Overview of ANDY

L.C.BlandBrookhaven National LaboratoryBNL Review of the ANDY Proposal

30 March 2012

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Where is the spin of the proton?

• Proton characterized by basic properties of mass, spin, size, …

• Global fits to Parton Distribution Functions find that ~50% of the momentum of the proton is carried by gluons

• Polarized deep inelastic scattering finds that quarks account for only ~1/3 of the proton spin: =0.33 0.03 (stat) 0.05 (syst) d’Hose (INT, 2012)

• RHIC spin addresses this question

• Overall, RHIC is addressing the role of color

e.g. INT Workshop INT-12-49W

Orbital Angular Momentum in QCD

6-17 February 2012

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arXiv:0901.2828

RHIC Spin (2006) HighlightsNew insights from RHIC after 30 years of polarized deep inelastic scattering

Where is the spin of the proton?

Gluon polarization is not large…If not from gluons, then is the spin from orbital motion?

STARSTAR

PRL 101 (2008) 222001

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Why polarized Drell Yan?Best answer: RBRC workshop in May, 2011 had 31 talks and ~80 participants from all over the world due to the intense interest in measuring transverse SSA, and other aspects, for Drell-Yan production

John Collins, in his Workshop Summary, concluded with these words…

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Simple QEDexample:

DIS: attractive Drell-Yan: repulsiveSame in QCD:

As a result:

Attractive vs Repulsive Sivers EffectsUnique Prediction of Gauge Theory !

Transverse Spin Drell-Yan Physics at RHIC (2007)

http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf

DOE performance milestone HP13

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Why ANDY?• Drell-Yan production is believed to be best understood by theory for transverse

momentum-dependent effects, such as the Sivers function.

• Suggested surrogates for DY production, such as di-jets, have led to confusing results. The best way to test the sign-change prediction from theory is DY.

• Forward DY is important, to ensure kinematic overlap between DY and SIDIS.

• It is expected that future efforts in forward DY will provide the most robust connections to the low-x physics program of an EIC, so developing capabilities at RHIC are essential.

• Forward instrumentation at RHIC is limited, as is available space at STAR and PHENIX. The major engineering efforts to instrument the forward direction at STAR and PHENIX are best done after demonstrating the basic requirements for DY.

• Run-11 demonstrated that RHIC can collide polarized proton beams at 3 IR, albeit with the need to further reduce backgrounds. Consequently, ANDY can run in parallel with the W program.

ANDY is the best path to forward DY at RHIC

Forward DY at RHIC is the best path to EIC physics

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Modeling an Experiment

Run-11 goals…

• What is the impact of a third IR on polarized proton operations at RHIC?

• Can the hadron calorimeter planned for ANDY be robustly calibrated?

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Run-11 ANDYLeft/right symmetric HCal

Left/right symmetric ECal

Left/right symmetric preshower

Trigger/DAQ electronics

Blue-facing BBC

Beryllium vacuum pipe

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Impact of Collisions at IP2The anatomy of initiating collisions at IP2

Early after a RHIC store is set up, beams are colliding at IP6 (STAR) and IP8 (PHENIX). Beams are transversely separated at IP2 (ANDY). The arrow indicates when collisions begin at IP2

After the beam intensity decays to a threshold (here, 1.3 1011 ions/bunch), collisions begin at IP2. There is loss of beam in the Yellow ring.

The beam loss is monitored. The spikes in the Blue ring are due to insertions of carbon ribbons for measuring the beam polarization. Beam-beam tune shift causes loss of ions in Yellow when collisions begin at IP2. This loss typically decays with time, as shown.

Luminosity at IP6 (STAR) and IP8 (PHENIX) is mostly constant when collisions are initiated at IP2 (ANDY).

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Impact of IP2 Collisions

IP2 collisions have begun <3 hours after physics ON with minimal impact on IP6,IP8. Adequate luminosity for ANDY (10 pb-1/week for s=500 GeV polarized

proton collisions) is projected for subsequent runs.

Minimal impact on STAR,PHENIX

Fri. 8 April

1.501011/bunch

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arXiv:1112.1812

HCal Calibration• Reconstruction of from

HCal clusters sets the energy scale of the calorimeter

• The mass distribution from data is compared to reconstruction of PYTHIA/GEANT events, and agrees well in shape and magnitude

• Summed energy distribution (jet trigger) from HCal with photon calibration agrees well with absolutely normalized PYTHIA/GEANT simulations

arXiv:1109.0650

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Shower maximum detector

7x7 array of “Yerevan” lead glass from BigCal

Towards Dileptons from Run-11

• Run-11 configuration was supplemented by loan of 120 detectors from BigCal in October, 2010.

• A primary purpose was to establish color-trapping center development in glass at IP2. Transparency before/after run-11 was the same to within 10%

• Readout triggered on ECal was a “test trigger” in run-11, but ECal clusters paired with “HCal-EM” clusters have mass extending to >4 GeV/c2. Background dominantly from photon pairs

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Dileptons from Run 11 Data• ANDY profiling methods were applied to a limited data

sample (Lint=0.5 / pb) of run-11 ECal triggered data.

• Dominant backgrounds are now from , and are suppressed by using MIP response of beam-beam counters to tag clusters.

