ALICE EMCAL Technical Proposal First Discussion Paul Dauncey

ALICE EMCAL Technical Proposal: First Discussion Paul Dauncey, Michel Gonin, Junji Haba 10 May 2006 Paul Dauncey 1

Overview • EMCAL is lead-scintillator Shashlik sampling EM calorimeter • • Covers Dh = ± 0. 7, Df = 1100 • • Provides jet trigger and improved jet energy reconstruction Will also extend statistics and low energy range of p 0 spectrum Groups from US, France and Italy • • Much larger than PHOS, Dh = ± 0. 12, Df = 1000, but larger granularity Sufficient to contain jet using cone R ~ 0. 4 Relevant physics is jet quenching • • In addition to PHOS, a crystal EM calorimeter Total cost ~ CHF 8. 6 M US would fund ~80% of this; US not currently members of ALICE Rest funded by France and Italy; one new group from each country but others three groups already members of ALICE Installation: 10% for 2008, 50% for 2009, 100% for 2010 10 May 2006 Paul Dauncey 2

Proposed detector • Total is ten full plus two half supermodules • • Takes up effectively the whole space mechanically available Each full supermodule covers Dh = 0. 7, Df = 200 • • • Sampling frequency 1. 44 mm/1. 76 mm determines resolution Simulation gives EM resolution = 6. 9%/ E 1. 4% Exceeds physics requirement of 12%/ E 2% but comes “free” 10 May 2006 Paul Dauncey 3

Readout electronics • Reuse a lot of PHOS readout electronics • • • APD and preamplifier FEE card (with shaper shortened from 1 ms to 100 ns for late neutron rejection) Trigger also from FEE cards but needs extra electronics (not specified in detail in TP) • Electronics cost is CHF 3. 2 M • • 10 May 2006 Out of the total of CHF 8. 6 M Trigger electronics is small fraction of total Design granularity is twice Moliere radius Reducing to one MR would need × 4 channels and push cost up enormously Paul Dauncey 4

Jet quenching • • • Jet spectrum will be softened by QCD bremsstrahlung as hadrons pass through nuclear material Observe through softer fragmentation function of jets with given energy in Pb-Pb compared to p-p. Usual measure of quenching is energy loss of leading parton • • • Some models predict average loss is independent of jet energy Desirable to measure this over a wide range of jet energies; up to 200 Ge. V Effect is very model dependent • • • Size of energy loss varies; could be ~30 -40 Ge. V, could be much less Not clear if signal would ever be visible, particularly in high energy jets Even setting limit on parton energy loss would still restrict models 10 May 2006 Paul Dauncey 5

Jet energy bias • Fragmentation function in terms of x = pt hadron/Et jet • • pt hadron measured only for charged particles by TPC Et jet must be unbiased • Observed energy dominated by energy fluctuations in/out of jet cone, R = 0. 4 • • • Reasonably insensitive to detector resolution Tails can cause bias; upwards fluctuations more critical than downwards Et jet best measured by charged particles and photons • • Necessitates a large solid angle EM calorimeter But will still potentially have some remaining bias 10 May 2006 Paul Dauncey 6

Rates and trigger • Trigger enhances jet rate by ~10 for Pb-Pb, ~50 for p-p and p-A • • 10 May 2006 Raw jet rate in EMCAL acceptance above 100 Ge. V is around 300 k/year and above 200 Ge. V is around 10 k/year Without EMCAL trigger, would get ~30 k/year and ~1 k/year Need to bin by jet E bins and impact parameters (and other reality factors) Trigger is required to get high energy (i. e. up to 200 Ge. V) jet rate to useful level Paul Dauncey 7

Issues: 1 – Funding and effort • This would bring US into ALICE • • The other ~20% is France and Italy • • • They would pay ~80% of EMCAL They would also contribute between 6% and 10% of computing They would also contribute to the Common Fund, removing the deficit Some groups already in ALICE; involved in ITS and m Spectrometer ALICE are confident this will have no impact on existing responsibilities Only one other detector in ALICE currently not fully funded • • • This is the other EM calorimeter, the PHOS Very important for p 0 and direct g measurements Already staged with completion only by 2010 (assuming funding found) 10 May 2006 Paul Dauncey 8

Issues: 2 – Bias/resolution limit • Both the quenching effect and the jet energy bias are unknown • • • Need real jet data before these effects can be determined • • Very model dependent Size of systematic errors on fragmentation function not known We have not seen an estimate even using non-quenched PYTHIA Cannot tell where systematic limit is and where more statistics will be useful Could be done for jet E < 100 Ge. V with TPC alone with 2008 Pb-Pb data But would probably delay installation of EMCAL to after 2012 Not yet clear if higher energy (~200 Ge. V) jets will be interesting Installation of EMCAL in time for first few years of data is a risk • • Not to physics; the EMCAL will definitely improve the physics performance of ALICE The risk is financial; the systematic limit may be too large so effectively no improvement for jet quenching beyond TPC-only is found 10 May 2006 Paul Dauncey 9

Issues: 3 – Size of EMCAL • The 11 × “ 100 module” design fills available space • • Basic measure of required size due to R = 0. 4 jet cone definition • • Roughly; centre of jet must be more than 0. 4 from edge EMCAL design is h×f = 1. 4× 1. 9 • • How would performance degrade with fewer modules? Gives ~0. 6× 1. 1 acceptance for central jet direction Each “ 100 module” is 0. 17 in f and extends the full length in h E. g. reducing from 11 to 8 “ 100 modules” gives roughly half the acceptance resulting in roughly equivalent size in hand f Cost/acceptance trade-off hard to judge without knowing systematic limits 10 May 2006 Paul Dauncey 10

Conclusions • Technically, the design seems robust • • • The issues are mainly to do with physics outcome • • • Will the extra statistics due to the trigger be useful for quenching? Will including the EM energy in the jet reconstruction reduce the bias sufficiently? In addition, should consider • • • No challenging new detector technologies Reusing existing electronics designs There are PHOS modules which have no funding Some EMCAL European groups are working in other systems What happens next? • • We collect questions and forward them to ALICE Rediscuss and make a recommendation at the next LHCC 10 May 2006 Paul Dauncey 11