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F2bb from muon+jet final states at ZEUS

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Presentation on theme: "F2bb from muon+jet final states at ZEUS"— Presentation transcript:

1 F2bb from muon+jet final states at ZEUS
B. Kahle, DESY Hamburg Introduction Beauty measurements Beauty contribution to F2 Summary and Conclusions

2 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
Motivation Heavy flavour production in DIS is a test of pQCD providing an additional hard scale M to the momentum transfer of the boson Q and pt Beauty contribution to F2 is directly sensitive to the gluon distribution in the proton Beauty production is of increasing interest for higher energies -> LHC HERA LHC, e.g. H / Z 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

3 Beauty contribution to the proton structure function F2
~negligible 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

4 Heavy Flavour production mechanism
Dominant process in ep-collisions: Boson-Gluon-Fusion Kinematic variables: Q2 = -q 2 photon virtuality, squared momentum transfer x = Bjorken scaling variable, for Q2>>(2mQ)2: momentum fraction of p constituent b b Kinematic regime: Deep inelastic scattering (DIS): Q2 > 1GeV2 Multiple scales: mb ~ 5 GeV ptb ~ typically few GeV Q 2 > 1 GeV 2 in DIS ~ different pQCD approaches good testing ground for pQCD 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

5 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
pQCD approximations Massive scheme: b massive neglects [as ln (Q2/mb2)]n scale mb ,pt b produced perturbatively (not part of the Proton or Photon) Massless scheme: b massless resumes [as ln (Q2/mb2)]n scale: Q2, pt b also in Proton and Photon Variable flavour number scheme (VFNS): massive at small Q2 massless at large Q2 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

6 Beauty identification
Process : ptrel method: ptrel is the momentum of the muon transverse to the axis of the associated jet (including the muon) ptrel spectrum is harder for b than for c statistical separation using MC e p Jet axis m c2 fit of b MC against c+lf MC to the data in ptrel resulting beauty fraction of about 21% scale Rapgap-b MC up by a factor 2.49 ptrel 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

7 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
Cross section Beauty cross section for the DIS process: Cuts on MCtrue quantities: Q 2 > 4 GeV2 0.05 < y < 0.7 Et,jet > 5 GeV -2 > ηjet > 2.5 pt,µ > 1.5 GeV -1.6 > ηµ Data: σbb= 77.1 ± 7.8 (stat.) ± 9.6 (sys.) pb 14.9 MC (LO+PS): σbb= 31.0 pb lab NLO (HVQDIS): σbb = 32.9 ± 3.3 (sys.) pb R,F2 = pt2+4mb2 (simultaneous variation: factor 1/4 to 4) mb= 4.75 GeV (variation: 4.5 GeV to 5 GeV) Peterson frag. function  = Proton parton distribution: CTEQ5F4 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

8 Cross sections in pt and h
hm ptm hjet ptjet 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

9 Cross sections in Q2 and Q2x
Q2x (plot 1) Q2x (plot 3) Q2x (plot 2) 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

10 Calculation of F2bb = beauty contribution to F2
„Reduced cross section“ is defined as: Cross section calculated using hvqdis(CTEQ5F4) for a tiny bin around (x,Q2) Expected to be compatible with calculations by Riemersma et al. used for F2cc Neglecting the small contribution from FL, the reduced cross section is equal to F2: neglected 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

11 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
F2bb measurement The reduced cross section for data is the reduced cross section of the NLO multiplied by the ratio of data to NLO in a x,Q2 bin: Cross section for NLO using hvqdis with same settings as for (but requiring SL decay to m and jet) H1 uses the impact parameter method to measure F2bb and F2cc with an inclusive charm and beauty sample of 57pb-1: H1 Collab., A. Aktas et al., Eur. Phys. J. C45 (2006) 23-33 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

12 Kinematic plane (ZEUS)
03/04 data Q2x plot 3 (x,Q2) values chosen for F2bb to compare with H1‘s results Q2x plot 2 Q2x plot 1 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

13 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
F2bb at ZEUS and H1 ZEUS data lie above H1 data but compatible within errors. HVQDIS+CTEQ5F4 agrees with similar predictions by H1 ZEUS: 39 pb-1 H1: 57.4 pb-1 Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/ ZEUS data point at Q2=200GeV2; x=0.13 is shifted to lower x value to be separated from the H1 point 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

14 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
F2bb vs. Q2 Same ZEUS data. Some points are recalculated for other values of x to be comparable with H1 data and theory curves. ZEUS data are derived using HVQDIS+CTEQ5F4 and should strictly compared only with this curve. For comparison with other curves, model dependencies have to be taken into account. Some ZEUS data point are shifted to higher Q2 values to be separated from the H1 point 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

15 PDF Schemes and Parameters
Order Scheme mM2 Mb(GeV) MRST04 as2 VFNS Q2 4.3 MRST NNLO as3 CTEQ6HQ 4.5 HVQDIS+CTEQ5F4 FFNS pt2+4M2 4.75 CTEQ5F3 MRST FF3 CTEQ6.5 Q2+M2 Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/ 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

16 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
F2bb at ZEUS and H1 Same plot as before, but with additional theory curves. ZEUS: 39 pb-1 H1: 57.4 pb-1 Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/ ZEUS data point at Q2=200GeV2; x=0.13 is shifted to lower x value to be separated from the H1 point 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

17 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
Summary and Outlook First measurement of F2bb at ZEUS (39 pb-1), ~10 times more data to come -> much reduced errors Results agree with H1’s using a very different method to obtain F2bb but similar uncertainties (both statistical and systematical) NLO predictions agree with data within large spread. Questions to this meeting: What are the reasons for the large NLO spread? Does this affect the PDF extraction from inclusive F2? 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

18 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
BACKUP 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

19 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle
NLO calculations The calculation of the NLO QCD visible cross section predictions proceeds in three steps: HVQDIS (B.Harris, J.Smith, hep-ph/ ): *gbb, *gbbg, *qbbq, etc. (pointlike only) using CTEQ5F4 (FFNS) PDF Fragmentation of the b-quark into a B-meson (Peterson function with =0.0035) Semileptonic decay of the B-meson (Muon momentum spectrum extracted from RAPGAP, including primary and secondary muons) 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

20 CTEQ5F4 with different scales
F2bb using different scales for CTEQ5F4: Q2 Q2+4M (M=4.5GeV) Q2+4M (M=4.75 GeV) large differences at low Q2 for different masses 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

21 Extrapolation to full phase-space
Q2 Extrapolation factor: 25 GeV2 ~6 110 GeV2 ~4 200 GeV2 ~3 Extrapolation factor excluding branching fraction to m of Extrapolation factor includes ptb and hb spectrum, fragmentation, and decay kinematics (jet and m) Similar to extrapolations for F2cc 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

22 Inclusive lifetime tags
H1 mirrored inclusive DIS most significant impact parameter S1 charm 2nd most significant impact parameter S2 beauty 13th March 2007 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

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