Examining Z’ decays to 3rd gen. fermions (b, t, ) Travis Martin with Stephen Godfrey, Ross Diener Carleton University, Ottawa August 30, 2011 @ SUSY2011 arXiv:1006.2845
Outline ‣ Discovery of a Z’ - Early and Late LHC ‣ Identification of a Z’ ‣ tt and bb channel ‣ ττ channel ‣ Forward Backward Asymmetry ‣ Summary 2 /18
Deviations from SM ‣ N( ν ) = 2.985 ± 0.008 1 ‣ A FBt (SM) = 5.0 ± 1.5% A FBt (Teva) = 19.3 ± 6.9% 2 ‣ A FBb (SM) = 10.33±0.07% A FBb (LEP) = 9.92±0.16% 3 ‣ Muon (g-2): (SM) 4511.07±0.74 (BNL E821) 4509.04±0.09 3 ‣ Extra neutral gauge boson, Z’, possible! ‣ Non-Universal Couplings? 1 See Erler and Langacker, PhysRevLett.84.212 2 See Cao, Heng and Yang, PhysRevD.81.014016 3 See Erler, et al, JHEP 0908:017 3 /18
Current Limits ‣ FNAL, SLAC, CERN, L=1.08 fb -1 e + e - L=1.21 fb -1 µ + µ - JLab, LEP, Tevatron... e + e − µ + µ − + − Model Z SSM 1.70 (1.70) 1.61 (1.61) 1.83 (1.83) G 1.51 (1.50) 1.45 (1.44) 1.63 (1.63) Z M Z [GeV] EW (this work) CDF DØ LEP 2 E 6 Z Models Z χ 1,141 892 640 673 Model/Coupling Z ψ Z N Z η Z I Z S Z χ Z ψ 147 878 650 481 Mass limit [TeV] 1.49 1.52 1.54 1.56 1.60 1.64 427 982 680 434 Z η 1,204 789 575 Z I ATLAS Collaboration, CERN-PH-EP-2011-123 Z S 1,257 821 Z N 623 861 Z R 442 Theory Estimate ( µµ only): Z LR 998 630 804 Z L (803) (740) 1605 GeV SSM Z SM 1,403 1,030 780 1,787 Z string 1,362 1517 GeV E6 χ Erler, et al, JHEP 0908:017 E6 ψ 1385 GeV E6 η 1429 GeV 4 /18
A Plethora of Models ‣ Non-exhaustive list: ‣ GUT Motivated - E6 χ , η , ψ (couplings ~ θ E6 ) ‣ Left Right Symmetric (couplings ~ g R /g L ) ‣ 3-3-1 Model ‣ Little Higgs (variants) ‣ Topcolor & Technicolor (couplings ~ θ TC2 , θ ETC ) ‣ Un-unified Model (couplings ~ θ UUM ) ‣ Topcolor, Technicolor, Un-unified models - non-universal couplings 5 /18
LHC Discovery Potential http://lpc.web.cern.ch/lpc/lumiplots.htm Discovery Reach (GeV) 3 4 10 10 χ E6 ψ E6 1.96 TeV - 8.0 fb -1 E6 η LRSM Alt. LRSM UUM SSM 7 TeV - 1 fb -1 TC2 Littlest Higgs Simplest LH AFSLH 331 (2U1D) 7 TeV - 5 fb -1 ETC RS Graviton Sneutrino 7 TeV - 10 fb -1 14 TeV - 1 fb -1 14 TeV - 10 fb -1 14 TeV - 100 fb -1 Diener, Godfrey & Martin, arXiv:0910.1334 [hep-ph] 7 /18
Identify with 3rd Gen Fermions ‣ Motivation: Uniquely identify non-universal models ‣ Benefits: ‣ Access coupling info, unavailable otherwise ‣ Useful for global fit ‣ Difficulties: ‣ ID is challenging, low statistics ‣ Large backgrounds ‣ Analysis assumes M Z’ , Z’ known from µ + µ - measurements ‣ Calculations done with MC w/ weighted events, at √ s = 14 TeV, L = 100 fb -1 7 /18
