Measuring the bb cross- section using B  D o X   decays Liming Zhang & Sheldon Stone Syracuse University

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

DfB (Data) Right-sign Wrong-sign Group Meeting May 7, All available 2010 data: ~800  b -1, 24 signal events are expected with  bb =250 mb

D o IP distributions (B  D o X   ) Group Meeting May 7, signal inc_charm MC09 =10xdata Real D 0 only RS WS Data Signal Bkg from b Bkg from prompt Clear B signal |M(K  )-m D0 |<20 Sideband scaled DfB BKG contribution is negligible

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,

IP distribution from Generic D 0 To study both prompt D0 and DfB has to remove IPCHI2 and DIRA cuts. Group Meeting May 7, Sideband subtracted inc_charm MC09 Data without sideband subtraction IP<0.1mm IP>0.1mm

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 D 0 signal events compared to 3300 in Data. When studying the distributions of a variable which is used in the selection for Prompt D 0, I remove the cut. Data is sideband subtracted, MC is real matched D 0 events. Group Meeting May 7,

IP of Kaon and Pion from D 0 Group Meeting May 7, IP for tracks is reasonable in agreement

P and PT for Kaon and Pion Group Meeting May 7,

D0D0 10 D 0 IP DIRA & IPCHI2 cuts removed

Further check on D 0 IP Only D 0 IP seems worse in Data Check Velo half  Deification: x(K)>0 & x(  )>0 means in same velo half? Group Meeting May 7,

The End

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  D o X   )=(6.82  0.35)%, but additional uncertainty due to B s &  b fractions ~5% changing from LEP to LHC. Hugh B for 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,

B (B  D o X   )=(6.82  0.35)% This value is listed in PDG 2010 in B d /B u /B s /b- baryon admixture section. It’s the average of the measurements from DELPHI and OPAL experiments. It’s dominated by B  and B 0 contributions, but also contains B s  D s **  X    D s **  D 0 K & possible some from  b Also we need to increase the B a little bit, since we also include B  D ( * ) D (s) ( * ) (K), D (s) ( * )    X (~7.5%) and B  D o X  ,        as signal  while their efficiencies are lower because of B vertex cut.] Group Meeting May 7,

Analysis Strategy Signal: Measure right-sign D o   combinations using tracks not pointing at primary vertex but which form a common vertex. (Use D o  K -   decays only.) The two types of D o 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 D o direction and primary vertex position.) Group Meeting May 7,

MC Efficiencies So far I generated ~30k MC events each for B -  D o  - X and B 0  D o  - X Group Meeting May 7, Efficiency (%)B-B- B0B0 Acceptance16.93 ± ± 0.14 Rec.+ Sel ± ± 0.23 Total2.21 ± ± 0.04 Selection efficiencies may be different in B - and B 0 due to different P t distributions Will provide detailed efficiency due to each of cuts v38r4 Gauss, v21r1 Boole and v37r1 Brunel

Background estimate from MC RS: 283 real D 0, in which 45 are backgrounds (15%)  37 from prompt D 0 (80% of BG) 28 cc with c   - X& 9 from fake   8 from B 4 bb where b  D 0 X and b  c   - X 4 from fake  WS: 23 real D 0 background  13 from prompt, dominated by fake   10 from bb where b  D 0 X and b  + X Group Meeting May 7, ~10M MC09 inclusive charm used for this study WS does not provide accurate information on RS background. Better to:  Fit D 0 IP dist. to separate prompt & DfB  Estimate bb background from MC  Check by separating prompt & DfB D 0 in WS Signal + Bkg Bkg

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” D o sample for much of this. For example, we will compare the resolution on the D o 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 D o  K        / D o  K    ; other modes are also possible. With more data we can check the particle i.d. efficiency by using D o  K - K + /D o    . 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/     events. See CERN-LHCb-PUB 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,

Summary and Plan A clear signal of semileptonic B decays is observed Will fit IP distributions for separating prompt from secondary D 0  We need to check if MC represents the distribution in data using prompt D 0 Will translate the event yield to a meaningful cross-section number Group Meeting May 7,

B+ decays in.dec file Group Meeting May 7, Decay B+sig Myanti-D*0 mu+ nu_mu HQET ; Myanti-D0 mu+ nu_mu ISGW2; Myanti-D_10 mu+ nu_mu ISGW2; Myanti-D_0*0 mu+ nu_mu ISGW2; Myanti-D'_10 mu+ nu_mu ISGW2; Myanti-D_2*0 mu+ nu_mu ISGW2; Myanti-D0 pi0 mu+ nu_mu GOITY_ROBERTS; Myanti-D*0 pi0 mu+ nu_mu GOITY_ROBERTS; MyD*- pi+ mu+ nu_mu GOITY_ROBERTS; # correct for the fact that we force tau -> mu anti_nu_mu nu_tau (17.3%) Myanti-D*0 Mytau+ nu_tau ISGW2; Myanti-D0 Mytau+ nu_tau ISGW2; Myanti-D_10 Mytau+ nu_tau ISGW2; Myanti-D_0*0 Mytau+ nu_tau ISGW2; Myanti-D'_10 Mytau+ nu_tau ISGW2; Myanti-D_2*0 Mytau+ nu_tau ISGW2; Enddecay All D* are set to 100% decay to D 0

B0 decays in.dec file Group Meeting May 7, Decay B0sig MyD*- mu+ nu_mu HQET ; MyD_0*- mu+ nu_mu ISGW2; MyD_1- mu+ nu_mu ISGW2; MyD'_1- mu+ nu_mu ISGW2; MyD_2*- mu+ nu_mu ISGW2; MyD*- pi0 mu+ nu_mu GOITY_ROBERTS; Myanti-D*0 pi- mu+ nu_mu GOITY_ROBERTS; Myanti-D0 pi- mu+ nu_mu GOITY_ROBERTS; # correct for the fact that we force tau -> mu anti_nu_mu nu_tau (17.3%) MyD*- Mytau+ nu_tau ISGW2; MyD_0*- Mytau+ nu_tau ISGW2; MyD_1- Mytau+ nu_tau ISGW2; MyD'_1- Mytau+ nu_tau ISGW2; MyD_2*- Mytau+ nu_tau ISGW2; Enddecay All D* are set to 100% decay to D 0

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,