Giuseppe Martellotti - 24/02/2014

Performance at high luminosity - efficiency - accidentals - detector layout (contributions from Alessia and Roberta)

Some Update and more quantitative Summary of what I discussed in previous meetings

PROCEDURE - Monte Carlo

# Considering the Trigger Sector (TS) geometry of a given region # Given a particle rate/cm2 counting rate in the single FE

(using AND/OR measurements) Inefficiency due to dead time

(assuming δcarioca = 75ns)Average number of logical pads in

the TS hit by particles (I assumed a uniform hit distribution in the TS)

Logical pads reconstructed (X & Y crossing) hits with ghostsAccidentals in a given PAD/FOI

# different chamber layouts tested

Rates of particles (no ghosts) at L=2x1033 Rates in kHz/cm2 (with shielding)

M2R1TS = 95 cm2

X,Y= 6+8 phys.strips48 crossings

N h

its in

the

TS

Rate/cm2 (kHz)

Particlesε=1, ε<1

Reco hits (with ghosts)ε = 1, ε < 1

Rate/cm2 (kHz)

M5R4TS = 1.85 m2

24x4 pads6+4 strips24 crossings

Very high inefficiency and accidental rate in some regionsHere the two more critical regions are illustrated (red lines are indicative rates)

Min Max Aver

N h

its in

the

TS

In black the percentage of correlated and uncorrelated hits measured (at 2.76 TeV) on the physical channel counters with the FE of the two layers in OR - AND

Recall:Most of the hits detected in the chamber layers are uncorrelated

R = K(P + 3FP + 4S) is the rate in the present 4-gap detector. The rate on the single FE determining the CARIOCA dead time (and inefficiency) is R1FE = K(P + FP + 2S) In M2R1, R1FE = 0.54xR = R(1+7%)/2 being 7% the fraction of correlated hits in M2R1 S = fraction of single-gap tracks in each gap P = fraction of penetrating tracks F = fraction of penetrating tracks P crossing one pad in a gap and a different pad in the next gap, not giving the And but giving one more hit in the OR of two consecutive gaps

FE FE

OR

Switch off one gap per FE Switch off the two EXTERNAL gaps. It is convenient to reduce probability of double hits from penetrating tracks (cross-talk). Moreover it permits easy calculation of rate and efficiency.The rate of the detector becomes R2GOR = R(0.54) Same number of hits (and accidentals) of 1 FE presently.The rate of single FE determining the CARIOCA dead time and inefficiency is R1G = R(0.3) = K(P + S) = R(1+3x7%)/4

HV off

HV off

Proposal to reduce dead-time inefficiency

INEFF. % - present layoutChamb Min Aver Max M2R1 2.4 9.2 29.1M3R1 0.3 1.9 5.2M2R2 0.0 1.0 3.2M5R4 0.0 0.7 10.7

INEFF. % - 1 Gap /FE off Min Aver Max M2R1 0.7 2.8 8.6M3R1 0.0 0.4 1.4M2R2 0.0 0.3 1.1M5R4 0.0 0.1 4.2

TDR Ineff %(average region)

M2R1 7.1M3R1 3.3M2R2 4.1M5R4 2.3

For chambers with large inefficiency ~ (1 - ε > 1%) it is convenient to switch off one gap per FE (and increase HV…)

INEFF. % - M2R1,M3R1 pad Min Aver Max M2R1 0.0 0.0 0.0M3R1 0.0 0.0 0.0M2R2 0.0 0.3 1.1M5R4 0.0 0.1 4.2

Summary of inefficiencies at L = 2x 1033

Not mentioned regions are not critical

After this we can just improve the shielding behind M5

What about OCCUPANCY (and accidentals) ? The vertical scale must be divided by the XY crossing number logical pad occupancyThe blue lines are the Min. Max. Aver. rates expected when removing 1 gap/FE

Logi

cal p

ad o

ccup

ancy

M2R1

/48

M5R4

/24

Rate/cm2 (kHz)

ghosts

Pad detector

Rate/cm2 (kHz)

M2R2

/48

M3R1

/48

Logi

cal p

ad o

ccup

ancy

Rate/cm2 (kHz)

M2R3

/96

M2R4

/96

Logi

cal p

ad o

ccup

ancy

OCC. % - Pad detector Chamb Min Aver Max M2R1 1.2 2.3 4.2M2R2 0.5 2.0 4.6M2R3 0 0.6 1.5M2R4 0 0.3 1.2M3R1 0.4 1.0 1.7M5R4 0 5.8 22

Summary of logical pad occupancy (ε = 1)Not mentioned regions are less critical

OCCUPANCY %Chamb Min Aver Max M2R1 1.6 4.0 8.8M2R2 0.5 2.0 4.6M2R3 0 0.8 2.7M2R4 0 0.3 1.9M3R1 0.4 1.3 2.7M5R4 0.4 10 51

OCC. % - 1 Gap /FE off Chamb Aver Max M2R1 1.3 2.2M2R2 1.0 2.0M2R3 0.3 0.9M2R4 0.2 0.8M3R1 0.5 0.9M5R4 2.9 13

OCC % reducing Pad size Chamb Max M2R1 Y/2 1.1M2R2 Y/2 1.0

(M3R2 Y/2 0.2) M3R1 Y/2 0.5M5R4 X/4 3.3

Pad detector (excluding M2R2)- M2R1 M3R1 : build new chambers- OTHERS : modify readout from IB on # in the last step the occupancy refers to the reduced PadThe MUID FOI measured in pad units will be larger.

