Probing Higgs Yukawa Couplings with Rare Decays

Transcription

1 Probing Higgs Yukawa Couplings with Rare Decays Birmingham HEP Seminar Andy Chisholm University of Birmingham 13th May 215 his project has received funding from the European Union s 7th Framework Programme for research, technological development and demonstration under grant agreement number (EWSB Probing Higgs Yukawa Couplings with Rare Decays 1 / 39

2 Introduction - Overview Higgs Boson Yukawa Couplings What is the Higgs boson and Yukawa coupling? How can we study them through rare Higgs decays? Experimental Investigations How can we study these rare decays at the LHC? First search: Phys. Rev. Lett. 114 ( (arxiv: Discussion What have we learnt from this search? What can we expect from future studies? Probing Higgs Yukawa Couplings with Rare Decays 2 / 39

3 Introduction - he BEH Mechanism Figure from Philip anedo Complex scalar SU(2 doublet φ introduced to SM, he Higgs field (4 real d.o.f. hen consider the symmetry spontaneously broken Potential of the field has non-zero VEV, 3 d.o.f. become Goldstone bosons hree Goldstone bosons mix with W ±, fields Provides gauge invariant mass terms (and longitudinal pol to the W ± and he fourth d.o.f. is a scalar Higgs boson! Provides masses to the W ± and bosons! Probing Higgs Yukawa Couplings with Rare Decays 3 / 39

4 Introduction - Yukawa Couplings Now we have a Higgs field, Yukawa couplings between the Higgs and Fermion fields are possible: L fermion = y f [ ψl φψ R + ψ R φψl ] If φ has a non-zero VEV, expansion leads to: L fermion = y f v ψψ y f h ψψ 2 2 }{{}}{{} mass term Yukawa coupling term where h is the physical Higgs boson field... he End Result: Gauge invariant Fermion mass terms Higgs-Fermion coupling proportional to the Fermion mass (g Hf f = m f /v H f f g Hf f While y f are still free parameters in the model, v 246 GeV is known from Electroweak measurements and we know the fermion masses... We can predict the couplings in the SM! Probing Higgs Yukawa Couplings with Rare Decays 4 / 39

5 In 212, the ALAS and CMS experiments discovered a new boson, with a mass of around 125 GeV ALAS Preliminary m H = GeV H H * +.28 µ = 1.17 obs µ = 1. exp µ = 1.46 obs -.34 σ(obs. σ(exp. otal uncertainty ± 1σ on µ Signal strength (µ ALAS and CMS LHC Run 1 ALAS H ALAS H 4l CMS H CMS H 4l All combined Best fit 68% CL +.31 µ =.99 exp -.26 H WW* +.24 µ = 1.18 obs -.21 H bb +.21 µ = 1. exp µ =.63 obs µ = 1. exp [GeV] m H H ττ H µµ H +.42 µ = 1.44 obs µ = 1. exp µ = -.7 obs µ = 1. exp µ = 2.7 obs µ = 1. exp -4.2 All subsequent measurements suggest compatibility with the Higgs boson of the Standard Model... Combined µ +.15 = obs +.13 µ = 1. exp -.12 s = 7 ev, fb s = 8 ev, 2.3 fb Signal strength (µ Probing Higgs Yukawa Couplings with Rare Decays 5 / 39

6 Higgs Yukawa Couplings - Experimental Status What do we know about Higgs couplings to: t quark: No firm evidence for t th production from LHC experiments b quark: No firm evidence for H b b decays from LHC experiments, only 1 2σ excesses c quark: No direct evidence, only loose bounds from H b b searches u, d, s quarks: Nothing! τ lepton: Evidence for H(125 ττ decays from ALAS and CMS! e, µ leptons: No evidence, but that suggests lepton coupling isn t universal! Evidence for Higgs Yukawa couplings (H τ τ from the LHC! Events / bin JHEP 4 ( (arxiv: H ττ ALAS s = 8 ev, 2.3 fb s = 7 ev, 4.5 fb Background (µ=1.4 Background (µ= H (125 ττ H (125 ττ (µ=1.4 (µ= log (S / B suggest lepton Yukawa couplings are present and non-universal... But not too much else! Probing Higgs Yukawa Couplings with Rare Decays 6 / 39

