ppt - COMPASS - CERN by qingyunliuliu

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									Proposal to study ‘’GPDs @ COMPASS’’ in 2 phases

Phase 1: DVCS experiment in 2011 to constrain GPD H:
  with +, - beam of 100 GeV + unpolarized LH2 (proton) target
 + recoil detector + ECAL1,2 (possibly 0) + all COMPASS equipment

           d /dt       impact parameter b

    d  ( +  , )   + d( -, )  Im(F1 H) sin 
    d  ( +  , )   - d( -, )  Re(F1 H) cos 

Phase 2: DVCS experiment in ~2013 to constrain GPD E:
  with + and transversely polarized NH3 (proton) target
 + recoil detector + ECAL1,2 (possibly 0) + all COMPASS equipment

    d(, S) - d(, S+π)       Im(F2 H – F1 E) sin (- S) cos 
From the drafting committee and internal discussions:

General remarks on luminosity and efficiency

General remarks on the target/RPD

   Simulation Andrzej and Etienne

   Data taking in 2008 and its analysis




                            Nicole d’Hose 15 October 2008
Projections for phase 1

DVCS Beam Charge and Spin Asymmetry and difference and d /dt

         +, -   at E = 100 GeV        or 140 GeV?

Q2
                     Goal:
 7                   Best Q2 and x coverage in all the COMPASS domain
 6
                     in each (Q2,x) bin, 1000 evts for 10 bins in    and 4 bins in t
 5
                              Contribution of DVCS and BH
 4
 3
 2                             Unique COMPASS domain: 0.01 < x < 0.15

                               Range in Q2  if the luminosity 

     0.05 0.1 0.2    xBj
                     Muon beam intensity
hypothesis

      spill:    4.8s every 16.8s      9.6s every 48s
    on T6      1.31013 protons       2.61013 protons

   at 160 GeV     2.3108 +/spill      4.6108 +/spill
                1.94108 +
                                  2.55                  2008 DVCS tests
                 0.76108 -

   at 100 GeV    3.5108 +                  7108 +
                 1.64108 -       2.13

     N+ /N- was supposed ~ 1.6             4.4 108 - in 9.6s every 48s
                                              is used in the simulations

Search for improvements:
 - Can we increase the long flat top to increase N but keep a constant flux?
 - Can we increase the flux  problem of radioprotection (around T6, in the
   tunnel ramp, in the experimental area, at the end of the CERN territory…)
               Length of the target

 - 2.5m of Liquid H2 target
   + N = 4.4 108 in a spill of 9.6s every 48s (+ no inefficiency)
        L = 0.97 1032 cm-2s-1 = 0.97 10-4 pb-1s-1
 - 140 days of data taking in one year or ~6 months
        L = 1173 pb-1
Search for improvement:

     In NMC a 6m long target (larger radius)

     with 6m of Liquid H2 target       L  2.4
     (delta rays contamination has to be evaluated)
                       Overall efficiency
SPS availability      0.7  0.8    Andrzej’s simu
Data taking           0.3  0.9     overall (with )    0.25 (now 0.30)

Trigger                  0.8       But detailled efficiencies:
                                   Incident BMS muon      0.93 NIMp15
Veto dead time           0.8
                                   Scattered muon         0.9 Yann 2006
Reconstruction                     Vertexing              0.9
             0.13  0.25 (tbc)     Recoil proton          0.8 ?
Photon detection     0.5 (tbc)     Photon detection       0.9 ?
 Overall          ~0.01  ~0.06   Photon interaction     0.5 ?



