B Physics at the Hadron Colliders Physics of
B Physics at the Hadron Colliders: Physics of the Bs Meson Introduction to Bs Physics Tevatron, CDF and DØ Selected Bs Results Tevatron and LHC Prospects Conclusion Matthew Herndon, February 2007 University of Wisconsin FNAL Academic Lectures BEACH 04 J. Piedra 1
If not the Standard Model, What? Standard Model predictions validated to high precision, however Standard Model fails to answer many fundamental questions Gravity not a part of the SM What is the very high energy behaviour? At the beginning of the universe? Grand unification of forces? Dark Matter? Astronomical observations of indicate that there is more matter than we see Where is the Antimatter? Why is the observed universe mostly matter? Look for new physics that could explain these mysteries Look at weak processes which have often been the most unusual FNAL Academic Lectures M. Herndon 2
Searches For New Physics How do you search for new physics at a collider? Direct searches for production of new particles Particle-antipartical annihilation Example: the top quark Indirect searches for evidence of new particles Within a complex process new particles can occur virtually Tevatron is at the energy frontier and a data volume frontier: ~2 billion B and Charm events on tape So much data that we can look for some very unusual processes Where to look Many weak processes involving B hadrons are very low probability Look for contributions from other low probability processes – Non Standard Model Rare Decays, CP Violating Decays and Processes such as Mixing Present unique opportunity to find new physics M. Herndon 3
A Little History Everything started with kaons Flavor physics is the study of bound states of quarks. Kaon: Discovered using a cloud chamber in 1947 by Rochester and Butler. Could decay to pions and had a very long lifetime: 10 -10 sec Bound state of up or down quarks with a new particle: the strange quark! K 0 Needed the weak force to understand it’s interactions. Neutron kaons were some of the most interesting kaons Rich ground for studying new physics M. Herndon s d 4
Physics of Neutral Mesons New physics(at the time) of neutral particles and antiparticles - K 0 and K 0 Interacted differently with weak and strong force. Different eigenstates - Strong force quark eigenstates: K 0 and K 0 Weak force mass and CP eigenstates: K 0 S and K 0 L Weak force violated C and P thought to conserve CP The Schrödenger equation H not diagonal - K 0 and K 0 not mass eigenstates M. Herndon 5
Physics of Neutral Mesons Treat the particle and anti-particle as one two state system (Gelmann, Pais) New states mass eigenstates Weak force mass and CP eigenstates: K 0 S and K 0 L explained m = 2 M 12 and width difference Even more interesting behaviours predicted M. Herndon 6
Classical Analogue Coupled spring system Energy Eigenstates: Normal Modes Start the system with one spring moving and over time it will evolve to a state where the other spring is moving and then back again. An oscillation or mixing from one state to the other m = 2 M 12 is the coupling strength and gives the oscillation frequency M. Herndon 7
Oscillations Time dependence Given a pure K 0 state at t = 0 Then at time t m is the coupling strength -A K 0 component exists! and M. Herndon gives the oscillation frequency 8
Why? The Weak force is the cause! K 0 The flavor changing weak interaction is necessary to get from K 0 to K 0 The weak force provides the coupling between the states that leads to the oscillations Also the CP eigenstates KS and KL are not changed by the weak force making them the weak force eigenstates M. Herndon 9
Neutral Kaons 1954: Mixing Predicted 1956: CP Eigenstates PR 103, 1901 (1956) Observed 1964: CP Violation Observed New Physics in a rare decays: CP violating KL(odd) 2 (ev Very Rare decays observed in the Kaon system: M. Herndon en) BF(K 0 L → + -) = 2. 1 x 10 -3 BF(K 0 L → μ+μ-) = 7. 3 x 10 -9 10
