some recent qcd results at the tevatron
DESCRIPTION
Some recent QCD results at the Tevatron. N. B. Skachkov (JINR, Dubna). Outline. Jet Production a) Inclusive jets b) Dijets c) 3-jets Z/W + Jet(s) Photon Production (+ Jet) D ouble P arton I nteractions DPI as bkgd for Higgs. Kinematical regions in x - Q**2 plane. - PowerPoint PPT PresentationTRANSCRIPT
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Some recent QCD results at the Tevatron
N. B. Skachkov (JINR, Dubna)
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Outline
• Jet Production• a) Inclusive jets• b) Dijets• c) 3-jets• Z/W + Jet(s) • Photon Production (+ Jet)• Double Parton Interactions• DPI as bkgd for Higgs
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Kinematical regions in x - Q**2 plane
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Unique sensitivity to new physics: - new particles decaying to jets, - quark compositeness, - extra dimensions, - …(?)…
theory @NLO is reliable (±10%) Precision phenomenology - sensitivity to PDFs high-x gluon
- sensitive to
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Jets and Parent Partons
xT
largest high pT cross sectionat a hadron collider
highest energy reach
In the absence of new physics:
jet
jet
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Inclusive jets , CDF
* 5 IyI intervals * L = 1.13 fb-1 * CTEQ6.1 & MRST2004
comparison with 2 other jet clustering
algorithms: k-t and SISConereasonnable
Phys. Rev. D 78, 052006 (2008) Phys. Rev. D 78, 052006 (2008)
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Inclusive jets , D0
pT (GeV)
*6 IyI intervals with 110 data points* L = 0.7 fb-1*FASTNLO(based on NLOJET++) and the PDFs from the CTEQ6.5M are compared to the data*correction for nonpertubative effects (underling events and hadronization) was done by PYTHIA *8 orders of magnitude from PT=50 to PT>600GeV
Phys. Rev. Lett. 101, 062001 (2008)
data/theory (CTEQ6.5M) - - - - CTEQ6.5 uncertainty . . . . . MRST2004 predictions * factoriz. and renormaliz. scales uncertanties ~10% --15% * the full systematic uncertainties are similare in size to PDF uncert.
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Strong Coupling Constantinclusive jet cross section is sensitive to
jet
jet
previous CDF result from Run I: PRL88, 042001 (2002)
previous CDF result from Run I: PRL88, 042001 (2002)
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Strong coupling constant from D0 inclusive jets data
“World average”: 0.1184 +/- 0.0007
From combined HERA jet data:
22 (out of 110) inclusive jet Xsectiondata points at 50 < P_T < 145 GeV
NLO + 2-loop threshold corrections
MSTW2008NNLO PDFs
0.1189 +/- 0.0032
D0:
Phys. Rev. D 80 111107(R) (2009) Phys. Rev. D 80 111107(R) (2009)
The only Run II result on alfa_s
The only Run II result on alfa_s
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Strong coupling constant from D0 inclusive jets data
Highest PT measurement of strong coupling constant to date
Review of Particle Physics 2008 Review of Particle Physics 2008
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central dijet production |y|<1 test pQCD predictions
• sensitive to new particles • decaying into dijets: • excited quarks, Z’, W’, • Randall-Sundrum gravitons, • color-octet, techni-rho,
axigluons, colorons
data with Mjj > 1.2 TeV! all described by NLO pQCD no indications for resonances set limits on new particles
Phys. Rev. D 79, 112002 (2009) Phys. Rev. D 79, 112002 (2009)
Dijet Mass Spectrum , CDF
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Compare data to predicted signal shapes,
e.g. exited quarks
Dijet Mass Spectrum , CDF
Phys. Rev. D 79, 112002 (2009) Phys. Rev. D 79, 112002 (2009)
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Dijet Mass Spectrum , CDF Phys. Rev. D 79, 112002 Phys. Rev. D 79, 112002
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Dijet mass spectrum , CDFis sensitive to new particles decaying into dijets: exited quarks, Z’, W’,
Randail-Sundrum gravitons, coler-octet, techni-rho,axigluons, colorons
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* L = 0.7 fb-1
* 6 |y| - regions * 0 < |y| < 2.4
Extend QCD test to forward region
NLOpQCD predictions(fastNLO, based on NLOJET+
+ ) using MSTW2008NLO
Dijet mass spectrum , D0
Data with Mjj described by NLO pQCD + non-Perturbative correctionsNo indications for resonanses
arXiv: 1002 .4594v1 [ hep-ex] 24Feb 2010arXiv: 1002 .4594v1 [ hep-ex] 24Feb 2010
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Ratio of data over theoretical prediction(NLO pQCD + non-Perturbative)
usung MSTW2008NLO PDFs
. . . . . . . CTEQ6.6 prediction too high
- - - - - PDF MSTW2008NLO uncertanty
- - - - - scale uncertainty
Data are well described by NLO QCDpredictions using MSTW2008NLO inall six rapidity regions.
