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* LHCb experiment, the “must know” * Why Cascade might be useful for LHCb?

Forward studies with Cascade at LHC energies E. Rodrigues , Niels Tuning NIKHEF, Amsterdam HERA-LHC Workshop, DESY. * LHCb experiment, the “must know” * Why Cascade might be useful for LHCb? * Comparisons with Pythia - general event kinematics and variables

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* LHCb experiment, the “must know” * Why Cascade might be useful for LHCb?

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  1. Forward studies with Cascade at LHC energiesE. Rodrigues, Niels TuningNIKHEF, AmsterdamHERA-LHC Workshop, DESY * LHCb experiment, the “must know” * Why Cascade might be useful for LHCb? * Comparisons with Pythia - general event kinematics and variables - tracks and jets * Conclusions NB: Updated plots after the presentation! HERA-LHC Workshop, DESY, 22th March 2005

  2. LHCb experiment LHCb Goal: B-physics studies CP violation rare B-decays Acceptance: 1.8 < h < 4.9 Luminosity: 2·1032 cm-2 s-1 Nr of B’s /year: 1012 20 m HERA-LHC Workshop, DESY, 22th March 2005

  3. LHCb experiment • Unique forward spectrometer • at high energy! • Excellent tracking • Excellent PID HERA-LHC Workshop, DESY, 22th March 2005

  4. How forward is LHCb? How forward is LHCb?: • B hadrons mainly produced in forward region(s) • both B’s tend to be correlated HERA-LHC Workshop, DESY, 22th March 2005

  5. Why cascade? DGLAP (Pythia) vs CCFM (Cascade): • Differences expected in forward region Cascade and LHCb: • Estimate uncertainty of PYTHIA predictions: Track multiplicity in LHCb affects: • Trigger • Tracking • Tagging • Study b-jets: • Jet-charge: b orb tagging • Jet reconstruction: bb invariant mass • Study QCD evolution itself: • Validity of DGLAP vs CCFM HERA-LHC Workshop, DESY, 22th March 2005

  6. DGLAP: kT ordering: kTn>>kTn-1>>kT1 BFKL: x ordering: xn<<xn-1<<x1 CCFM: angular ordering: θn<<θn-1<<θ1 DGLAP and CCFM evolution DGLAP vs CCFM: • If ln(1/x) terms are large: DGLAP evolution expected to fail •  Differences expected in forward region • DGLAP evolution suppressed when small phase space for Q2 evolution •  select jets with Q2 ~ E2T,jet • CCFM evolution enhanced when large phase space for x evolution •  select jets with xjet >> xBjorken (xjet=Ejet/Eproton ) NB: Cascade needs pdf’s: f(x,Q2,kT), ie. unintegrated over kT HERA-LHC Workshop, DESY, 22th March 2005

  7. Outline In the following we will show CASCADE vs PYTHIA comparisons … in minimum bias: • Event kinematics • x1, x2, Q2 • Event topology • multiplicity, E, pT, etc. (of tracks) • Jets • Multiplicity, ET, etc • PYTHIA “6.2 series” with LHCb tune (cf. P. Szczypka’s talk) • Cascade 1.2009 out of the box HERA-LHC Workshop, DESY, 22th March 2005

  8. Pythia versus Cascade • Only unintegrated gluons available in CASCADE • Compare CASCADE with following subprocesses in PYTHIA: • Inclusive QCD: (MSEL=2) • fg fg 50% • ggff 15% • gggg 25% -> named “Pythia gluon” in the following … • 90% HERA-LHC Workshop, DESY, 22th March 2005

  9. Event kinematics (1) • PYTHIA: • Q2 = PARI(18) = PT2 of hard process ? • x1,x2 = PARI(33), PARI(34) ? (as used in the pdf’s) • CASCADE: • Q2 = pT2 ? [outgoing parton] • x1,x2 = (E+pz)/2Eproton ? [ingoing parton] • NB: x1<x2 HERA-LHC Workshop, DESY, 22th March 2005

  10. Event kinematics (2) • Large overlap with HERA kinematic region •  CASCADE: more equal x values PYTHIA CASCADE • NB: x1<x2 HERA-LHC Workshop, DESY, 22th March 2005

  11. Event distributions • Event distributions: • Multiplicity in 2<η<5 • Acoplanarity of outgoing partons (Df) • <pT> of particles in 2<η<5 • Max pT in2<η<5 • Df • CASCADE: lower multiplicity • PYTHIA: more back-to-back HERA-LHC Workshop, DESY, 22th March 2005

  12. Track distributions • Track distributions: • η • pT • No dramatic difference in 2<η<5 … still Pythia tracks less forward HERA-LHC Workshop, DESY, 22th March 2005

  13. Jets • Jets finding • In the laboratory frame • Using the KTCLUS algorithm in inclusive mode • Jets selection • distributions shown only for jets in the LHCb acceptance • ET,jets > 10 GeV … and also loose sample with ET,jets > 1 GeV NB: following distributions correspond to ~ 1ms of LHCb running… HERA-LHC Workshop, DESY, 22th March 2005

  14. Jet distributions ET,jets > 1 GeV • Loose selection ET,jets > 1 GeV • CASCADE: lower jet multiplicity …(?) -> ET and η dists. are similar HERA-LHC Workshop, DESY, 22th March 2005

  15. Jet distributions ET,jets > 10 GeV • Harder selection ET,jets > 10 GeV • CASCADE: many events with no jets -> ET and η dists. are similar HERA-LHC Workshop, DESY, 22th March 2005

  16. Highest ET jet – select phase space? Forward jets selection E2T,jet1 Q2 to suppress DGLAP xjet1 >> xBjorken to enhance BFKL  non-negligible phase space for low x phenomena (e.g. cuts in HERA forward jet analyses) HERA-LHC Workshop, DESY, 22th March 2005

  17. Conclusions • LHCb can be interesting for CASCADE • Investigate DGLAP vs CCFM • CASCADE can be interesting for LHCb • Investigate uncertainties of present Monte Carlos • Interesting first comparison: • PYTHIA and CASCADE not wildly different, despite their different philosophy, though differences are present • More studies to follow in selected regions of phase space where differences might be enhanced (e.g. multiplicities, …) • Some issues risen: • Are the comparisons fair? E.g. choice of Pythia sub-processes • Are the x, Q2 definitions consistent between MCs? • Caveats: • CASCADE out of the box: parameters need tuning and investigation … HERA-LHC Workshop, DESY, 22th March 2005

  18. Backup slide Why do we care about multiplicity? Tracking: eff and ghost rate Tagging: εeff Track multiplicity Nlong< 20 εeff = 5.4 ±0.3 Nlong> 20 εeff = 3.9 ±0.3  Relative multiplicity • Multiplicity affects: • Trigger • Tracking • Tagging Trigger: CPU time • Plots from: • Massi F.-L. Apr. ’03 • Jeroen v.T. Thesis • Marco Musy: May ‘03 HERA-LHC Workshop, DESY, 22th March 2005

  19. Reminder (slide from March 2004…) LHCb: • can we use the reconstructed b-jet for inclusive triggering (at high level trigger)? • b-jet (charge) useful for flavour tagging? • what kind of jet algorithms are best to use in (very) forward region? - is KTCLUS good (enough) ? Alternatives? => where can HERA help? • LHCb can simulate and make studies • HERA can also analyse data and make comparisons • HERA measurements: forward jet production, particles/energy flow in forward region … … ongoing analyses / plans in ZEUS/H1? -> areas where discussions / feedback / between both groups can be profitable … Any interests from HERA on addressing these points? HERA-LHC Workshop, DESY, 22th March 2005

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