CKM Physics Our knowledge of the flavor physics can be expressed in the CKM matrix Translation between strong and weak eigenstantes Sets magnitude of flavor changing decays: Strange type kaons to down type pions CP violating phase Also in higher order terms Unitarity relationship for b quarks Several unitarity relationships to preserve probability b quark relationship the most interesting Largest CP violating parameter Best place to look for explanations for mater-antimatter asymmetry M. Herndon 11
Bs and CKM Physics B quark unitarity relationship Can be expressed as triangle in the complex plane Mixing strength set by Vts parameter Most poorly understood side of the triangle M. Herndon Pierini, et al. , 12
Physics of the Bs Meson Look at processes that are suppressed in the SM Bs(d) → μ+μ-: FCNC to leptons SM: No tree level decay, loop level suppressed BF(Bs(d) → μ+μ-) = 3. 5 x 10 -9(1. 0 x 10 -10) G. Buchalla, A. Buras, Nucl. Phys. B 398, 285 NP: 3 orders of magnitude enhancement tan 6β/(MA)4 Babu and Kolda, PRL 84, 228 Bs Oscillations Z' SM: Loop level box diagram Oscillation frequency can be calculated using electroweak SM physics and lattice QCD NP can enhance the oscillation process, higher frequencies Barger et al. , PL B 596 229, 2004, one example of many Closely Related: and CP violation Hadron colliders have many opportunities to look for New Physics M. Herndon sm value 13
Bs Mesons New physics and the Bs Meson ? Very interesting place to look for new physics(in our time) ? Higgs physics couples to mass so B mesons are interesting s b Same program. Rare decays, CP violation, , oscillations State of our knowledge on the Bs last year The Bs seen: known about since UA 1 experiment in 1987. In fact know to oscillate extremely fast! SS vs OS leptons However 79 Oscillation not directly seen GHz not measured b d CP violation not directly seen Most interesting rare decys not seen A fresh area to look for new physics! M. Herndon 14
Bs Oscillations With the first evidence of the Bs meson we knew it oscillated fast. How fast has been a challenge for a generation of experiments. > 2. 3 ms > 14. 4 THz 95% CL ps-1 expected limit (sensitivity) Amplitude method: Fourier scan for the mixing frequency Run 2 Tevatron experiments built to meet this challenge M. Herndon 15
- The Tevatron 1. 96 Te. V pp collider Excellent performance and improving each year Record peak luminosity in 2007: 2. 7 x 1032 sec-1 cm-2 CDF/DØ Integrated Luminosity ~1 fb-1 with good run requirements through 2005, now ~2 fb-1 All critical systems operating including silicon Doubled data in 2005 almost double again in 2006 Bs physics benefits from more data M. Herndon 16
CDF and DØ Detectors CDF Tracker Silicon |η|<2, 90 cm long, r. L 00 =1. 3 - 1. 6 cm 96 layer drift chamber 44 to 132 cm EXCELLENT TRACKING: MASS RESOLUTION Triggered Muon coverage: |η|<1. 0 EXCELLENT TRACKING: TIME RESOLUTION DØ Tracker Silicon and Scintillating Fiber Tracking to |η|<2 EXCELLENT TRACKING: EFFICIENCY New L 0 on beam pipe Triggered Muon coverage: |η|<2. 0 M. Herndon 17
The Real CDF Detector Wisconsin Colloquium M. Herndon 18
The Trigger Hadron collider: Large production rates σ(pp → b. X, |y| < 1. 0, p. T(B) > 6. 0 Ge. V/c) = ~30μb, ~10μb TRIGGERS ARE CRITICAL Backgrounds: > 3 orders of magnitude higher 2 Billion B and Charm Events on Tape Inelastic cross section ~100 mb Single and double muon based triggers and displaced track based triggers M. Herndon 19
The Results! Combining together excellent detectors and accelerator performance Ready to pursue a full program of Bs physics Today… Bs → μμ Bs and CP violation Direct CP violation Bs Oscillations M. Herndon 20
Bs(d) → μ+μ- Method Relative normalization search Measure the rate of Bs(d) → μ+μdecays relative to B J/ K+ Apply same sample selection criteria Systematic uncertainties will cancel out in the ratios of the normalization 9. 8 X 107 B+ events Example: muon trigger efficiency same for J/ or Bs s for a given p. T 400 pb-1 M. Herndon 21
