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Measuring the bb cross-section using B  D o X m - n decays

Measuring the bb cross-section using B  D o X m - n decays. Liming Zhang & Sheldon Stone Syracuse University. Selection criteria. Common cuts K & p PT>300 MeV , Sum PT>1400 MeV K and p IPCHI2>9 K DLL(K- p )>4, p DLL( p -K)> -10 all tracks fit c 2 /NDOF<10

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Measuring the bb cross-section using B  D o X m - n decays

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  1. Measuring the bb cross-section using BDo X m-n decays Liming Zhang & Sheldon Stone Syracuse University

  2. Selection criteria • Common cuts • K & p PT>300 MeV, Sum PT>1400 MeV • K and p IPCHI2>9 • K DLL(K-p)>4, p DLL(p-K)> -10 • all tracks fit c2/NDOF<10 • D0 vertex fit c2<6 • D0 Flight Distance c2>64 • vz(D0) – vz(B) > 0 • DfB (D from B) Cuts only • m PT > 500 MeV & IPCHI2>4 • m ISMUON and DLL(m-p)>0 • B vertex fit c2<5 • B DIRA>0.998 • B invariant mass in [3, 5] GeV • Prompt Do cuts only • D0 lifetime > 0 • D0 DIRA > 0.9999 • D0 IPCHI2 < 25 ~800 mb-1 Group Meeting May 7, 2010

  3. DfB (Data) • Right-sign • Wrong-sign All available 2010 data: ~800 mb-1, 24 signal events are expected with sbb=250 mb Group Meeting May 7, 2010

  4. Do IP distributions (BDoXm-n) Clear B signal inc_charm MC09 =10xdata Data Signal Bkg from b Bkg from prompt |M(Kp)-mD0|<20 Sideband scaled 238 signal Real D0 only RS DfB BKG contribution is negligible WS Group Meeting May 7, 2010

  5. Signal Yield with ln(IP) > -2 • Selecting events with ln(IP) > -2 gives 20 events • The background estimate from WS ln(IP) > -2 is 1 event, but this event is reduced to 0 if we use the sideband subtraction • The RS yield is 20 events minus 1 for sideband = 19.0  4.6 events • Total signal yields without IP cut from our rough guess is 21 (compare to 24 expected) • Instead of cutting, we will fit the distributions of IP. Group Meeting May 7, 2010

  6. IP distribution from Generic D0 • To study both prompt D0 and DfBhas to remove IPCHI2 and DIRA cuts. Data without sideband subtraction Sideband subtracted inc_charmMC09 IP<0.1mm IP>0.1mm Group Meeting May 7, 2010

  7. Comparison between MC2010 & Data • 10 M Min-bias MC2010 Sim01Rec01 • Data Brunel v36r2 (new processing with Brunel v37r1 is out now) • Not enough MC: the 10M only gives 700 D0 signal events compared to 3300 in Data. • When studying the distributions of a variable which is used in the selection for Prompt D0, I remove the cut. Data is sideband subtracted, MC is real matched D0 events. Group Meeting May 7, 2010

  8. IP of Kaon and Pion from D0 IP for tracks is reasonable in agreement Group Meeting May 7, 2010

  9. P and PT for Kaon and Pion Group Meeting May 7, 2010

  10. D0 D0 IP DIRA & IPCHI2 cuts removed Group Meeting May 7, 2010

  11. Further check on D0 IP • Only D0 IP seems worse in Data • Check Velo half • Deification: x(K)>0 & x(p)>0 means in same velo half? Group Meeting May 7, 2010

  12. The End

  13. Goal • Measure the bb cross-section over the LHCb acceptance and extrapolate to find total bb cross-section • Limitations on precision • Luminosity determination ~10% • B(BDo X m-n)=(6.820.35)%, but additional uncertainty due to Bs & Lb fractions ~5% changing from LEP to LHC. Hugh Bfor early x-section measurement, later can use exclusive decays • Tracking, pid & muon detection efficiencies ~10% • Pythia extrapolation to full acceptance ~5% Group Meeting May 7, 2010

  14. B(BDo X m-n)=(6.820.35)% • This value is listed in PDG 2010 in Bd/Bu/Bs/b-baryon admixture section. • It’s the average of  the measurements from DELPHI and OPAL experiments. • It’s dominated by B- and B0 contributions, but also contains Bs Ds**Xm-n, Ds** D0K & possible some from Lb • Also we need to increase the B a little bit, since we also include BD(*)D(s)(*)(K), D(s)(*) m-X (~7.5%) and BDo X t-n,t- m-nn (~5%) as signal [while their efficiencies are lower because of B vertex cut.] Group Meeting May 7, 2010

  15. Analysis Strategy • Signal: Measure right-sign Dom- combinations using tracks not pointing at primary vertex but which form a common vertex. (Use DoK-p+ decays only.) • The two types of Do produced are “prompt” and those from B’s “DfB”. They can be separated statistically by examining the impact parameter (IP) with respect to the primary vertex (Definition IP: smallest distance between Do direction and primary vertex position.) Group Meeting May 7, 2010

