HERMES Status Report

Transcription

1 HERMES Status Report Sergey Yaschenko for the Collaboration DESY PRC, Hamburg, April 1, 008

2 Outline Introduction Physics Highlights from HERMES Isoscalar extraction of ΔS Model-dependent constraint on J u, J d Recoil Detector Status Detector calibration Noise studies Tracking and alignment Particle identification Summary and Outlook S. Yaschenko HERMES Status Report

3 Spin Structure of the Nucleon 1 = 1 ( Δu v + Δd v + Δus + Δds + Δu + Δd + Δs + Δs Δq sea ) + ΔG + L q + L g Quark spin is small ~1/3 (HERMES, ) ΔΣ Gluon spin ΔΣ = Δu + Δd + Δu + Δd + Δs + Phys. Rev. D 75, (007) ΔG Δs ΔS Orbital angular momentum L q + L g S. Yaschenko HERMES Status Report 3

4 Physics Highlights Isoscalar extraction of ΔS arxiv: , DESY 07-3, submitted to PRL, A. Airapetian et al., Measurement of Parton Distributions of Strange Quarks in the Nucleon from Charged Kaon Production in Deep-Inelastic Scattering on the Deuteron Model-Dependent Constraint on J u, J d arxiv: , DESY 07-5, submitted to JHEP, A. Airapetian et al., Measurement of Azimuthal Asymmetries with Respect to Both Beam Charge and Transverse Target Polarization in Exclusive Electroproduction of Real Photons S. Yaschenko HERMES Status Report 4

5 Semi-Inclusive DIS Semi-inclusive DIS, observation of a coincident hadron, allows probing of flavor in more detail because of the correlation between flavor structure of the hadron and struck quark Measure asymmetries A ( ) ( ) ( ) LO h Δq x,q E x,q,z = Pq x,q,z ( ), z q x,q υ h 1 = q A h 1 σ = σ h 1/ h 1/ σ + σ h 3/ h 3/ h K ± us, us P h q (x,q,z) Purity is a conditional probability that a hadron of type h observed in the final state originated from a struck quark of flavor q. Purity depends on fragmentation functions and unpolarized PDFs S. Yaschenko HERMES Status Report 5

6 Isoscalar Extraction of S Longitudinally polarized deuterium target Strange quark sea in proton and neutron identical Analysis of purities simplifies All needed information can be extracted from HERMES data alone: Inclusive A and Kaon K K 1,d (x,q ) A (x,q,z) double spin, d asymmetries Kaon multiplicities Only assumptions used Isospin symmetry between proton and neutron Charge-conjugation invariance in fragmentation S. Yaschenko HERMES Status Report 6

7 Extract A K A 1, d Isoscalar Extraction of S Inclusive purities are simple combinations of unpolarized PDFs P Q 1,d K + + ΔS(x) ΔQ(x) (x) (x) (x) = 5Q(x), P 5Q(x) + S(x) S(x) 5Q(x) + S(x) Kaon purities can be computed from the unpolarized Kaon multiplicity assuming only charge symmetry in fragmentation D K q P = Q PS + + K + K K + K PQ PS + Δs(x) + Δs(x) Δu(x) + Δu(x) + Δd(x) + Δd(x) + K (z) = S. Yaschenko HERMES Status Report 7 S D (x) K q + = + K ΔQ(x)/Q(x) ΔS(x)/S(x) (z)

8 Results on Isoscalar Extraction of S No dependence on fragmentation model No hint of negative strange sea in measured range ΔQ = ± 0.06 ± ΔS = ± ± 0.07 Blue curves - results of calculation in LO [Phys. Rev. D 73 (006) 03403] S. Yaschenko HERMES Status Report 8

9 Results on Isoscalar Extraction of S No dependence on fragmentation model No hint of negative strange sea in measured range Result is consistent with full 5 flavor extraction at HERMES x.δs(x) Isoscalar 08 PRD71(5 parameter fit) PRD71(Isoscalar) X Bj S. Yaschenko HERMES Status Report 9

10 Access to the Orbital Angular Momentum Nucleon spin: 1 = 1 ΔΣ + L q + J g Quark spin: measured ~1/3 (HERMES, ) Quark orbital momentum: Lq unknown Generalized parton distributions (GPDs) Incorporate our knowledge about PDFs and FF to a new theoretical framework Access the orbital angular momentum of quarks in nucleon S. Yaschenko HERMES Status Report 10

11 Access to GPD via Deeply Virtual Compton Scattering (DVCS) Cleanest way to access GPDs: DVCS Bethe-Heitler d σ (en enγ ) TBH + TDVCS + T 14 BHT 444 DVCS + T 4BHT 444 DVCS 3 interference term DVCS and Bethe-Heitler: the same initial and final state Bethe-Heitler dominates at HERMES kinematics GPDs accessible through cross-section differences and azimuthal asymmetries via interference term S. Yaschenko HERMES Status Report 11 * *

12 Transverse Target Spin Asymmetry (TTSA) Ji relation access to the total angular momentum of quarks Bethe-Heitler DVCS interference term in ep epγ induces azimthal asymmetries access to GPDs H and E Jq 1 = lim dx x Hq ( x, ξ, t) + Eq ( x, ξ, t) t GPDs Measure Transverse Target Spin Asymmetry (TTSA) A I UT [ ] [ ] + + dσ ( φ, φ ) dσ ( φ, φ ) dσ ( φ, φ + π ) dσ ( φ, φ π ) ( φ, φ ) + s TTSA provides access to GPD E s s s s S. Yaschenko HERMES Status Report 1

13 Results on TTSA Asymmetry Amplitudes Sensitivity of GPD model predictions to J u at fixed J d =0 [Phys. Rev. D74(006) 05407] S. Yaschenko HERMES Status Report 13

