Heavy Quark Physics @ HERA II

Brian Foster - HQ physics @ HERA II1

Heavy Quark Physics@ HERA II

What’s new for HERA II and what does it meanfor HQ physics – a reminder..

Brian FosterOxford University DESY

11.11.03

HQs in DIS, diffraction, photoproduction

Spectroscopy – is there a role for HERA II?

Production mechanisms

Single t production?

Summary


HERA II PhysicsBoth ZEUS & H1 have made major upgrades in order toutilise the increase in HERA luminosity to the full.


Vertex RegionThe ZEUS MVD mostly 3 layers in barrel and 4forward wheels; > 200K readout channels.


Vertex RegionH1 Si – 2 very thin CST layers; 5 disks covering 8 < < 17o


Forward PhysicsZEUS major upgrade in forward direction replacement of TRD’s with two stations of straw-tube chambers, each with 3 stereo layers.

H1 have madeimprovementsto various partsof their trackingsystems.


Forward PhysicsH1 forward disks

Extends charm coverageto higher x – similar improvement for ZEUSSi disks and STT.


Vertex PhysicsH1 fast track trigger – now installed and beingcommissioned – can produce mass peaks within 100 s.


HERA II prospects

So optimistically HERA II promises factor 5 increase inluminosity, with lepton polarisation, greatly improvedtracking, DAQ and triggering.

This implies generally order of magnitude improvementin statistics and increased kinematic range and coverage.

What does this mean for the physics reach of HERA II?


HQ in DISHERA I has already told us a lot about the charm quarkdensity inside the proton.


HQ in DISSome of the open questions are obvious.


HQ in DISSome are (much) more obscure.


HQ in DISThe promise of HERA II is great, since charm productionin DIS is sensitive probe to all sorts of dynamical models.

Saturation modelof Kowalski &Teaney.


HQ in DISThe D* tagging method in D* → Ks will not be as effective(@ ZEUS) because of increased multiple scattering from the MVD.

However this will be more than offset by ability to useseparated vertex or large impact parameter tag, as alreadydemonstrated at HERA I by H1.


HQ in DISWe will need substantial part of the HERA II statistics toresolve many of the interesting issues in charm in DIS, evenwith substantial improvement in tagging efficiency.

The mechanism to take charm mass into account can givesubstantial mods. to theoretical expectation as function of Q2 athigher x. Intrinsic charm can also modify these predictions but unlikely we can get useful info. on this at HERA II.

Thorne, Roberts1998


HQ in DISVery precise measurements of F2

c willbe possible for HERA II;also gives accurategluon determination andcross-check with the more global QCD fits.

Accurate b contributionto F2 will becomepossible – cross-check ofVFNS and clean test ofphoton-gluon fusionprocess.

500 pb-1500 pb-1


HQ in DISHERA II should allow both collaborations to make a full flavour decomposition of the inclusive F2 structure function.For example, charm signal in charged currents (expect ~ 50Kevents) in principle measures the s-quark density (+ leading particles in NC etc.; but also competing non-s diagrams fromgluon splitting in CC).

At HERA II, both singlet & non-singlet pdfs - u,d,s (CC DIS)& c,b,g (NC DIS) - can be determined with good accuracy.

Constrain fit with s fromleading ?


HQ & PolarisationPolarisation in DIS will be a unique tool @ HERA IIfor exploring EW couplings.

In principle the spin orientation of the struck quarkcan carry through a memory into the final-statehadron.

In c and b production, one can be sure that the struckquark is in one of the c or b hadrons and there is acorrelation between the detected heavy-quark hadronand the struck quark.

Using weak decay of c, can analyse for spin orientation of struck quark and hence disentangle spin-dependent s.


HQ & Polarisation

But first signal reported forinclusive c productionreported at this year’s conferences, so difficult to believe that statistically significant results can be obtained via this technique.


HQ in DiffractionThe structure of diffraction and its mechanism and explanation in the framework of pQCD is one of the mostfruitful areas of HERA I physics.

In the charm sector, verystrongly limited by statistics.

However, also very gooddiscrimination amongstmodels – one of the areaswhere we will mostbenefit from the statisticsof HERA II.


HQ in DiffractionCharm production cf inclusive F2 will also be additionalconstraint on gluon pdf of diffractive exchange.In exclusive processes,the heavy c quarkgives clearly differentbehaviour to light quarks – opening the relationship of QCD models of diffraction.One of the areas whereone clearly sees the effectof mc as a hard scale. Again, in all of thesestudies, the statistics ofHERA II will be decisive.


HQ in DiffractionDiffractive VM production in photoproduction now inmuch better agreement between H1 and ZEUS.

Some statistics gain still to be expected at the highest W, and some extra kinematic reach from the extendedtracking in the detectors,but generally HERA IIdata will not add somuch to the currentpicture.


HQ in DiffractionDiffractive J/ production in photoproduction athigh t sensitive tool to QCD evolution in diffraction. Again, obviouslystatistics limitedand these type ofstudies will greatlybenefit from HERA IIdata; the very distinctivefinal state and kinematicregime should allowefficient triggers atHERA II.Saturation models canalso describe manyfeatures of J/ data.


HQ in PhotoproductionIn general statistics not a problem with photoproductionresults, except where extra requirements on tagging – e.g.double jet tags.

However, we still haveconsiderable work to do to understand the details even of relativelysimple quantities such as inclusive differentialcross sections.


HQ in PhotoproductionStudy of angular distributions in dijet events where one ofthe jets contains a D* can disentangle the dynamics of thec-production process.

