bb cross section: blessing
Sofia VallecorsaUniversity of Geneva
CDF note 8589
Outline
• Jet Corrections• Tagging efficiency• bb-fraction• Scale factor• Unfolding factors• Systematics• bb cross section
« SVT » JET• JetClu cone 0.4 SecVtx TIGHT tagged jet
• corrected ET>30 GeV, |η|<1.2• Matched to L3 jet with ET>20 GeV (δR<0.4)• Matched to L2 cluster ET>15 GeV, |η|<1.5 (δR<0.4)• Matched to SVT track, |d0|>120 µm,
pT>2GeV/c, |η|<1.2 (δR<0.4)• Matched to Si track |d0|>120 µm (δφ, δcurv)
On JET20: only 0.1% events TWO « SVT » jets have HIGH_PT_BJET bit off
Negligible effect compared to other systematics
bb cross section
!
d"
dEtd#=
N2SVT
$ f2SVT
2b
%# $ %ET$L $ &
2SVT $ SFjet1 $ SFjet2
• N2SVT: Events with two « SVT -tag » jets:• Leading jet: ET
corr>35 |η|<1.2• Second jet: ET
corr>32 |η|<1.2 (changed from pre-blessing!)• f2b
2SVT: bb-jets fraction− Use Secondary vertex masses− TFractionFitter standard routine− Templates for Σjet Mjet (Mjet : SecVtx Mass)
• ε2svt: Efficiency for 2 SVT-jets− Measured from PYTHIA bb
• SFjet1, SFjet2: Official scale factor, (run a check first):SF = 1.029 ± 0.009 (stat) ± 0.034 (syst)
Standard vertex quality cuts
Jet Energy CorrectionsNeed additional correction for b jets:
• Calculate average Et correction (relative to L5 generic corrections):• Match CAL jets to HAD jets (ΔR<0.4)• Fit correlation Et(CAL) vs Et(HAD)• Check fit consistency
R= (Et(HAD) - Et(CAL)corr) / Et(HAD)
• Calculate unfolding factor to correct Et smearing effect
Fit - SVT tagged jets
!
R =Et
HAD" Et
CORR
EtHAD
Correction is of the order of 5%:Cut on the SVT-tag jet L5 ET >30is raised to take it into account:
(L5+ add.c.) ET>35 GeV, (L5+ add.c.) ET>32 GeV (second jet)
Taggingefficiency
Efficiency for 2SVT-tag jets in event:• Calculate directly « per event »
efficiency• Systematics: b-quark content ofthe jet
bb fraction• Two SVT tagged jets• Sum-up the SecVtx masses of the two jets: one entry per event• Mass template:
• bb template• Bkgd template (bc, cc, cl, ll, bl ..)
• Fit fraction using TFractionFitter in different di-jet average Et bins
0.88 ± 0.04 %ET> 320.75 ± 0.09 %ET> 1000.84 ± 0.06 %(80,100)0.78 ± 0.05 %(60,80)0.86 ± 0.04 %(50,60)0.88 ± 0.03 %(40,50)0.87 ± 0.04 %(32,40)
B fractionET bin (GeV)
bb fraction
Systematics:• Background composition (light vs charm)• Track reconstruction ineff.
UnfoldingUse dijet PYTHIA bb-HEPG filtered sample( pt>10, pt >18, pt>40, pt>60, pt>90, pt>120 GeV) - Apply L5 jet energy corrections + additional corr. - Build JetClu calorimeter/hadronic jets - Identify each as a b-jet (match to a B-hadron) - Only central jet (|η|<1.2) Et>35 GeV,Et>32 GeVat the pre-blessing: Et>30, Et>30 GeV
Unfolding factors:
Invariant mass Δφ
Leading jet Et
Systematics
• Jet Corrections:– Standard systematics
• Tagging:– Efficiency: quark multiplicity in the jet– Fraction:
– Quark multiplicity in the jet– Background template composition– Track reconstruction efficiency– b-jets correlation in templates
• Unfolding:– Et dependence
Total Jet Corr. systematics• Use Jet Energygroup standard routine• Add systematics from specific corrections
(-1 σ) (+1 σ)ET bin (GeV)
14%17%(47,54)
20%17%(180,230)14%14%(140,180)7%18%(110,140)15%10%(99,110)18%18%(88,99)10%11%(78,88)13%18%(69,78)11%13%(61,69)13%15%(54,61)
15%20%(41,47)
17%19%(35,41)
Total Jet Corr. systematics (2)Invariant Mass & Δφ
Mass Δφ
Unfolding
• Compare Et spectrum indata and MC.