Nevertheless I expect a significant gain in M2 M3 R1 R2

SUMMARY ABOUT EFFICIENCY and ACCIDENTALS• EFFICIENCY: # A Pad detector solve the problem in M2R1, M2R3, M2R4, M3R1 # Some chambers of M2R2, M5R4 require the switching off of 1 gap/FE # Further shielding improvement in M5R4 would be desirable • OCCUPANCY: # A Pad detector (no ghosts) significantly reduces the accidentals but does not fully solve the problem. The accidental probability remains high in various regions. I think that further occupancy reduction is welcom not only if we want to have a fast Muon Pt filter stand alone, but also for MuID (to be quantified) # Switch off 1 gap/FE helps in M2R1, in some chambers of M2R2, M2R3, M2R4, in some chambers of M3R1 and M5R4 # Reduce the vertical pad size (Y/2) in M2R1 M2R2 M3R1 M3R2 - The vertical pad size is ‘’large’’ w.r.t. MS we could have a significant gain not only from occupancy reduction but also from improved track matching. - In M2R2 and M3R2 the logical pads are already divided in two vertically (we should act only from IB on as for the regions M2R3 M2R4 and M5R4) • new M2R1, M3R1 detectors should be done

How should be the new M2R1 M3R1 detectors ?

Pad detectors (MWPC or GEM) having only two gas gaps, instead of four, to avoid doubling the number of sinlgle gap track hits. # this will increase timing inefficiency (small) but reduce dead time inefficiency (large) The granularity w.r.t. the present logical pads, should possibly be the same in X and twice in Y # The fact that we have a reduced chamber thickness (2 gaps only) would leave a large space for the FE electronics

• Try to eliminate 1 cm of foam in between the 2 gaps.The fraction of penetrating tracks crossing two different pads in the OR of the 2 gaps would be significantly reduced

FE

FE FE

FE OR

How to simulate inefficiency and occupancy in the upgrade conditions

• We have a table of hit rates measured at low luminosity. I have the feeling that regions are too large, it would be better to use a finer granularity.

• Let’s consider the granularity of Trigger Sectors needed for the evaluation of the XY crossings.If for some TS of this table the local rate is not sufficiently low to make negligible the rate of accidentals, we can estimate the fraction of ghosts and eventually subtract their rate

table of particle rates for the standard layout at a reference luminosity• Starting from this table, given any new luminosity, we can calculate the expected local

occupancy and the local efficiency (we can produce a new table or apply a simple formula).• In the Data analysis when a hit is found in the X Y position of a station, from the table we

have the local efficiency to be used and the local level of occupancy• To simulate MisID we have to select data samples with higher track multiplicity giving the

foreseen occupancies in the regions (see Matteo et al…)I think that one should look at the event track multiplicity and not to the PV number because the occupancy is proportional to the tracks while the event track multiplicity per event could be biased (reduced in events with high PV number)

Problems arise if we want to test different detector layoutsShort term:Use existing data (with the standard detector layout)In the MC or in the Data analysis when a hit is found in a station in the X Y position the corresponding efficiency can be correctly applied (modulo the Table granularity).If the detector layout is modified (e.g. 4 gaps 2 gaps) , this is an approximation- inefficiency is underestimated because geometrical cross talk is overestimated - MisID study is not obvious (in particular if different layouts are used in the same

regions of different stations). Nevertheless the use of data samples having an appropriate track multiplicity can approximately indicate the expected effect.

Longer term:We have to discuss how to modify the MC (which layouts to test?)- We can take out the (deadtime) inefficiency and apply inefficiency afterward- Detector geometry-materials (we can continue to use old configuration)- Digitization has to be changed – If we only switch off 2 gaps some ‘’easy’’ way out can be envisaged (Alessia: week work) but, if we go to pad chambers, different MAPS are required and Tell1 readout has to be havily modified (Alessia: months)

SPARES

In black the percentage of correlated and uncorrelated hits measured in the past at 2.76 TeV Comparison with MC

Check what is reported in the plot. In the MC Alessia & Rob note, I find (not much) different numbers

CORRELATED-UNCORRELATED HITS

In black the percentage of correlated and uncorrelated hits measured in the past at 2.76 TeV Comparison with MC

Check what is reported in the plot. In the MC Alessia & Rob note, I find (not much) different numbers

CORRELATED-UNCORRELATED HITS

Possible explanation of the apparent disagreement Data - Monte Carlo (valid only for inner regions) :

