1 Outline: HERA, H1 and ZEUS open beauty and charm photoproduction open charm spectroscopy charmonium production summary and conclusions A. Bertolin Heavy.

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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 =

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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