7 Introduction - Charm Quark Yukawa Coupling he traditional approach is to search for inclusive H c c decays 3 5fb 1 7eV 2fb 1 8eV Stat. Monte Carlo Error Direct searches suffer from very large backgrounds from inclusive jet production Recent dedicated efforts to develop charm tagging! (AL-PHYS-PUB-215 Not yet applied to H c c searches... Fraction of jets ALAS Preliminary t t simulation, s = 8 ev p jet > 2 GeV, ηjet < 2.5 JetFitterCharm b jets c jets Light jets log(p c /P b Μ b e c Μ c See arxiv: for details Existing H b b searches an be reinterpreted to include the possibility of anomalous H c c production Exploit the non-zero rate of charm quarks mistagged as bottom ALAS and CMS data provide κ c < 234 at 95% CL upper bound f a b Probing Higgs Yukawa Couplings with Rare Decays 7 / 39

8 Introduction - H Q H Q decays could provide a clean probe of the charm (and bottom Yukawa couplings Q is a vector (J PC = 1 quarkonium state Interference between direct (top and indirect (bottom contributions Indirect (bottom amplitude provides dominate rate contribution Direct (top amplitude provides sensitivity to Hc c and Hb b couplings Very rare SM decay (c.f. B (H 2 3 Will need a HL-LHC with (at least 3 fb 1 to approach observation B (H J/ψ = B (H Υ(1S, 2S, 3S = {.6, 2., 2.4} 9 More details: Phys. Rev. D 88, 533 (213 (arxiv: and Phys. Rev. D 9, 113 (214 (arxiv: Probing Higgs Yukawa Couplings with Rare Decays 8 / 39

9 Introduction - Q Q decays could provide a stepping stone towards the observation of the Higgs decays at the LHC J/ψ Analogous to Higgs decay, could provide useful control channel Similar interference between direct (top and indirect (bottom contributions Indirect amplitude suppressed w.r.t. Higgs case While a rarer decay in the J/ψ case, bosons much more copiously produced than Higgs at the LHC, better prospects for observation J/ψ B ( J/ψ = 1. 7 B ( Υ(1S = More details: (arxiv: Further work: Nucl. Phys. B 174, 317 (198, heor. Math. Phys. 17, 39 (212, arxiv: Probing Higgs Yukawa Couplings with Rare Decays 9 / 39

10 H/ Q Decays - Experimental Status Experimental limits on Q decays Only information from LEP measurements of inclusive Q X decays LEP only produced around 17 million bosons... Can expect only around one J/ψ decay in the dataset! Existing knowledge on these exclusive decays is in the form of upper bounds from inclusive Q X measurements/limits Combined (PDG LEP Measurements: B ( J/ψ X = ( B ( Υ(nS = (1. ±.5 4 Nearly 4 orders of magnitude away from SM branching fraction! Experimental limits on H Q decays Nothing known, until now... Probing Higgs Yukawa Couplings with Rare Decays / 39

11 Analysis - he ALAS Analysis (arxiv: he first experimental information on H/ Q decays, from the ALAS experiment! PRL 114, (215 P H Y S I C A L R E V I E W L E E R S week ending 27 MARCH 215 Search for Higgs and Boson Decays to J=ψ and ϒðnSÞ with the ALAS Detector G. Aad et al. * (ALAS Collaboration (Received 15 January 215; published 26 March 215 A search for the decays of the Higgs and bosons to J=ψ and ϒðnSÞ (n ¼ 1; 2; 3 is performed with pp collision data samples corresponding to integrated luminosities of up to 2.3 fb 1 collected at pffiffi s ¼ 8 ev with the ALAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% C.L. upper limits are placed on the branching fractions. In the J=ψ final state the limits are and for the Higgs and boson decays, respectively, while in the ϒð1S; 2S; 3SÞ final states the limits are ð1.3; 1.9; 1.3Þ 3 and ð3.4; 6.5; 5.4Þ 6, respectively. DOI:.13/PhysRevLett PACS numbers: 14.8.Bn, Dg, 14.7.Hp, 14.8.Ec Probing Higgs Yukawa Couplings with Rare Decays 11 / 39

