First measurements of final state neutron polarisation in deuterium photodisintegration. Stephen Kay University of Edinburgh. NP Summer School 2015

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1 First measurements of final state neutron polarisation in deuterium photodisintegration Stephen Kay University of Edinburgh NP Summer School 2015

2 Overview - Deuterium Photodisintegration - Motivation - the d* 2380 Resonance - Experimental Facility - Crystal Ball at MAMI - Analysis Progress Stephen Kay University of Edinburgh NP / 13

3 Deuterium Photodisintegration - An Unexpected Result - Work by Kamae [1][2] et al. in 1977 discovered an unexpected result for the spin polarisation of protons from deuterium photodisintegration - At s 2380 MeV protons from photodisintegration highly polarised - The neutron polarisation was not measured in this experiment - This result cannot be explained by standard theories of deuterium photodsintegration. Kamae [2] speculated that this result could indicate a possible J π = 3 + resonant state [1] - PRL 38, 9, PP (1977), [2] - PRL 38, 9, PP (1977) Stephen Kay University of Edinburgh NP / 13

4 Hadron Production Channels - Various experiments looking at hadron production channels have seen anomalous structure at s 2380 MeV Figure: Left [1] - A plot of σ as a function of s for the shown reaction from WASA at COSY. Right [2] - The analysing power as a function of s for polarised neutron-proton scattering from WASA at COSY [1] - PRL 106, (2011), [2] - PRL 112, (2014) Stephen Kay University of Edinburgh NP / 13

5 The Nature of the Resonance - Observations so far have suggested the resonance is found at s 2380 MeV with a width of Γ 70 MeV and J π = What is this resonance? Difficult to explain using standard nucleon resonances. This width is far narrower than would be expected for a resonance for example - Some propose the exciting interpretation of the resonance [1][2] as a d* 2380 dibaryon. A dibaryon is a six quark object, in this case consisting of 3 u quarks and 3 d quarks - Key expectation from a genuine 3 + resonance is that both the proton and neutron would show a high degree of polarisation - As mentioned there is no previous data on the neutron polarisation, this needs to be measured [1] - arxiv: [hep-ph], [2] - PRL 38, 9, PP (1977) Stephen Kay University of Edinburgh NP / 13

6 The MAMI Facility - MAMI is an electron beam facility in Mainz, Germany - The Edinburgh group work in the A2 hall which houses the crystal ball detector Stephen Kay University of Edinburgh NP / 13

neutrons via (n,p) scattering in the PID - this has a low probability (roughly 0.

7 The Crystal Ball at MAMI - The crystal ball detector consists of 672 NaI(Tl) scintillation detectors covering 94 % of 4π - Within the crystal ball is the PID which surrounds the target - We observe neutrons via (n,p) scattering in the PID - this has a low probability (roughly 0.5%), these events can be analysed to obtain the neutron polarisation however Stephen Kay University of Edinburgh NP / 13

Current Analysis - The current analysis effort focuses on examining data taken in March 2013 - Particles are identified by comparing the energy

8 Current Analysis - The current analysis effort focuses on examining data taken in March Particles are identified by comparing the energy deposited in the PID compared to that deposited in the crystal ball Figure: A typical E de plot for A2 data Stephen Kay University of Edinburgh NP / 13

9 Analysis Progress - With various cuts in place the proton and neutron from the photodisintegration have been identified - A plot of the missing mass from the perspective of the proton and E de plots for the protons and neutrons identified Stephen Kay University of Edinburgh NP / 13

Analysis Progress - A Monte Carlo simulation of the detector setup is also available - The real data was compared to the output of this simulation

10 Analysis Progress - A Monte Carlo simulation of the detector setup is also available - The real data was compared to the output of this simulation Figure: A comparison of the EdE plots for the neutrons as seen in real (left) and MC (right) data Stephen Kay University of Edinburgh NP / 13

Analysis Progress - The MC simulation allowed us to test whether the two different regions the neutrons were found it corresponded to scattering from different materials Figure: A

11 Analysis Progress - The MC simulation allowed us to test whether the two different regions the neutrons were found it corresponded to scattering from different materials Figure: A comparison of the EdE plots for the neutrons in the MC data with (left) and without (right) deuterium gas filling the target cell Stephen Kay University of Edinburgh NP / 13

Analysis Progress - Once identified the neutrons are rotated to a new frame - In this frame the polarisation, P, is related to the angle φ of the particles in this frame via dσ dω = dσ 0 dω (1 + A y

12 Analysis Progress - Once identified the neutrons are rotated to a new frame - In this frame the polarisation, P, is related to the angle φ of the particles in this frame via dσ dω = dσ 0 dω (1 + A y P cos φ) - Therefore the polarisation can be determined by fitting a cosine to the measured φ distributions Figure: An illusatration of the frame rotation and an example φ distribution with a cosine fit Stephen Kay University of Edinburgh NP / 13

13 Summary - Current analysis has identified p,n photodisintegration events - MC Analysis has shown that two regions of detected neutrons appear to be due to scattering from two different materials - Adjustments to the real data based upon observations in the simulated data will be carried out - Polarisation results should be available very soon Stephen Kay University of Edinburgh NP / 13

14 Thanks for listening, any questions?

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