the hmpid performance during the lhc run period 2010-2013 detector stability and pid performance...

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The HMPID performance during the LHC run period

2010-2013

Detector stability and PID performance

(with the contribution of: G. Volpe, S. Bansal, A Franco, L. Olah)

HMPID Plenary meeting 19/07/2013

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Summary as outlines of the presentation• September 2006, the HMPID installed on the cradle was slide in the ALICE magnet;

• The detector performance has been stable except some concerns with:– the tightness of the C6F14 trays: 4 out 21 trays have shown leakages ;– 3 HV sectors out of 42 are off.

• Combining faulty systems, they have gradually reduced the detector acceptance down to 72%. Nevertheless this has not prevented the detector to carry out successfully its PID task!

• The long term stability and Q.E. of the CsI Photocathodes is confirmed. In principle no degradation will be observed up to the end of the 2021(RUN3), during the HL LHC period ;

• During the LHC run period 2010-2013 the HMPID has efficiently collected data in p-p, p-Pb and Pb-Pb collisions;

• A Technical Internal note with all the details is being prepared, its temporary title is: The HMPID performance during the LHC run period 2010-2013 ;

• On the same subject a contribution to the RICH 2013 workshop is ready to be submitted;

Thanks to you all for the excellent results and for the efforts in building, operating the detector up to now and for analyzing data!HMPID Plenary meeting

19/07/2013

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Sept 2006: HMPID, the first detector sliding in the empty ALICE magnet


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Leaking radiator

Faulty HV sector


2013: Leaking C6F14 trays and faulty HV sectors

01

234

56

Leaking 8/2006

Leaking 10/2010

Leaking 6/2012

Leaking 6/2010

The detector performance have been stable. There have been some concerns with:• the tightness of the

C6F14 trays: 4 out 21 trays have shown leakages ;

• 3 HV sectors out of 42 are off.

Combining faulty systems, they have gradually reduced the detector acceptance down to 72%. Nevertheless this has not prevented the detector to carry out successfully its PID task!

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NEOCERAM-quartz trays for the liquid C6F14 Cherenkov radiator


1.4 m

1.4 m

Liquid C6F14 inlets

Fixations

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Details of the C6F14 Inlet


Delicate connection

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Possible main causes of the C6F14 leakages and perspective!

1. Detachment of pieces on the C6F14 inlet (inox-NEOCERAM contact surfaces)?

2. Glue etching (or ageing) with consequent separation of the quartz-NEOCERAM plates?

3. On thermal dilatations (mechanical stress) difficult sliding of the radiators in the fixation with consequent cracking of the plates?

4. ?…………….5. Perspective: difficult to say, more care in filling/empting phase of the

trays; hope to keep the situation stable at least up to the end RUN2 ( dec 2017);


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Monitoring of MWPC Gas gain stability


2010 2011 2012

2010 2011 2012

11_c run period

• Monitoring of the CH4 Gas gain stability and uniformity in the seven RICH modules up to the end 2012. Its stability can affected by variations of the gas density in the MWPC r(T,P).

• An equalization of the 42 HV setting values has been done during the run period 11_c (coordinated by Antonello). An optimal gas gain value (Ao~35) is reached where the ratio of resolved Č ph.e. over ph. feedback is maximised. Ao

in A

DC

chan

nels

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CsI photocathodes: long term performance and ageing effects

• The long term stability refers to the Q.E. stability of the 300nm thick CsI layer on the pad-photocathode, since its production time, in “normal” storage conditions, not necessarily exposed to the radiation;

• Ageing effects are those caused on the CsI photocathode by the ion-bombardment produced in the CH4 MWPC by both the ionizing particles and photons (Cherenkov and feedback);

• In two works (mainly carried out by H. Hoedelmoser and lead by F. Piuz NIM A 553

(2005)187-195 and NIM A 574 (2007) 28-38)[ref.1-2], these two effects have been carefully analyzed and today let us to know in advance the possible effects on the CsI photocathodes due to the integrated charge dose during the LHC operation.