• Ratio Data/MC afterunfolding data crosssection
• Fit ratio to third orderpolinomial
• Reweight MC• Calculate new unfolding• Take the difference as a
syst. err.
Unfolding
Total systematics
Add all uncertaintiesin quadrature6% from lumi is not
included
ET bin (GeV)
-23%23%(47,54)
-21%24%(180,23)-19%23%(140,180)-21%25%(110,140)-16%19%(99,110)-21%24%(88,99)-18%20%(78,88)-19%24%(69,78)-19%21%(61,69)-22%23%(54,61)
-24%26%(41,47)
-23%25%(35,41)
NLO predictionUse MC@NLO + Herwig v6.510 + Jimmy v4.3
• bb events with:• CTEQ6m PDFs, µR = µF= sqrt(p2 +m2)• Pt (bquark) > 10 GeV/c (before pt >22 GeV/c)• |η|<1.75
• Full simulation 6.1.4mc (redecay using EvtGen)
• Stntuple dev243• Hadron level jet cross sections
UnfoldedCross section - Leading jet ET
UnfoldedCross section - Invariant Mass
UnfoldedCross section - Δφ
Summary
• Questions and remarks:• Changed Et cut• Unfolding systematics• MC@NLO generation cut• Total cross section
2259 ± 44 (stat)MC@NLO
2201 ± 29 (stat)Herwig
2140 ± 22 (stat)Pythia2360 ± 70 (stat) ± 133 (syst)Data
σ(bb) [pb]|η1,2|<1.2,ET,1>35 GeV, ET,2>32 GeV
CDF Run II Preliminary
More..
Cross section- linear scale
Reweighted MC samples
• Scale each ptHat bin forrelative luminosity
• Normalize to highest ptsample luminosity
3.97(nb)
20.5 (nb)
0.178
1.33
49.8
570
σ (µb)
Pt > 120
Pt > 90
Pt > 60
Pt > 40
Pt > 18
Pt > 10
PYTHIA bb
!
ˆ p t
HAD jet Et
CAL jet Et
Tagging efficiencyFound a correlation between SVT
tagged jetsSelect events with:
>2 jets ET>30 GeV, |η|<1.2>2 good SVT tracks
Order jets (ET,φ,η.. etc..)
Count:1. First jet is SVT-tagged -> Look at the second jet (RED)2. First jet is NOT SVT-tagged -> Look at the second jet (BLACK)
-->DIFFERENCE!NOT the same problem for« simple tag »
SVT tag
simple tag
Tagging efficiencyMain difference: matching to the track• Select « good » tracks (|d0|>120µm,pt>2 GeV/c)• Track-Track and Jet-Track show the SVT tracks
are « grouped »
ΔR(jet-track)ΔR(track-track)
bb fraction - fit32<ET<40 GeV 40<ET<50 GeV 50<ET<60 GeV
60<ET<80 GeV 80<ET<100 GeV ET>100 GeV
Scale Factor
• Use muon jets ( jet Et - up to 100-120 GeV)• MC: btop7a, btop8a Herwig dijet + HEPG filter e>8 GeV, µ pt> 9 GeV
• Run TrigSim. with correct beamline• good run list - but exclude some run (beamline)
• Data: inclusive µ sample (bmcl0d,bmcl0h)• goodrun list CMU+CMP+Si+SVT
• Measure efficiency for « SVT - TAG » jets (JetClu 0.4 - tight SecVtx - SVT track (d0>120 µm)
Scale factor• Select « good muon »:
• Pt > 9 GeV/c• CMU stub |dx|<3cm, CMP |dx|<5cm• Track |z0|<60cm, |z0 -Zvtx|<5cm• Iso(cone 0.4) > 0.1• Require track to hit all SVX layers
• Match good muon to jet (taggable, Et>20, |η|<1.2)• Correct jet Et, and P
• Select only highest Pt muon• Search for away jet (Et>20, |η|<2, |Δφ|>2rad, mass>1.5)
!
