1. Lepton Flavor Violation at LHCb The τ → μμμ decay Matt Jaffe Physics Department, Penn State University 7.7.20111

2. The LHCb Experiment 7.7.2011 Matt Jaffe Penn State University 2 Indirect search for new physics – CP Violation – Measurement of rare decays 700 scientists from 52 institutions Lepton Flavor Violating Decays

3. Outline The τ → μμμ Decay – Why study it? – How to study it? Data Analysis Results 7.7.2011 Matt Jaffe Penn State University 3 {

4. Motivation: Why τ → μμμ ? Study Lepton Flavor Violation Standard Model forbidden process Test and constrain New Physics models 7.7.2011 Matt Jaffe Penn State University 4 SM + Heavy Majorana ν r SUSY SO(10) mSUGRA + seesaw OR (more likely)

5. Methods: How τ → μμμ ? Select signal, reject background – Draft sets of cuts – Study cut effects on signal and background distributions 7.7.2011 Matt Jaffe Penn State University 5 Example of a variable distribution which might be cut on.

6. Control Channels 7.7.2011 Matt Jaffe Penn State University 6 D s → π π π D s → φ(μμ) π – Distributions as similar as possible to signal – Want cuts with similar effects across all three channels Example of a variable distribution demonstrating good agreement between signal and control channels.

7. Data Analysis 7.7.2011 Matt Jaffe Penn State University 7 40 MHz L0 Trigger 1 MHz High Level Trigger 3 kHz “Online” Analysis “Offline” Analysis Stripping Lines Stored Data Selection Cuts PHYSICS! My Decay Channel Other Decay Channels

8. Step 1: Stripping 7.7.2011 Matt Jaffe Penn State University 8 Data τ -> μ μ μ Normalization Channels < 0.05 % Selectionε r (τ -> μμμ)ε r (Ds -> πππ)ε r (Ds ->φπ) Proposed 0.6830.5010.563 Previous0.6230.1160.234 Selectionε r (τ -> μμμ)ε r (Ds -> πππ)ε r (Ds ->φπ) Proposed 0.04% 0.21% (Prescale) 0.044% Signal Monte Carlo Efficiency Background Elimination – Remaining Events

9. Step 2: Selection 7.7.2011 Matt Jaffe Penn State University 9 3 596 228 events Selection Cuts Selection Cuts Efficiencies ε r (τ -> μμμ) * (Monte Carlo) ε r (Ds -> πππ)* (Monte Carlo) ε r (Ds ->φπ)* (Monte Carlo) LHCb Real Data (Background) Currently: 8.6 %17.7%19.0 %0.00046 % Efficiency = ( # candidates after stripping + selection ) / (# candidates after stripping ) D s mass peak reconstructed by our selections from LHCb data *(Not yet signal specific selection) LHCb Internal

10. Control Channel Mass Peaks 7.7.2011 Matt Jaffe Penn State University 10 D s peak split into the 2 channels Signal MCs on top Extracted peaks below LHCb Internal D s -> 3 Pi Signal Monte CarloD s -> Phi Pi Signal Monte Carlo D s -> Phi Pi from dataD s -> 3 Pi from data

11. Future Work 7.7.2011 Matt Jaffe Penn State University 11 Re-optimize D s →π π π stripping to eliminate need for pre-scaling Further study of daughter PID cuts to split the three channels Analyze selection of τ→μ μ μ. We imagine starting with an earlier, looser version of the D s cuts, then optimizing to the channel. Perform rigorous statistical analysis of cut effects at all stages Look at a lot of data!

12. Thank You! I cannot thank the following people enough: CERN Summer Student Program – Dr. Johannes Albrecht – Supervisor – Dr. Marco Gersabeck – Substitute Supervisor The University of Michigan REU program – Dr. Homer Neal – Dr. Jean Krisch – Dr. Junjie Zhu – Dr. Steve Goldfarb – Lauren Rigani 7.7.2011 Matt Jaffe Penn State University 12

13. Thank you! 7.7.2011 Matt Jaffe Penn State University 13

14. 7.7.2011 Matt Jaffe Penn State University 14

15. BACKUP SLIDES 7.7.2011 Matt Jaffe Penn State University 15

16. Backup Slides - τ -> μ μ μ Stripping Line Previous Cuts Mother Cuts Mass Window = ± 400 MeV Vchi2 < 25 c * τ > 70 μm Child with P t > 1 GeV Daughter Cuts (for all 3) P t > 300 MeV mu track χ 2 / DoF < 5 (Mu IPS) 2 > 6 7.7.2011 Matt Jaffe Penn State University 16 Proposed Cuts Mother Cuts Mass Window = ± 400 MeV Vchi2 < 20 c * τ > 100 μm τ IPS < 15 Daughter Cuts (for all 3) P t > 300 MeV mu track χ 2 / DoF < 5 (Mu IPS) 2 > 9

