Fermilab E791 Collaboration. Charmed Mesons. David A. Sanders University of Mississippi. Physics Motivation, Search for New Mediators

Transcription

1 Fermilab E791 Collaboration Search for Rare an Forbien ecays of D, D s +, an Charme Mesons + D Davi A. Saners University of Mississippi Introuction Physics Motivation, Search for New Meiators Detector Description, Fixe Target Metho, Blin Analysis Results Conclusion Fermilab Wine an Cheese, October 29, 1999

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3 Why Search for Rare an Forbien ecays? Tests Stanar Moel an allows investigation of phenomena in mass ranges beyon those available to current accelerators Stanar Moel preicts Branching Ratio < Short Range Long Range D + c W + ν µ + µ u W u s π + W + c µ + D + ρ µ BR<1-9 BR<1-6 π + Search for violations from Flavor Changing Neutral Currents, Lepton Number an/or Flavor Violations (via Neutrino Oscillations, Leptoquark, Horizontal Gauge Bosons, etc.?)

4 Feynman Diagram Examples Stanar Moel Flavor-Changing Neutral-Current D + c W + ν s l + W l u π + X l + l c u D + π + D + π + l + l

5 Lepton Flavor Violating Moes Neutrino Oscillations Horizontal Gauge Boson D + c W + ν s ± µ e m W u π + D + c X ' ± µ e m u π + D π µ e + + ± m

6 Lepton Number Violating Moes Leptoquark c X ' D + l + X " l + u l + π D π l l Note: If the two leptons are a ifferent flavor then this woul be a Lepton Flavor Violating moe.

7 Rare an Forbien Decay Moes Flavor Changing Neutral Currents Lepton Flavor Violating Lepton Number Violating D π µ µ + + ± D π µ e D π µ µ D π ee D π µ e D π ee D K µ µ + + ± D K µ e K + + µ µ D K ee K ± µ e K ee K + µ µ K + µ + e + + π µ µ K ee + ± π µ e π ee + + π µ µ + + π µ e π + ee D µ ± e D µ + µ D + ee

8 Explore New Mass Ranges For simplicity assuming g X, X = g Flavor Changing Neutral Current - Using: W ( + + µ ν ) µ m m B R D ~ K X W B R + ( D FCNC) µ + 14 µ + D + c W + ν µ s K X µ c u D + π + Lepton Flavor Violating - Using: ( + + µ ν ) µ + R( D LFV) m X mw B R D ~ K B µ + 14 µ + D + c W + ν µ s K D + c X ' e + u π + A. Schwartz, Mo. Phys. Lett. A8 (1993) 97.

9 Detector Description The E791 experiment use a 5 GeV π beam hitting a target Targets π Beam Pt C C C C The E791 Spectrometer consiste of the following etectors: Particle Tracking Detectors 23 planes of Silicon Microstrip Detectors (SM) 45 planes of wire chambers (PWCs an DCs) Momentum Measurement 2 ipole magnets Particle Ientification 2 multi-cell Cerenkov ( counters Muon etector Energy Measurement Electromagnetic an haronic calorimeters

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11 Electron Ientification The Segmente Liqui Ionization Calorimeter (SLIC) Separate electrons from pions by: 1) Matching SLIC energy with Drift Chamber momentum. 2) Matching SLIC position with Drift Chamber positions. 3) Fining no energy in the Haron Calorimeter behin the caniate electron shower. 4) Transverse energy eposition. 5-7% efficient. Pion misientification ~1%.

12 Muon Ientification 16 Horizontal Scintillator strips 14 cm X 3 m with PMT/TDCs on one en. 14 Vertical Scintillator strips covering a 3m X 6m area. Locate behin ~2.5 meters of Iron (15 IL) Stops haronic showers. 1) Extrapolate tracks with > 8 GeV/c momentum to muon wall. 2) Di not allow caniates to share hits in a horizontal strip. 3) Use TDC information to improve horizontal resolution. 99% Efficient. Pion misientification rate ~1.5%.

13 Vertexing D s Lifetime τ( φπ)=. 518±. 14±. 7 ps ( ) τ τ D (6σ ifference from unity) ( ) = ± Physics Letters B 445 (1999)

14 D + Semileptonic measurements + + D K * µ ν µ ν + * + D K e e = + + Mmin P p 2 2 t t m vis Combine Form-Factor results an r 2 = 73. ± 6. ± 8. r v= ± ± Physics Letters B 44 (1998)

15 Data Acquisition an Offline Computing System E791 use a loose transverse energy (or open Charm) trigger. More ata = more Charm. 1 Recore 2 1 events 5 Terabytes of raw ata on 24, 8mm tapes. (CDF 1 TB ) Golen Convergence: High spee electronics 5 µs Silicon ADCs/TDCs. (4 events/secon to tape.) New ata storage evices Exabyte 8mm tape rives. Fast reconstruction computer farms Commercial UNIX RISC-base computers. Beginning of cheap commoity computing. 1/3 of the ata was reconstructe at the University of Mississippi Computer Farm the remainer at Kansas State University, Fermilab, an CBPF - Brazil.

