prompt fits Candidates / LHCb Candidates / LHCb Candidates / LHCb prompt µ µ 150 µ Qµ Q hh +hµ Q 0 50 Pull min[χ 2 (µ)] IP 1/2 Pull min[χ 2 (µ)] IP 1/2 Pull min[χ 2 (µ)] IP m(a ) 0.5 GeV/c 2 m(a ) 5 GeV/c 2 m(a ) 50 GeV/c 2 1/2 Illustrative fits used to extract heavy-flavour (µ Q ) and misidentified hadron (h) background fractions 1 LHCb, Search for dark photons produced in 13 TeV pp collisions, Phys. Rev. Lett. 120, (2018), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

22 Projected Run 3 dark photon sensitivity - / ϵ / / μμ - * η ρ/ω ϕ /ψ ψ( ) Υ( ) μμ - - μμ μμ - * - / [ ] 1 P. Ilten et al., Proposed Inclusive Dark Photon Search at LHCb, Phys. Rev. Lett. 116, (2016), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

23 LHCb complementing the GPDs Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

24 LHCb complementing the GPDs Muon HCal ECal Tracking Illustration of the η overlap between ATLAS, CMS and LHCb ATLAS CMS LHCb Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

25 t t production backgrounds N(Z 0 + jet) = 0.32 ± 0.03 e ± µ produced through Z 0 τ + τ or misidentified real b-jet, or misidentified lighter jet determined from Z 0 µ + µ N(Wt) = 1.8 ± 0.5 Identical final state, determined using POWHEG and scaled N(QCD) = 3.9 ± 1.9 multi-jet events producing two leptons and an associated jet determined by extrapolating from same-sign control region N(WW, WZ, ZZ) 0 Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

26 t t production systematic uncertainties Source % trigger 2.0 muon reconstruction 1.1 electron reconstruction 2.8 muon identification 0.8 electron identification 1.3 jet reconstruction 1.6 event selection 4.0 jet tagging.0 background 5.1 acceptance 0.5 total 12.7 Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

27 Jet LHCb LHCb s = 8 TeV Data POWHEG amc@nlo Anti-k T, particle flow, R = % energy resolution Used in several other measurements, e.g.w ± and Z 0 production in association with jets at 7 TeV 1 and 8 TeV 2, J/ψ production in jets Theory/Data + σ(w j) σ(w j ) σ(zj) R WZ R W + Z R W Z R W ± 1 LHCb, Study of forward Z + jet production in pp collisions at s = 7 TeV, JHEP 01, 033 (2014), arxiv: A(Wj) 2 LHCb, Measurement of forward W and Z boson production in association with jets in proton-proton collisions at s = 8 TeV, JHEP 05, 131 (2016), arxiv: LHCb, Study of J/ψ production in jets, Phys. Rev. Lett. 118, (2017), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

28 Jet flavour tagging jet Inclusive b- and c-jet tagger at LHCb exploits excellent tracking and vertexing Reconstruct 2-body vertices, merge into n-body verticies (SVs) Jet is SV-tagged if there is a SV within R < 0.5 SV 1 LHCb, Identification of beauty and charm quark jets at LHCb, JINST, P06013 (2015), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

29 Jet flavour tagging Two separate BDTs trained, one to separate b-jets from c-jets, one to select heavy flavour from light jets BDT(b c) b-jets BDT(b c) c-jets BDT(b c) udsg-jets LHCb simulation BDT(bc udsg) LHCb simulation BDT(bc udsg) LHCb simulation BDT(bc udsg) Input: SV displacement, kinematics, charge, multiplicity, m corr., jet properties 1 LHCb, Identification of beauty and charm quark jets at LHCb, JINST, P06013 (2015), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

30 Jet flavour tagging efficiency (b,c)-jet tag efficiency Performance shown in simulation Also validated in data LHCb simulation b-jet c-jet 2.2 < η(jet) < < p (jet) < 0 GeV T efficiency in data/simulation LHCb (b,c)-jet p (jet) [GeV] T light-parton mistag probability % here = systematic in the t t measurement 1 LHCb, Identification of beauty and charm quark jets at LHCb, JINST, P06013 (2015), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

31 Z 0 b b Candidates / (3.75 GeV) LHCb 8 TeV Signal Region Dijet Mass [GeV] Z QCD Data Candidates / (3.75 GeV) LHCb 8 TeV Control Region Dijet Mass [GeV] Z QCD Data Signal and control regions defined by MVA 1 LHCb, First observation of forward Z b b production in pp collisions at s = 8 TeV, Phys. Lett. B776, 430 (2017), arxiv: Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18

32 Dimuon resonance limits Excluded mass ranges are defined by excessive correlation between φ signal yield and Υ(nS) yield, or when alternative background models are not compatible (pp (8TeV)! ) B(! µµ) [pb] LHCb Preliminary R L =3.0 fb 1 p s =7, 8 TeV (1S) (2S) (3S) 95% CL upper limits Median expected 68% expected 95% expected Observed CMS expected CMS observed m( ) [GeV] Olli Lupton (CERN) LHCb Electroweak & Exotic Signatures 23 March / 18