News on quarkonia Laurent Rosselet December 3rd 2008

4 strategies to measure quarkonia +- have been considered: “Global fit”  both ‘s are fully reconstructed in the -spectrometer & ID “Global+tag”  at least one  is fully reconstructed, the other one may be partially reconstructed (tag) to increase statistics Additional way to increase the heavy quarkonia acceptance is to reduce the toroidal field of the -spectrometer, e.g. of a factor 2 (B/2 mode) => 4 studies: ”Global fit” and “Global+tag” with full field (4 Tm) or half field (B/2 mode) statistics vs purity statistics vs resolution The best compromise between these different scenarios will mainly depend on the REAL charged multiplicity and then on TRT performances. This issue is crucial for the statistics of the J/, not so much for the  => We have to keep open all the possibilities (CERN-ATL-PHYS-PUB-2008-003)

These studies use more severe cuts than in pp to take into account the higher track density, and include also a comparison ATLSIM-ATHENA for the “Global fit”, full field method, with full statistics, same events and same cuts (thanks to Sergey Timoshenko). See the ATLAS note CERN-ATL-PHYS-PUB-2008-003, and see in particular in Table 1 for the  and in Table 2 for the J/. A fifth study is done by Sasha Lebedev for the , corresponding to “Gobal fit”, full field, but with different samples and cuts (pp inspired). See US proposal. This last analysis agrees with the corresponding analysis described in the ATLAS PUB note.

A concatenation of all analyses seems possible by interleaving the different subchapters of the PUB note and of the US proposal, keeping the text basically untouched. E.g. see the synopsis for a common paper from previous presentation of October 8th in extra slides. A draft can be found in: http://dpnc.unige.ch/users/ros/quarkoniav12.ps Which is currently studied by the authors of the US proposal quarkonia chapter and by the authors of the ATLAS PUB note.

Content of the common quarkonia paper of CERN-ATL-PHYS-PUB-2008-003 and US proposal Introduction and physics motivation. ATLAS muon spectrometer. First analysis for the upsilon: Methods to measure muons (global fit and tagging methods, cuts and B/2 mode). Upsilon generation, acceptance and reconstruction (comparison of performances with different techniques and cuts, including a comparison ATLSIM-ATHENA). Background (HIJING and effects of cuts, di-muon vertex cut). Upsilons embedded into HIJING events (effects on mass resolution, on purity of the result; S/B estimation, significance, expected rates for 4 different strategies).

Content II Second analysis for the upsilon: Upsilon mass resolution. Upsilon reconstruction efficiency. Expected upsilon rates and backgrounds (with comparison with the first analysis). Charmonium measurements (generation, acceptance, reconstruction, S/B, significance, expected rates for 4 different strategies, including a comparison ATLSIM-ATHENA). Di-muon trigger (necessity for a low pT trigger, constraints on first level trigger, to be continued). Perspective for observing heavy-quarks decaying into e+e- (to be continued). Some remarks on TRT, and on Z0 . Summary.

Work on some trigger aspects that I did this summer with Mauricio Ipinza from PUC, presented on October 8th, and that was continued with Raul Santos from PUC, Chile, adding Z0 to the previous comparison of ’s, J/’s and Hijing.

High level trigger for the muons Based on reconstruction in regions of interest defined by LVL1 trigger On-line reconstruction inside the -spectrometer ~ easier than in pp On-line reconstruction using the inner detector is very challenging => A selection should be made using mainly -spectrometer information, as the correlation between pT, mass and ,  of the 2  candidates, e.g.: J/+- +- Z0+- pT   under study

,  and pT are obtained only from the MS. J/+- +- HIJING pT ,  and pT are obtained only from the MS. 

 pT    “good” Z0+- (with correctly reconstructed mass using ID and MS). But ,  and pT are obtained only from the MS. pT 

 pT   J/+- +- HIJING Z0+- pT Rejection of bad candidates by asking a muon pair with  min at low pT and r= (2+ 2) max inside the event. 

drmax or dradmax= r= (2+ 2) max inside the event. J/+- +- drmax or dradmax= r= (2+ 2) max inside the event. HIJING Z0+-

  drmax pTmax J/  Z0 Even a better selection is achievable, as the allowed regions are:   drmax pTmax J/ <1 <2 >0.4 >2& <10  / >0.8 >3.5&<15 Z0 <5 >1.2 >15,fct of  Define hyperspace cubes and kill events without  pair candidates in these cubes Or use neurone network

pT    J/+- +- HIJING pT 

Summary Selection of good quarkonia candidates at low pT by requiring at least one muon pair combination with a  below a given cut and a r above another cut seems desirable, using only info provided by the MS, before starting the ID reconstruction. These cuts have to be function of pT (we do not want loosing Z0). Exact gain (>2?) has to be estimated.

Extra slides:

Synopsis for a common paper From US proposal: 5.1 except last paragraph, 5.2 “Two analyses were pursued for the +- which corroborate each other and which are described in details below.” Subchapter: “First analysis for the ” From pub-note: 2 to 5 Subchapter: “Second analysis for the ” From US proposal: 5.3 without the first paragraph, with “…generated independently of the first analysis…” with “…120 MeV as in the first analysis…” From US proposal: 5.4 with, before the last paragraph: ”These results agree with those obtained in the first analysis method (12.0% for ’s alone with ATLSIM and “Global Fit”, and 12.8% with ATHENA, using different cuts and samples).”

Synopsis for a common paper (II) From US proposal: 5.5, with at the end of the first paragraph: “This approach is different from the one used in the first analysis where backgrounds are estimated from reconstructed muon pairs in HIJING events, which can explain differences in the estimation of S/B.” Then rewrite the end of paragraph 4. Subchapter:”Charmonium measurements” From US proposal: 5.6, just the first paragraph From pub-note: 6 to 8 Concatenation of summary from pub-note and US proposal.

“good” J/+- No mass selection “good” +- No mass selection

+- reconstruction || <2 global fit pT >3 GeV global+tag || <1 || <2 || <2.5 Acceptance 2.6% 8.1% 12.0% +efficiency 4.7% 12.5% 17.5% Resolution 123 MeV 145 MeV 159 MeV S/B 0.4 0.3 0.3 0 0 0.3 0.2 0.2 S/√ S+B 31 45 55 u 37 46 55 Rate/month 10000 0 15000 For |η| < 2 (12.5% acc+eff) we expect 15K /month of 106s at L=41026 cm-2 s-1 No improvement with the B/2 mode: acceptance/resolution ~ cte … The Transition Radiation Tracker has not been considered for this study. If Nch allows its use, the mass resolution is improved by 25%

J/+- reconstruction || <2.5, pT >1.5 GeV global fit B/2 global+tag pT >3 pT >1.5 pT >1.5 Acceptance 0.039% 0.151% 0.529% +efficiency 0.055% 0.530% 1.100% Resolution 68 MeV 68 MeV 76 MeV S/B 0.5 0.2 0.25 0 0.4 0.15 0.15 S/√ S+B 52 72 140 u 56 113 164 Rate/month 8000 30000 104000 0 11000 104000 216000 We expect 8K to 216K J/+- per month of 106s at L=41026 cm-2 s-1 Resolution is 15% worse, but acceptance is 2-3 times better with B/2. Significance is also much better. Possibility of measuring c decaying into J/.

Next: tagging method comparison: Global+Tag vs MUTAG of b ATHENA low pT trigger with ATHENA (see slides of HI meeting of b March 22nd 2006) TRT studies with ATHENA improve mass resolution Access to e+e- decay channels