12 Introduction - he ALAS Detector Muon Spectrometer (MS: riggering η < 2.4 and Precision racking η < 2.7 Inner Detector (ID: Silicon Pixels and Strips (SC with ransition Radiation racker (R η < 2.5 LAr EM Calorimeter: Highly granular + longitudinally segmented (3-4 layers Muon rigger: Single and di-muon triggers - several p µ thresholds (4 4 GeV Resolution in m µ + µ : Around 5 MeV at J/ψ and 15 MeV at Υ(nS Probing Higgs Yukawa Couplings with Rare Decays 12 / 39

13 Analysis - Overview Experimental Signature High p isolated photon recoiling against a high p isolated quarkonium state Analysis Aim Search for both Higgs and boson decays Study both J/ψ and Υ(nS decay channels Exploit full ALAS data sample collected at s = 8 ev, around 2 fb 1 How to reconstruct the quarkonium? Decay Rate Background rigger Reconstruction Q hadrons B = 8 9%? Q e + e B = 2 6%? Q µ + µ B = 2 6% Of the several options, choose to reconstruct Q µ + µ only... Probing Higgs Yukawa Couplings with Rare Decays 13 / 39

14 Analysis - rigger Selection Photon is too soft (by single photon trigger standards to provide a trigger he Q produced in a H/ boson decay is often highly boosted (< p > 5 GeV he opening angle between muons in such boosted Q µ + µ decays is very small his presents a challenge when using muons to trigger such events! Events/ ALAS Simulation H J/ψ H ϒ(nS Before selection After selection R µµ J/ψ Channel: With < R µ + µ >.1, dimuon or isolated muon triggers have low efficiency Use single non-isolated high p muon trigger Υ(nS Channel: Broader < R µ + µ > distribution Can use an isolated single high p muon trigger with a lower threshold dimuon trigger Probing Higgs Yukawa Couplings with Rare Decays 14 / 39

15 Event Selection - Q µ + µ Selection Oppositely charged dimuon pairs with η µ < 2.5 and p µ > 3. GeV that are: Hard: At least one muon must have p µ > 2 GeV, require µ pµ+ > 36 GeV Isolated: Require the sum p of tracks and calo. deposits within R <.2 of the leading p muon to be less than % of its p Prompt: ransverse decay length significance L xy /σ Lxy < 3. to reject b J/ψ he correct mass: m µ + µ m J/ψ <.15(.2 GeV in barrel(endcap OR 8. < m µ + µ < 12. GeV Events /.2 GeV Fit J/ψ Background ALAS = 8 ev L dt = 19.2 fb [GeV] s Loose Isol. Soft p J/ψ channel Barrel Categories σ = 44 ± 1 MeV m µ + - µ Events /.1 GeV Fit ϒ(nS Background ALAS = 8 ev L dt = 2.3 fb [GeV] s Loose Isol. Soft p ϒ(nS channel Barrel Categories σ 1S = 8 ± 13 MeV m µ + - µ Probing Higgs Yukawa Couplings with Rare Decays 15 / 39

16 Event Selection - Photon Selection Select converted and unconverted photons within η < 2.47 and outside of 1.37 < η < 1.52 that are: Unlikely a Jet: Require tight shower shape identification criteria Hard: Require p > 36 GeV Isolated: Require the sum p of tracks and calo. deposits within R <.2 of the photon to be less than 8% of its p Recoiling against Q: Require φ(µ + µ, >.5 Events/2 GeV ALAS Simulation H J/ψ H ϒ(nS Before selection After selection Events/2 GeV ALAS Simulation J/ψ ϒ(nS Before selection After selection p [GeV] p [GeV] Probing Higgs Yukawa Couplings with Rare Decays 16 / 39