1) There are 2 different definitions: - In Data the AND of projectively aligned pads is required to have correlated hits. - In MC the fraction of tracks crossing all the 4 gaps is shown.2) The MC, in the inner regions, underestimates rates by about a factor 2.3) I assume that the rate of ‘’high energy’’ tracks crossing 4 gaps is well reproduced while the rate of single gap tracks is strongly underestimated and must be increased up to saturate the total rate (gamma converted into low energy electrons in the high density material before each gas gap) corrected MC

# The OR/AND measurements are consistent with the corrected MC in a reasonable simple model (not taking in to account cross-talk) # This model can help to estimate the performance of different chamber layouts

In M2R1 the MC gives ~ 40% penetrating tracks crossing 4 gaps. Negligible number of tracks crossing 2 or 3 gaps.~ 60% single gap tracks equally populating the 4 gaps1) The number of penetrating tracks is assumed to be the one given by the MC.2) The number of single gap tracks is increased.Corrected MC: 20% of penetrating tracks and 80% of single hit tracks (20% in each gap)

From the measurements with OR – AND of the two FE, we get the percentage of penetrating tracks crossing one gap hitting next gap in the same pad (small angle/pad centered tracks) and the percentage hitting a different pad (large angle/peripheral tracks). These tracks don’t give AND but contribute to the OR

Lets call:S = fraction of single-gap tracks in each gap (20% of the total tracks in M2R1)P = fraction of penetrating tracks crossing 4 gaps (20% of the total in M2R1)F = fraction of penetrating tracks P crossing one pad in a gap and a different pad in the next gap, not giving the And but giving one more hit in the OR of two consecutive gaps F can be determined

The hit rate on the first gap is RG = K(P + S). FP tracks of this gap will give a new hit in the next gap The rate of the OR of the 2 contiguous gaps is R2G = R1FE = K(P(1-F) + 2FP + 2S) = K(P + FP + 2S). When going from gap 2 to gap 3, by definition of F, again a fraction F of P tracks (not necessarily the same previously jumping tracks) will give a new hit in the third gap The rate of the OR of 3 contiguous gaps is R3G = K(P(1-F) + 3FP + 3S).

The rate of the OR of 4 gaps is R4G = K(P(1-F) + 4FP + 4S) = K(P + 3FP + 4S).

FE FE

OR

The rate measured in the detector (with the OR of the 2 FE) is ROR = R4G

The rate measured with the And of the 2 bi-gap isRAnd = K(1-F)P (S hits are eliminated and ~ FP track hits are lost from gap2 to gap3) With this naive picture we obtain a reasonable explanation of the apparent disagreement between Data and MC: Using the P and S values from corrected MC, to have RAnd /ROR = 7% measured in M2R1 F = 54% Given the chamber geometry, it is reasonable that ~ half of tracks don’t go through projective pads (low energy tracks or tracks coming from beam pipe).

More realistic geometry of two adjacent gaps

The fraction F depends on the chamber geometry - on the distance of the two gaps

If R = K(P + 3FP + 4S) is the rate in the present detector M2R1. The rate on the single FE (OR of 2 gaps) to be used to calculate the effect of CARIOCA dead time is R1FE = K(P + FP + 2S) = R(0.535) = R(1+7%)/2 being 7% the fraction of correlated hits

FE FE

OR

FE Switch off one gap per FE Switching off the two EXTERNAL gaps is convenient to reduce the probability of double hits from penetrating tracks (and cross-talk). The rate R2SGOR = R1FE = R(0.535) Same number of hits (and accidentals) but higher efficiency.The rate of the single FE (to calculate the CARIOCA dead time) is RG = K(P + S) =R(0.3) = R(1+3x7%)/4

Equivalent rate to evaluate efficiency = 0.3/0.535 = 0.565

HV off

HV off

Effect of inefficiency due to CARIOCA dead time in M2R1

Real particles

Inefficiency due to dead time is applied to each FE physical channel (1)

Carioca dead time =75ns is assumed for both wires and cathodes (to be updated).The AND of XY is required Then the two bi-gap layers are Ored. two comments:- Cross-talk not considered- Ghosts don’t give dead time

Vertical red lines are the average rates/cm2 for the chambers with minimal, average, maximal population.

Particle HITS not in dead time

Rate/cm2 (kHz)

N h

its o

n th

e TS

(1) Efficiency = (1 - δeff R/0.7) Where R is the rate (in GHz) measured on the FE channels δeff = δcar -12.5 ns

Reconstructed hits (with ghosts)

Assuming efficiency = 1

With inefficiency

TS = 95 cm2

XY= 6x8 crossings

inefficiency

M2R1

M2R2Inefficiencies reported in TDR

M3R1Apparent disagreement with the inefficiencies reported in TDRTo be investigated

particles

Detectedparticles

N h

its o

n th

e TS

Rate/cm2 (kHz)

Pay attention New shielding effect is in

TS = 95 cm2

XY= 6x8 crossings

TS = 109 cm2

XY= 6x8

TS = 380 cm2

XY= 12x4