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1 Searching for New Physics in Beauty and Charm Brendan Casey Brown University Stony Brook HEP Seminar February 13, 2007
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2 What is new physics? Current theories explain the entire dynamics of our universe from about 1 second after birth. What was happening before the 1 st second? –New physics is what ever it takes to answer this question.
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3 Matter at t ≥ 1 second: BBN Burles, Nollett, Turner astro-ph/99003300 Evolution of light elements in first hour of the universe Extraordinary success of GR, astro, particle, nuclear physics But: Small excess of baryons is an initial condition of BBN, not a prediction. No explanation of the evolution of anti- elements
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4 CPV: Standard Model to the rescue? mass basis, d,s,b weak basis, d, s, b quarks: d I = V ij d j antiquarks: d i = V ij *d j Provides a mechanism to generate a net baryon number through decay of heavy to light particles V ub ≠ V ub *, V td ≠ V td * CPV production decay
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5 Standard Model CPV Mag(CPV) ≈ f(m 2 j -m 2 i ) × f( ij ) × sin CP Three properties govern size of CPV in SM: quarks: –Large mass splitting ↑ –Small mixing angles ↓ –Large CP ↑ neutrinos: –small mass splitting ↓ –large mixing angles ↑ – CP ? ~15 orders of magnitude too small Huet, Sather PRD51 379 (1995) Jury still out Need new sources of CPV! More generations, more interactions….new particles
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6 Direct versus Indirect Year quark mass (GeV/c 2 ) t t 1 TeV p 5 GeV B t t b d b d W W charm discovered 1974 bottom discovered 1977 top discovered 1995 charm predicted, mass scale set by K→ 1970 bottom and top predicted from CPV in kaon mixing 1973 Top mass scale set from B d mixing 1987 direct indirect
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7 Cast of Characters Mesons B 0 : ( b d ), B s : ( b s ), D + : ( c d ), D s : ( c s ) Flavor Changing Interactions b t s b t s Box: Penguin:
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8 Apparatus
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9 The Tevatron and DØ Detector 400 MeV 150 GeV ~1 TeV + 1 TeV
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10 Why the Tevatron? Don’t they do B physics at B factories now? B factory on (4S) @ L = 10 34 cm -2 s -1 Tevatron @ L = 10 32 cm -2 s -1 B production rate~10 Hz~1 kHz B s production rate0~100 Hz Longitudinal boost~0.5~1-2 Transverse boost~0~1-2 Tevatron is the only B s factory
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11 Why DØ? Excellent muon identification Large semileptonic B samples ideal for mixing and CPV studies Uranium Iron
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12 Why DØ? Excellent vertexing capabilities for flight length determination Just enough resolution to probe SM expected value of the B s mixing frequency Error on the flight length determination
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13 Tevatron Data Set >2.3 fb -1 delivered FY01 FY02 FY03 FY04 FY05 FY06 FY07 Run IIa: 1.3 fb -1 on tape Run IIb: 700 pb-1 analyzed
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14 Tevatron Data Set >2.3 fb -1 delivered FY01 FY02 FY03 FY04 FY05 FY06 FY07 Run IIa: 1.3 fb -1 on tape Run IIb: 700 pb-1 analyzed Fast turn around in the heavy flavor group 10 1.0 fb -1 results last winter Pushing for close to 2 fb -1 results this winter
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15 B s Mixing
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16 General rule of neutral flavor changing processes: –New physics: Second order loop or box New particles can enter the loop SM contribution is suppressed –Precision SM tests: no new physics? Measure fundamental Standard Model parameters clean in B mesons –b quark is heavy, –top loop dominates. Every measurement of mixing has lead to a major discovery: K: CPV, 3 rd generation, B d : top mass, : neutrino mass Why Mixing? b ??? s b t V td(s) s,d Rate ≈ ( m t / m W ) 2 s,d
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17 Analysis Overview ++ K+K+ KK +,e + q B s Candidate Recoil system Primary and secondary vertices Reconstruct the B s in a flavor specific final state Determine lifetime in the B s rest frame Determine initial flavor by studying recoil system Extract the mixing frequency from the time dependence of mixed and unmixed samples
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18 Mixing Frequency Extraction Reconstructed decay length (cm)
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19 Mixing Frequency Extraction Reconstructed decay length (cm) Looking for this Reconstructed decay length (cm)
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20 Mixing Frequency Extraction Reconstructed decay length (cm) Perform a Fourier analysis of the decay length distribution to extract the mixing frequency Power Spectrum for winter data set Time domain Frequency domain 1/ m mm
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21 Winter 06 Mixing Frequency Results m s < 21 ps -1 @ 90% CL Maximum likelihood at m s = 19 ps -1 1 fb -1 First time m s bounded on both sides!!!!! Change in –log(L) versus m s D s → only
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22Reflections m( ) m( S ) D s →K*K D + →K c →pK D s →K S K D + →K S c →K S p Original results based on D s → Needed to add more channels: K*K and K S K Difficult to include these modes without particle identification
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23 Taming Reflections Momentum asymmetry between K S and K candidate Take advantage of the fact that the mass shift is a function of the particle momentum D + →K S MC m( S ) m( * ) High p low p
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24 Fall 06 Results K*K e S Extra data ‘cured’ fluctuation
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25 Time Evolution of Results LEP/SLD/CDF I were able to exclude values below about 15 ps -1 New Physics Realm msms LEP/SLD Era SM expectation