In principle, thismethod, with greatlyincreased statisticsat HERA II, can leadto determination ofc (and g) density in.


HQ in PhotoproductionSince charm taggingworks over a wide rangeof momenta, has ratherhigh efficiency and highpurity, charm is a usefulmethod to look at fragmentation.The study of all thesecharm particles hasallowed the determinationof fragmentation probs.to u,d, ratios of P/V, strangeness suppression etc.to ~5 – 10%. This can certainly be improved at HERA II.

D±

D0

Ds


HQ in PhotoproductionBy looking at eventscontaining leading neutrons and a charmtag, we can get a handle on the c (& g) density in the .

This is a classic “double-tag”experiment whichneeds the increasedstatistics of HERA II(and more!).


B productionB production both inphotoproduction andDIS is really in itsinfancy at HERA I andwill be a major studyat HERA II. The most recent resultsfrom H1 & ZEUS forphotoproduction implya much smallerdiscrepancy betweendata and NLO QCDRelated to differences inextrapolation from meas. for fully inclusive and dijet final states.


B production

Good agreement between H1 & ZEUS,and with NLO QCD.

However…


ZEUSdijet +

B productionJetweb – http://jetweb.hep.ucl.ac.uk allows comparison betweendifferent experiments withimplementation of experimental cuts. Comparison with PYTHIALO +PS scaled to HERA jet predicts HERA & Tevatronetc. (b). There may still be a problemwith the QCD prediction of (b) being too low – but it issurely less than we thoughtand this will have to waitfor HERA II.

http://jetweb.hep.ucl.ac.uk/


B productionHowever, at leastin DIS, we seem tohave a reasonable understanding of the differentialcross sections also.

But we need manymore than 3 bins!=> HERA II.


B production

One of the things we have seen start at HERA I has been the use of the vertex detectors to do vertex tagging.

This will be the name of the game at HERA II.


Charm spectroscopy in p The large HERA I data sample gave the opportunity to makeuseful contributions to charm spectroscopy.

Rich spectrum - D1 ,D2* established; D*' seen by DELPHI, not OPAL/CLEO.


Charm spectroscopy in p However, the B and c/ factories are now going full steamahead and will make even the HERA II data samplesinsignificant e.g. in 2004, CLEO-c plans 6M tagged D decays.

D+ +0

D+ +0D0K00


Charm spectroscopy in CDF And that is even before thinking about CDF….

For “standard” spectroscopy, HERA II not competitive.


Charm spectroscopyHowever HERA II can reach states that other machinescannot reach – e.g. states coupling strongly to gluons canbe copiously produced at HERA.Not obvious why suchstates should want todecay to charm; but then we didn’t expectto see them in light-quark decayseither. Pentaheavyquarks?HERA II can do charmspectroscopy – we shouldlook in those places wherewe are competitive.


Production mechanismsAs an electron-proton collider, HERA II has access tounique production mechanisms that can provide strongtests of QCD.



Rather good general agreement between Lipatov-Zotovand the data.



Interplay with Tevatron can giveextra constraints onrelative importance ofCO & CS; large uncertainties in MEs mean not so obvious that HERA II statisticsvery helpful withoutsignificantly moretheoretical work.

Inelastic J/photoproduction



Study of the J/polarisation givesnormalisation-independentinformation todiscriminate betweenmodels.

Clearly muchmore accuratedata at HERA IIrequired – and preferably less uncertainty in theory.


Production mechanismsOne process at leastwhere we know HERA II will be vital, and which may well bea help in unraveling theJ/ problems, is Υ production – at HERA I we barely (?)saw elastic production,let alone inelastic. However, we probablycan expect only < 100events even at HERA II- probably not enough.


Single top production

Observation of events with high pt lepton, jet and high missing pt sensitive to this process – and lots of otherthings.

HERA cannot produce tt pairs and single productionis highly suppressed in the SM – FCNC process.


Single top productionAs is well known, there is an excess of such events in H1,although not in ZEUS and not in either experimentin the hadron channel.


Single top production


Single top productionFinally ZEUS sees an anomaly wrt Standard Model (?)

See 2 events with pTX > 25 GeV2 c.f. 0.12±0.02 from S.M.


Single top productionThis is perhapsthe clearest andmost importantarea where justthe statistics gain(and the better b tagging) atHERA II willreally paydividends.


SummaryHeavy quark physics at HERA I has been exceptionallyrich. Not only have we measured production cross sectionsover wide range of Q2, we have made contributions toQCD understanding of heavy quarks, to spectroscopyand to diffraction.

HERA II promises much. There will be factors of ~5 inintegrated luminosity; the tagging efficiency and kinematicreach for heavy quark measurements will increase becauseof the improvements to the detectors in general and the vertexdetectors in particular.

Many areas will benefit – particularly DIS and heavy quarkstructure functions, and everything to do with B production.This is a very exciting prospect indeed.


SummaryHERA II is starting up in earnest – first dataare starting to come through.

The Si detectors, although being baked nicely, are notyet cooked and still there and working…


SummaryBackground conditions under study.

ZEUS - reflected synchrotron rad. greatly reduced. Particle backgrounds also look good if machine carefully tuned. Proton-related backgrounds still under study – but promising.

H1 – vacuum conditioning worked.Need factor 3 better vacuum torun with HERA II design currents.


SummaryFirst HQ signals starting to emerge from HERA II data.

These signals from H1 – the opening of the HERA II floodgates?


The WeizmannWorkshop


Summary

Fingers crossed, touch wood, etc. etc. –

The next five or so years promise to besome of the most exciting at HERA yet.

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Heavy Quark Physics @ HERA II