* lhcb experiment, the “must know” * why cascade might be useful for lhcb?

Eduardo & Niels HERA-LHC Workshop, DESY, 22th March 2005 1/17

* LHCb experiment, the “must know”

* Why Cascade might be useful for LHCb?

* Comparisons with Pythia

- general event kinematics and variables

- tracks and jets

* Conclusions

Forward studies with Cascade at LHC energiesForward studies with Cascade at LHC energies

E. RodriguesE. Rodrigues, , Niels TuningNiels TuningNIKHEF, AmsterdamNIKHEF, Amsterdam

HERA-LHC Workshop, DESYHERA-LHC Workshop, DESY NB: Updated plots

NB: Updated plots afterafter

the presentation!

the presentation!


LHCbLHCb

Goal: B-physics studies CP violation rare B-decays

Acceptance: 1.8 < < 4.9

Luminosity: 2·1032 cm-2 s-1

Nr of B’s /year: 1012

LHCb experiment

20 m20 m


LHCb experiment

Unique forward spectrometer

at high energy!

Excellent tracking

Excellent PID


How forward is LHCb?:How forward is LHCb?: B hadrons mainly produced in forward region(s)B hadrons mainly produced in forward region(s)

both B’s tend to be correlatedboth B’s tend to be correlated

How forward is LHCb?


Why cascade?

DGLAP (Pythia) vs CCFM (Cascade): Differences expected in forward region

Cascade and LHCb:Cascade and LHCb:

Estimate uncertainty of PYTHIA predictions:Estimate uncertainty of PYTHIA predictions:

Track multiplicity in LHCb affects:Track multiplicity in LHCb affects:

TriggerTrigger

Tracking Tracking

TaggingTagging

Study b-jets:Study b-jets: Jet-charge: b orJet-charge: b orb taggingb tagging

Jet reconstruction: bJet reconstruction: bb invariant massb invariant mass

Study QCD evolution itself:Study QCD evolution itself: Validity of DGLAP vs CCFMValidity of DGLAP vs CCFM


DGLAP and CCFM evolution

DGLAP vs CCFM:DGLAP vs CCFM: If ln(1/x) terms are large: DGLAP evolution If ln(1/x) terms are large: DGLAP evolution

expected to failexpected to fail

Differences expected in forward regionDifferences expected in forward region

DGLAP evolution suppressed when small phase DGLAP evolution suppressed when small phase spacespace

for Qfor Q22 evolution evolution

select jets with Qselect jets with Q22 ~ E ~ E22T,jetT,jet

CCFM evolution enhanced when large phase spaceCCFM evolution enhanced when large phase space

for x evolutionfor x evolution

select jets with xselect jets with xjetjet >> x >> xBjorken Bjorken ((xxjetjet=E=Ejetjet/E/Eproton proton ))

nn

11 DGLAP:DGLAP:

kT ordering:

kTn>>kTn-1>>kT1

BFKL:BFKL:

x ordering:

xn<<xn-1<<x1

CCFM:CCFM:

angular ordering:

θn<<θn-1<<θ1

NB: Cascade needs pdf’s: f(x,Q2,kT), ie. unintegrated over kT


Outline

In the following we will show CASCADE vs In the following we will show CASCADE vs PYTHIA comparisons … in PYTHIA comparisons … in minimum biasminimum bias::

Event kinematicsEvent kinematics

x1, x2, Qx1, x2, Q22

Event topologyEvent topology

multiplicity, E, pmultiplicity, E, pTT, etc. (of tracks), etc. (of tracks)

JetsJets

Multiplicity, EMultiplicity, ETT, etc, etc

PYTHIA “6.2 series” with LHCb tune (cf. P. Szczypka’s talk)PYTHIA “6.2 series” with LHCb tune (cf. P. Szczypka’s talk)

Cascade 1.2009 out of the boxCascade 1.2009 out of the box


Only unintegrated Only unintegrated gluonsgluons available in CASCADE available in CASCADE

Compare CASCADE with following subprocesses in Compare CASCADE with following subprocesses in PYTHIA:PYTHIA:– Inclusive QCD: Inclusive QCD: (MSEL=2)(MSEL=2)

fg fg 50% ggff 15% gggg 25% -> named “Pythia gluon” in the following … 90%

Pythia versus Cascade


Event kinematics (1)

PYTHIA:PYTHIA:– QQ22 = PARI(18) = P = PARI(18) = PTT

22 of hard process ? of hard process ?