Discriminating Variables 4 primary discriminating variables Mass M CDF: 2. 5σ window: σ = 25 Me. V/c 2 DØ: 2σ window: σ = 90 Me. V/c 2 CDF λ=cτ/cτBs, DØ Lxy/ Lxy α : |φB – φvtx| in 3 D Isolation: p. TB/( trk + p. TB) CDF, λ, α and Iso: used in likelihood ratio D 0 uses optimized cuts Optimization Unbiased optimization Based on simulated signal and data sidebands M. Herndon 22
Bs(d) → μ+μ- Search Results CDF Result: 1(2) Bs(d) candidates observed consistent with+ background expectation BF(Bs - ) < 1. 0 x 10 -7 at 95% CL BF(Bd + - ) < 3. 0 x 10 -8 at 95% CL Worlds Best Limits! D 0 Result: with 300 pb-1 4 events. 700 pb-1 still blind - expected limit: BF(Bs + - ) < 2. 3 x 10 -7 at 95% CL CDF 1 Bs result: 3. 0 10 -6 Ba. Bar Bd result: 8. 3 10 -8(90%) Deca y CDF Bs CDF Bd D 0 Bs Total Expected Background Observed 1. 27 ± 0. 36 1 2. 45 ± 0. 39 2 4+2. 2 ± 0. 7 4+? ? PRD 57, 3811 1998 PRL 94, 221803 2005 M. Herndon 23
New Physics in Bs Width-lifetime difference between eigenstantes Bs, Short, Light CP even Bs, Long, Heavy CP odd New physics can contribute in penguin diagrams Measurements Directly measure lifetimes in Bs J/ Separate CP states by angular distribution and measure lifetimes Measure lifetime in Bs K+ KCP even state Search for Bs → Ds(*) CP even state May account for most of the lifetime-width difference M. Herndon Many Orthogonal Methods! 24
Bs Method: Bs J/ Directly measure lifetimes in Bs J/ Separate CP states by angular distribution and measure lifetimes A 0 = S + D wave P even A|| = S + D wave P even A = P wave P odd Bs, Short, Light CP even CP Violation will change this picture Bs, Long, Heavy CP odd DØ Run II Preliminary M. Herndon 25
Bs Results: Bs J/ DØ Run II Preliminary Assuming no CP violation Bs = 0. 12 0. 08 0. 03 ps-1 Non 0 Bs Putting all the measurements together M. Herndon 26
Bs CP Violation Results Allowing for CP Violation Bs = 0. 17 0. 09 0. 03 ps-1 = NP + SM = -0. 79 0. 56 0. 01 Combine with searches for CP violation in semileptonic B decays Bs = 0. 15 + 0. 09 - 0. 08 ps-1 = NP + SM = -0. 56 + 0. 44 - 0. 41 Consistent with SM Bs = 0. 10 0. 03 SM = -0. 03 - +0. 005 M. Herndon U. Nierste hep-ph/0406300 27
Bs: Direct CP Violation Direct CP violation expected to be large in some Bs decays Some theoretical errors cancel out in B 0, Bs CP violation ratios Challenging because best direct CP violation modes, two body decays, have overlapping contributions from all the neutral B hadrons Separate with mass, momentum imbalance, and d. E/dx M. Herndon First Observations 28
B 0: Direct CP Violation Precision between Babar and Bell: Hadron colliders competitive with B factories at their own game! M. Herndon 29
Bs: Direct CP Violation BR(Bs K ) = (5. 0 0. 75 1. 0) x 10 -6 Good agreement with recent prediction ACP expected to be 0. 37 in the SM Ratio expected to be 1 in the SM Lipkin, Phys. Lett. B 621 (2005) 126 New physics possibilities can be probed by the ratio M. Herndon 30
Bs Mixing: Overview - Measurement of the rate of conversion from matter to antimatter: Bs Determine b meson flavor at production, how long it lived, and flavor at decay to see if it changed! tag Bs p(t)=(1 ± D cos mst) M. Herndon 31
Bs Mixing: A Real Event CDF event display of a mixing event Bs Ds- +, where Ds- -, K+KPrecision measurement of Positions by our silicon detector B flight distance Charge deposited particles in our drift chamber Momentum from curvature in magnetic field Hits in muon M. Herndon system 32
Bs Mixing: Signals Fully reconstructed decays: Bs Ds (2 ), where Ds , K*K, 3 Also partially reconstructed decays: one particle missing, but can still tell how far the particle flew. Semileptonic decays: Bs Dsl. X, where l = e, : D 0 includes Ds K 0 s. K Decay Candidates CDF Bs Ds (2 ) CDF Bs Ds-* +, B s D s- + CDF B D l. X 5600 3100 61, 500 M. Herndon 33
Bs Mixing: Flavor Tagging D 0 Opposite side tag(OST): Combined Jet finding, b vertex and lepton tag Information combined in a likelihood ratio CDF OST: Separate Jet with b vertex and lepton tags Tags then combined with a Neural Net, NN CDF Same side tag(SST): Kaon PID Taggers calibrated in data where possible OST tags calibrated using B+ data and by performing a B 0 oscillation analysis SST calibrated using MC and kaon finding performance validated in data Tag Performance( D 2) D 0 OST CDF 2. 48 0. 21 0. 07% 1. 8% M. Herndon 34