17. Backup Slides - Control Channel Stripping Line 7.7.2011 Matt Jaffe Penn State University 17 Previous Cuts Mother Cuts Mass Window = ± 250 MeV Vchi2 < 25 c * τ > 200 μm D s IPS < 3 P t > 2 GeV Daughter Cuts (for all 3) P t > 300 MeV mu track χ 2 / DoF < 5 (Mu IPS) 2 > 12 Proposed Cuts Mother Cuts Mass Window = ± 80 MeV Vchi2 < 20 c * τ > 200 μm D s IPS < 15 Ds->3π required to be TIS Daughter Cuts (for all 3) P t > 300 MeV mu track χ 2 / DoF < 5 (Mu IPS) 2 > 9

18. Backup Slides - Current Selection Cuts (e) 7.7.2011 Matt Jaffe Penn State University 18 Current Working Version of Selection Cuts 1)Mother Impact Parameter Significance ( = √(χ 2 ) ) < 1.8 2)Mother Vertex χ 2 < 6 3)max ( Delta Log Likelihood( Pion - Kaon ) ) < 0 4)max ( Daughter Track χ 2 ) < 1.4 5)Cos ( angle ) > 0.999875 6)max ( Daughter P tot ) < 40 GeV 7)max ( Delta Log Likelihood( Pion - Proton ) ) < 5

19. Stripping Cuts Tuning: Step 2 7.7.2011 Matt Jaffe Penn State University 19 Selection #ε r (Tau -> 3 Mu)ε r (Ds -> 3 Pi)ε r (Ds -> Phi Pi ) 2_60.6830.68250.762 2_70.5170.5540.532 2_80.2570.3060.347 ε r := ( # candidates after new stripping lines) / ( # candidates after truth matching )

20. 7.7.2011 Matt Jaffe Penn State University 20 Selection #Ds -> 3 PiDs -> Phi PiSignal Blinded Data (a)0.2990.3470.00301 (b)0.3010.2820.00197 (c)0.17900.15950.000385 (d)0.1270.1140.000185 (e)0.1770.1900.000462 Selection Cuts - efficiencies Efficiency = ( # candidates after stripping + selection ) / (# candidates after stripping )

21. More Detailed Efficiency 7.7.2011 Matt Jaffe Penn State University 21 CutDs -> 3 PiDs -> Phi PiBackgroundDs -> 3 PiDs -> Phi PiBackground (e) 10.5650.5640.09360.7320.7350.106 20.7500.7570.3510.8570.9000.454 30.7300.6640.1180.9520.9350.541 40.9520.9700.8950.9230.9730.893 50.6390.6600.1900.6590.7580.250 60.8410.8740.6480.9841.000.995 70.7140.6640.4850.800 0.465 8-- (N-1) ε for this cutε for this cut only

22. Mass Peak Fit Parameters 7.7.2011 Matt Jaffe Penn State University 22 (a)(b)(c)(d)(e)S / B - fits integrated on (1900,2050) Ds -> 3 Pi (1) -166.39201.1129.291.0100.53(a):0.380 (2) 0.244-0.021-0.042-0.04-0.033(b):0.374 (3) 809.1440.03223.070.2183.6(c):0.680 (4) 1965.61965.71965.5 1965.6(d):0.734 (5) 8.8608.128.4437.518.28(e):0.719 Ds -> Phi Pi (1) 127.7188.2110.530.84106.9(a):0.340 (2) -0.03-0.076-0.05-0.014-0.05(b):0.375 (3) 110.573.8238.716.5834.5(c):0.591 (4) 1977.71976.91976.41975.41976.4(d):0.664 (5) 12.6211.5710.7347.6510.07(e):0.791 #Parameter (1)Linear fit constant (2)Linear fit slope (3)Gaussian amplitude (4)Gaussian Center (5)Gaussian Sigma

23. Backup Slides - Kinematics Plots 7.7.2011 Matt Jaffe Penn State University 23

24. Backup Slides - More Plots 7.7.2011 Matt Jaffe Penn State University 24

25. Backup Slides - Flight/IPS Plots 7.7.2011 Matt Jaffe Penn State University 25

26. Backup Slides - More Plots 7.7.2011 Matt Jaffe Penn State University 26