17 Event Selection - Efficiency and Acceptance Overall acceptance efficiency (including trigger: Channel H J/ψ H Υ(nS J/ψ Υ(nS A ɛ 22% 28% 12% 15% Events/2 GeV.1.8 µ 1 p ALAS Simulation H J/ψ Before selection After selection Events/2 GeV µ 1 p µ 2 p p ALAS Simulation J/ψ Before selection After selection.6 µ 2 p p p [GeV] p [GeV] Lepton and photon p distributions in fiducial volume ( η < 2.47 and η µ < 2.5 and after all selection, final state particles slightly softer in decays... Probing Higgs Yukawa Couplings with Rare Decays 17 / 39

18 Event Selection - Event Categorisation Events are split into four individual categories based on η µ and photon conversion status (i.e. converted or unconverted: B UNCONV: Both muons within η µ < 1.5 and an unconverted photon B CONV: Both muons within η µ < 1.5 and an converted photon EC UNCONV: Either muon with η µ > 1.5 and an unconverted photon EC CONV: Either muon with η µ > 1.5 and an converted photon Events /.2 GeV Fit J/ψ Background ALAS s = 8 ev L dt = 19.2 fb Loose Isol. Soft p J/ψ channel Barrel Categories σ = 44 ± 1 MeV Events /.2 GeV 25 Fit 2 15 J/ψ Background ALAS s = 8 ev L dt = 19.2 fb Loose Isol. Soft p J/ψ channel Endcap Categories σ = 74 ± 3 MeV [GeV] m µ + - µ [GeV] Resolution and S/B vary across categories, separate treatment enhances sensitivity m µ + - µ Probing Higgs Yukawa Couplings with Rare Decays 18 / 39

19 Converted Unconverted Events ALAS Simulation Barrel Converted H J/ψ Sigma = 1.7 ±.3 GeV Mean = ±.3 GeV Events ALAS Simulation Barrel Unconverted H J/ψ Sigma = 1.5 ±.2 GeV Mean = ±.2 GeV Barrel m µµ [GeV] m µµ [GeV] Endcap Events ALAS Simulation EndCap Converted H J/ψ Sigma = 2.23 ± Mean = GeV ±.4 GeV m µµ [GeV] Events ALAS Simulation EndCap Unconverted H J/ψ Sigma = 1.95 ± Mean = GeV ±.3 GeV m µµ [GeV] hree body m µ + µ mass resolution varies from 1.2% (barrel to 1.8% (endcap Probing Higgs Yukawa Couplings with Rare Decays 19 / 39

20 Analysis - Signal Modeling σ(pp H+X [pb] 2 1 pp H (NNLO+NNLL QCD + NLO EW pp qqh (NNLO QCD + NLO EW pp WH (NNLO QCD + NLO EW pp H (NNLO QCD +NLO EW pp tth (NLO QCD s= 8 ev M H [GeV] LHC HIGGS XS WG 212 Composition of Higgs boson production with m H = 125 GeV at s = 8 ev: Channel σ [pb] Fraction ggh % VBF % WH.7 3% H.42 2% t th.13 1% Source: LHCXSWG (arxiv: he POWHEG MC generator is used to model Higgs and boson production: All H, Q signals are modeled with exclusive samples of simulated events Separate samples of gluon fusion and VBF production are used for Higgs channels VBF sample is rescaled to model H, W ± H and t th production contributions (accounting for small acceptance differences PYHIA 8.1 is used to simulate parton showering and hadronisation while PHOOS used to simulate QED final state effects (e.g. FSR Probing Higgs Yukawa Couplings with Rare Decays 2 / 39

21 Backgrounds - Introduction Exclusive Backgrounds Electroweak production of an isolated dimuon pair and isolated photon µ + µ µ + µ decays with a catastrophic FSR, effect depends strongly on m µ + µ region of interest Important in Υ(nS channel BU negligible for J/ψ channel Other Higgs decays e.g. H µ + µ - Negligible at current sensitivity... Small, but peaking backgrounds, modeled with MC simulation Inclusive Backgrounds QCD production of quarkonia, jets and photons Processes such as pp Q g X where jet is identified as a photon Smaller contributions such as +jets, b b production (with b J/ψX Large, but smooth backgrounds, modeled with a data-driven approach Probing Higgs Yukawa Couplings with Rare Decays 21 / 39