14 Model-Dependent Constraint on J u, J d χ (J u,j d ) ( ) δa δa sin (φ φ )cos nφ sin (φ φ )cos nφ = AUT,I exp A s s UT,I theo(ju,jd) stat + syst J u, J d are free parameters in GPD models Double Distribution (DD) [Phys.Rev.D 60 (1999) , Prog. Part. Nucl. Phys. 47(001)401] J u +J d /.8 = 0.48±0.17 Dual Parameterization (Dual) [hep-ph/007153, Phys. Rev. D74(006) 05407] J u +J d /.8=-0.0±0.7 Jlab DD (neutron cross section data) [Phys. Rev. Lett. 99(007)4501] Lattice calculations QCDSF, LHPC S. Yaschenko HERMES Status Report 14

15 Recoil Detector Motivation: exclusivity, background suppression, t-resolution 1 Tesla Superconducting Solenoid Photon Detector (PD) detect gammas p/π PID for momentum > 650 MeV/c Scintillating Fiber Tracker (SFT) Momentum reconstruction by bending in magnetic field Silicon Strip Detector (SSD) Momentum reconstruction by energy deposit for low-momentum protons and deuterons Target Cell S. Yaschenko HERMES Status Report 15

16 Outline Introduction Physics Highlights from HERMES Isoscalar extraction of ΔS Model-dependent constraint on J u, J d Recoil Detector Status Detector calibration Use MIPs for calibration by selecting π + and π - Noise studies Tracking and alignment Particle identification Summary and Outlook S. Yaschenko HERMES Status Report 16

17 Detector Calibration: Photon detector MIP peaks seen for all strips in all layers Fit Landau-Gaussian convolution to all ADC spectra Need to understand large width of MIP peak Implement correction for attenuation Refine MC digitization Get absolute energy calibration Final check with reconstructed π 0 S. Yaschenko HERMES Status Report 17

18 Detector Calibration: Scintillating Fiber Tracker MIP peak seen in all fibers Some fibers show higher noise typical Calibration currently in number of photoelectrons Use MC to get reference energy deposits and get the absolute calibration S. Yaschenko HERMES Status Report 18

19 Detector Calibration: Silicon Strip Detector Strong variations in momentum and path length seen by strips Acceptance, geometry Introduce Path Length vs. Momentum histograms for each strip and lookup table to get nominal energy deposit histogram for each strip Stability has been studied, studies of nonlinearities in progress S. Yaschenko HERMES Status Report 19

20 Noise Studies Noise studies with random bunches Different data sets Beginning of the fill (positron beam current 8mA) End of the fill (15mA) Empty target (35mA) Noise studies for SFT Occupancy of the background is strongly correlated with the positron beam current No correlation between hits in the SFT - random distributed noise is implemented in MC Similar studies are done for the Silicon and Photon detectors S. Yaschenko HERMES Status Report 0

21 Tracking status Track finding works and is efficient, studies of ghost tracks in progress Detector alignment is done Track fitting takes energy losses and multiple scattering into account Track fitting done for proton and pion hypotheses Different tracking reconstructed parameters for future PID Accuracy of momentum reconstruction by bending in magnetic field is in agreement with the technical design report Tracking is used for calibration Until detector calibration is done - time for improvements S. Yaschenko HERMES Status Report 1

22 Tracking status Momentum reconstruction by energy deposit in the Silicon Strip Detector First method with simplifications in use Two methods under development Lookup tables for momentum as a function of energy deposit and path length, direct reconstruction of momentum Fitting method will treat energy deposits the same way as measured coordinates during track fitting Protons rec. with SSD Protons rec. with SFT Pions rec. with SFT S. Yaschenko HERMES Status Report

23 Particle Identification Plan SFT, experimental data Particle identification possible in all 3 subdetectors of the Recoil Proton-pion separation in momentum range below 700 MeV/c possible with the SSD and SFT π + π p SSD, experimental data Photon detector will be used for proton-pion separation at energies above 650 MeV/c π + π p S. Yaschenko HERMES Status Report 3

24 Summary and Outlook Analysis of HERMES data is ongoing, new physics results coming soon 10 HERMES talks accepted for DIS08 Recoil Detector calibration and tracking nearly finished, tracking improvements under implementation First results from the Recoil Detector are expected this fall S. Yaschenko HERMES Status Report 4

25 Backup Slides S. Yaschenko HERMES Status Report 5

26 r A 1 = A A A A A 1, p + π 1, p π 1, p 1, d K d 1, Measured Method of 5-Flavor q Extraction A r P h q 1 ( x) = = P Q r e q q q e h ( x) dzd ( z) q q h ( x) dzd ( z) S. Yaschenko HERMES Status Report 6 Simulated q q Purity is a conditional probability that a hadron of type h observed in the final state originated from a struck quark of flavor q. Purities extracted from LUND string model MC simulation (LEPTO+JETSET) tuned to HERMES unpolarized data Q r Δu/u Δd/d = Δu / u Δd / d Δs/s Extracted System of asymmetries and purities solved through χ minimization of polarizations

27 Generalized Parton Distributions GPDs PDF Hq (x,0,0) = q(x) H ~ (x,0,0) = Δq(x) q GPD FF 1 H, dxh 1 1 dxe 1 q H~ q q q (x, ξ, t) = (x, ξ, t) = F F q 1 q (t) (t) conserve nucleon helicity x ± ξ ξ t parton longitudinal momentum fractions fraction of the momentum transfer invariant momentum transfer to the nucleon Eq, E~ q flip nucleon helicity S. Yaschenko HERMES Status Report 7

28 Asymmetries Measurable at HERMES S. Yaschenko HERMES Status Report 8