• Individual detector calibration for HCal was an essential step to reconstruct J/

• Limited granularity of BBC and poor position resolution of HCal-EM cluster results in less photon suppression than expected for final ANDY apparatus (project ~100x better suppression)

• Hadron suppression is not yet required, but will be in going from dileptons to DY

• J/e+e- peak has ~120 events with 5.4 statistical significance. PYTHIA 6.425 with NRQCD expects 420 events in the run-11 acceptance, approximately consistent with observation after crude efficiency correction. From PYTHIA 6.425, DY with M>4 GeV/c2 is 170x smaller in this acceptance.

• J/ is a window to heavy flavor via BJ/K and bJ/p that would help quantify intrinsic b from proton backgrounds to DY

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Dileptons from Run 11 Data versus Simulation

• Compare run-11 mass distribution to model used to make background estimates for DY

• Large-mass background found to be well-represented by fast-simulator model in both magnitude and shape

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ANDYRun-13 elements and their purpose

• ECal – primary detector for detecting dielectrons

• HCal – hadron rejection

• Preshower – hadron rejection and photon/electron discrimination

• Tracking – the value of accurate space points / deflections through magnet

• DY relative to reducible backgrounds

• DY relative to irreducible backgrounds

3/30/2012 AnDY Overview 16Projected precision for proposed ANDY apparatus

Goal of ANDY ProjectMeasure the analyzing power for forward Drell-Yan production to test the predicted change in sign from semi-inclusive deep inelastic scattering to DY associated with the Sivers function

GEANT model of proposed ANDY apparatus (run-13)

17

arXiv:0906.2332

Proposed ANDY ECal

• 1596-element TF1 lead-glass calorimeter borrowed from JLab, with return date of July, 2014

• ECal dimensions are driven by optimizing the acceptance for forward DY production

• ANDY ECal has similar scope to earlier projects completed by the proponents

• Full GEANT response of ~18X0 and ~1 hadronic interaction length glass can be parameterized for fast simulation of detector response

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ECal

HCal

Side View

Top View

Proposed ANDY HCal• Primary purpose of ANDY HCal

is to veto hadrons that deposit E=fE in ECal, by observing (1-f)E in HCal

• Full GEANT simulations of ECal+HCal show 82% hadron rejection with 99% electron retention.

• Uses existing E864 detectors (117-cm long / 47x47 scintillating fiber matrix embedded into lead)

Proposed run-13 configuration requires borrowing 60 additional detectors from PHENIX

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ANDY Preshower

• HCal rejection of hadrons that deposit f>0.7 of their energy in ECal is not very effective

• A preshower+converter detector upstream of the ECal rejects 86% of hadrons while retaining 98% of the electrons and positrons

• First component of preshower (prior to converter) is needed for discrimination between photons and electrons. 98% of photons are vetoed here while retaining 98% of electrons

• Segmenation of proposed preshower minimizes multiple occupancy in a PS detector

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Tracking + Split-Dipole• Prior experience with ECal shows

(x,y) position localization to ~1/10 cell size, or ~4mm.

• A single tracking station provides space point of resolution better than 0.2mm robust zvertex and robust ECal/PS association even without magnet

• Split-dipole magnet is planned for RHIC run 14.

• Radial deflections through split-dipole result in effective shift of zvertex from tracking, relative to true value, that depends on charge sign

• Charge sign discrimination can determine if hadronic backgrounds are suppressed

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Strategy for Estimates• Experience with run-11 analysis, shows that full PYTHIA/GEANT required

~2.5 weeks to generate 0.5 pb-1 of QCD background simulation.

• We are exploring the possibility of using NSERC for GEANT simulations.

• Until then, use fast simulator, benchmarked to run-11 data

• Reducible backgrounds: QCD hadron + photons

• Irreducible backgrounds: heavy quarks

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Reducible Backgrounds

pz,* and pT,* require M*>4 GeV/c2

Estimate that QCD backgrounds are <10% of the DY signal for 0.05<xF,*<0.3 and pT,*<2 GeV/c (to overlap SIDIS).

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Irreducible Backgrounds

pz,* and pT,* require M*>4 GeV/c2

Estimate that open-bottom backgrounds are ~5% of the DY signal for 0.05<xF,*<0.3 and pT,*<2 GeV/c (to overlap SIDIS).

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ANDY Projections

Projected precision for proposed ANDY apparatus

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Summary• Measurement of AN for DY tests a fundamental QCD prediction of color dynamics

producing a sign-change from SIDIS to DY for transverse single-spin asymmetries

• The ANDY design and the ANDY team can complete the measurement of AN for DY in two RHIC runs (FY13 and FY14). This would address a DOE performance milestone for RHIC (HP13)

• As discussed at the May, 2011 RBRC workshop (and summarized in the subsequent Outlook), large-rapidity DY production is of interest for low-x physics and the physics of transverse-momentum dependence. ANDY would identify the basic requirements for future upgrade paths at STAR and PHENIX.

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Outlook

• Low-x physics at RHIC

• There’s more to Drell Yan than just the sign change

• There’s more to forward physics than just DY

• From RHIC-DY to EIC