22 Backgrounds - Inclusive Background Composition: J/ψ Channel he m µ + µ and Lxy /σlxy requirements are removed to study the background dimuon composition Events /.2 GeV 22 2 Fit Prompt J/ψ 18 Non-prompt J/ψ 16 Combinatoric Bkgd. Accepted Region ALAS = 8 ev L dt = 19.2 fb [GeV] s Loose Isol. Soft p J/ψ channel Barrel Unconverted m µ + - µ Events / ALAS s = 8 ev Loose Isol. Soft p J/ψ channel Barrel Unconverted L dt = 19.2 fb L xy σ[l ] xy Fit Prompt J/ψ Non-prompt J/ψ Combinatoric Bkgd. Accepted Region Composition estimated from simultaneous fit to m µ + µ and Lxy /σ L xy distributions, an example fit shown for relaxed control region (not full event selection Background dimuon composition for full selection: 56% prompt J/ψ, 3% non-prompt J/ψ and 41% combinatoric dimuons Probing Higgs Yukawa Couplings with Rare Decays 22 / 39

23 Backgrounds - Background Composition: Υ(nS Channel Similarly, the background composition of the Υ(nS channel can be studied Events /.3 GeV Fit 8 6 ϒ(nS Bkgd. Combinatoric Bkgd. + - µ µ ALAS s = 8 ev Loose Isol. Soft p ϒ(nS channel L dt = 2.3 fb Endcap Unconverted Events /.1 GeV Fit ϒ(nS Bkgd. Combinatoric Bkgd. + - µ µ ALAS s = 8 ev Loose Isol. Soft p ϒ(nS channel L dt = 2.3 fb Endcap Unconverted [GeV] m µ + - µ [GeV] m µ + - µ Composition estimated from simultaneous fit to m µ + µ and m µ + µ distributions, an example fit shown for relaxed control region (not full event selection Background dimuon composition for full selection: 7% Υ(nS, 27% µ + µ and 66% combinatoric dimuons Probing Higgs Yukawa Couplings with Rare Decays 23 / 39

24 Backgrounds - Inclusive Background Model Event mixing model for Inclusive backgrounds: Start with a very loose sample of Q events with p and isolation cuts significantly relaxed w.r.t. nominal selection - high statistics data sample dominated by background events Use the kinematic and isolation distributions of this background dominated sample to generate toy background Q candidates Can apply nominal selection (tight p and isolation cuts to these toy candidates to model the background in the signal region Events / 4 GeV 4 ALAS 35 s = 8 ev L dt = 19.2 fb J/ψ channel Inclusive Category Loose Isol. Soft p Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ (B = H J/ψ (B = 2 m µ m µ + - µ µ + m J/ψ [GeV] Events / 4 GeV ALAS s = 8 ev L dt = 19.2 fb J/ψ channel Inclusive Category Loose Isol. Nominal p Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ (B = H J/ψ (B = 2 m µ m µ + - µ µ + m J/ψ [GeV] Events / 4 GeV 25 ALAS Inclusive Category s = 8 ev L dt = 19.2 fb Signal Region 2 J/ψ channel Incl. Bkgd Incl. Bkgd. Shape Syst m µ m µ + - µ µ + m J/ψ [GeV] Provides good description of the shape and normalisation of inclusive background contribution to important kinematic distributions J/ψ H J/ψ Probing Higgs Yukawa Couplings with Rare Decays 24 / 39 (B = 5 (B = 2

