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Novosibirsk

Moscow State University. For the D0 collaboration. Valentin Kuzmin. Novosibirsk. February 27 - March 2. Phi Psi 2006. Russia. 2006. In this talk we report On. D** mesons Observed by D0 detector and Searches of Flavor Changing Neutral Current Charm Decays. -.

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Novosibirsk

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  1. Moscow State University For the D0 collaboration Valentin Kuzmin Novosibirsk February 27 - March 2 Phi Psi 2006 Russia 2006

  2. In this talk we report On D** mesons Observed by D0 detector and Searches of Flavor Changing Neutral Current Charm Decays PhiPsi 2006

  3. - • Run I (1992 – 1995) √s = 1.8 TeV • delivered ~ 260 pb-1 • Run II (2002 – ) √s = 1.96 TeV • collisions every 396 ns • rate to tape 50 Hz • delivers ~ 15 pb-1/week (January 2006) • max luminosity 1.58·1032 (January 2006) - Tevatron pp-collider More than 1.4 fb-1 delivered &1.2 fb-1 recorded data for physics Feb 2002 April 2001 Jul 2002 first data for analyses detector commissioning • So far reconstructed ~1 fb-1 ~10x the total Run I data PhiPsi 2006

  4. The DZero Experiment • Beam line shielding • Reduces accelerator background • Silicon tracker • Coverage up to |η| <2 • Fiber tracker • Coverage up to | η| <2 • 8 double layers • Solenoid (2 Tesla) • Forward + central muon system • Coverage up to | η | <2 • Three level trigger system • Outputs 50 Hz PhiPsi 2006

  5. D** mesons Four orbitally excited D-meson states, collectively known as D** • Previous studies by various experiments • Theoretical interest of Heavy Quark Effective Theory (HQET) • hyperfine splitting between states • with different jq • semileptonic branching fractions (B  D**) are among least model-dependent predictions • D0 has studies on the narrow (jq=3/2) resonances D1(2420),D2*(2460) decaying  D*+π Four (L=1) resonant states decaying thru • S-waves expected to be wide (~100MeV) (jq=1/2) • D-waves expected to be narrow (~20MeV) (jq=3/2) seen by various experiments PhiPsi 2006

  6. _ _ _ _ _ D**, signal selection • Data: 460 pb-1 • Search for : BD1,2* + µνX in chain:D1,2* D*- + π+ , D*-D0 + π- ,D0K+ + π- • selection all events with D0 and µ, (216870±1280 events) • combine withπ-and selectD* (55450±280 events) • suppression cc by cuts on significance and proper decay length of theBmeson (31160±230 D*- events) • in such events combine D*- and π- • Fit found signal with two relativistic Breit-Wigner’s functions convoluted with the detector • resolution and 2nd order polynom(bkgnd). Fixed [PDG] M(D2*)-M(D1)and widths PhiPsi 2006

  7. D** mesons properties Semileptonic (B→D**) branching fractions and their ratio PDG PDG MC • Assuming that the D1 meson decays • only intoD*π • Assuming that the D2* meson decays • into D*π in (30±6)% of the cases [PDG] • Ratio (first direct measurement) • HQET = 1.6│mc= ∞ Different from PDG value (0.74 ±0.16)% by 2.5σ In agreement with [PDG] 95% CL upper limit 0.65% PhiPsi 2006

  8. DS1 meson search are orbitally excited states of meson We will look for narrow (L=1,jq=3/2,JP=1+) in Data: 485pb-1 Muon plus 5-Track final state 52670±330 D* candidates In 0.142-0.149GeV mass difference window 5900±100 candidates 0.47 0.52 PhiPsi 2006

  9. Evidence of DS1(2536)meson D±s1(2536) signal Gaussian for the signal plus an exponential with a threshold cutoff at M(D*) +M(KS) 0 • 18.5±5.5 D±s1(2536) candidates • 2536±1 MeV/c2 position • 3.4σ significance Towards investigation of D±s1(2536) properties — there are no experimental measurements of Br(BS→DS**) PhiPsi 2006

  10. D±→m+m- p PRD66 (2002) 014009 f RPV SUSY ω SM c→u m(m+m-) (GeV/c2) FCNC searches Motivation • For every rare SM process there is a “beyond the SM” theory in which it is enhanced. • RPV SUSY can enhance SM suppressed FCNC processes. • FCNC processes with down type quarks • s->d type studied with kaons (K±,K0) • b->s type studied with B mesons. • FCNC processes with up type quarks • Still lot of room for new results • In this talk we focus on c→u transitions PhiPsi 2006

  11. FCNC c -> u transitions with D± & Ds± D±→μ+μ- π Ds±→μ+μ- π • Non-resonant decays (GIM suppressed, Br~10-8) • Non-resonant decays (Penguin & Box diagrams absent) • Resonant decay • (Analogous to b->sl+l- studies after • B+->K+J/ψ->K+μ+μ- observation) Penguin Box Br(Ds± → φπ) (3.6±0.9)x10-2 Br(φ → μ+μ-) (2.85±0.19)x10-4 • Resonant decay (dominant, Br~10-6) • Observation = essential step to study c->ul+l- FCNC transitions – – – • In pp collisions at √s = 1.96 TeV σ(pp → cc) ~ microbarns • Ds± production mechanisms at the Tevatron: • Prompt production: pp -> cc -> Ds±+X • Secondary production: pp ->bb ->B+X -> Ds±+Y+X • Ds±and D± decay products tend to be within a narrow jet – – – – PhiPsi 2006 – – – –