16 Great Wall of Exabytes E791 DAQ

17 Mississippi Computer Farm The computer farm, consisting of 68 DECstations, was running in the backgroun uring an E791 collaboration meeting at the University of Mississippi.

18 E791 Data Reconstruction University of Mississippi Kansas State University FNAL/CBPF-Brazil

19 Blin Analysis Metho Metho: Cover signal region with a box Optimize ALL cuts before opening box Maximize Monte Carlo Signal/ Data Wings Open box covering signal region Blin Analysis Close mass box withs: + D hµµ 6 MeV c 2 + D hee(or hµe) 12 MeV c 2 + D hµµ 4 MeV c 2 s + D hee(or hµe) 8 MeV c 2 s D µµ 7 MeV c 2 D ee(or µe) 14 MeV c 2

20 Illustration of the close box mass using D Monte Carlo generate events Note the asymmetry of the box ue to the Bremsstrahlung tail (We trie to keep tails insie the box but, as Schröinger woul have foun out, sometimes the tails stick out a little.)

21 Description of the Kinematics Variables Vertex Separation (SDZ) Z D + π + Beam π Primary Vertex σ pri π σ sec Seconary Vertex µ + e Transverse Momentum Balance (PTB) K - D + P D + P t Primary Vertex P K - π + π + Seconary Vertex π + π +

22 Kinematics Cuts D + D D s + Separation of Vertices > 2 σ > 12 σ > 12 σ Vertex separation from > 5 σ Target > 5 σ > 5 σ Lifetime < 5 ps < 3 ps < 3 ps Impact parameter <.4 mm <.4 mm <.4 mm Transverse momentum <.2 GeV/c <.25 GeV/c <.3 GeV/c balance Cuts were etermine to maximize Monte Carlo signal / Backgroun. (Backgroun is ata outsie the signal region.) Other cuts: Removal of reflections ue to particle misientification Particle ID cuts

23 Branching Ratio Calculation BR = N X ε X X N norm ε norm BR norm = N N ε ε X norm BRnorm norm X MC Where the efficiency ratio ε norm norm = N MC ε X N X is the ratio of the number of events from a Monte Carlo simulation. If you have enough caniates to use Gaussian statistics then N X is the number of observe events, after subtracting backgrouns. If not, you have to use Poisson statistics an make an upper limit calculation.

24 Monte Carlo Simulation Use PYTHIA/JETSET 1 from Lun Monte Carlo Moe # Generate # Passe Cuts % Yiel D K π π 25, 2, D π µ µ 25, 2, D π ee 25, ± D π µ e 25, 1, D π µ µ 25, 2,88.84 D π ee 25, D π µ e 25, D K µ µ 25, D K ee 25, ± D K µ e 25, D K µ µ 25, 1, D K ee 25, D K µ e 25, D s φ π + 25, 1, K µ µ 25, K ee 25, ± K µ e 25, K µ µ 25, K ee 25, K µ e 25, D s + π µ µ 25, π ee 25, ± π µ e 25, D s + + π µ µ 25, π ee 25, π µ e 25, D K π + 25, 4, D µ + µ 25, 5, D ee 25, 1, µ ± e 25, D 1 H.-U. Bengtsson an T. Sjöstran, Comp. Phys. Comm. 82 (1994) 74; T. Sjöstran, PYTHIA 5.7 an JETSET 7.4 Physics an Manual, CERN-TH.7112/93, 1995.

25 Upper Limit Branching Ratio Calculation BR < N X ε X X N norm ε norm BR norm < N N ε ε X norm BRnorm norm X MC Where ε norm norm = N an MC ε X N X N X is now the 9% CL upper limit preiction on the number of events. Since there was some backgroun, N X is calculate using the metho of Felman an Cousins. One also has to correct N X for systematic errors. This was one using the metho of Cousins an Highlan.

26 9% Confience Level Upper Limit CL=9% No backgroun n (Number observe) µ 1 (Lower Limit) µ 2 (Upper Limit) Metho of Felman an Cousins 2 2 G. J. Felman an R. D. Cousins Phys. Rev. D 57 (1998)

27 Sources of Backgroun Reflection Backgroun K π,l Gets ri of e.g.: D K π π ecays from D D + K π µ µ (K π) π ecays from D µ µ + ( K l) Reflecte outsie of the box Were explicitly remove before opening the box Pion Misientification Backgroun π l Combinatoric Backgroun Ranom Tracks

28 Reflection Backgroun K π (or K l) Misientification The shae region shows events ientifie as coming from D K π + that are reflecte into the D µ + µ mass winow. Thus, a Kaon is misientifie as a muon an reflecte outsie of the box (ashe lines).