25 Backgrounds - Inclusive Background Model: J/ψ Channel Events / 4 GeV 4 ALAS 35 s = 8 ev L dt = 19.2 fb J/ψ channel Inclusive Category Loose Isol. Soft p Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ (B = H J/ψ (B = 2 m µ m µ + - µ µ + m J/ψ [GeV] Events / 4 GeV ALAS s = 8 ev L dt = 19.2 fb J/ψ channel Inclusive Category Loose Isol. Nominal p Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ (B = H J/ψ (B = 2 m µ m µ + - µ µ + m J/ψ [GeV] Events / 4 GeV 25 ALAS Inclusive Category s = 8 ev L dt = 19.2 fb Signal Region 2 J/ψ channel Incl. Bkgd Incl. Bkgd. Shape Syst. J/ψ (B = H J/ψ (B = 2 m µ m µ + - µ µ + m J/ψ [GeV] Events / 4 GeV 6 ALAS s = 8 ev L dt = 19.2 fb J/ψ channel Inclusive Category Loose Isol. Soft p Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ H J/ψ (B = 5 (B = 2 Events / 4 GeV 16 ALAS Inclusive Category s = 8 ev L dt = 19.2 fb Loose Isol. Nominal p 14 J/ψ channel 12 8 Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ H J/ψ (B = 5 (B = 2 Events / 4 GeV 3 ALAS Inclusive Category 25 s = 8 ev L dt = 19.2 fb Signal Region J/ψ channel 2 15 Incl. Bkgd. Incl. Bkgd. Shape Syst. J/ψ H J/ψ (B = 5 (B = µ + µ p [GeV] µ + µ p [GeV] µ + µ p [GeV] Loose Selection Validation Selection Final Selection Probing Higgs Yukawa Couplings with Rare Decays 25 / 39

26 Backgrounds - Inclusive Background Model: Υ(nS Channel Events / 4 GeV ALAS s = 8 ev L dt = 2.3 fb ϒ(nS channel Inclusive Category Loose Isol. Soft p Incl. Bkgd. Incl. Bkgd. Shape Syst. + - µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = 2 Events / 4 GeV 18 ALAS Inclusive Category s = 8 ev L dt = 2.3 fb 16 Loose Isol. Nominal p ϒ(nS channel 14 Incl. Bkgd. Incl. Bkgd. Shape Syst µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = 2 Events / 4 GeV 12 ALAS Inclusive Category s = 8 ev L dt = 2.3 fb Signal Region ϒ(nS channel Incl. Bkgd. Incl. Bkgd. Shape Syst. + - µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = m µ - [GeV] + µ m µ - [GeV] + µ m µ - [GeV] + µ Events / 4 GeV 4 ALAS s = 8 ev L dt = 2.3 fb 35 ϒ(nS channel Inclusive Category Loose Isol. Soft p Incl. Bkgd. Incl. Bkgd. Shape Syst. + - µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = 2 Events / 4 GeV 14 ALAS s = 8 ev L dt = 2.3 fb 12 ϒ(nS channel Inclusive Category Loose Isol. Nominal p Incl. Bkgd. Incl. Bkgd. Shape Syst. + - µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = 2 Events / 4 GeV 7 ALAS s = 8 ev L dt = 2.3 fb 6 ϒ(nS channel Inclusive Category Signal Region Incl. Bkgd. Incl. Bkgd. Shape Syst. + - µ µ ϒ(nS H ϒ(nS ( B = 5 ( B = µ + µ p [GeV] µ + µ p [GeV] µ + µ p [GeV] Loose Selection Validation Selection Final Selection Probing Higgs Yukawa Couplings with Rare Decays 26 / 39

27 Systematics Uncertainties - Signal and Background Signal Yield Uncertainty: Several sources of systematic uncertainty on the H and signal yields are considered, all modeled with nuisance parameters in likelihood: Source Signal Yield Uncertainty Estimated From otal H cross section 12% QCD scale variation and otal cross section 4% PDF uncertainties Integrated Luminosity 2.8% rigger Efficiency 1.7% Photon ID Efficiency Up to.7% Muon ID Efficiency Up to.4% Photon Energy Scale.2% Muon Momentum Scale Negligible Calibration observable and vdm scan uncertainties driven techniques with l + l, l + l and J/ψ µ + µ events Background Shape Uncertainty: Estimated from modifications to modeling procedure (e.g. shifting/warping input distributions, shape uncertainty included in likelihood as a shape morphing nuisance parameter See EPJC 73 ( (arxiv: for details Probing Higgs Yukawa Couplings with Rare Decays 27 / 39