  12. MC Sum Prompt secondary FCNC, data selection Data: 508pb-1 • Μ = χ2πμμ-vtx + (1/pT(π))2 + (ΔRπ)2 • χ2πμμ-vtx - three particle vertex • ΔRπ– transverse distance between • π and (μμ)system ω f  min(M) Sideband data for background studies 0.96 < m(μ+μ-) < 1.06 GeV/c2 π track selection • Track in the same jet as μ+μ- pair. • Track from the same vertex as the μ+μ- pair. Ds± and D± signal region Ds± and D± selection • μ+μ- & π track form a good vertex • 1.3 < m(μ+μ- π ) < 2.5 GeV/c2 • p(μ+μ- π) in the PV→SV direction 3.3 candidate/event Do you see the Ds± or D± ? PhiPsi 2006

  13. FCNC, background suppression variables To minimize background, we employ 4 variables: • ID: tracking isolation of Ds± ID=p(D)/Σp(cone), cone ΔR < 1 • SD: transverse flight length significance of Ds± SD = Lxy/σ(Lxy) • RS: ratio of π impact parameter significance to SD • RS= (IPπ/σ(IPπ))/SD • θD: collinearity angle Angle between direction PV→SV and p(Ds±) we use likelihood function of these variables to extract Ds± and D± PhiPsi 2006

  14. Correlated Independent Combined likelihood variable θD vs SD • Isolation ID is independent of SD,θD & RS • SD,θD & RS are independent if SV well separated from PV • Combined likelihood “L” reflecting correlations: L=L(ID)xL(SD,θD,RS)if SD <20 L=L(ID)xL(SD)xL(θD)xL(RS) if SD >20 Likelihood Ratio “d” Signal Background • Plot likelihood ratio “d” : • d=L(Signal)/(L(Signal)+L(Background)) PhiPsi 2006

  15. FCNC, signal extraction • The red histogram is after selection d>0.9 In the Ds± region 1.91 <m(μ+μ- π) <2.03 GeV/c2 • 51 events found • 18±4 background events expected 31±7 Ds± events observed (corresponds to >7σ significance) • Relax cut on likelihood ratio to 0.75 and Fit 2 Gaussians (signal) & exponential (background) • Free Number(Ds±),mean(Ds±), σ(Ds±), Number(D±) • Fix mean(Ds±)-mean(D±) to 1.969-1.869 GeV • Fix σ(D±) to m(D±)/m(Ds±) x σ(Ds±) • Use the above found mean(Ds±), σ(Ds±) and fit the d>0.9 distribution need more data for observation, we will set the upper limit on D± -> μ+μ-π decays 13.2+5.6-4.9 D± events observed (corresponds to >2.7σ significance) PhiPsi 2006

  16. Br(D± →φπ →μ+μ- π) Br(D± →φπ →μ+μ- π) <0.28 (90% C.L) = 0.17 Br(Ds± →φπ →μ+μ- π) Br(Ds± →φπ →μ+μ- π) FCNC, branching ratios Br(D± →φπ →μ+μ- π) N(D±) f(Ds±) ε(Ds±) x x = ε(D±) Br(Ds± →φπ →μ+μ- π) N(Ds±) f(D±) Measured or Limit Setting To determine PDG Literature From MC ±0.08±0.06 ±0.07±0.07 PDG: Br(Ds± →φπ)·Br(φ→μ+μ-) +0.79+0.76 Br(D± →φπ →μ+μ- π) = (1.70 )x10-6 Br(D± →φπ →μ+μ- π) <3.14x10-6 (90% C.L) -0.73 -0.82 In agreement with expected [PDG]:Br(D± →φπ)· Br(φ→μ+μ-) =1.75 x10-6 +3.6 and the CLEO measurement: (2.7 -1.8 ±0.2) x10-6 PhiPsi 2006

  17. Conclusion • Using 460pb-1 of DØ’s data sample we observe semileptonic decays of B in D10(2420),D2*0(2460). The narrow D** mesons branching fractions were separately measured for such decays. The ratio between semileptonic fractions of the two modes is R=1.31±0.29(stat)±0.47(syst) in agreement with HQET • The D0 Collaboration also observes the Ds1(2536) resonance and the measurement of its properties is in progress. • We see final state of the decay Ds± →φπ →μ+μ- πwith a significance of 7 standard deviations. DØ has nice sensitivity to study FCNC in charm decays and we now continue to search the non-resonant continuum for signs of physics going beyond the Standard Model. • Tevatron is doubling the luminosity each year MORE GREAT PHYSICS RESULTS are coming soon PhiPsi 2006

  18. Back up

  19. PhiPsi 2006

  20. Result: Br ( D± → π± μ+μ- ) limit UL ∞ ∫drL (r) ∫drL (r) 0 0 Br(D±→fπ→μ+μ- π) N(D±;>0.9) f(Ds±) ε(Ds±;d>0.75) = x x Br(Ds±→fπ→μ+μ- π) N(Ds±;>0.75) f(D±) ε(D±;d>0.9) To determine PDG Literature From Limit Setting From MC • 90% C.L. upper limit on Br(D±→fπ→μ+μ- π) found by: N(D±;>0.9) = 0.9, where r= N(Ds±;>0.75) Uncertainties summary Br(D±→fπ→μ+μ- π) < 0.28 (at 90% C.L.) Br(Ds±→fπ→μ+μ- π) Br ( D± →π± μ+μ-) < 3.14 x 10-6 (at 90% C.L.) PhiPsi 2006

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