Charm and bottom quark production at the LHC

Friday 3 Dec 2010, 09:00 → 18:30 Europe/Zurich

TH Theory Conference Room (CERN)

Maurizio Pierini (Conseil Europeen Recherche Nucl. (CERN)), Michelangelo Mangano (CERN)

LHC physics day dedicated to the review of current experimental results on heavy quark and quarkonium production at the LHC, and the discussion of the implications for the theoretical description and of the prospects for future measurements.

The meeting will be broadcast via EVO (detailed info will appear at the time of the meeting in the "Video Services" item on the left menu bar)

For those attending, information on accommodation, access to CERN and laptop registration is available from http://lpcc.web.cern.ch/LPCC/index.php?page=visit

09:00 → 12:20 Open heavy quark production

09:00 ALICE: forward charm production, using leptonic final states

Speaker: Min Jung Kweon (Ruprecht-Karls-Universitaet Heidelberg)

Slides Dec032010_LPCC_MinJungKweon_final.pdf

09:20 ALICE: central charm production, using hadronic decays

Speaker: Andrea Dainese (INFN Padova)

Slides DaineseLPCC.pdf

09:40 ATLAS

Speaker: Leonid Gladilin (Moscow State University)

Slides gladilin_talk.pdf

10:00 CMS

Speaker: Vincenzo Chiochia (Universitat Zurich)

Slides CERN_LPCC_2010_12_03.pdf

10:20 LHCb

Speaker: Phillip Urquijo (Syracuse University)

Slides LPCC_2010.pdf

10:40 Coffee break

11:00 Status of QCD predictions

Speakers: Matteo Cacciari (LPTHE Paris), Matteo Cacciari (LPTHE Jussieu)

Slides hvq.pdf

11:40 Status of QCD predictions, 2

Speaker: Bernd Kniehl

Slides kniehl1.pdf

12:00 Some opportunities and challenges for b-production dynamics studies

Speaker: Michelangelo Mangano (CERN)

Slides mangano.pdf

12:30 → 13:30 Lunch break

13:30 → 18:00 Quarkonium production

13:30 LHCb

Speaker: Wenbin Qian (Lab. de l'Accelerateur Lineaire (IN2P3) (LAL)-Universite de Pari)

Slides OniaLHCb.pdf

13:50 CMS

Speaker: Zoltan Gecse (Purdue University)

Slides CMSquarkonium2010_12_03.pdf

14:10 ATLAS

Speaker: Vato Kartvelishvili (Lancaster University)

Slides vk.cern.workshop.pdf

14:30 ALICE

Speaker: Enrico Scomparin

Slides Psi_ALICE_Enrico2.pdf Psi_ALICE_Enrico2.ppt

14:50 Status of XYZ exotics, and prospects for studies at the LHC

Speaker: Fulvio Piccinini (Unknown)

Slides piccinini.pdf

15:10 Coffee break

15:40 Quarkonium production modeling in CASCADE

Speakers: Nikolay Zotov (Lomonosov Moscow State University-Unknown-Unknown), Sergey Baranov (JINR)

Slides baranov.pdf

15:55 Recent theoretical progress in quarkonium production, I

Speaker: Bernd Kniehl

Slides kniehl2.pdf

16:25 Recent theoretical progress in quarkonium production, 2

Speaker: Fabio Maltoni (Universite' catholique de Louvain (CP3))

Slides maltoni_lpcc.pdf

16:55 Discussion on onium production

Slides prompt_lambda.pdf

PROPOSALS FOR DISCUSSION TOPICS (C.Lourenco)