28 Statistical Analysis - Procedure and J/ψ Channel Model Limit Setting Procedure Limits set using CLs modified frequentist formalism with the profile likelihood ratio test statistic Unbinned likelihood built from multi dimensional PDFs Systematic uncertainties included in likelihood as nuisance parameters J/ψ Channel: Simultaneous fit to m µ + µ and p µ+ µ distributions Arbitrary Units.5 For Illustration Only.4 H Signal Signal Inc. Background Arbitrary Units -2 For Illustration Only H Signal Signal Inc. Background p µ+ µ [GeV] m µ + - µ p [GeV] information provides further discrimination between signal and background Probing Higgs Yukawa Couplings with Rare Decays 28 / 39 µ + µ

29 Statistical Analysis - Υ(nS Channel Model Simultaneous fit to m µ + µ, p µ+ µ and m µ + µ distributions Arbitrary Units 4. For Illustration Only H Signal Signal FSR Background Inc. Background Arbitrary Units 1-2 For Illustration Only H Signal Signal FSR Background Inc. Background Arbitrary Units For Illustration Only H Signal Signal FSR Background Inc. Background m µ + - µ [GeV] µ + µ p [GeV] m µ + - µ [GeV] Addition of m µ + µ distribution provides discrimination between Υ(nS signal and µ + µ FSR. Also allows µ + µ FSR normalisation to be reliably fitted directly with data! Probing Higgs Yukawa Couplings with Rare Decays 29 / 39

30 Fit Results - J/ψ Channel Events / 4 GeV ALAS s=8 ev Ldt = 19.2 fb m µµ [GeV] S+B Fit Background H [B= ] [B= ] Events / 4 GeV ALAS s=8 ev Ldt = 19.2 fb [GeV] S+B Fit Background H [B= ] [B= ] No significant Higgs or boson signals observed... µµ p Probing Higgs Yukawa Couplings with Rare Decays 3 / 39

31 Fit Results - Υ(nS Events / 4 GeV 8 ALAS s=8 ev Ldt = 2.3 fb 7 S+B Fit 6 Combinatoric ϒ(nS FSR 5 H [B= ] [B= ] m µµ [GeV] Events / 4 GeV 5 ALAS s=8 ev Ldt = 2.3 fb S+B Fit 4 Combinatoric ϒ(nS FSR H [B= ] 3 [B= ] µµ p [GeV] Events /.125 GeV 35 ALAS s=8 ev Ldt = 2.3 fb 3 S+B Fit Combinatoric ϒ(nS FSR H [B= ] [B= ] m µµ [GeV] No significant Higgs or boson signals observed... Probing Higgs Yukawa Couplings with Rare Decays 31 / 39

32 Fit Model - Results Summary Limits are set on the branching fractions and σ B for each decay channel: 95% CL s Upper Limits J/ψ Υ(1S Υ(2S Υ(3S B ( Q [ 6 ] n Υ(nS Expected Observed B (H Q [ 3 ] Expected Observed σ (pp H B (H Q [fb] Expected Observed Upper limit of around 54 SM rate for H J/ψ decay Upper limit of around 26 SM rate for J/ψ decay Probing Higgs Yukawa Couplings with Rare Decays 32 / 39

33 Upper limits set on Higgs decays at the level of 3! Remember, this is at the level of the H decay rate! (2 3 95% CLs upper limit on Branching Fraction 95% CL upper limit on Branching Fraction fb fb 1 ALAS s = 8 ev 2.3 fb fb fb 1 H/ Q 3 Observed Expected (±1, 2σ 2.3 fb fb fb fb fb 1. 6 H J/ψ H Υ(1S H Υ(2S H Υ(3S H Υ(nS J/ψ Υ(1S Υ(2S Υ(3S Υ(nS H J/ψ H Υ(1S H Υ(2S H Υ(3S H Υ(nS J/ψ Υ(1S Υ(2S Υ(3S Υ(nS Upper limits set on decays rule out several predictions in the literature! e.g. heor. Math. Phys. 17, 39 (212 (up to 5 predicted! Probing Higgs Yukawa Couplings with Rare Decays 33 / 39

