Probing Baryogenesis with Displaced Vertices at the LHC Yanou Cui - PowerPoint PPT Presentation

Probing Baryogenesis with Displaced Vertices at the LHC Yanou Cui Perimeter Institute • Phys.Rev.D, 87,11603, YC and Raman Sundrum • JHEP 1312 (2013) 067, YC • JHEP 1502 (2015) 049, YC and Brian Shuve • Ongoing corporation with ATLAS displaced jets working group GGI LHC13 Workshop Oct 1 2015 1

Outline • A mini-review of long-lived particle (displaced vertex) searches at the LHC: motivation, status • A general cosmological motivation: baryogenesis triggered by weak scale new particle decay • A motivated example: WIMP baryogenesis embed in natural/split SUSY • Recast existing LHC analyses with theorists’ tools: Baryogenesis as an example, easy to generalize! • Conclusion/Outlook 2

Long-lived Particle Searches at the LHC • Nearly all SM particles decay promptly or have small masses relative to the LHC partonic CM energy • Energetic objects reconstructing a high mass can emerge from all parts of the detector, giving displaced vertices (DV) Displaced vertex signal is spectacular! ‣ low SM background, sensitive to rare signal events (new long-lived particles…) 3

Long-lived Particle Searches at the LHC Displaced vertex signal is spectacular! ‣ But, we could easily miss it entirely!… • Most LHC searches require that objects pass through the primary vertex (PV) to reject cosmics, mis-reconstructed objects, etc. • In most searches, the transverse impact parameter (distance of closest approach to the beam) has to be ≲ 100 µ m - 1 mm (= prompt ) (track quality cut) Without dedicated efforts, DV signal events may fail to be even triggered on! 4

Long-lived Particle Searches at the LHC Rising interests+ endeavours from both experimentalists and theorists in the recent years! • A (incomplete) list of related ATLAS/CMS publications based on 8 TeV data: ‣ ATLAS displaced dijets (arxiv:1504.03634) ‣ ATLAS displaced lepton pairs/multitrack (arxiv:1504.05162) ‣ ATLAS displaced muon+tracks (ATLAS-CONF-2013-092) ‣ CMS displaced dijets (arxiv:1411.6530) ‣ CMS displaced dilepton (CMS-PAS-B2G-12-024) … • Rising # of related papers by theorists… • Displaced higgs decay : A focus of the exotic Higgs decay working group of the LHC collaboration • Dedicated workshop: e.g. at UMass-Amherst, Nov 2015… 5

Theoretical Motivations • Naturalness: long lifetime from approximate Z 2 symmetry TWIN HIGGS SUPERSYMMETRY Approximate Z 2 symmetry • Can evade MET searches with • relates SM fields to `twin’ fields, (small) R -parity violation cancelling the top divergence ‘Displaced SUSY’ • Breaking must be non-zero to • (Graham, Kaplan, Rajendran, Saraswat 2012…) obtain observed EWSB, but small to obtain a natural theory Long-lived LSPs can also arise • (Craig, Katz, Strassler, Sundrum 2015…) with split spectra e + _ e b σ v q b η ’ η ’ U v v b • General hidden valley type of Z’ b d ω v v d b new physics (Strassler, Zurek 2006…) q U η ’ v b 6

Theoretical Motivations (new) Baryogenesis from Metastable Weak-scale New Particle Could LHC shed light on prominent puzzles in modern cosmology? Ω DM ≈ 23% , Ω B ≈ 5% , Ω B ~ Ω DM • Familiar/well-studied case: WIMP dark matter ( Ω DM ) ‣ Mass ~O(10-100) GeV, can be produced within E LHC =14 TeV ‣ Pair produced (Z 2 ) , MET χ DM invisible, MET + X p p χ DM ISR MET 7

Theoretical Motivations (new) Baryogenesis from Metastable Weak-scale New Particle • New opportunity : baryogenesis (address Ω B , possibly + Ω B ~ Ω DM ) ‣ New metastable particle (baryon parent), w/mass ~O(10-100) GeV ‣ Pair produced (approx. Z 2 ), via Z/Z’, or Higgs portal j/ ` / MET ‣ Cosmological condition χ BG typical decay final states: p p Displaced decay , to j/ ` / MET χ BG ( c τ χ & 1 mm) 8 j/ ` / MET

Mini-Review of Baryogenesis • Origin of Ω B ? = Where do we ourselves come from? 10 B � ¯ Initial asymmetry B We do not know! ⇡ B ) /n γ ⇠ 10 � 10 η B = ( n B � n ¯ symmetric annihilation Baryon Anti-baryon Baryon Anti-baryon Sakharov Conditions (1967): B • Require baryon number violation • Require C-, CP-symmetry violation ¯ B B ≠ 9

Mini-Review of Baryogenesis Sakharov Conditions (cont.): In thermal equilibrium: ✓ ◆ � q q n B ( p ) eq ⇠ exp B ( p ) eq ⇠ exp h⇣ ⌘ i p 2 + m 2 p 2 + m 2 � B + µ /T , n ¯ � B � µ /T ¯ ¯ q B B µ = 0 Ω B ≈ 5%: CPT symmetry = 0 m B = m ¯ B Need beyond the B Standard Model n eq B = n eq B , h B i eq = 0 ¯ Physics! • Require departure from equilibrium! ❖ Existing baryogenesis mechanisms: (leptogenesis, EWBG…) Most involve high M or/and T, direct experimental test impossible (c.f. WIMP DM for Ω DM ) 10

