1. 1 D *+ production Alexandr Kozlinskiy Thomas Bauer Vanya Belyaev 25.06.2010

2. 2 Outline Introduction Selections Yield extraction Cuts optimization procedure Efficiencies (reconstruction, PID, generator) Trigger efficiencies Comparison of MC and Data Yields Systematics Summary

3. Introduction 3 Study of tagged D *+ → (D 0 → μμ)π + needs: understanding of charm production cross section D * polarization Study of D *+ → (D 0 → K – π + )π + : production cross section: versus P t and rapidity up to zero P t D * polarization additional measurements and crosschecks: D 0 life time tracking efficiencies, PID efficiencies, etc. Data sets used: Minimum bias TCKx51710 (magnet up and down) ‘Good’ TCKx51710 (charm stream) ‘Good’ TCKx81710 (charm stream) Note: Cuts optimization made on minimum bias magnet down data All mass plots and yields are made using ‘good’ TCKx51710 data MC comparison made with all ‘good’ data Systematics were studied using minimum bias data

4. Cuts were optimized on minimum bias magnet down data (133M events) to have minimum σS/S (the most precise yield measurement), where S is the yield of D * ’s. Following cuts were applied beforehand (no optimization): D 0 mass window: 100 MeV |M(D * ) – M(D 0 ) – 145.5| < 2.5 MeV (σΔM = 0.75 MeV) No PID were used during cuts optimization. Optimized cuts: D 0 daughters IP χ 2 > 9 (D 0 daughters do not point to primary vertex) D 0 vertex χ 2 < 9 D 0 life time fit χ 2 < 9 (pointing to primary vertex) D 0 life time > 90 μm (background has “0” life time) cos(θ π ) in D 0 rest frame < 0.9 (signal has flat distribution) D * vertex χ 2 < 16 The optimal values are stable with respect to PID: K from D 0 : Δ LL (K) – Δ LL (π) > 0 π from D 0 : Δ LL (π) – Δ LL (K) > 0 Selections 4 cos(θ π ) in D 0 rest frame M(D * ) – M(D 0 )

5. D 0 mass distribution 5 D 0 mass distribution shows the total number of D 0 ’s in the selected sample, but it still contains wrong combination of soft pion and D 0. The methods to subtract this wrong combination are explained on next slides. N = 1476 ± 43 Mean = (1863 ± 0.3) MeV σ = (9.3 ± 0.3) MeV

6. 6 Yield of D * ’s (method 1) Points in the plots are number of D 0 ‘s within corresponding ΔM slice. The distribution is fitted with Gaussian + (ΔM – 139.6) 0.5. N = 1149 ± 46 Mean = 145.4 MeV σ = (0.78 ± 0.03) MeV N(D 0 )

7. The following procedure to get number of D * ’s were used as second method: Fit number of D 0 ’s in signal region Fit number of D 0 ’s in sidebands of delta mass Calculate number of background D 0 ’s in signal region from sidebands using ratio: ratio = 1.2 Calculate number of true D * ’s: N = N signal – ratio · N bg = 1185 ± 51 7 M(D * ) – M(D 0 ) sideband signal region M(Kπ) fit in signal region M(Kπ) fit in sidebands N = 1476 ± 43 σ = 9.3 ± 0.3 N = 245 ± 2 σ = 7.7 ± 0.8 Yield of D * ’s (method 2)

8. 8 Yield of D * ’s (method 3 – default) One can also directly subtract sideband histogram (from previous slide) from signal histogram (taking into account errors in bins and ratio factor). After subtraction the number of D * ’s can be extracted from fit resulted histogram. The first method gives the most precise value of D * ’s but cat be used only for high statistics points (not applicable for fitting in bins of P t and rapidity). All three methods give similar values within ±20 events which can be thought of as systematic error of 1.7% for the yield extraction method. N = 1168 ± 52 σ = 9.5 ± 0.4 N bg,3σ = 1 ± 16 Method 1N = 1149 ± 46 Method 2N = 1185 ± 51 Method 3N = 1168 ± 52

9. To optimize one particular cut the value of that cut was varied with all other cuts fixed on their optimal values (iterative process). The values of cuts were chosen to be close to minimum of the σS/S dependency (see plots below). Ranges of optimal values are wide in most cases. The only cut that change it’s optimal value with PID is D 0 vertex χ 2 (from 4 to 9). D * vertex χ 2 does not have minimum but still cut on 16. Optimization procedure D 0 daughters IP χ 2 > 9D 0 vertex χ 2 < 9D 0 life time fit χ 2 < 9 D 0 life time > 90 μmcos(θ π ) < 0.9D * vertex χ 2 < 16 9

10. Reconstruction efficiencies, no PID Efficiency versus P t Efficiency versus rapidity Reconstruction efficiency was calculated using 2.5M magnet up and 2.5M magnet down MC events without use of PID cuts. 10

11. PID Efficiencies, using Andrew Powell (AP) tables 11 The PID efficiencies calculated using tables provided by Andrew Powell. This tables contain efficiencies for identifying kaon as kaon and pion as pion in the specified bin of P t and Eta. By reweighting every event in MC sample that passed all selections with weigh (ε K · ε π ) –1, where ε K is efficiency from the table for kaon from D 0 and ε π is efficiency for pion from D 0, one can do back transformation of PID cut and extract efficiency. The same procedure can be done using data sample (the result will be the same, this is because for specific P t and rapidity of D * the kinematic for kaon and pion for D 0 is well described in MC).