  16. MC Efficiencies • So far I generated ~30k MC events each for B-Dom-nX and B0Dom-nX Selection efficiencies may be different in B- and B0 due to different Pt distributions Will provide detailed efficiency due to each of cuts v38r4 Gauss, v21r1 Boole and v37r1 Brunel Group Meeting May 7, 2010

  17. Background estimate from MC • RS: 283 real D0, in which 45 are backgrounds (15%) • 37 from prompt D0 (80% of BG) • 28 cc with c  m- X& 9 from fake m • 8 from B • 4 bb where b  D0 X and b  c  m- X • 4 from fake m • WS: 23 real D0 background • 13 from prompt, dominated by fake m • 10 from bb where b  D0 X and b m+ X ~10M MC09 inclusive charm used for this study • WS does not provide accurate information on RS background. Better to: • Fit D0 IP dist. to separate prompt & DfB • Estimate bb background from MC • Check by separating prompt & DfB D0 in WS Signal + Bkg Bkg Group Meeting May 7, 2010

  18. Detection Efficiency Checks • The MC estimate of the efficiency is correct only if the vertex chi2, etc.. are reproduced accurately. Here we are not concerned with small effects, but we need to show that the most sensitive cuts are not wildly inaccurate. We can use the “prompt” Do sample for much of this. For example, we will compare the resolution on the Do vertex given by the MC for prompt production with what is seen in the data. • Another concern is the tracking efficiency. One way of checking is to compare the relative rate for DoK-p+p+ p-/ DoK-p+; other modes are also possible. With more data we can check the particle i.d. efficiency by using DoK- K +/Dop+ p-. • We rely on the muon group to give us an efficiency for detecting a single muon. Gaia mentioned that this work is ongoing using J/ym+m- events. See CERN-LHCb-PUB-2010-002. So far the efficiency is expected to be quite high ~100% • We also need to have a good estimate of the integrated luminosity Group Meeting May 7, 2010

  19. Summary and Plan • A clear signal of semileptonic B decays is observed • Will fit IP distributions for separating prompt from secondary D0 • We need to check if MC represents the distribution in data using prompt D0 • Will translate the event yield to a meaningful cross-section number Group Meeting May 7, 2010

  20. B+ decays in .dec file Decay B+sig 0.05588 Myanti-D*0 mu+ nu_mu HQET 0.92 1.18 0.72; 0.02248 Myanti-D0 mu+ nu_mu ISGW2; 0.00368 Myanti-D_10 mu+ nu_mu ISGW2; 0.00130 Myanti-D_0*0 mu+ nu_mu ISGW2; 0.00338 Myanti-D'_10 mu+ nu_mu ISGW2; 0.00185 Myanti-D_2*0 mu+ nu_mu ISGW2; 0.00057 Myanti-D0 pi0 mu+ nu_mu GOITY_ROBERTS; 0.00143 Myanti-D*0 pi0 mu+ nu_mu GOITY_ROBERTS; 0.00097 MyD*- pi+ mu+ nu_mu GOITY_ROBERTS; # correct for the fact that we force tau -> mu anti_nu_munu_tau (17.3%) 0.002770 Myanti-D*0 Mytau+ nu_tau ISGW2; 0.001300 Myanti-D0 Mytau+ nu_tau ISGW2; 0.000149 Myanti-D_10 Mytau+ nu_tau ISGW2; 0.000146 Myanti-D_0*0 Mytau+ nu_tau ISGW2; 0.000320 Myanti-D'_10 Mytau+ nu_tau ISGW2; 0.000173 Myanti-D_2*0 Mytau+ nu_tau ISGW2; Enddecay All D* are set to 100% decay to D0 Group Meeting May 7, 2010

  21. B0 decays in .dec file Decay B0sig 0.0353 MyD*- mu+ nu_mu HQET 0.77 1.33 0.92; 0.00242 MyD_0*- mu+ nu_mu ISGW2; 0.00390 MyD_1- mu+ nu_mu ISGW2; 0.00359 MyD'_1- mu+ nu_mu ISGW2; 0.00268 MyD_2*- mu+ nu_mu ISGW2; 0.0009 MyD*- pi0 mu+ nu_mu GOITY_ROBERTS; 0.00133 Myanti-D*0 pi- mu+ nu_mu GOITY_ROBERTS; 0.00054 Myanti-D0 pi- mu+ nu_mu GOITY_ROBERTS; # correct for the fact that we force tau -> mu anti_nu_munu_tau (17.3%) 0.00175 MyD*- Mytau+ nu_tau ISGW2; 0.00027 MyD_0*- Mytau+ nu_tau ISGW2; 0.00016 MyD_1- Mytau+ nu_tau ISGW2; 0.00036 MyD'_1- Mytau+ nu_tau ISGW2; 0.00025 MyD_2*- Mytau+ nu_tau ISGW2; Enddecay All D* are set to 100% decay to D0 Group Meeting May 7, 2010

  22. First Guesstimate of x-section • Make first guess at L • Give number of signal & wrong-sign background • Correct for efficiencies • Give x-section in LHCb & extrapolated to entire eta-pt….. (This is not necessary but would be nice….) Group Meeting May 7, 2010

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