Tagging - b-quark ‣ ε b ~60%, ε j <1% fake ATLAS Preliminary Light jet rejection ‣ Worse fake rate for higher p T 4 JetProb 10 SV0 IP3D SV1 3 10 IP3D+SV1 JetFitter Light jet rejection IP3D+JetFitter ATLAS Preliminary 2 10 1000 JetProb SV0 800 10 IP3D t t simulation, s =7 TeV SV1 jet jet p >20 GeV, | |<2.5 IP3D+SV1 � 600 T 1 JetFitter 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 IP3D+JetFitter b-jet efficiency 400 t t simulation, s =7 TeV jet | |<2.5, =60% � � b 200 The ATLAS Collaboration, ATLAS-CONF-2011-102 50 100 150 200 250 300 350 400 450 500 jet p T 8 /18
Tagging - t-quark ‣ Traditional: tt ➝ bbjjl ν 0.6 0.06 0.5 0.05 ‣ High p T top ➝ fully hadronic Ε t ‣ fully hadronic BR: 46% 0.4 0.04 ‣ semi leptonic BR: 30% 0.3 0.03 0.2 0.02 Ε miss ‣ ε t ~40%, ε j ~1% 0.1 0.01 0 0 600 800 1000 1200 1400 1600 1800 ‣ New methods? p T GeV 10 5 10 4 10 3 d Σ dM fb 100 GeV 10 2 10 1 10 1 dijet 10 2 tt dijet after toptag Current Dilepton & Semi-Leptonic: 10 3 tt after toptag 10 4 ε tt = 1-2% (low p T ) 1000 1500 2000 2500 3000 3500 4000 dijet tt invariant mass M GeV Kaplan, Rehermann, Schwartz and Tweedie, The ATLAS Collaboration, ATLAS-CONF-2011-100 Phys. Rev. Lett.101:142001 (2008) 9 /18
A Signal in the Background ‣ p T >0.3M Z’ improves S/B 5 10 (fb/GeV) 4 10 (a) 3 10 ‣ Invariant mass window: � dM 10 2 d 10 ‣ |M-M Z’ |<2.5 Γ Z’ 1 10 -1 10 -2 -3 10 (fb/GeV) -4 10 1000 1400 1800 2200 2600 3000 M (GeV) 1 b b 1 (fb/GeV) � dM d -1 10 -1 10 � dM d 10 -2 -2 10 -3 10 1000 1200 1400 1600 1800 2000 M (GeV) -4 10 b b 1000 1400 1800 2200 2600 3000 10 /18 M (GeV) b b
Detector Capabilities ‣ Currently ~7% resolution T )/p 2 2 2 2 Fit to MC: � (p )/p = N /p + S /p + C T T T T T 0.2 (p ‣ May achieve 5% res. � Anti-k R = 0.6 cluster jets T EM+JES calibration |y|<2.8 � -1 = 6 nb 0.1 L ‣ Measured Signal/Ideal: Dijet Balance: Monte Carlo (PYTHIA) Dijet Balance: Data 2010 s = 7 TeV Bisector: Monte Carlo (PYTHIA) ATLAS Preliminary Bisector: Data 2010 s = 7 TeV 0.04 20 30 40 50 60 70 80 90 100 , Data) LR LH UUM 20 MC 0 Rel Diff (Fit ideal 1.0 MC Dijet Balance Rel. Diff (Fit , Data) -20 MC Bisector Rel. Diff (Fit , Data) 3% 5% 7% 9% 20 30 40 50 60 70 80 90 100 p (GeV) � 0.9 T / meas https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/ 0.8 CONFNOTES/ATLAS-CONF-2010-054/ � 0.7 ‣ Assume no change to 0.6 0.5 invariant mass window 0.4 0.3 ‣ Still maintain event rate for 0.2 0.1 wider models 0.0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 /M � Z' Z' 11 /18
Ratio of events: R t/ µ vs R b/ µ ‣ R t/µ ~ K(R t2 +L t2 )/(R µ 2 +L µ 2 ) ε tt = 0.075, ε jj = 1/100 2 , σ t =5% ε bb = 0.36, ε jj = 1/100 2 , σ b =5% ε mm = 0.92, σ µ =3% ‣ R b/µ ~ K(R b2 +L b2 )/(R µ 2 +L µ 2 ) M Z’ = 1500 GeV (dark), 2500 GeV (light) 70 9 b/ � b/ � R R 8 60 LRM 7 ETC 50 6 40 5 SSM 4 AFSLH 30 UUM LH 3 SLH E6 - � 20 E6 - � 2 E6 - � LRM 10 3-3-1 1 TC2 Alt. LRM 0 0 0 1 2 3 4 5 6 7 0 10 20 30 40 50 60 70 R R t/ � t/ � 12 /18 Diener, Godfrey and Martin, Phys.Rev.D83:115008,2011
