Search for heavy resonances decaying to long- lived neutral - PowerPoint PPT Presentation

Search for heavy resonances decaying to long- lived neutral particles Emyr Clement on behalf of the CMS Collaboration E Clement 5 Apr 2013

Motivation • Many new physics scenarios predict heavy long-lived particles ➡ Weak R-Parity Violating SUSY ν ➡ Split SUSY ➡ Hidden Valley Scenario ➡ Exotic decays of recently discovered Higgs boson? • Search for neutral long-lived particles using CMS ➡ Decay to pairs of displaced electrons or muons ➡ Proton-proton data at √ s = 7 TeV ➡ 4.1 - 5.1 fb -1 integrated luminosity ➡ Arxiv link to public result E Clement 5 Apr 2013 2

CMS E Clement 5 Apr 2013 3

CMS • Pixel Detector & Silicon Tracker ➡ Reconstruct tracks of charged particles ➡ Measure p t of charged particles E Clement 5 Apr 2013 4

Reconstruction of Displaced Tracks • CMS exploits an iterative tracking CMS algorithm Tracking efficiency 1 Simulation ➡ First iterations find tracks originating near the primary vertex Data 0.8 ➡ Final iterations find displaced tracks 0.6 0.4 • Can reconstruct displaced leptons with impact parameters (d 0 ) up to 0.2 ~ 30 cm 0 ➡ Efficiency to reconstruct track decreases 0 10 20 30 40 50 at larger displacements |d | [cm] 0 E Clement 5 Apr 2013 5

Displaced Vertex Signature Long-lived particle, X electron or Simulation muon pairs m H = 400 GeV ➡ Travel ~20cm in m X = 150 GeV transverse plane before decaying Some heavy resonance ( not necessarily a Higgs ) • Tracks and vertex are displaced from centre of CMS ➡ Makes analysis almost background free ➡ Only need to reconstruct one displaced vertex E Clement 5 Apr 2013 6

Dilepton Mass Spectrum • Look for a narrow resonance in dilepton mass spectrum -1 CMS s =7 TeV L=5.1 fb -1 CMS s =7 TeV L=4.1 fb Entries 3 3 10 Entries 10 - + H(1000) XX(350), 1 pb → µ µ - + H(1000) XX(350), 1 pb e e → QCD QCD tt 2 tt 10 2 Z/ * γ → µ µ 10 Z/ * ee γ → Z/ * γ → τ τ Z/ * γ → τ τ WW WW 10 WZ WZ 10 ZZ ZZ Data Data 1 1 -1 10 -1 10 -2 10 -2 10 -3 10 -4 10 0 100 200 300 400 500 0 100 200 300 400 500 2 mass [GeV/c ] 2 mass [GeV/c ] Expected 0.02 +0.09-0.02 background Expected 1.38 +1.78-1.19 background candidates candidates E Clement 5 Apr 2013 7

Results • See no significant excess • Set 95% CL upper limit on σ (H → XX) × B(X → l + l - ) ➡ Range of H and X masses • Main systematic uncertainty due to displaced tracking efficiency -1 CMS s = 7 TeV L = 5.1 fb -1 CMS s = 7 TeV L = 4.1 fb ) [pb] ) [pb] 2 2 2 m = 125 GeV/c 10 m = 400 GeV/c H H - 2 - µ 10 e Observed 95% CL limits Observed 95% CL limits + + µ e 2 10 → m = 20 GeV/c 2 → m = 20 GeV/c X X 2 B(X m = 50 GeV/c B(X X 2 10 m = 50 GeV/c 2 X m = 150 GeV/c X XX) 1 Expected 95% CL limits XX) Expected 95% CL limits → 1 → -1 10 0 0 (H (H σ σ -1 10 -2 10 -2 -3 10 10 3 -1 2 2 3 10 1 10 10 10 1 10 10 10 c [cm] τ c [cm] τ m H = 400 GeV/c 2 , m X = 20 → 150 GeV/c 2 m H = 125 GeV/c 2 , m X = 20 → 50 GeV/c 2 E Clement 5 Apr 2013 8

Summary -1 CMS s = 7 TeV L = 5.1 fb ) [pb] 2 m = 125 GeV/c H - 2 µ 10 • A search for neutral long-lived particles Observed 95% CL limits + µ → 2 m = 20 GeV/c X B(X 2 ➡ Decay to pairs of electrons or muons 10 m = 50 GeV/c X XX) Expected 95% CL limits → 1 • No significant excess seen 0 (H σ -1 10 ➡ Set upper limits ➡ m H = 125 → 1000 GeV/c 2 -2 10 ➡ m X = 20 → 350 GeV/c 2 3 2 1 10 10 10 c [cm] τ • Limits in range 0.7 fb → 100 fb ➡ For X with L xy in laboratory frame of ~2 → 100cm • Further information : arxiv.org/abs/1211.2472 E Clement 5 Apr 2013 9

Backup

Online Selection • Muon channel ➡ Two muons reconstructed in muon systems only ➡ No primary vertex constraint ➡ No tracker requirement ➡ p t >30 GeV/c • Electron channel ➡ Two clustered energy deposits in the ECAL ➡ E t >38 GeV ➡ No tracker requirement E Clement 5 Apr 2013 11