34 Impact - Constraint on Charm Yukawa Coupling he limit on σ B for the H J/ψ channel was recently reinterpreted as a constraint on the charm Yukawa coupling (arxiv:153.29: Κ b CMS total ALAS total 5fb 1 7eV 2fb 1 8eV h J ΨΓ /ψ Γ Γ τ Κ c μ [ ] In the SM the ratio of y t/y c Exploiting measured ALAS H 4l rate (to cancel Γ H dependence, obtain a bound of κ c 22 Suggests that limit on H J/ψ (with world data on t th can exclude universal quark Yukawa couplings! Probing Higgs Yukawa Couplings with Rare Decays 34 / 39

35 Future - What could be done with the HL-LHC? What could one expect with 3fb 1 at s = 14 ev? For a total Higgs cross section of around 57 pb at s = 14 ev, can expect around 48 H J/ψ decays to occur within each experiment Accounting for B ( J/ψ µ + µ gives around 29 signal events... Assume A ɛ = 22% from existing result... Expect around 6 reconstructed H J/ψ µ + µ events! Expected number of events far from the whole story, existing result demonstrates backgrounds can be formidable! One would surely have to consider J/ψ e + e or even J/ψ hadrons along with a combination of ALAS and CMS! Can expect improvements such as multivariate techniques and exploitation of angular distributions, all combined upgraded detectors! Clearly a challenge, but there are many possibilities to explore! Will certainly be very complimentary to direct H c c search! Probing Higgs Yukawa Couplings with Rare Decays 35 / 39

36 Conclusion Exclusive rare decays of the Higgs boson to quarkonia can be used to probe Higgs Yukawa couplings to the charm quark! ALAS have performed the first search for such Higgs decays and the analogous rare boson decays he existing constraints experimentally establish the non-universality of Higgs couplings to quarks his study and the associated theoretical work represent an important emerging subfield of Higgs physics! We can expect other such rare decays to further elucidate light quark Yukawa couplings through LHC Run 2 and beyond! Probing Higgs Yukawa Couplings with Rare Decays 36 / 39

37 Probing Higgs Yukawa Couplings with Rare Decays 37 / 39

38 Backgrounds - Non-resonant H µ + µ H ( µ + µ : H µ + µ branching fraction around 1.7% relative to H [1] Model decay distribution with calculation from [1] (right plot Contributions from are small and populate high m µ + µ region close to pole [2] wo orders of magnitude below for m µ + µ < 12. GeV [2] dbr(h µ + µ dm µ + µ * H µ + µ = 125 GeV m H m µ + µ [GeV] Effective branching fractions (integrate right plot within J/ψ or Υ(nS mass regions used in analysis calculated to be (J/ψ and (Υ(nS [1] Phys. Rev. D (arxiv: [2] JHEP 135 ( (arxiv: Probing Higgs Yukawa Couplings with Rare Decays 38 / 39

39 Observed (Expected Background Signal Mass Range [GeV] H All B [ 6 ] B [ 3 ] J/ψ BU 3 9 (8.9±1.3 5 (5.± ± ±.24 BC 29 8 (6.±.7 3 (5.5±.6.63±.3 1.6±.13 EU 35 8 (8.7±1. (5.8± ± ±.18 EC 23 6 (5.6±.7 2 (3.±.4.99±.5.93±.12 Υ(nS BU (39±6 16 (12.9± ±.9 2.6±.3 BC (27.7±2.4 5 (9.7±1.2.79± ±.18 EU (47±6 16 (17.8± ± ±.3 EC (31±5 18 (12.3± ±.8 1.6±.2 Category Probing Higgs Yukawa Couplings with Rare Decays 39 / 39