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CsI Q.E. by particles at saturated Č angle 2010-2012


RICH 6 RICH 5

RICH 4 RICH 3 RICH 2

RICH 1 RICH 0

2010 2011 2012

2010 2011 2012 2010 2011 2012

2010 2011 2012

2010 2011 20122010 2011 2012

2010 2011 2012

Monitoring of the average number of reconstructed Č photons by particles at the saturation. It depends on the CsI Q.E. and it doesn’t show any loss during the LHC run RUN1.


CsI Q.E. by particles at saturated Č angle 2013



CsI Q.E. by particles at saturated Č angle 2010-2013


• The average number of about10 photons/ring is less than the about fifteen measured during the photocathode characterization in dedicated beam tests (2004-2006).

• Unfortunately the available statistics in the LHC data set doesn’t allow a particle selection for reproducing the same experimental conditions as in the beam tests. So, a direct comparison is not yet possible.

• Nevertheless, due to the absence of any CsI Q.E. loss we are convinced that also the long term stability of the photocathodes has not been affected.

• These results are also consistent with the measurement of the average dose of the integrate charge of 0.013 mC/cm2, which is less than the charge threshold value of 0.2 mC/cm2, where ageing effects of CsI photocathodes resulting in a Q.E. loss may appear[ref1-2].


The integrated charge dose on the CsI photocathodes

• A bit of history: 2002, on request of F. Piuz, a dedicate HV board with 1 nA of current resolution was developed: (in the CAEN catalogue A1821PH where H is for HMPID!);

• Below as an example, the Io values 2010-2013 of the six HV sectors of the RICH0 (each HV sector covers two halves photocathodes): the black curves refer to the HV channel rampup/down , the red curves show the Io values when the operational HV values were set and particle collisions were taking place in IP2.


RICH0 HV-S0-5

RICH0 HV S0

RICH0 HV S5


Some comparisons p-p, Pb-Pb and p-Pb

p-Pb2013Pb-Pb 2010

p-p 2010 p-p 2012



Integrated Charge dose


RICH0 HV S0-5

2010 2011 2012 2013

Inte

grat

ed c

harg

e do

se

RICH0 HV S0

RICH0 HV S5RICH0 HV S3=lowHV

How much of this current flown trough the CsI fotocathodes? A simple model (to be refined) suggests that a conservative value of 2/3 of the anodic Io, (in details: ½Io from ionizing particles + IČ photons assumed equivalent to ½ Io since on the average, there are 10 Č ph./radiating particle)


Summary of the integrated charge dose


From this analysis there are no concerns about the CsI Q.E. during RUN2 (2015-2017).In principle the detector can be operational also during the full RUN3 period, with HL LHC up to 2021. This has been possible thanks to the fortunate condition of the measured particle multiplicity (~1 Kparticles/ h in Pb-Pb) a factor 6 less than what expected from the simulation (~6 Kparticles/ h in Pb-Pb).


HMPID PID performance• The PID performance have already been presented several times during the weekly meetings where more

details can be found;• To summarize the excellent PID performance of the detector, I have just put the scatter plot of Č angles vs.

momentum at 7 TeV and the K/p and /p K separation in p-p @2.76 TeV (newest); for the protons up to 6 GeV/c at 2 sigmas (REM: measured Č angle resolution ~ 4 mrad);

• Refined method for the background subtraction and track-by-track ID algorithm, as already shown in the previous presentations, are permitting the HMPID to provide interesting physics results in p-Pb and Pb-Pb collisions as well.



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Number of photons for LHC 10b


* Number of photons for LHC 10bWe have used a strip of 10 cm in the y-direction* p>4GeV

the hmpid performance during the lhc run period 2010-2013 detector stability and pid performance...

Documents

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hmpid performance

detector stability

leaking c6f14 trays

detector performance

olahhmpid plenary meeting

c6f14 leakages

detector acceptance