Parameterized Couplings 2 g q 2 L 2 ) 2 g u g d g L 2 ) 2 ( ˆ ( ˆ ˆ ˆ γ q R 2 R 2 γ L = L = U = D = g q g q g L 2 ) 2 + ( ˆ g L 2 ) 2 + ( ˆ g R 2 ) 2 g R 2 ) 2 ˆ ˆ ( ˆ ( ˆ L 2 L 2 M. Cvetic and P. Langacker, Phys. Rev. D46, 4943 (1992) L − 1) × (1 − . 753 ˜ U − . 247 ˜ . 387(2 γ l D ) A F B 1+ . 684 ˜ U + . 316 ˜ D 1 . 796 1+ . 652 ˜ U + . 348 ˜ D r y 1 1+ . 736 ˜ U + . 264 ˜ ‣ R t/µ ~ K(R t2 +L t2 )/(R µ 2 +L µ 2 ) D . 726 1 − . 731 ˜ U − . 269 ˜ D A F B y 1 1 − . 769 ˜ U − . 231 ˜ D L (2 + ˜ U + ˜ γ l ‣ R t/µ ~ K Lq (U+1) B qq D ) 0 . 067 γ l r lνW L ‣ R b/µ ~ K(R b2 +L b2 )/(R µ 2 +L µ 2 ) 10 − 3 (7 . 55+ . 924 ˜ U +0 . 098 ˜ d ) R Z Z 1+ . 684 ˜ U + . 316 ˜ D 24 . 53 × 10 − 3 R Z W ‣ R b/µ ~ K Lq (D+1) 1+ . 684 ˜ U + . 316 ˜ D 5 . 38 × 10 − 3 (1+ . 896 ˜ U + . 104 ˜ D ) R Z γ 1+ . 684 ˜ U + . 316 ˜ D Cvetic & Godfrey, arXiv.org:hep-ph/9504216 13 /18
Varying Model Parameters ‣ Only measurement to depend on mixing angle from UUM, ETC and TC2 models 10 � b/ 9 R UUM 8 ETC 7 LRM 6 5 SSM AFSLH SLH 4 3 E6 Model TC2 ALRM LH 2 3-3-1 1 0 0 1 2 3 4 5 6 7 8 9 10 R t/ � 14 /18
R τ / μ - Generation Universality ‣ Directly tests generation M Z’ = 1500 GeV (dark), 2500 GeV (light) universality E6 - � E6 - � ‣ Use collinear E6 - � LRM approximation for M ττ ALRM UUM SSM TC2 The ATLAS Collaboration, ATL-PHYS-PUB-2010-001 LH 5 SLH 10 Rejection ATLAS Preliminary AFSLH 4 10 Simulation 3-3-1 E > 100 GeV T 3 10 ETC 2 10 0 5 10 15 20 25 10 R ��� 1 Likelihood ‣ O(10%) invariant mass resolution Tight/Medium/Loose settings �� 10 ��������������������� not included * �� 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Efficiency Fully Hadronic * 10% cited by Plehn, et al. Phys.Rev.D61:093005,2000 ~7% cited by Mellado, et al. Phys.Lett.B611:60-65,2005 ε ,1p = 0.31, ε ,3p = 0.34, ε j < 0.0025 ~8% cited in CERN-OPEN-2008 detector paper (pg 1299) 15 /18
Forward Backward Asym. - A FB ‣ Improve systematics by using pseudorapidity 0.4 (off-peak) UUM E6 ψ TC2 ‣ Forward: | η f | > | η f | LH 331 0.3 E6 η SLH ETC FB 0.2 A E6 χ 0.1 LRM AFSLH β = x a − x b 0 ALRM x a + x b 1500 GeV -0.1 SSM µ + µ - -0.2 2 ln 1 + β 1 1 − β + 1 2 ln 1 + z Y = 1 2 ln 1 + β η f = -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 1 − z 1 − β A (on-peak) FB 0.4 (off-peak) UUM E6 ψ 2 ln 1 + β 2 ln 1 + z Z = 1 2 ln 1 + z 1 1 − β − 1 TC2 η ¯ f = 1 − z LH 1 − z 331 0.3 E6 η SLH ETC FB 0.2 A η f = Y + Z η ¯ f = Y − Z E6 χ 0.1 LRM AFSLH 0 | Y + Z | > | Y − Z | when both Y and Z are like signed. (“Forward”) ALRM | Y + Z | < | Y − Z | when Y and Z are opposite signed. (“Backward”) 2500 GeV -0.1 recalling that Y and Z are signed the same as y Z ‘ and z . SSM µ + µ - -0.2 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 16 /18 Diener, Godfrey & Martin, Phys.Rev.D80:075014 A (on-peak) FB
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