godparents: w. wester, j. dittman, g. feild. the b cross section introduction nlo calculation...
TRANSCRIPT
Godparents: W. Wester, J. Dittman, G. Feild
The B cross sectionThe B cross section
IntroductionNLO calculationPrevious measurements
Final RUN 1 CDF measurementNew theoretical developmentsLow energy SUSY and the b
cross sectionConclusion
D. Bortoletto
Todd Keaffaber’s Thesis
Heavy quark NLOHeavy quark NLOCalculations of heavy quark production in hadronic
collisions follow the approach developed by Collins, Soper and Sterman:
Explicit calculation were done at NLO (O(s3)) by Nason,
Dawson and Ellis (NDE), Mangano Nason and Ridolfi (MNR)
Nason et al., Nucl., Phys. B327 (1989) 49, B335 (1990) 260W. Beenakker et al., Nucl. Phys. B351 (1991) 507M. Mangano et al., Nucl. Phys B373 (1992) 295
mOm;QQijdff
)m;QQHH(
QCD
ijH/jH/i
21
21
Theoretical predictions are usually presented varying R and F in the range
The largest cross section (2) corresponds to large F and small
R
The uncertainty due to the PDF is small due to the tighter constraints set by DIS and HERA data (12-20%).
The mass of the b quark is varied between
In this range the cross section can change by about 10%
Heavy quark NLOHeavy quark NLO
2b
2T000
0 mp22
GeV575.4m5.4 b
Heavy quark NLOHeavy quark NLO
The largest uncertainty in the cross section determination is the scale uncertainty which is sensitive to higher order corrections.
630GeV1800GeV0/
10GeV 20GeV
40GeV 60GeV
Hadron collider experiments historically studied the b-quark cross section
More recently the differential cross section has also been studied.
Measurements have been performed using different data sets with electrons or muons and/or jets in the final state:
Inclusive decays e/Muon+jets J/
Experimental MeasurementsExperimental Measurements
T
2
pp
T
yy
minT dydp
ddpdy)p(minTTmax
uB+
K+
u u
B cross section measurementsB cross section measurements
The single b inclusive cross section has been measured at several energies: 540 GeV by UA1 630 GeV by UA1,
CDF and D0 1.8 TeV by CDF
and D0
630 GeV630 GeV
Early CDF measurementsEarly CDF measurements
1.8 TeV
B cross section measurementsB cross section measurements
Excellent agreement between experiments
Significant excess in the data
1800 GeV
B cross section measurementsB cross section measurements
The experimental measurements find a cross section higher than the theoretical prediction by a factor 2-3
630 GeV 1800 GeV
Ratio of the cross section
Reduced theoretical and experimental uncertainties
B cross section measurementsB cross section measurements
)GeV1800(
)GeV630(b
b
D0-b Jet measurementD0-b Jet measurementD0: b tagging jets using muons.Require ET(Jet)>25GeV, and PT()>6GeV
Agreement with theory upper band for pT>55 GeV
Summary of the measurementsSummary of the measurements
B cross sectionB cross section In Run 1A first measurement of the B cross section by
CDF. (PRL 75, 1451 (1995))
K/JB0*
K/JB0
GeV9)B(p6 T
GeV12)B(p9 T
GeV15)B(pT
GeV15)B(p12 T
B cross sectionB cross sectionMeasurement confirms discrepancy between theory
and experiments
CDF published
2.02.09.1Theory
Data
L=984 pb-1
Use only the decay
Require muons in SVX to have more precise ct information
Require CMU muons
Run 1 MeasurementRun 1 Measurement
L=19.30.7 pb-1
Use the decays
Muons can be both in SVX and CTC
Require CMU muons
RUN 1A RUN 1
K/JB
0*0* K/JB
K/JB
/J/J
Track quality cuts 4 hits in at least 2 axial superlayers 2 hits in at least 2 stereo superlayersRexit(Kaon)>110 cm
Muons:All muons have CMU stubMuon matching
3 hits in the SVXPrimary vertex
Data SelectionData Selection
0.12)z(0.9)x( 22
cm60z
J/J/ reconstruction reconstruction
c/GeV8.2)(p 2T
c/GeV8.2)(p 2T
c/GeV8.1)(p 1T
c/GeV8.1)(p 1T
c/GeV0.2)and(p 21T
Run 1A:
and
Run 1B
and
or
J/ reconstruction
+ - are vertex constrained
3.3MM /J
B reconstruction SVX information used if available for the kaon + - K are vertex constrained + - mass constraint to J/ mass
Data SelectionData Selection
m100
1
)p(
pX)B(ct
BBT
BT/J
c/GeV0.6)B(pT
c/GeV25.1)K(pT
Event yieldEvent yield Event yield
for Run 1 analysis
The B meson cross section is determined using
whereMi and i mass and width from the kinematic fit