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26 Time Evolution of Results March 06: DØ provides first upper bound on the B s oscillation frequency. Rules out large new physics effects at high confidence level. Still 5% chance of background fluctuation. msms New Physics Realm SM expectation DØ, March 2006
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27 Time Evolution of Results Confirmed by CDF in April 2006. >5 measurement Fall 2006. Closes the chapter on the magnitude of the Bs oscillation frequency. msms New Physics Realm SM expectation Tevatron Era 17.7+/- 0.12 ps -1
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28 Indirect Searches so far Now reached SM level for one of our key indirect NP search modes, m s. –No new physics. Not just a Tevatron problem, problem for B physics in general. Choice: –Wait for new energy frontier –Expand current physics program beauty → charm
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29 Flavor Changing Neural Current Charm Decay
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30 Up versus Down Generation Mass (MeV/c 2 ) up line q = 2/3 down line q = 1/3 t c u d s b
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31 Up versus Down Generation Mass (MeV/c 2 ) up line q = 2/3 down line q = 1/3 t c u d s b Very different mass hierarchy
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32 Up versus Down Generation Mass (MeV/c 2 ) t c u d s b c u b W+W+ WW up FCNC ~ ( m b / m W ) 2 WW W+W+ b s t down FCNC ~ ( m t / m W ) 2
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33 Up versus Down Generation Mass (MeV/c 2 ) t c u d s b c u b W+W+ WW up FCNC ~ ( m b / m W ) 2 WW W+W+ b s t down FCNC ~ ( m t / m W ) 2 Down the down line: suppressed but measurable (eg. mixing) Down the up line: almost impossible for SM, any signal = new physics
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34 Why 3 body FCNC charm? D + m( GeV) 0.5 1.0 1.5 (1/ )(d /dm 2 ) GeV -2 ) 10 -4 10 -6 10 -8 10 -10 Long distance Short distance c u Two processes: Long distance (strong scale), short distance (weak scale) Clear separation of long distance and short distance components New Physics only effects short distance. (rare clean channel) c s s u d D+D+ ++ D→ D→
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35 New Phenomena in c u New Phenomena in c u Strict limits from b s, interesting scenarios effect up sector quarks and not down sector quarks.
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36 New Phenomena in c u New Phenomena in c u Strict limits from b s, interesting scenarios effect up sector quarks and not down sector quarks. D + m( GeV) 0.5 1.0 1.5 (1/ )(d /dm 2 ) GeV -2 ) 10 -4 10 -6 10 -8 10 -10 RPV in the up sector and not the down sector Burdman et al. hep-ph/0112235 c u
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37 New Phenomena in c u New Phenomena in c u Strict limits from b s, interesting scenarios effect up sector quarks and not down sector quarks. D + m( GeV) 0.5 1.0 1.5 (1/ )(d /dm 2 ) GeV -2 ) 10 -4 10 -6 10 -8 10 -10 RPV in the up sector and not the down sector Burdman et al. hep-ph/0112235 c u Little Higgs models with new up sector vector quark Fajfer et al. hep-ph/0511048 factors of >1000 over SM not ruled out.
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38 D Selection Require well reconstructed track in the muon spectrometer matched to a central track with p T >2 GeV, p > 3 GeV First select 0.96 < m( ) < 1.06 GeV 1.3 fb -1 Combine with a track in the same jet and select D candidate 1.4 < m ) < 2.4 GeV
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39 Best Track Selection Large track multiplicity leads to several candidates per event. Select best track based on the D vertex 2, and distance between the track and the dimuon system M = 2 + R 2 All candidates false candidates correct candidate Candidate multiplicity 0 5 10 15 20 25 MC
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40 Background Suppression Isolation Flight length significance impact parameter significance Colinearity angle SS D s MC D + MC data sidebands
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41 Results for Resonance Production Long Distance D Dimuon invariant mass n(D + ) = 115 +/- 33 > 4 sigma n(D s ) = 254 +/- 38 BF( D (1.41 +/- 0.40 +/- 0.46) x 10 -6 (PRL for 1.3 fb -1 result about to be released.) D significance > 5 Pion IP significance > 0.5 1.3 fb -1
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42 Next Step: Continuum Production By making a cut on m( ) around the , we clearly see the long distance component Now make a veto Large background → enormous background Long Distance D n(D + ) = 115 +/- 33 > 4 sigma n(D s ) = 254 +/- 38 1.3 fb -1
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43 More Background Reduction Next step: continuum production. Much larger dimuon phase space requires more stringent requirements
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44 Continuum Results n = 19 n(bkg) = 31 +/- 4 Short Distance D (PRL for 1.3 fb -1 result about to be released.) 1.3 fb -1 BF( D )<2.85×10 6 @90% CL
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45 Continuum Results n = 19 n(bkg) = 31 +/- 4 Short Distance D How are we doing? factor of ~4 better than dedicated charm experiments Factor of ~10 better than B factories 1.3 fb -1 BF( D )<2.85×10 6 @90% CL (PRL for 1.3 fb -1 result about to be released.)
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46 Conclusions
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47Conclusions DØ Heavy Flavor program producing several world’s first or world’s best results –4 years ago prevailing opinion was that you don’t do B physics at DØ Presented today: –First upper limit on the B s mixing frequency no smoking gun for new physics in m s –Best limits on new physics in rare charm decays. Basically rules out possibility of finding a smoking gun in charm. Results: –Demonstrated a lack of enhancement in almost all low energy FCNC processes. Tells you that the next theory beyond the standard model must have mechanisms that supress FCNC Next steps: –Go find these new particles directly at the LHC
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