Regarding the specific physics topic of quarkonium production and polarization, we already had some
very nice discussions among us during the workshop in Palaiseau, just after ICHEP.  And we agreed at
that moment to "keep in contact" and share our questions and answers to ensure that our experiments
will provide high-quality measurements (and hopefully consistent with each other).  A few emails have
been exchanged and some nice discussions took place among some of us in Eilat, during the Hard Probes
2010 conference.  The meeting in Dec. 3rd offers an ideal setting to have more discussions and learn from
each other what the prospects are, which problems we have found, how we solved them, etc.  There are a
few "trivial details" which we can quickly review.  For instance, when we give differential cross sections as
a function of pT, how do we calculate the <pT> in each bin?  Before or after efficiency corrections?  And do
we subtract the contribution from non-J/psi events in the J/psi peak in the calculation?  And do we use the
reconstructed pT or do we apply some method to recover the "generated" pT?  If so, do we use an "ansatz"
method or something else?  Then, there are less trivial details like how we "normalize by the width of the
rapidity bin" to calculate a "double differential" cross section, dsigma/dpTdy, which can more easily be
compared to other experiments or theory.  We cannot simply divide by the bin width, given the limited
acceptance in the bin.  And how do we take into account the polarization of the J/psis from B decays in the
extraction of the "J/psi B fraction"?  Do we all use EvtGen?  I am sure that we can collect a nice list of all
the details that are important to make a solid comparison of the cross sections obtained by each LHC
experiment, and with theory.  If you tell us about your items, we could prepare a list of how those "details"
are dealt with in each experiment's analyses.  We could then go through the list and see if the differences
are important or not.

An even more interesting point we should discuss at the meeting is what we have already learned from the
existing results, of relevance to the other experiments.  For instance, ALICE does not yet have enough data
in the barrel (electrons) to measure a pT distribution of the J/psi and verify that the function used to calculate
acceptances is suitable.  They can use a CDF-inspired function (if the energy dependence is small) or the
function they measure in the forward muon arm (if the rapidity dependence is small).  By looking at the data
in several rapidity bins, CMS and ATLAS can see that the more "mid-rapidity" the events are, the harder is
their pT distribution, and ALICE can benefit from this information.  Also the comparison between LHC data
and CDF data for the J/psi B fraction is quite "illuminating": no strong rapidity dependence has been seen so
far and the increase from 2 to 7 TeV is rather small.  It would be nice to prepare new "compilations", as those
which Hermine did for the workshop in Palaiseau, with the latest results from each experiment, profiting from
increased data samples.  What other quarkonium-related results should we compare among us?

The more difficult questions we are facing in our work are, as far as I know, "how do we take into account the
polarization inputs" and "how do we compare the measurements with theory".  Concerning the polarization
issue, we should review in the meeting what we have learned since ICHEP.  CMS explored four "extreme"
scenarios: full transverse and full longitudinal polarizations in two different frames.  ATLAS stayed in one
frame but added extreme values for the azimuthal anisotropy, a very nice idea.  Then some of us gave the
results in different columns of a table, others presented the polarization "uncertainty" as an error band.  We
should see if we have now better procedures, aimed at combining the results of the different experiments
in a consistent way.

The data-theory comparison is the most difficult problem to solve.  The "best model in the market", NRQCD,
provides direct J/psi production cross sections, versus pT, and includes a certain polarization trend, which
becomes increasingly transverse as pT increases.  The data, so far, corresponds to prompt production,
including feed-down contributions from psi(2S) and chi_c1 and chi_c2, and the corresponding states for the
Upsilon family.  We do not know the NRQCD prediction for the pT dependent feed-down contributions and
we do not know the polarizations of the 2S and 1P states, an important ingredient to calculate their respective
acceptances.  My own talk at the workshop in Palaiseau addressed these problems (feed-down and
polarization unknowns, and how they affect the comparisons between data and theory).  In short, we are in a
situation where we can probably get an excellent agreement between our data and "NRQCD" as long as we
select a suitable set of assumptions regarding feed-down yields and their polarizations (versus pT). 

What can be done to improve this situation?  Restricting the data-theory comparisons to Pythia is not really a
suitable solution.  Nobody believes that the Pythia settings / code are particularly good at describing quarkonia. 
If they are, it would be mostly by chance than because of some enlightening idea of our Pythia friends.  In this
topic we really need more interactions with the theorists making calculations.  By the way, Jean-Philippe might
have news on calculations of the psi(2S), etc, in the CSM.  CASCADE seems to be a good complement to
PYTHIA.  I would like to learn more about it.  Maybe we could ask Hannes to give a short talk at the meeting.
Also the CEM, complemented with FONLL calculations for the open beauty part, seems to be doing a pretty
good job at describing the J/psi B fraction vs. pT and rapidity (Ramona Vogt and Randy Nelson, at HP2010).