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Outline:
• HERA, H1 and ZEUS
• open beauty and charm photoproduction
• open charm spectroscopy
• charmonium production
• summary and conclusions
A. Bertolin
Heavy flavour production and spectroscopy at HERA
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HERA, H1 and ZEUS: a brief introduction
• e p collider at high CMS energy (like having an about 50 TeV e beam on fixed target)
• two large multipurpose experiments: H1 and ZEUS
• running ended mid 2007 after about 2500 days of activity and 470 pb-1 of integrated luminosity per experiment
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Open beauty and charm production at HERA
main process:
• direct
• boson gluon fusion
• 0.8 < xobs < 1
other processes:
• resolved processes
• 0 < xobs < 0.8
• photoproduction (PHP) regime scattered electron is undetected Q2 < 1 GeV2
key points:
• mQ (or ETjet …) >> QCD
region of applicability of pQCD
• collinear vs. kT parton dynamics
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fully inclusive beauty tag with 2 jet events
Open beauty and charm PHP at HERA
• exploits the large lifetime of b/c hadrons with respect to light hadrons
• silicon microvertex detector to have a good measurement of
• can measure beauty AND charm at the same time
Significance =
5
fully inclusive beauty tag with 2 jet events
• xobs peaks at 1 BGF
is dominant
• what is called resolved-in the Pythia collinear MC is also reproduced in the Cascade kT MC without the need of a resolved-component …
• NLO QCD had is slightly underestimating the data for beauty but NLO QCD is as good for charm as for beauty … scale set by the jets pt
Open beauty and charm PHP at HERA
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likelihood function based on 5 discriminant variables:
• dE/dx
• EEMC / ECAL
• ECAL / ptrack
• electron pt w.r.t. the associated jet axis
• azimuthal angle difference between the electron and the missing transverse momentum vector (// for signal)
beauty tag with two jets and one associated semileptonic electron
bkg enriched c enrichedb enriched
Open beauty and charm PHP at HERA
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beauty tag with two jets and one associated semileptonic electron
• NLO QCD is as good for charm as for beauty
• PYTHIA gives a fair description of the shapes but the normalization is significantly wrong … missing NLO corrections …
Open beauty and charm PHP at HERA
beauty
charm
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beauty tag with D* + (no jets)
Open beauty PHP at HERA
unlike-sign D*
unlike-sign D*
like-sign D*
beauty charm
beauty
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• many very different experimental methods in fair agreement
• can measure down to <pTb> ~ 5 GeV (~ mb) and up to ~ 25 GeV
• data are already as precise as theory … need more accurate theoretical predictions
• most recent points are right on top of the NLO predictions …
Open beauty PHP at HERA
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Open charm production at HERA
charm spectroscopy at HERA:
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Open charm production at HERA
basic building blocks:
D* K s D* K s
D K
D0 K
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Open charm production at HERA: D* cross sections
• Pythia collinear massive fails
• Pythia collinear mass less fails
(except for )
• Cascade kT fails
(except pt shape)
• NLO is quite reasonable except for
lots of beautiful data but theory is poor … may be NLO is on the right track …
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Open charm production at HERA
excited charm mesons:
D01
/ D*0
2 D*
D*02 D
in this particular decay mode difficult to separate D0
1 and D*02
due to spin parity conservation D0
1 can NOT decay in this mode
excited charm strange mesons:
D
s1 D*Ks
D
s1 D0 K
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Open charm production at HERA
tabular summary:
• hopefully errors will be reduced extending the analysis to HERA II data and using microvertex detector data (available also for ZEUS in HERA II)
• the HERA rates are in reasonable agreement with those measured in others (e+ e-) experiments
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Charmonium production at HERA (1S) andS
direct CS model
0.2 < z < 0.9p-rest frame: z =
EE()
direct CO model
• this particular diagram: 0.2 < z < 0.9
• more “typical” ones:z > 0.9
resolved CS model
z < 0.2
open issues:
• size of the CO contributions
• collinear vs. kt parton dynamics (as in the CASCADE MC)
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• < 1/10 of the total available luminosity
• (2S)toScross sectionratio consistent with being flat
• (2S)SX contribution NOT subtracted from the data … not easy experimentally !
• 15 % increase of the J/cross section
other contributions:
• diffractive charmonium: suppressed restricting the z – ptJ phase space
• charmonium from B mesons decay: much smaller than at TEVATRON
• contribution: tiny at HERA
Charmonium production at HERA (1S) andS
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J/cross section measurements
PHP regime:
• NLO CS calculation with LARGE scale uncertainties describes the shapes
• LO CS + kt factorization (CASCADE) describes the data well
• LO CS + collinear factorization (EPJPSI) fine in shape
DIS regime (3.6 < Q2 < 100 GeV2):
• no NLO prediction
• LO CS + kt factorization (CASCADE) describes the data well
• LO CS + collinear factorization (EPJPSI) fine in shape
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J/cross section measurements
PHP regime DIS regime
ddp2T for different z rages d2dp2
T dz
• should be a stringent test of the matrix elements involved … would be nice to have NLO predictions as well …
• LO CS + kt factorization (CASCADE) describes the data well
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J/helicity at HERA
• helicity: study of the angular distributions in the J/rest frame learn about production channels
• contrary to TEVATRON at HERA mostly “prompt” J/… cleaner environment
• can measure 2 out of 3 helicity parameters
BKV collinear factorization
Baranov CS LO CS kt factorization
• large differences in the predictions (sign is different …)
• none of the predictions is able to describe simultaneously all measurements …
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Conclusions
• several beauty inclusive measurements have been performed and will be refined in the immediate future … almost fully reconstructed final states (like D*+ ) have also been measured
• measurements are not easy due to the small beauty cross section at HERA
• remarkably enough all measurements are giving a rather consistent picture on the experimental side
• in general beauty production is reasonably well described by NLO even at small pTb
• charm and charmonium states are produced copiously at HERA
• inclusive as well as precise exclusive final state measurements are available … can also perform charm spectroscopy at HERA
• in the presence of a reasonably large scale (ETjet >> mC) NLO QCD is as good for open
charm as for open beauty
• charmonium production at HERA is well described by the CASCADE MC with kT
factorization … but polarization is not well described … looking forward to better theoretical predictions …
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• Alessandro Bertolin (Padova)"Heavy flavour production and spectroscopy at HERA"• Lorenzo Bellagamba (Bologna)"Search for new physics at HERA"• Jan Figiel (Inst. of Nucl. Physics, Krakow)"Measurements of diffraction at HERA“• Hans-Christian Schultz-Coulon, Heidelberg University"Structure Function Measurements at HERA"• Guenter Grindhammer, MPI Munich"Jet Production and alpha_s Measurements at HERA"
Heavy flavour production and spectroscopy at HERA