31 July 2005HjC at STAR in Warsaw Forward Meson Spectrometer (FMS) status report Hank Crawford for FMS group L.Bland, F.S.Bieser, R.Brown, A.A.Derevschikov,

31 July 2005 HjC at STAR in Warsaw

Forward Meson Spectrometer (FMS)

status report

Hank Crawford for FMS group

L.Bland, F.S.Bieser, R.Brown, A.A.Derevschikov, J.Drachenberg, C.Eskew, C.Gagliardi, S.Heppelmann, J.Engelage, L.Eun, E.Judd, V.I.Kravtsov, Yu.A.Matulenko, A.P.Meschanin, D.A.Morozov, M.Ng,

L.V.Nogach, S.B.Nurushev, A.Ogawa, J.Passaneau, C.Perkins, G.Rakness, J.Rothenberg, K.R.Shestermanov, M.Tatarowicz,

A.V.Vasiliev, M.Zucker


Overview

STAR Forward Detector (FPD) proved we can reconstruct forward in pp, dAu, and CuCu environments


Overview (2)Spin Physics Results

• Discovered π0 asymmetry in pp• Proved NLO pQCD works in forward region at RHIC

J. Adams et al. (STAR), Phys. Rev. Lett. 92 (2004) 171801


Overview (3)Probing the gluon density in the Au nucleus

Showed suppression of forward π0 in dAu

G. Rakness, for STAR [hep-ex/0507093]


Overview (4)FPD++ and Forward Meson Spectrometer (FMS)

FMS proposed to enlarge acceptance for gluon distribution studies

Stage FPD++ for Run6 as FMS engineering run

Stage full FMS for Run7 dAu


FMS Physics GoalsThese we know we can do from FPD analysis of π0

1. Measure gluon distributions xg(x) in protons and gold nuclei from 0.001<xb<0.1

Check universality of xg(x) in region of overlap with DIS (0.02<xb<0.1)

2. Characterize correlated pion distributions as a function of Q2 to search for onset of saturation effects

Is Au a Color Glass Condensate (CGC)?

3. Resolve the origin of large transverse spin asymmetries in p+p -> 0+x for forward 0 production


Expanded FMS Physics GoalsWe intend to test these ideas using an FPD++ in Run6

4. Measure g(x) using direct photons

Is known asymmetry in pp π0 present in pp ?

Much simpler probe because no final-state effects

5. Measure J/ (with small acceptance)

Simulations underway


How do we measure g(x)?

Quark from Blue beam scatters off gluon in Yellow beam to produce π0 or in forward direction (2.8<<4.2)

We measure E, , and for π0 or in coincidence with π0 , or leading hadron jet surrogate from BEMC, EEMC, or accompanying (s) within FMS to cover 0.001< x <0.1


How do we tell if there is a CGC? ln(1/x) and the scale (Q) is taken as pT

Require two (jets) in FMS probes smallest x gluons in Au nucleus (largest )Look for broadening or disappearance of peak as pT decreases

pT decreasing


Run-5 FPDRun-6 FPD++Run-7 FMS

FPD++ Physics for Run6

We intend to stage a large version of the FPD to prove our ability to detect direct photons. These give a cleaner signal of the underlying qg interaction because they are free of final state interactions.


How do we detect direct photons?

Isolate photons by having sensitivity to partner in decay of known particles:

π0 M=0.135 GeV BR=98.8%

K0 π0π0 0.497 31%

0.547 39%

π0 0.782 8.9%

’ 0.958 2.1%

Other decay modes yield more photons with less Q

Background simulations underway


Where do decay partners go?

• Gain sensitivity to direct photons by making sure we have high probability to catch decay partners• This means we need dynamic range, because photon energies get low (~0.25 GeV), and sufficient area (typical opening angles few degrees at our ranges).

m = di-photon parameters

z = |E1-E2|/(E1+E2)

= opening angle

Mm = 0.135 GeV/c2 ()

Mm=0.548 GeV/c2 ()

mesonfor factor Lorentz of in terms angle opening minimum gives ,1

2sin

yprobabilit with angle opening maximum gives ,1

1

22sin

photon second ofenergy gives ,1

1,Eh photon wit candidatefor

21

2min

2max

2

1

m

m

m

EE

cM

zz

z

E

cM

Ez

zE

E


Sample decays on FPD++

With FPD++ module size and electronic dynamic range, have >95% probability of detecting second photon from decay.


On to the Full FMS

Following Run6 we will have shown direct photon capability which will only improve with larger detector. We will have proven electronics and trigger schemes and may well have shown J/ capability, which will also only improve with acceptance of FMS


STAR detector layout with FMS

TPC: -1.0 < < 1.0

FTPC: 2.8 < < 3.8

BBC : 2.2 < < 5.0

EEMC:1 < < 2

BEMC:-1 < < 1

FPD: || ~ 4.0 & ~3.7FMS: 2.5<< 4.0


Calorimeter cells - all for freeThanks to FNAL (U.Col) and Protvino

800 cells (5.8x5.8x60 cm3: 25 Lrad) of lead glass (PbGl) from E831 at FNAL including PMTs (XP2202) with active bases

Arrived at BNL in June. Students from PSU, UCB, and TAMU working to refurbish, test, and characterize in bldg 510 rm 3-180

650 cells (3.8x3.8x45 cm3: 25 Lrad) of PbGl from IHEP Protvino including PMTs (FEU-84) needing bases

150 on site and used in FPD West.

500 more expected to arrive at BNL in September

These are fully understood in terms of response


FNAL E831Cells head to BNL


Students prepare cells at test Lab at BNL


FPD++ and FMS Timeline


Electronics

New digitizer boards - 32 channels in 9U VME12 bit ADC - 0.25 pC sensitivity 5 bit TAC - 5 ns sensitivity10 MHz operation - fully pipelined bit selection for L0 triggering (sum, HT, ID, other?))

Use existing FPDW DSM tree


Conclusions

We have shown we can do π0 reconstruction in the FPD for CuCu and pp and discovered large spin asymmetry at large in polarized pp where the cross section is explained by NLO pQCD. We have observed suppression of forward π0 in dAu

We intend to use the FPD++ arrays to show that we can measure direct signal and to continue the study of asymmetry in pp

Run6 will allow engineering test of “new” calorimeter cells and of the new 12 bit digitizer boards

We will work with BNL management to produce the full electronics set for the FMS and stage it for Run7 measurements of the gluon distribution in protons and Au nuclei covering 0.001<x<0.1, checking the universality of the pdf’s determined through DIS


Sivers Geometry


FMS

Inner cells are 3.8 cm edge, outer are 5.8 cm

Showing FPD N,S,T,B for size scale

Circles indicate range of detector

Documents

31 July 2005HjC at STAR in Warsaw Forward Meson Spectrometer (FMS) status report Hank Crawford for FMS group L.Bland, F.S.Bieser, R.Brown, A.A.Derevschikov,