November 30th, 2001 P. Demine (ISN Grenoble) 1

Off-line b-taggingfirst look at the data

Pavel Demine (ISN Grenoble)

November 30th, 2001 P. Demine (ISN Grenoble) 2

b propertiesb properties– efficient mass mb 4.25 GeV/c2

– B hadrons have m < 5 GeV/c2 and 1.56 ps– B decay length c 3mm

– particles coming from B have large pT

– tracks from B decay are displaced

– semi-leptonic decay of B• BR (B) 10%

November 30th, 2001 P. Demine (ISN Grenoble) 3

vtxTagReco

impTagReco

muTagReco

Jets

SecondaryVertices

eTagReco

Tracks

Muons

Electrons

EVENT

vtxTags

impTags

muTags

eTags

likeTagReco likeTags

bId bId data data flowsflows

November 30th, 2001 P. Demine (ISN Grenoble) 4

First Look at the DataFirst Look at the Data

• only “good” runs*:– 5 416 014 evts processed with p10.07.01

• Analysis steps:– Select good JCCA jets (Run II 0.7 cone)

– Select good (block MuoTrfit)

– Select good displaced vertices (block SKSEL)

– Associate selected jets with selected – Associate selected jets with selected vtx– Apply b-tagging cuts over selected objects

* for details: www-d0.fnal.gov/computing/production_runs/p10.07.01.pdf

November 30th, 2001 P. Demine (ISN Grenoble) 5

jet selectionjet selection

• runnum > 131087

(calorimeter software group)• 0.05 < EM fraction < 0.95• CH fraction < 0.4• HotF < 10 (ratio of hottest and next-

to-hottest cell ETs)• n90 > 1 (number of towers

comprizing >90% of jet scalar ET)

• pT > 15 GeV/c

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jet detailsjet details

jet pT, GeV/c

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selectionselection

• Cuts based on muon local tracks (from F. Deliot J/ presentation)– no trigger requirement– at least 2 A wire hits– at least 3 BC wire hits– at least 1 A scint. hit– at least 1 BC scint. hit 2 > 0

November 30th, 2001 P. Demine (ISN Grenoble) 8

detailsdetails

pT, GeV/c

November 30th, 2001 P. Demine (ISN Grenoble) 9

displaced vertex selectiondisplaced vertex selection

• Cuts based on selected secondary Kalman vertices:– vertex constructed from at least 3 tracks

– decay length significance Lxy/Lxy> 2.0

November 30th, 2001 P. Demine (ISN Grenoble) 10

selections in numbersselections in numbers

• Total events processed: 5 416 014• 2 017 340 (~37%) events with at least 2

selected jets• 46 043 (~0.9%) events with at least 1

selected associated with selected jet• 9 439 (~0.17%) events with at least 1

selected vtx associated with selected jet

November 30th, 2001 P. Demine (ISN Grenoble) 11

b-tagging related selectionb-tagging related selection

• at least 2 selected jets - tag:

R(jet axis – ) < 0.5

– 1.0 < PTrel( w.r.t jet axis) < 2.5 GeV/c (recommended by O.Peters)

• vtx tag: R(jet axis – sec vtx) < 0.3

– Lxy/Lxy> 2.0

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tagging variablestagging variables

pTrel, GeV/c Lxy/Lxy

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inv. mass reconstructioninv. mass reconstruction

• For each jet tagged with or vtx:– find a jet in opposite direction ( > 2.5)– at least 1 of the jets with || < 1.1

– Ejet1/Ejet2 < 5.0

M(jet-jet), GeV/c2

November 30th, 2001 P. Demine (ISN Grenoble) 14

ConclusionConclusion

• only b-tagging with is really available• still needs more studies• displaced vertices reconstruction depends

much on CFT tracks• they hopefully will be available in the post-

shutdown data