     Starting point in simulation overall  = 0.10
     Work to be done to determine efficiency in the data for
                      reconstruction and photon detection
      Hunt for every improvement
           Recoil detector and target

                                                           ~1m
Phase 1:                                  ~1m
 - Liquid H2 target of 6m                               45°
 - Long RPD but reduced to 7m
    protons emitted at angle < 45° are not well detected
      this effect will appear for x > 0.15

 - delta rays contamination has to be well estimated
                                                       !
 - extra ° contamination in p    N*
                                        p °
    this is not an important contamination according
                                          Andrzej’s simulation
           Recoil detector and target

Phase 2:
2 options can be studied:

     a) Recoil Proton Detector
        + a new transversely polarized NH3 target
          inserted inside a RPD (Werner Meyer)

     b) the present (transversely) polarized NH3 target
        + a new Recoil System (with SciFi?)
          inserted around the target (Jaakko K., Fabrice G)
  RPD      in a 15cm space between target and magnet

Only two layers of SciFi wound helically in opposite direction

   good phi determination
   we need an external element to build a ToF and reconstruct t
    with a good resolution

Value of tmin ?
 Polarized NH3                              Present LH2 target
polarized NH3         NH3 15mm               Liquid H2 15mm
Target cell           Kevlar 0.5mm              Mylar 0.125mm
 Gas mixing chamber   Fiber glass <1mm
 Microwave cavity     Cu 1mm
 Cu thermal screen    Cu 1mm     in extra
 Vaccum cell          Carbon fiber 1mm         Al     1.8mm

 SciFi 2 layers       2mm                    5mm in A + 1mm in B
                             in balance
                                     Calorimetry
Ecals (best coverage without leakage for a flat acceptance)

             - ECal2 @ 33m has to be completed
             - ECal1 @ 11m at its nominal position ideal ECal1, 2
                   (moved back after hadron run)

             - ECAL0 would extend the kinematical domain at large x
                                             (R&D Dubna)
                                           SM2
  Horizontal
                            ECAL1
               SM1                                       ECAL2


                                     56
             286



                                                                  3 setups studied in simulation
                   179
                           48         37         6




  Vertical
                                                                        - 2009 ECal 1,2
                                                                        - ideal Ecal 1,2
             190     129
                                                                        - ideal ECal 1,2 + ECal0
                                                     6
                           28




             @ 4m           11.11m         18m           33.25m
Trigger extension for Q2 > 1 GeV2

                                   (Bonn/mainz)


 It depends of the selected muon energy

 100 GeV  scattered muons detected after SM1

 160 GeV  scattered muons detected after SM2
              DVCS Tests in 2008
E-=160 GeV   0.59 108 - per spill (9.6s 33.6s) 1319 spills
E+=160 GeV   1.54 108 - per spill (9.6s 33.6s) 2216 spills

SM1(2105A) SM2(4211A) important for alignement

Trigger: MT + CT + MT&RPD

RPD:                                  &
- trigger thresholds= 60/500
                                                    5 oct. 2008
       (and not 30/60)
                                                    Run 71447
    to minimise the huge
    electromagnetic background
- read out thresholds=30/60
    as in hadron runs

ECal threshold= 7 SADC counts

      Rare protons are observed in the RPD
            DVCS Tests in 2008
 RPD (Kasia, Etienne)
   - better optimization for  and t determination
      sum of all the runs and sectors to see
       recoil protons with the muon beam
   - delta rays determination
      extrapolation for a long RPD

 RPD + COMPASS spectrometer
     (all the coral team with Sergei, alignement made by Alex,
      with Yann, Guillaume, Kasia, Etienne, Frank, Oleg)
  with ° study (at Q2 > 1)
   with  or ° or +
    study of signals and background
    Comparison Data/Simulations


             This complete study has to be done for December 15
              to ask for a GPD pilot run in 2009
Workshop
       ‘GPD studies at COMPASS’
  Freiburg, Saturday 15 November 2008, starting at 10:00

  Long and pedagogical talks of experts:

  10:0011:15 Matthias Burkardt: spin bugdet of the proton

  11:3012:45 Markus Diehl: physics case for GPD @ COMPASS

  14:3015:45 Dieter Mueller: Review of existing GPD Models and plans

  16:0016:45 Andreas Schaefer: Lattice projection for > 2012

   +…

                              1rst workshop of a series
Towards a GPD pilot run in 2009

Goal: first determination of d /dt (impact parameter)

      test of DVCS Beam Charge and Spin difference

      collect BH for precise efficiency determination

								
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