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Godparents: W. Wester, J. Dittman, G. Feild. The B cross section Introduction NLO calculation Previous measurements Final RUN 1 CDF measurement New theoretical.

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Presentation on theme: "Godparents: W. Wester, J. Dittman, G. Feild. The B cross section Introduction NLO calculation Previous measurements Final RUN 1 CDF measurement New theoretical."— Presentation transcript:

1 Godparents: W. Wester, J. Dittman, G. Feild

2 The B cross section Introduction NLO calculation Previous measurements Final RUN 1 CDF measurement New theoretical developments Low energy SUSY and the b cross section Conclusion D. Bortoletto Todd Keaffaber’s Thesis

3 Heavy quark NLO Calculations of heavy quark production in hadronic collisions follow the approach developed by Collins, Soper and Sterman: Explicit calculation were done at NLO (O(  s 3 )) by Nason, Dawson and Ellis (NDE), Mangano Nason and Ridolfi (MNR) Nason et al., Nucl., Phys. B327 (1989) 49, B335 (1990) 260 W. Beenakker et al., Nucl. Phys. B351 (1991) 507 M. Mangano et al., Nucl. Phys B373 (1992) 295

4 Theoretical predictions are usually presented varying  R and  F in the range The largest cross section (  2) corresponds to large  F and small  R The uncertainty due to the PDF is small due to the tighter constraints set by DIS and HERA data (  12-20%). The mass of the b quark is varied between In this range the cross section can change by about 10% Heavy quark NLO

5 The largest uncertainty in the cross section determination is the scale uncertainty which is sensitive to higher order corrections. 630GeV 1800GeV 10GeV 20GeV 40GeV 60GeV

6 Hadron collider experiments historically studied the b- quark cross section More recently the differential cross section has also been studied. Measurements have been performed using different data sets with electrons or muons and/or jets in the final state: Inclusive decays e/  Muon+jets J/  Experimental Measurements u B+B+ K+K+ u u

7 B cross section measurements The single b inclusive cross section has been measured at several energies: 540 GeV by UA1 630 GeV by UA1, CDF and D0 1.8 TeV by CDF and D0 630 GeV

8 Early CDF measurements 1.8 TeV

9 B cross section measurements Excellent agreement between experiments Significant excess in the data 1800 GeV

10 B cross section measurements The experimental measurements find a cross section higher than the theoretical prediction by a factor  2-3 630 GeV1800 GeV

11 Ratio of the cross section Reduced theoretical and experimental uncertainties B cross section measurements

12 D0-b Jet measurement D0: b tagging jets using muons. Require E T (Jet)>25GeV, and P T (  )>6GeV Agreement with theory upper band for p T >55 GeV

13 Summary of the measurements

14 B cross section In Run 1A first measurement of the B cross section by CDF. (PRL 75, 1451 (1995))

15 B cross section Measurement confirms discrepancy between theory and experiments CDF published

16 L=98  4 pb -1 Use only the decay Require muons in SVX to have more precise ct information Require CMU muons Run 1 Measurement L=19.3  0.7 pb -1 Use the decays Muons can be both in SVX and CTC Require CMU muons RUN 1ARUN 1

17 Track quality cuts 4 hits in at least 2 axial superlayers 2 hits in at least 2 stereo superlayers R exit (Kaon)>110 cm Muons: All muons have CMU stub Muon matching  3 hits in the SVX Primary vertex Data Selection

18 J/  reconstruction Run 1A: and Run 1B and or J/  reconstruction  +  - are vertex constrained

19 B reconstruction SVX information used if available for the kaon  +  - K are vertex constrained  +  - mass constraint to J/  mass Data Selection

20 Event yield Event yield for Run 1 analysis

21 The B meson cross section is determined using where M i and  i mass and width from the kinematic fit s=scale factor b=slope of the background w=fit mass range Fitting method

22 Event yield in P T bins Event yield for Run 1 analysis divided in 4 p T bins

23 The product of the acceptance and trigger efficiency was calculated with BGEN, QQ, QFL, DIMUTG using the MRST structure functions The QCD-NLO MC was run with: Results: Acceptance

24 Efficiencies that are not included in the MC acceptance were calculated using data Efficiencies that are not equal in Run 1A and Run 1B are averaged and weighted by the luminosityEfficiency

25 The B meson cross section is determined using Where: N is the number of B mesons from a unbinned likelihood fit  p T is the width of the p T bin L is the corrected integrated luminosity A is the MC acceptance which included the trigger efficiency.  is the reconstruction efficiency B=BR(B +  J/  K + )  BR(J/    +  - )=(5.88  0.60)  10 -5 Cross Section

26 The measured J/  cross section fell as a function of the instantaneous luminosity We correct for this effect: Luminosity Correction Feild, Lewis CDF note 4769

27 Systematic uncertainties Fully correlated systematic uncertainties which do not depend on p T Uncorrelated systematic uncertainties which depend on P T

28 The measured cross section is: To compare with the theory we plot the results at Differential Cross Section

29 The cross section is higher than the theoretical NLO

30 Total Cross Section P T >15GeV/c QCD NLO central value  1.2  b Replace the last bin of the differential cross section CDF measures:

31 Shape are well described by perturbative QCD Large discrepancy on the cross section measurement Presence of higher order terms Fragmentation effects Intrinsic k T of partons New physics Fixed order calculation have terms Which could be quite large for Heavy quark NLO

32 New Theoretical developments Variable Flavor Number Scheme (VFN) (F.I Olness, R.J. Scalise and Wu-Ki Tung hep-ph/9712494) Hadronization of heavy quarks Harder b  B fragmentation (Colangelo-Nason)  30% (40%) higher B cross section in the central (forward) region

33 New Theoretical developments Studies of the k T effect

34 New Theoretical developments Correlated b production seems to disfavor large k T effects.

35 ….

36 New Physics Hypothesis Supersymmetry could make a substantial contribution to the observed b cross section Berger, Tait, Wagner et al. have a model with intermediate mass gluinos that decay into b and sbottom The contribution is large if

37 New Physics Hypothesis The new contribution peaks at b quarks have  and  similar to QCD production Authors claim that this scenario is not ruled out by current limits.

38 Conclusion Final run 1 measurement of the B cross section confirms discrepancy with QCD NLO predictions CDF and D0 measurements on different data sets give consistent measurements of the b cross section NLO calculations model the shape but under-estimate b production Puzzle in b production is now emerging also at LEP and at HERA

39 B physics program at hadronic machines continues to be complementary to B-factories All B species are produced High production cross section Higher luminosity will bring higher statistic but also systematic effects that will need to be investigated. Higher statistic will allow: To probe higher E T region Investigate the possibility to study the b-fragmentation at the Tevatron Correlation studies Prospects for Run II

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