Bs Mixing: Proper Time Resolution Measurement critically dependent on proper time resolution Full reconstructed events have excellent proper time resolution Partially reconstructed events have worse resolution Momentum necessary to convert from decay length to proper time DØ Run II osc. period M. Herndon 35
Bs Mixing: DØ Results Key Features Result Sen: 16. 5 ps 1 95%CL Sen: 0. 7 A(@17. 5 ps ) A/ A 1. 6 Prob. 8% Limits: 17 -21 ps-1 @90 CL Fluctuation One experiment with more sensitivity -1 than a whole generation of experiments! Peak value: 19 ps PRL 97, 021802 2006 m s -1 M. Herndon 36
Bs Mixing: Results March 2005 Nov 2005: Add Ds- 3 and lower momentum Ds-l+ March 2006: Add L 00 and SST April 2006: Use 1 fb-1 Data Add PID and NNs 37
L 00 s primary effect is to improve proper time resolution A Bs Oscillations: Expected Sensitivity Improves proper time resolution by 20% from 109 fs to 87 fs CDF Bs Oscillations Sensitivity L = 1 fb-1 95% CL sensitivity Without 3 sensitivity 5 sensitivity L 00 With L 00 Observe d value of ms With L 00 should reach 5 ! m s
Bs Mixing: Results Key Features Result Sen: 31. 3 ps 1 95%CL Sen: 0. 2 A(@17. 5 ps ) A/ A 6 -8 Prob. 8 x 10 A >5 Observation! Fluctuation PRL 97, 242003 2006 Peak value: 17. 75 p Can we see the oscillation? ms s-1 2. 8 THz -1 M. Herndon 39
Bs Mixing: CKM Triangle Tevatron ms = 17. 77 0. 10 (stat) 0. 07 (syst) ps-1 |Vtd| / |Vts| = 0. 2060 0. 0007 (stat + syst) +0. 0081 -0. 0060(lat. QCD) 40
Bs Results - New Physics Many new physics models that predict observable effects in flavor physics Consider a SUSY GFV model: general rather than minimal flavor violation Makes predictions for Non Standard model BF(Bs → μ+μ-) and ms Basically corrects quark mass terms with sqark-gluino loop terms in a general way Size of effects depends on tan and m. A hep-ph/0604121 M. M. Herndon 41
What’s Next? Bs and CPV in Bs J/ Often called the sin 2 s analysis Sensitivity for s in tagged and untagged analysis M. Herndon 42
2 s in Bs J/ Time independent measurement D 0 analyzed 1 fb-1 CDF will have a 1 fb-1 measurement with comparable sensitivity Can use TTT trigger as well(20% overlap) Time dependent analysis A key measurement that builds on the work of the mixing measurement Needs precision vertexing Needs large sample with low background Needs flavor tagging Use many modes Also comparable sensitivity M. Herndon 43
What Else? Consider B factory sin 2 in charmonium vs. s penguin decays ccs vs css: Polarization and 2 s Equivalent test is Bs J/ vs. Bs (sss) Larger sample than used for similar angular analysis at the B factories 40 events In 360 pb-1 M. Herndon 44
LHCb Dipole magnet Tracking system Muon system Calorimeters ad r 250 m Vertex Locator p 10 mrad p RICH detectors A detector optimized just for B physics M. Herndon 45
LHCb 2 s in Bs J/ Key detector performance considerations Tevatron LHCb Lumin 1 fb-1/year 2 fb-1/year osity 87 fs 33 fs ct Taggin 2. 5 -4. 8% 7 -9% Time g dependent analysis should be very good! 0. 1 accuracy on Tevatron currently 0. 4 from one 1 fb-1 analysis Not to mention the potential for rare particle searches at LHCb and ATLAS/CMS M. Herndon 46
Bs Physics Conclusion Tevatron making large gains in our understanding of Bs Physics Concentrating on areas where there might be hints of new physics New stringent limits on rare decays: Factor of 30 improvement BF(Bs + - ) < 1. 0 x 10 -7 at 95% over run 1 CL measurement of B Precise s And first look at the Bs = 0. 12 + 0. 09 - 0. 08 ps-1 CP violating phase On the hunt for direct CP violation ACP(Bs K ) = 0. 39 0. 15 0. 08 2. 5 First measurements of ms -0. 18 ms = 17. 77 0. 10 (stat) 0. 07 (syst) ps-1 Study of the Bs meson well on its way M. Herndon One of the primary goals of the Tevatron accomplished! 47
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