HERA-LHC Workshop, DESY, 22th March 2005 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 - tracks and jets * Conclusions NB: Updated plots after the presentation! Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 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 Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 LHCb experiment Unique forward spectrometer at high energy! Excellent tracking Excellent PID Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

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

HERA-LHC Workshop, DESY, 22th March 2005 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 Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

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 ) DGLAP: kT ordering: kTn>>kTn-1>>kT1 BFKL: x ordering: xn<<xn-1<<x1 CCFM: angular ordering: θn<<θn-1<<θ1 NB: Cascade needs pdf’s: f(x,Q2,kT), ie. unintegrated over kT Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 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 Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 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% Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 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 Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

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

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

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

HERA-LHC Workshop, DESY, 22th March 2005 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… Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

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

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

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) Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

HERA-LHC Workshop, DESY, 22th March 2005 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 … Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005

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

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? Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005