– x1,x2 = PARI(33), PARI(34) ?x1,x2 = PARI(33), PARI(34) ?

(as used in the pdf’s)

CASCADE:CASCADE:– QQ2 2 = p= pTT

22 ? [outgoing parton] ? [outgoing parton]

– x1,x2 = (E+px1,x2 = (E+pzz)/2E)/2Eproton proton ? [ingoing parton]? [ingoing parton]

NB: xNB: x11<x<x22


Event kinematics (2)

Large overlap with Large overlap with HERA kinematic regionHERA kinematic region

CASCADE: more CASCADE: more equal x valuesequal x values

PYTHIAPYTHIA CASCADECASCADE

NB: xNB: x11<x<x22


Event distributions:– MultiplicityMultiplicity in 2<η<5– AcoplanarityAcoplanarity of

outgoing partons ()– <p<pTT>> of particles in

2<η<5– Max pMax pTT in 2<η<5

CASCADE:CASCADE:

lower multiplicitylower multiplicity PYTHIA:PYTHIA:

more back-to-backmore back-to-back

Event distributions


Track distributions:– ηη– ppTT

No dramatic difference in 2<η<5 … still Pythia tracks less forward

Track distributions


Jets finding– In the laboratory frameIn the laboratory frame– Using the KTCLUS algorithm in inclusive modeUsing the KTCLUS algorithm in inclusive mode

Jets selection– distributions shown only for jets in the LHCb acceptancedistributions shown only for jets in the LHCb acceptance– EET,jetsT,jets > 10 GeV … and also > 10 GeV … and also looseloose sample with E sample with ET,jetsT,jets > 1 GeV > 1 GeV

Jets

NB: following distributions correspond to ~ 1ms of LHCb running…


Loose selection

EET,jetsT,jets > 1 GeV > 1 GeV

CASCADE:CASCADE:

lower jet multiplicity …(?)lower jet multiplicity …(?)

-> ET and η dists.

are similar

Jet distributions ET,jets > 1 GeV


Harder selection

EET,jetsT,jets > 10 GeV > 10 GeV

Jet distributions ET,jets > 10 GeV

CASCADE:CASCADE:

many events with no jetsmany events with no jets

-> ET and η dists.

are similar


Forward jets selection

EE22T,jet1T,jet1 Q Q22

to suppress DGLAPto suppress DGLAP

xxjet1jet1 >> x >> xBjorkenBjorken

to enhance BFKLto enhance BFKL

non-negligible non-negligible phase space for phase space for low x phenomenalow x phenomena

(e.g. cuts in HERA forward jet (e.g. cuts in HERA forward jet analyses)analyses)

Highest ET jet – select phase space?


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 …


Backup slide

Why do we care about multiplicity?

Plots from:• Massi F.-L. Apr. ’03• Jeroen v.T. Thesis• Marco Musy: May ‘03

Multiplicity affects:– Trigger– Tracking– Tagging

Trigger: CPU time

Track multiplicity

Nlong< 20 εeff = 5.4 ±0.3

Nlong> 20 εeff = 3.9 ±0.3

Tagging: εeff

Tracking: eff and ghost rate

Relative multiplicity


LHCb:LHCb: can we use the reconstructed b-jet for inclusive triggering (at high level trigger)?can we use the reconstructed b-jet for inclusive triggering (at high level trigger)?

b-jet (charge) useful for flavour tagging?b-jet (charge) useful for flavour tagging?

what kind of jet algorithms are best to use in (very) forward region?what kind of jet algorithms are best to use in (very) forward region?

- is KTCLUS good (enough) ? Alternatives?- is KTCLUS good (enough) ? Alternatives?

=> where can HERA help?=> where can HERA help? LHCb can simulate and make studiesLHCb can simulate and make studies

HERA can also analyse data and make comparisonsHERA can also analyse data and make comparisons

HERA measurements: forward jet production, particles/energy flow in forward region …HERA measurements: forward jet production, particles/energy flow in forward region …

… … ongoing analyses / plans in ZEUS/H1?ongoing analyses / plans in ZEUS/H1?

-> areas where discussions / feedback / between both groups can be profitable …-> areas where discussions / feedback / between both groups can be profitable …

Any interests from HERA on addressing these points?Any interests from HERA on addressing these points?

Reminder (slide from March 2004…)

* lhcb experiment, the “must know” * why cascade might be useful for lhcb?

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