12. 12 Comparison of PID Efficiencies (directly from Data and MC and using AP tables) The PID efficiency can be directly extracted in MC and Data by comparing the yield of D * ’s with and without use of PID cuts. The PID efficiency versus P t looks quite different (can be due to wide bins in P t in AP tables). Biggest difference in bins with smallest yields. Efficiency versus rapidity looks good. The overall systematic on PID can be estimated to be less then 5% on average (need to be investigated in more details). PID efficiency versus P t PID efficiency versus rapidity

13. Generator level efficiencies Generator level efficiencies are calculated by looking at how many signal events pass ‘DaughtersInLHCb’ cut after Gauss generation step. Current table is done using 10K magnet down and 10K magnet up generated events. redo for 1M magnet up and down to reduce errors. 13

14. 14 Total efficiency Total efficiency includes reconstruction efficiency, PID efficiency and generator efficiency.

15. 15 Trigger efficiencies TCKx51710TCKx81710 For TCKx51710 the efficiency for MicroBias* triggers on selected events is 100% For TCKx81710 the MicroBias*RateLimited trigger is limited to 100 Hz MicroBias*RateLimited triggers can increase statistic by factor 2-3 MicroBias*RateLimited, DiHadron and SingleHadron triggers – factor 5-6 MicroBias*RateLimited and MicroBias* (pre- and post-scaled by 10000?) triggers can be used to extract real MicroBias* rate. ~85%

16. D 0 daughters IP χ 2 D 0 vertex χ 2 D 0 life time fit χ 2 D 0 life timecos(θ π ) in D 0 rest frameD * vertex χ 2 Data and MC comparison Following plots are comparison of different distributions (that are used in selections) for Data and MC. Every point in the plots is the number of D * ’s obtained with method 3 (background subtracted distributions). In general the MC describes Data on a good level, except D 0 life time χ 2 (looks wider). 16

17. IP distribution, D from B D 0 IP (logarithmic scale)D 0 life time χ 2 (equivalent to D 0 IP χ 2 ) The distribution of D 0 IP in Data shifted a bit to the right when compared to MC. It is possible that the D * sample is contaminated by D from B. Those D’s should be visible on IP distribution as a bump on right side (nothing is seen in current sample). The D 0 life time χ 2 distribution is wider then in MC and has strange behavior around 7-9 (goes down). Need to study more wide range (difficult due to cut in stripping – will be removed, and due to low statistic). 17

18. D * production versus P t 18 Method 3 was used to get number of D * ’s for every P t slice. Both distribution (for Data and MC) are normalized to one. no efficiency correction

19. 19 D * production versus rapidity Method 3 was used to get number of D * ’s for every rapidity slice. Both distribution (for Data and MC) are normalized to one. no efficiency correction

20. 20 Raw yields 2 < P t < 3 3.0 < y < 3.5 3 < P t < 4 3.0 < y < 3.5 4 < P t < 5 3.0 < y < 3.5 The raw yield is extracted by fitting with method 3 in every bin of Pt and rapidity with fixed width and mean of Gaussian (N signal and N background are free parameters). The width and mean are fixed on corresponding values obtained from the fit of all events.

21. 21 Yields Yield corrected for: reconstruction efficiency PID efficiency generator efficiency

22. 22 Systematics (using minimum bias data) The cuts systematics are calculated by releasing them one by one and comparing the corrected by reconstruction efficiency (obtained from MC) raw yields. The difference will give estimate of systematic error for corresponding cut. D 0 daughters IP χ 2 : > 9 → > 4: 42837 → 41888 : 2.2% D 0 vertex χ 2 : < 9 → < 25: 42837 → 43895 : 2.5% D 0 life time fit χ 2 : < 9 → < 25: 42837 → 44522 : 3.9% : < 9 → < 16: 42837 → 43967 : 2.6% increase in the yield due to D from B? release this cut to reduce systematic (may be this is already estimate for D from B) will allow to study D from B contribution D 0 life time: > 90 → > 60 μm: 42837 → 42519 : 0.7% cos(θ π ) in D 0 rest frame: < 0.9 → < 1.0: 42837 → 43205 : 0.9% D * vertex χ 2 : < 16 → < 25: 42837 → 43334 : 1.2% release or remove cut (no minimum → may be not really needed?) The total selections systematic is 5.4% (excluding PID systematic). Method systematic: 1.7% PID systematic: less then 5% (need to be investigated in more details)

23. 23 Yields (TCKx51710 + TCKx81710)

24. 24 Summary All efficiencies are taken into account Redo generator efficiencies with more events The data and MC agree quite well Still have to study in details D 0 life time χ 2 distribution release or remove cut D from B The total systematic for selections is 5.4%, PID – less then 5%, method – 1.7% Calculate trigger efficiencies and include TCKx81710 in analysis increase in statistic: factor 5-6 Try extracting D * polarization in P t bins