s=scale factor b=slope of the backgroundw=fit mass range
Fitting methodFitting method
backtotal
sigtotalsig
total
sig fN
)NN(f
N
NL
2
i
i
s
MM
2
1
i
sig es2
1f
w
1
2
wMbf iback
Event yield in PEvent yield in PTT bins bins
Event yield for Run 1 analysis divided in 4 pT bins
02T
2b0
0
P2
b
2pm2
002.0006.0c/GeV25.075.4m
The product of the acceptance and trigger efficiency was calculated with BGEN, QQ, QFL, DIMUTG using the MRST structure functions
The QCD-NLO MC was run with:
Results:
AcceptanceAcceptance
Efficiencies that are not included in the MC acceptance were calculated using data
Efficiencies that are not equal in Run 1A and Run 1B are averaged and weighted by the luminosity
EfficiencyEfficiency
The B meson cross section is determined using
Where: N is the number of B mesons from a unbinned likelihood
fit pT is the width of the pT bin
L is the corrected integrated luminosityA is the MC acceptance which included the trigger
efficiency. is the reconstruction efficiencyB=BR(B+ J/K+) BR(J/ +-)=(5.880.60) 10-5
Cross SectionCross Section
BALp2
N
dp
)B(d
TT
The measured J/ cross section fell as a function of the instantaneous luminosity
We correct for this effect:
Luminosity CorrectionLuminosity Correction
04.088.0dtL
LdtR
dt)L(
)0(LdtL
L
Feild, Lewis CDF note 4769
Systematic uncertaintiesSystematic uncertaintiesFully correlated
systematic uncertainties which do not depend on pT
Uncorrelated systematic uncertainties which depend on PT
The measured cross section is:
To compare with the theory we plot the results at
Differential Cross SectionDifferential Cross Section
T
p
T
theory
TpT
theory
dpdp
d
p
1
dp
d T
T
Differential Cross SectionDifferential Cross SectionThe cross section is higher
than the theoretical NLO
%72.L.C
4.02.09.2Theory
Data
Total Cross SectionTotal Cross Section
PT>15GeV/c
4
1i i
i
T
BRAL2
N
)1,c/GeV6p(
nb)syst(26)syst(5)stat(28207
)c/GeV15p(
fcuc
T
b)syst(4.0)syststat(4.06.3
)1y,c/GeV6p(
fcuc
TB
QCD NLO central value 1.2 b
Replace the last bin of the differential cross section
CDF measures:
Shape are well described by perturbative QCD Large discrepancy on the cross section measurement
Presence of higher order termsFragmentation effects Intrinsic kT of partonsNew physics
Fixed order calculation have terms
Which could be quite large for
Heavy quark NLOHeavy quark NLO
n
2s
n
2
2
s Q
sln)Q(and
m
Qln)Q(
1Q
sand1
m
Q22
2
New Theoretical developmentsNew Theoretical developments
Variable Flavor Number Scheme (VFN) (F.I Olness, R.J. Scalise and Wu-Ki Tung hep-ph/9712494)
Hadronization of heavy quarksHarder bB fragmentation (Colangelo-Nason)
30% (40%) higher B cross section in the central (forward) region
z)z1()z(f
New Theoretical developmentsNew Theoretical developments
Studies of the kT effect
New Theoretical developmentsNew Theoretical developments
Correlated b production seems to disfavor large kT effects.
….
New Physics HypothesisNew Physics Hypothesis
Supersymmetry could make a substantial contribution to the observed b cross section
Berger, Tait, Wagner et al. have a model with intermediate mass gluinos that decay into b and sbottom
The contribution is large if
GeV52mGeV1510mb~g~
New Physics HypothesisNew Physics Hypothesis
The new contribution peaks at
b quarks have and similar to QCD production
Authors claim that this scenario is not ruled out by current limits.
GeV15mp g~T
ConclusionConclusionFinal run 1 measurement of the B cross
section confirms discrepancy with QCD NLO predictions
CDF and D0 measurements on different data sets give consistent measurements of the b cross section
NLO calculations model the shape but under-estimate b production
Puzzle in b production is now emerging also at LEP and at HERA
bbeeee
B physics program at hadronic machines continues to be complementary to B-factoriesAll B species are producedHigh production cross section
Higher luminosity will bring higher statistic but also systematic effects that will need to be investigated.
Higher statistic will allow:To probe higher ET region
Investigate the possibility to study the b-fragmentation at the Tevatron
Correlation studies
Prospects for Run IIProspects for Run II