Baryogenesis from Out-of-Equilibrium Decay A general class of baryogenesis models (e.g. leptogenesis) • Assume a massive neutral particle χ Baryon asymmetry can be produced in its decay (B-, CP-violating) • Γ ( χ ! f ) 6 = Γ ( χ ! ¯ f ) n f � n ¯ f 6 = 0 • Typically, the inverse processes efficiently erase the asymmetry • But, if χ is long-lived, and decays only after T f < M χ : f f Inverse decay: X χ ✔ χ Boltzmann suppressed f f e − M χ /T decay 13 , X Out-of-equilibrium decay Sakharov conditions 11

Baryogenesis from Out-of-Equilibrium Decay f f χ ✔ X χ f f 13 • Asymmetry is robustly preserved if ( H : Hubble expansion rate) Weak washout scenario Γ χ < H ( T = M χ ), An intriguing observation ( YC , Sundrum 2012; YC , Shuve, 2014) • If χ has mass at weak scale (the new energy frontier LHC < H ( T EW ) ∼ 10 − 13 GeV is exploring!), numerology gives c ⌧ − 1 χ • Converting to decay length: c τ χ & mm Displaced vertex regime @LHC! 12

Displaced Vertices Motivated by Baryogenesis c τ χ & mm Γ χ < H ( T = M χ ), • A generic connection between cosmological slow rates at T ~100 GeV and displaced vertices at colliders • The universe around EW phase transition was just slightly bigger than LHC tracking resolution! H (100 GeV) ∼ 10 − 14 GeV ∼ (1 . 3 cm) − 1 10 GeV → (1 . 3 m) − 1 1 TeV → (0 . 13 mm) − 1 also see: Chang, Luty, 2009 13

Displaced Vertices Motivated by Baryogenesis • Production at the LHC? No conflict between a small decay rate and a large production rate j/ ` / MET • Long lifetime due to parity-preserving approximate symmetry χ parity-violating BG vertex (e.g. Z 2 parity) vertex p p • Recover MET signal for χ BG DM in the limit of exact ( c τ χ & 1 mm) symmetry! j/ ` / MET Concrete, motivated baryogenesis models as example? 14

Baryogenesis from WIMPs • YC and Raman Sundrum, Phys.Rev.D,11603 (2012) • YC, JHEP 1312 (2013) 067 15

WIMP Miracle for DM — Ω DM by weak scale new physics WIMP χ freez • Cosmic Evolution of a stable WIMP : h Equilibrium SM WIMP Time evolution of 𝜓 abundance: SM WIMP annihilation Universe expands, cools, T SM WIMP Thermal freezeout → time Γ ann ⇠ n eq χ h σ ann v i < H Departure from SM / e � M χ /T n eq WIMP χ equilibrium: key to Ω WIMP !

WIMP DM Miracle • Neat prediction for the absolute amount of Ω DM : Ω χ / h σ ann v i � 1 ◆ 2 ✓ M weak ◆ 2 ✓ G Fermi ⇠ 0 . 1 G χ m χ ! With , readily gives ! m χ ⇠ M weak , G χ ⇠ G Fermi , Ω DM ⇡ 23 % , 2 3 • Robust, insensitive to cosmic initial condition • Miracle: Predicts the right location of a needle in a haystack! Observed ! yet not precise , Ω DM ⇡ 23 % , 2 3 Vast possible range of a cosmological ⇠ (10 � 7 � 10 35 ) quantity: e.g. Ω theory DM 17

• The familiar story of a stable WIMP WIMP DM 𝜓 X thermal freeze out Ω DM out-of-equilibrium WIMP DM 𝜓 X • A different story of a (general) WIMP? Stable 𝜓 DM, WIMP 𝜓 X Ω DM thermal freeze out ? out-of-equilibrium Metastable 𝜓 B ? WIMP 𝜓 X (later decay) ✴ Diverse lifetimes : generic in nature + B-, C-, CP-violating decay (symmetry, mass/coupling hierarchy) YC and Sundrum 2012; e.g. long lifetime of b-quark, muon YC 2013 ( ), SUSY WIMP w/RPV m W � m b , m µ 18

Baryogenesis from Metastable WIMP Decay SM � • A new baryogenesis mechanism w/weak scale new physics: � SM A WIMP miracle for baryons, T ★ Thermal freezeout � SM can occur well below T EW WIMP Ω τ !1 WIMP • If + A stable WIMP DM Γ χ . H ( T freezeout ) SM � new path addressing Ω B ~ Ω DM T ★ Baryogenesis � �� CP from decay � SM � B ( � L ) � � M p M WIMP Ω τ !1 Ω B = ✏ CP WIMP 19

Consider a stable WIMP as DM; species � DM and WIMP χ B , In addition, a metastable WIMP as baryon parent • Cosmic evolution of the two WIMPs: species � DM and Equilibrium SM/DM’ WIMP χ B , Equilibrium SM/DM’ WIMP χ B , species � DM and SM/DM’ SM/DM’ Universe expands, co ols species � DM and WIMP χ B , SM/DM’ SM/DM’ Thermal Freezeout WIMP χ B , species � DM and SM/DM SM/DM’ H Γ ann < H p ¯ (Generalized) WIMP miracle Ω τ →∞ B Ω DM χ B B Universe expands, co ols O ¯ µ u d u d ¯ O B − L B Ω DM WIMP χ B , WIMP χ B , ✏ CP u ¯ u d ¯ d O B − L u d u ¯ ¯ d Baryogenesis from decay of � B, �� WIMP χ B , m p � CP � Ω B = ✏ CP m χ B Ω τ →∞ χ B after its thermal freeze out 20