Dijet mass spectrum , D0 Data to Theory Ratio Data to Theory Ratio
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variable:
at LO, related to CM scattering angle
• flat for Rutherford scattering• slightly shaped in QCD • new physics, like
- quark compositeness - extra spatial dimensions enhancements at low
18small y large y
Phys. Rev. Lett. 103,191803 (2009) Phys. Rev. Lett. 103,191803 (2009)
Dijet angular distribution , D0
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Measurement for dijet massesfrom 0.25 TeV to >1.1 TeV
normalized distribution
reduced experimental and theoretical uncertainties
Dijet angular distribution , D0
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Measurement for dijet massesfrom 0.25 TeV to >1.1 TeV
normalized distribution
reduced experimental and theoretical uncertainties
First time: Rutherford experiment above 1TeV
Submitt
ed to Phys. Rev. Lett.
Dijet angular distribution , D0
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Dijet angular distribution , D0
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.
Photons
test theoryfixed order: NLO
resummationPDFs
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(all quark/anti-quarksubprocesses)
direct photons emerge unaltered from the hard subprocess direct probe of the hard scattering dynamics
sensitivity to PDFs (gluon!) …but only if theory works
also fragmentation contributions:
suppress by isolation criterion observable: isolated photons
Direct Photon Production
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pT (GeV)
• CDF and D0 measurements: 20< pT < 400GeV agreement
• data/theory: difference in low pT shape
• experimental and theory uncertainties > PDF uncertainty no PDF sensitivity yet
• first: need to understand discrepancies in shape
pT (GeV)
Phys. Lett. B, 639, 151 (2006), D0 Phys. Lett. B, 639, 151 (2006), D0
Inclusive Isolated Photons
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In D0 2006 publication on the prompt photons production the deviations from the corresponding pQCD predictions, previously founded in RunI data, are observed in a more wide kinematical region and with higher statistics. This result was confirmed by CDF measurement in 2009 (DIS09, Madrid).
D0 (2006) ratio data / QCD_NLO CDF (2009) ratio data / QCD_NLO
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Isolated Photon + Jet
pT (GeV)
quark-gluon subprocess fraction indifferent rapidity regions versus pT
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pT (GeV)
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L = 1 fbL = 1 fb-1-1
investigate source for disagreementin data/theory incl. photon pT shape:
measure more differential:• tag photon and jet
reconstruct full event kinematics
• measure in 4 regions of y/yjet
- photon: central - jet: central / forward - same side / opposite side
• different PDF sensitivity in different y/yjet regions
Phys. Rev. Lett. 102, 192002 (2009) Phys. Rev. Lett. 102, 192002 (2009)
look at ratios for quantitative statement …
Inclusive Isolated Photon + Jet
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Difference between data and QCD predictions for cross sections (left) and their ratios (right) in 4 different rapidity (y) regions
Inclusive Isolated Photon + Jet
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Phys. Rev. Lett. 102, 192002 (2009) Phys. Rev. Lett. 102, 192002 (2009)
Photon + (b/c) jet + XPhoton pT : 30-150 GeV
0.01<x<0.3 b, c, gluon PDF test gluon splitting contribution
tag photon and jet Rapidities:
triple differential
Isolated Photon + HF Jet
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photon+b: agreement over full pT range: 30-150 GeV no PDF sensitivity
photon+c: - agree only at pT<50GeV - disagreement increases with photon pT
- using PDF including intrinsic charm (IC) improves the theory pT dependence
pT (GeV)
L = 1 fbL = 1 fb-1-1
Isolated Photon + HF Jet
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. Double Parton Scattering
Signal DP background
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Phys. Rev. D, 81, 052012 (2010) Phys. Rev. D, 81, 052012 (2010)
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Double parton cross sections, D0
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Calculated for the pair that gives the minimum value of S:
Double parton events selection, D0
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Double parton cross sections, D0
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Double parton cross sections, D0
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. Double Parton Scattering
Signal DP background
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Backup
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