Detailed Candidate Selection • Selection cuts on track/leptons • Selection cuts on dileptons/X candidates ➡ High purity tracks, 6 valid hits, | η |<2 ➡ p t of tracks > 33 GeV (muon) > 41 ➡ Good vertex fit (electron) ‣ χ 2 /NDF < 5 ➡ d 0 / σ of tracks > 2 (muon), > 3 (electron) ➡ No more than one tracker hit in front of vertex ➡ Tracker isolation ➡ Decay length significance (L xy / σ ) cut > 5 (muons) > 8 (electrons) • Σ p t < 4 GeV within Δ R < 0.3 ➡ Reconstructed candidate momentum collinear with vertex flight direction • In electron channel, also match ‣ ΔΦ <0.2 (muons) <0.8 (electrons) track to offline supercluster p ll ΔΦ • In muon channel, reject back-to- L xy back muons and require Δ R DV between muons >0.2 PV E Clement 5 Apr 2013 12

Identification of Displaced Vertex • Select lepton pairs that form a vertex ➡ Our X candidates • Require tracks and vertex to be displaced from centre of CMS ➡ Selection makes analysis almost background free -1 CMS s =7 TeV L=4.1 fb 3 Entries 10 - + H(1000) XX(350), 1 pb → e e QCD tt Z/ * ee γ → 2 10 Z/ * γ → τ τ WW WZ ZZ Data 10 Signal MC in overflow 1 Background at low -1 10 displacements -2 10 0 2 4 6 8 10 12 14 16 18 20 L / σ xy xy E Clement 5 Apr 2013 13

Candidate Selection (II) • n-1 selection plot for transverse decay length significance (L xy /sigma) ➡ Good separation of signal from background -1 CMS s =7 TeV L=4.1 fb -1 CMS s =7 TeV L=5.1 fb 3 Entries 10 Entries - + H(1000) XX(350), 1 pb → e e 4 - + H(1000) XX(350), 1 pb → 10 µ µ QCD QCD tt tt Z/ * ee γ → 2 Z/ * γ → µ µ 10 Z/ * 3 γ → τ τ 10 Z/ * γ → τ τ WW WW WZ WZ ZZ ZZ 2 Data 10 10 Data 10 1 1 -1 10 -1 10 -2 10 -2 10 -3 10 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 L / σ L / σ xy xy xy xy E Clement 5 Apr 2013 14

Candidate Selection (III) • Can relax some selection to increase statistics ➡ Check agreement between data and background MC E Clement 5 Apr 2013 15

Systematic Uncertainties • Most crucial systematic uncertainty, how well do we understand tracking efficiency for CMS Tracking efficiency displaced tracks 1 Simulation ➡ Main method to study: use cosmic muons Data 0.8 ➡ Cosmic muon leaves a track in the muon systems ➡ Is cosmic also reconstructed in central tracker? 0.6 ➡ Assign 20% systematic uncertainty to account for 0.4 disagreement between data and MC 0.2 • Trigger Efficiency Uncertainty 0 ➡ Use standard tag & probe 0 10 20 30 40 50 |d | [cm] ➡ Assign 11% systematic uncertainty in muon channel 0 ➡ Assign 2.6% systematic uncertainty in electron channel E Clement 5 Apr 2013 16

Limits -1 -1 CMS s = 7 TeV L = 5.1 fb CMS s = 7 TeV L = 4.1 fb ) [pb] ) [pb] 2 2 2 2 10 m = 400 GeV/c 10 m = 1000 GeV/c H H - - e µ Observed 95% CL limits Observed 95% CL limits + + e µ 2 m = 20 GeV/c 2 10 10 m = 20 GeV/c → X " X 2 m = 50 GeV/c 2 X m = 50 GeV/c B(X B(X 2 X m = 150 GeV/c X 2 m = 150 GeV/c 2 m = 350 GeV/c X 1 1 XX) X XX) Expected 95% CL limits Expected 95% CL limits → " -1 -1 10 10 0 0 (H (H σ # -2 -2 10 10 -3 -3 10 10 3 3 -1 2 -1 2 10 10 10 10 10 10 1 10 1 10 c [cm] c [cm] τ ! -1 -1 CMS s = 7 TeV L = 5.1 fb CMS s = 7 TeV L = 5.1 fb ) [pb] ) [pb] 2 10 2 2 2 m = 1000 GeV/c m = 200 GeV/c 10 H H - - µ µ Observed 95% CL limits Observed 95% CL limits + + 10 µ µ 2 m = 20 GeV/c 10 → → X 2 m = 20 GeV/c 2 m = 50 GeV/c X X B(X B(X 2 m = 150 GeV/c 2 m = 50 GeV/c X X 2 1 m = 350 GeV/c 1 X XX) XX) Expected 95% CL limits Expected 95% CL limits → → -1 10 -1 10 0 0 (H (H σ σ -2 10 -2 10 -3 -3 10 10 3 -1 2 3 -1 2 10 1 10 10 10 10 1 10 10 10 c [cm] c τ [cm] τ E Clement 5 Apr 2013 17