Ecorr = EL5
Eraw "2gev
Eraw
+ pt,µ
!
r P corr =
r P +
r p µ 1"
2gev
pµ
#
$ % %
&
' ( (
Scale factor: single tag
!
" =Naway
e
Naway
#fafter
fbefore
• Reconstruct muon pt relative to corrected jet axis• Fit b fraction in muon jet before and after tagging• Two componets FIT: b jets and
• c templates from µ sample (btop7a, btop8a) (or light jet templates from dijet pythia (jqcd1f, jqcd2f))
Scale factor
Use official value:• 1.029 ± 0.009 ± 0.034 (tight SecVtx + SVT track)• (1.066 ± 0.045) - (0.00050 ± 0.00107)* ET
MC:N (µ+,away+) = 1795N (away+) = 7952
ε = 0.225 +/- 0 .007
DATA:N (µ+,away+) = 1191N (away+) = 7485
ε = 0.22 +/- 0 .01
SF = 0.98 +/- 0.05
bb fraction - templatesTo have enough statistics in the templatesCombine couple of jets coming from different events.
CHECK: 2 jets in different events vs 2 jets in the same event32<ET<40 GeV 40<ET<50 GeV 50<ET<60 GeV
60<ET<80 GeV 80<ET<100 GeV ET>100 GeV
Effect is small+Kolmogorov test
Templates: cc content
0.86 ± 0.04Et>30
0.76 ± 0.09Et>100
0.83 ± 0.0780<Et<100
0.80 ± 0.0760<Et<80
0.86 ± 0.0550<Et<60
0.87 ± 0.0340<Et<50
0.88 ± 0.0432<Et<40
b fractionEt bin (GeV)
0.87 ± 0.04Et>30
0.79 ± 0.09Et>100
0.84 ± 0.0780<Et<100
0.79 ± 0.0760<Et<80
0.87 ± 0.0550<Et<60
0.88 ± 0.0340<Et<50
0.88 ± 0.0432<Et<40
b fractionEt bin (GeV)
Double cc content Half cc content
b multiplicity in the jetEff. is different according to b
content in the jet
In 2SVT-tagged jets eventsselect couples with:• One jet including 2b quarks• Two jets including 2b quarks
< 1.5 %
< 3%
Quark multiplicity:b fraction (mass templates):
0.86 ± 0.04 (0.88) Et>30
0.79 ± 0.09 (0.75) Et>100
0.83 ± 0.07 (0.84)(80,100)
0.78 ± 0.07 (0.78)(60,80)
0.86 ± 0.05 (0.86)(50,60)
0.88 ± 0.03 (0.88)(40,50)
0.87 ± 0.04 (0.87)(32,40)
b fractionET bin(GeV)
Double fraction of bb jets events in mass templates and fit::(same check on jet including >1c quark)
32<ET<40 GeV 40<ET<50 GeV 50<ET<60 GeV
60<ET<80 GeV 80<ET<100 GeV ET>100 GeV
Templatescomposition
• Light jets contribution tomass templates
For light jet to c jetproportion rely on Pythia
-> change light jet fraction
2%(180,230)
2%(140,180
2%(110,140)
2%(99,110)
1%(88,99)
1%(78,88)
0.5%(69,78)
0.5%(61,69)
0.7%(54,61)
0.5%(47,54)
0.5%(41,47)
0.5%(35,41)
Syst.err.ET bin (GeV)
Other systematicsfor b fraction• Track reconstruction
efficiency (CDF 6894)-> 3% shift in mass template
7%(180,230)
7%(140,180
8%(110,140)
8%(99,110)
8%(88,99)
8%(78,88)
7%(69,78)
6%(61,69)
6%(54,61)
5%(47,54)
5%(41,47)
5%(35,41)
Syst.err.ET bin (GeV)