29 Pion Misientification Backgroun π l Misientification Rate We use these misientifie D K π π signals to etermine the pion-lepton backgroun misientification rate; therefore, we i not set limits for the D K ll moes.

30 Combinatoric Backgroun Ranom Tracks Because there was not enough combinatoric backgroun to characterize the shape we use a very conservative assumption to etermine the combinatoric backgroun rate. We assume either a flat istribution (top) or no combinatoric backgroun (bottom).

31 Systematic Error Sources of the systematic errors 1) Normalization Branching Ratio from the PDG. 2) Statistical errors on the normalization fit. 3) Monte Carlo statistics of the normalization an ecay moes. 4) Pion misientification backgroun. 5) Muon counter s an electron calorimeter s harware performance an Monte Carlo simulations. 6) Bremsstrahlung tails. 7) ( Cerenkov ID efficiency. Metho of Cousins an Highlan The 9% CL upper limit preiction is correcte for the systematic error using the metho escribe in Cousins an Highlan 3. Now N x = U x + U x where U x is the uncorrecte value that is calculate using the metho of Felman an Cousins. An x U U + B n x U x+ B = U xσ r where B is the preicte backgroun, n is the number of observe events, an σ is the total systematic errors. r 3 R. D. Cousins an V. I. Highlan, Nucl. Instr. Meth. A32 (1992)

32 Systematic Error Fractions Moe Total D π µ µ D π ee ± D π µ e D π µ µ D π ee D π µ e D K µ µ D K ee ± D K µ e K µ µ K ee ± K µ e K µ µ K ee K µ e D s + π µ µ π ee ± π µ e D s + + π µ µ π ee π µ e D µ + µ ee D D µ m ± e

33 + D Results + D ata. Dotte line is the shape that we expect if there were the number of events preicte at 9% CL upper limit. Soli line is estimate backgroun. Dashe lines are box. Bin with = 5 MeV/c 2

34 One of our Normalization Signals, D K π π. Dashe lines are box. Bin with = 5 MeV/c 2

35 D s + Results s D + ata. Dotte line is the shape that we expect if there were the number of events preicte at 9% CL upper limit. Dashe lines are box. Bin with = 5 MeV/c 2

36 Another Normalization Signal, D s + φπ + (φ K + K ). Dashe lines are box. Bin with = 5 MeV/c 2

37 D Results D ata. Dotte line is the shape that we expect if there were the number of events preicte at 9% CL upper limit. Dashe lines are box. Bin with = 5 MeV/c 2

38 + Yet another Normalization Signal, D K π. Dashe lines are box. Bin with = 5 MeV/c 2

39 Final Results 9% CL upper limit Moe E791 BR BR (1998 PDG) Previous Results D π µ µ E791 D π ee E ± D π µ e E687 D π µ µ E687 D π ee E687 D π µ e E687 D K µ µ E687 D K ee E ± D K µ e E687 K µ µ E653 K ee ± K µ e K µ µ E653 K ee K µ e D s + π µ µ E653 π ee ± π µ e D s + + π µ µ E653 π ee π µ e D µ + µ BEATRICE, E771 D ee CLEO µ ± e CLEO D

40 Final 9% CL Results 1 2 E791 Limit PDG Limit 1 3 9% CL Upper limit BR π + µ + µ π + e + e π + µ ± e + π µ + µ + π e + e + π µ + e + K + µ + µ K + e + e K + µ ± e + K + µ + µ K + e + e K + µ ± e + K µ + e + D + + D s D K e + e + K µ + µ + π + µ + µ π + e + e π + µ ± e + π µ + µ + π e + e + π µ + e + µ + µ e + e µ ± e +

41 What New Mass Regions Do We Probe? For simplicity assuming g X, X = Flavor Changing Neutral Current - Using: g W ( + + µ ν ) µ ~ W 22. BR D π µµ m m B R D K X mx 8 GeV/c 2 Horizontal Gauge Bosons ( ) ( ) 14 Lepton Flavor Violating - Using: ( + + µ ν ) µ + + ± m m X m B R D ~ K W 22. BR D π µ e mx 65 GeV/c 2 ( ) ( ) 14,, A. Schwartz, Mo. Phys. Lett. A8 (1993) 97.

42 Conclusion 24 measure moes 8 are completely new 14 improve on previous results These results have been publishe in Physics Letters B 462 (1999) E791 sees no evience for rare or forbien charm ecays at this level of sensitivity (~ 1 5 ).